Does time exist?

Morbert · 03-09-2011 5:41pm

roosh wrote: »

I don't think it ignores the fact that the speed of light is constant in every reference frame, at all; what it says is that the model used to represent the reality of the observed phenomena is flawed, that it doesn't take into account certain relevant information.

What it says, with regard to the original thought experiment Einstein used, is that there are four "time points" which are relevant, and which, when taken into consideration, would lead to both observers calculating that the flashes of lightning occured simultaneously.

What it says is:
The flashes of lightning occur at rods A (behind train) & B (in front of train) at time=t1 - neither observer sees the flashes in that instant.

The light from the flashes travels towards the midpoint (M) where Observer 2 is standing.

As the train is in motion, Observer 1 will meet the light from rod B at a point beyond M (call it X) at time=t2

Observer 2 will see light from rods A & B at the same time, at time interval t=3 (Observer 2 will have travelled a further distance along the track to Y)

The light from Rod A will reach Observer 1 at time=t4 when Observer 1 is at location Z along the track

According to the author, once all these times and co-ordinates are taken into account then both observers would calculate that the flashes occurred at A & B simultaneously.

The assumption as far as I am aware, is the speed of light is constant for both observers.

Let L be the length of the train, and c be the speed of light. Observer 2 would calculate that the flashes occurred at A & B simultaneously, at time t3 - L/2c. Observer 1 would calculate that flash A occurred at time t4 - L/2c, and that flash B occurred at time t2 - L/2c. We can see that, since the speed of light is the same for both observers (i.e. c is the same for observer 1 and 2), flash B happened before flash A for observer 1, and both flashes happened at the same time for observer 2. The only way they could both conclude that the flashes happened simultaneously is if they disagreed on the speed of light.

The time interval L/2c comes from the fact that time = distance / speed. So the time it takes for the flash of light to reach an observer is distance (L/2) / speed (c).

Real Space
With regard to the "real space" the author is insisting on I think the distinciton is made between
I think the distinction is more between conceptual space, as defined mathematically, and real, non-conceptual space.

Conceptual space is the co-ordinate system we apply to the universe. It defines distances, as well as present, past, and future. When the author describes "real space", they are defining an absolute, "true" co-ordinate system. There is no evidence for this "real space", as the co-ordinate system of any reference frame is no more or less meaningful than any other. Neither is more "true" than any other. What is real is the Light cone structure, or "causal structure" of the universe. This is the same for all observers.

Momentum of photons
Again, I don't think he/she is using the strange notion of photons without momentum, what is said is that the use of geometrical "zig-zeg" lines, to represent the beam of light, is an incorrect model of the phenomena of light, which doesn't take into account the fact that light isn't necessarily a single "ray" but rather is made up of quanta. They say that these quanta don't travel in the "zig zag" fashion as depicted in the models, but follows the trajectory as outlined in figure 9 on this page.

From what I can gather, it doesn't suggest the notion of photons without momentum, rather the idea that the photons will not inherit the velocity of the laser, that they will travel perpecdicular to the X-axis (along which the laser moves) as opposed to at an angle as suggested by the "zig-zag"! model.

Firstly, it sounds like you are assuming the website is authoritative on what is and is not a correct model. Why?

Secondly, and more importantly, it is the website that is presenting an incorrect model. The photon zigzags because it has momentum. It "inherits" the velocity of the emitter in the same way an egg thrown from a moving car, at a perpendicular angle, "inherits" the velocity of the car (until wind resistance slows it down.)

Tunnel vision
Unfortunately I can't engage in any meaningful critique of that part of your post, other than to assert that the observations from experiments applying GR won't actually change, but the manner in which they are interpreted might. Perhaps a change in model could lead to progress in the quest to unify GR and QM.

How would they be interpreted? How would gravitational time-dilation be interpreted? How would high-energy particle collisions, or slow muon decay be interpreted?

Julian Barbour is exploring the unification of GR and QM. Special relativity and quantum mechanics has already been successfully unified by abandoning the Galilean notion of an absolute present.

Objections to the notion of time
The challenge to the notion of time isn't necessarily on the basis that it is unobservable, or a derivitave quality, the objection is that it isn't even necessarily derived from other observations, it is assumed to exist a priori. The subsequent attempt to derive its existence simply isn't logical, and again relies on an unjistified assumption.

The assumption is that certain, either specific or non-specific, physical phenomena can be used to measure this thing called time, when, in fact, those physical phenomena are simply used as standard units of comparison - they [may indeed] exist, and the things which are measured against them [may indeed] exist, but the thing called time is not measured against them.

Time is* the name given to the system of measurement, it is not the thing which is measured.

*or at least it should be recognised for what it is.

We don't have to assume it exists a priori. Under Julian Barbour's formalism, it is an emergent quality, a shorthand for the structure of trajectories through configuration space, generated by the Hamiltonian.

You can talk about time in the context of a metric, the structure of events in the universe. Or you can talk about time in the context of configuration space. But however you talk about time. You cannot talk about a true present, because it an arbitrary notion, with no obeservational evidence to infer it from.

"True present"
The issue of "the derivative nature of time" does not necessarily apply to the notion of the "true present". If we all live in the same universe (as opposed to occupying our own separate but interacting universes) then the notion of a "true present" is a necessary consequence, even if we cannot observe it directly - much as we cannot observe sub-atomic particles directly but can create a model to represent reality.

A true present is not a necessary consequence. Let's say there is a radio in the centre of the room. Person A stands near the radio, Person B stands farther away. Person A will register a higher number of decibels than person B, but neither perspective is wrong. We do not need to infer a logically necessary "true" decibel level. Similarly, an event might be in the future for person A, and in the present for person B, but there is no need for a "true" co-ordinate system of events.

If we all live in the one universe, then we can imagine the entire universe being paused, or a snapshot of the entire universe; while each observer might have a different perspective of the present, we can still deduce that there would be a "true present" or snapshot of the universe. We could theoretically put an infinite number of observers in an infinite number of reference frames (or the corresponding number of observers in the corresponding number of reference frames) and work out what the "true present" would be. It's simply a lack of information that prevents us from doing it, as opposed it not being possible.

An infinite number of observers would not tell you what the "true" present is. Each reference frame will be just as physically meaningful as the others. An infinite number of people around the radio will not tell you the "true" decibel level of the radio.

roosh · 03-09-2011 8:02pm

Morbert wrote: »

Let L be the length of the train, and c be the speed of light. Observer 2 would calculate that the flashes occurred at A & B simultaneously, at time t3 - L/2c. Observer 1 would calculate that flash A occurred at time t4 - L/2c, and that flash B occurred at time t2 - L/2c. We can see that, since the speed of light is the same for both observers (i.e. c is the same for observer 1 and 2), flash B happened before flash A for observer 1, and both flashes happened at the same time for observer 2. The only way they could both conclude that the flashes happened simultaneously is if they disagreed on the speed of light.

The time interval L/2c comes from the fact that time = distance / speed. So the time it takes for the flash of light to reach an observer is distance (L/2) / speed (c).

I'm rushing out so I'll just respond to this first part.

I'm presuming that the length of the train L corresponds to the distance between rods A and B, such that the distance between A and B = L, is that correct?

Also, the flash of lightning occurs when both observers are at the midway point between the rods, is that also correct?

If so, and this is the point that the author makes: neither observer will see the lighning strike in the instant it strikes, as the light must travel from each rod toward the midpoint.

The lighning strikes both rods at time t1.

As the light travels from both rods towards the midpoint, observer 1 will have moved away from the midpoint towards rod B - as the train is in motion. That means, the distance the light from rod B travels is not actually L/2 but L/2 - the distance travelled. Observer 1 meets the light from rod B at time t2.

Observer 2 calculates that the light hits both A and B simultaneouly at time t3 - at that time, observer 1 has moved further along the track, because the train is in motion.

As the train continues to move, the distance the light from rod A has to travel to meet observer 1 is not L/2, but L/2 + the distance travelled. Obesrver 1 sees the flash of lighning strike rod A at time t4.

Morbert · 05-09-2011 5:02pm

roosh wrote: »

I'm rushing out so I'll just respond to this first part.

It is good that you are looking at this in some detail. It am going to take this as an invitation to treat the problem rigorously. Something I probably should have done in the beginning. There will be a bit of maths, but nothing more complicated than simple division, multiplication Etc.

I'm presuming that the length of the train L corresponds to the distance between rods A and B, such that the distance between A and B = L, is that correct?

Yes, but perhaps that is only confusing the matter. We can ignore what I said about the train and only consider the lightning rods. But now that we are taking a more rigorous look at the problem, we must take into account that the distance between the rods will be in different in each reference frame. The will be closer together in the reference frame of observer 1. I will go into further detail below.

Also, the flash of lightning occurs when both observers are at the midway point between the rods, is that also correct?

That is what observer 2 will have deduced. Observer 1 will disagree. Further detail below.

If so, and this is the point that the author makes: neither observer will see the lighning strike in the instant it strikes, as the light must travel from each rod toward the midpoint.

This has never been in dispute.

The lighning strikes both rods at time t1.

As the light travels from both rods towards the midpoint, observer 1 will have moved away from the midpoint towards rod B - as the train is in motion. That means, the distance the light from rod B travels is not actually L/2 but L/2 - the distance travelled. Observer 1 meets the light from rod B at time t2.

Observer 2 calculates that the light hits both A and B simultaneouly at time t3 - at that time, observer 1 has moved further along the track, because the train is in motion.

As the train continues to move, the distance the light from rod A has to travel to meet observer 1 is not L/2, but L/2 + the distance travelled. Obesrver 1 sees the flash of lighning strike rod A at time t4.

The short, handwavey answer to this is the author is not treating observer 1 correctly. Observer 1 would not say the distance the light has to travel is L/2 - distance travelled by the train. From observer 1's perspective, he is stationary, and instead the light has to travel a distance of ɣL/2.

Where does ɣL/2 come from? Let's go into more detail and treat the problem rigorously. When we are referring to times or distances in observer 2's reference frame, we will use the unprimed symbols t and x. When we are referring to observer 1's reference frame, we will use the primed symbols t' and x'. For example, let's say the speed of the train from observer 2's perspective is v = 0.8 c, wherec is the speed of light (I.e. The train is travelling 80% of the speed of light). From observer 1's perspective, the train is travelling at v' = 0. I.e. It is stationary from their perspective, since they are on the train.

According to observer 2: The rods are a distance L apart (Rod A is at location xA. Rod B is at location xB. Observer 2 is at x = 0). Let's say, for simplicity, that according to observer 2, the strikes both occur at t = 0. I.e. Observer 2 will detect both flashes simultaneously, at t = L/2c (Or t3 to use you name), and deduce that they occurred at t = 0. In this same reference frame, the light from rods A and B will reach observer 1 at times L/2(c+v) and L/2(c-v) respectively (or t2 and t4 to use your names).

I will introduce a set of relationships that can be used to transform one reference frame into another. By this, I mean you can use these relationships to "transform" the perspective from one observer to the other. The first set are called Galilean transformations. These are the transformations we use if we ignore relativity (I.e. if the speed of light is not the same for all observers). They look like this

t' = t
x' = x-vt

When we include relativity in our calculations, we must use Lorentz transformations. They look like this

t' = ɣ(t - vx/c^2)
x' = ɣ(x - vt)

Now let's look at observer 1's perspective. First let's ignore relativity by using the Galilean transformations. Considering times first, we use the relation t' = t. I.e. The times are all the same! Observer 1 deduces that the flashes occured at

t' = t = 0

that the light from rod A reaches him at

t2' = t2

and the light from rod B reaches him at

t4' = t4

What about locations? Rod A is struck at

xA' = xA-vt = xA-v(0) = xA

Rod B is similarly struck at

xB' = xB-vt = xB-v(0) = xB

Similarly, observer 1 will conclude that the rods are the same distance L apart. In other words, observer 1 will agree with observer 2 that the lighting was simultaneous, and that the reason he sees flash A before flash B is because of the relative motion between him and the rods.

So what happens when we take into account the fact that the speed of light is the same for all observers? Let's first look at locations. When rod A is struck by lightning, it is at

xA' = ɣ(xA - vt) = ɣ(xA - 0) = ɣxA

Similarly, Rod B is at

xB' = ɣxB

Notice that the length between the rods is no longer L, but instead ɣL.

Now let's look at the times. Lightning strikes Rod A at

t' = ɣ(t - vxA/c^2) = ɣ(0 - vxA/c^2) = -ɣvxA/c^2

It strikes Rod B at

t' = ɣ(t - vxB/c^2) = ɣ(0 - vxB/c^2) = -ɣvXB/c^2.

I.e. The light from Rod A reaches observer 1 at

t2' = ɣ(t2 - vx/c^2) = ɣ(t2 - t2v^2/c^2) = ɣt2(1 - v^2/c^2)

and the light from Rod B reaches the observer at

t3' = ɣ(t3 - vx/c^2) = ɣ(t3 - t3v^2/c^2) = ɣt3(1 - v^2/c^2)

Since rod A is at

xA' = ɣxA

the lightning must have struck rod A at

t2' - light travel time = ɣt2(1 - v^2/c^2) - ɣxA/c = -ɣvxA/c^2 = t' (Rod A)

Similarly, lightning struck rod B at

t3' - light travel time = ɣt3(1 - v^2/c^2) - ɣxB/c = -ɣvxB/c^2 = t' (Rod

Notice that t' is different for rod A and B. I.e. They didn't strike at the same time! Notice as well that it is not simply that the times t2' and t4' are different, but that t' the actual lightning events, are different.

roosh · 06-09-2011 1:19pm

before replying to both posts, I just want to say that I appreciate you taking the time to give such detailed replies

EDIT: apologies, I will reply to the most recent post for now, because there are a few issues I'd like to discuss which are more central I think.

EDIT 2: plus, I'm not entirely sure how to address some of the issues raised, so I've contacted the author for his opinions.

roosh · 06-09-2011 2:48pm

Just to address one of the things you mentioned in your second last post, with regard to my assuming that the website is authoritative: that probably is the case to a certain extent, but not entirely I would say.

Confrimation bias
Obviously there is the potential issue of confirmation bias, - although that doesn't necessarily invalidate the information - where I have come across something (directly from the video you posted) which confirms my own intuition. Unfortunately, I don't really know enough about the ins and outs, of SR or GR, to be able to identify the issues with what the author has posted on his website. The points made, however, do appear, to my mind, to be logical, hence I am tending towards accepting them, without fully accepting them as "gospel"; but the only way I have [at present] of scrutinising them is by presenting them and seeing what the arguments against them are.

Now, I have a certain level of understanding of SR and GR, and what the author has posted on his website, which means that there are certain issues that I can potentially discuss - specifically in relation to the logic of certain assumptions - which I will try and do in this post.

Observer 1
Based on your detailed explanation above, it appears as though there is a fundamental issue with how Observer 1 is treated. It appears either as though Observer 1 is coming to an incorrect conclusion, or that we are projecting an incorrect assumption onto Observer 1; that assumption, or incorrect conclusion, is in relation to the distance the light has to travel to reach Observer 1.

When the lightning strikes both rods, Observer 1 doesn't see the lightning but sees the rods, and at that point he concludes that the rods are equidistant to him.

When the light from rod B reaches him, given the same ability to measure distances, he will see that rod B is now closer to him, while rod A is now further away.

When the light from rod A reaches him, he will observe that rod A is now even further away from him, and that the distance between him and rod B has again changed.

On his approach to that section of the tracks between the rods, he would also observe the changing distances of rods A and B; on his approach he would pass rod A and on his exist he would pass rod B, so he should be able to deduce something with respect to the changing distances.

Observer 1(a)
To solve the problem of our Observer 1 who believes that he is not moving, can we introduce Observer 1 (a) who got on the train at the last stop. In this case Observer 1 (a) would have seen the train pulling into the platform and so could deduce that the train is in motion when the lightning strikes are witnessed. While Observer 1 (a), not knowing he is on a moving train, and failing to take notice of the changing distances of rods A and B, with respect to himself, might calculate that the lightning strikes didn't occur simultaneously, Observer 1 (a), with the additional information, should be able to carry out a more accurate calculation.

Observer 1 (b)
If we install another observer, Observer 1 (b), who is the driver of the train, or the co-pilot perhaps, who knows the exact velocity of the train; again, armed with this important information, he might come up with a different calcuation, no?

Observer 1 (c)
Alternatively, if we were to install Observer 1 (c), who has a highly-sophisticated, laser menasurement system, which continuously monitors the distance between her and each individual rod. When the light from a rod reaches her, or rather a device on her person, it registers the distance to that rod, giving her an extremely accurate measurement of the distance the light had to travel. Armed with this, she would definitely conclude that the distances, that each flash of light had to travel, were different.

Morbert · 07-09-2011 1:28pm

roosh wrote: »

Observer 1
Based on your detailed explanation above, it appears as though there is a fundamental issue with how Observer 1 is treated. It appears either as though Observer 1 is coming to an incorrect conclusion, or that we are projecting an incorrect assumption onto Observer 1; that assumption, or incorrect conclusion, is in relation to the distance the light has to travel to reach Observer 1.

When the lightning strikes both rods, Observer 1 doesn't see the lightning but sees the rods, and at that point he concludes that the rods are equidistant to him.

But you are again mixing observer 1 and observer 2's perspective. Observer 1, from the perspective of observer 2, is equidistant from the rods when the lightning strikes, while neither observer sees the lightning strike yet.

From observer 1's perspective, the lightning events are equidistant to him (The total distance being ɣL), but they occur at different times. When rod B is struck, it is a distance ɣL/2 away from observer 1. This occurs before both rods are equidistant to observer 1. (I probably should have shown in my last post that there is a length contraction between the rods. They are a distance L/ɣ. The ɣL should be called the distance between lightning strikes.) So by the time observer 1 is passing observer 2, there has already been a bolt of lightning.

When the light from rod B reaches him, given the same ability to measure distances, he will see that rod B is now closer to him, while rod A is now further away.

There is a very important clarification that needs to be made here. It might be the reason for the author's confusion.

He won't "see" the rod closer to him. When the lightning struck, rod B was a distance of ɣL/2 away from him. So the flash of light contains information about a rod of distance ɣL/2 away. At the instant he sees the flash, the rod will be closer, but he won't see a closer rod because that information has not reached him yet. So he sees a rod ɣL/2 away get struck. He knows he is seeing an image from the past, and by considering the speed of light and the distance it travelled, he can work how when, in the past, the lightning struck. He will reach a different conclusion to observer 2.

A common example is the moon. We don't actually see where the moon is. We see where it was about a second ago.

When the light from rod A reaches him, he will observe that rod A is now even further away from him, and that the distance between him and rod B has again changed.

The same goes for rod A. Rod A will be further away, but he will not observe rod A to be further away as that information has not reached him. What he sees is how far away rod A was when it was struck. This allows him to calculate the distance travelled by the light, and deduce when rod A was struck.

On his approach to that section of the tracks between the rods, he would also observe the changing distances of rods A and B; on his approach he would pass rod A and on his exist he would pass rod B, so he should be able to deduce something with respect to the changing distances.

This would only happen if there was a change in relative velocity between the train and the platform.

Observer 1(a)
To solve the problem of our Observer 1 who believes that he is not moving, can we introduce Observer 1 (a) who got on the train at the last stop. In this case Observer 1 (a) would have seen the train pulling into the platform and so could deduce that the train is in motion when the lightning strikes are witnessed. While Observer 1 (a), not knowing he is on a moving train, and failing to take notice of the changing distances of rods A and B, with respect to himself, might calculate that the lightning strikes didn't occur simultaneously, Observer 1 (a), with the additional information, should be able to carry out a more accurate calculation.

Observer 1 (b)
If we install another observer, Observer 1 (b), who is the driver of the train, or the co-pilot perhaps, who knows the exact velocity of the train; again, armed with this important information, he might come up with a different calcuation, no?

Observer 1 (c)
Alternatively, if we were to install Observer 1 (c), who has a highly-sophisticated, laser menasurement system, which continuously monitors the distance between her and each individual rod. When the light from a rod reaches her, or rather a device on her person, it registers the distance to that rod, giving her an extremely accurate measurement of the distance the light had to travel. Armed with this, she would definitely conclude that the distances, that each flash of light had to travel, were different.

Now we are getting to the crux of the matter. Observer 1(a) and 1(b) and 1(c) (Assuming 1(c) got on the train with 1(a) ) would intuitively conclude that the train is moving, and that the platform is stationary. But is this true? The earth is rotating, so the ground at the equator is moving at 1000 miles per hour. If the train heads off in the opposite direction, it would be stationary, even though observers would assume the train is moving.

So the train would be stationary with respect to the centre of the earth. But is the earth stationary? It is orbiting the sun at 30 kilometres per second. But is the sun stationary? Our solar system is orbiting the galactic centre at 250 kilometres per second. Is the galactic centre stationary? Is the centre of mass of all the galaxies in the universe stationary? Maybe everything is drifting.

This is the core lesson of relativity. No instrument or collection of instruments, no matter how sophisticated, no matter how many frames of reference you consider, can produce an absolute velocity. It must always be measured relative to the velocity of something else. This is similar to the abandonment of absolute time. So you should really be arguing against the author.

Morbert · 07-09-2011 1:36pm

EDIT 2: plus, I'm not entirely sure how to address some of the issues raised, so I've contacted the author for his opinions.

Has he gotten back to you? I am interested in hearing his response.

roosh · 07-09-2011 6:21pm

I think we are getting to the crux of the issue.

Morbert wrote: »

But you are again mixing observer 1 and observer 2's perspective. Observer 1, from the perspective of observer 2, is equidistant from the rods when the lightning strikes, while neither observer sees the lightning strike yet.

From observer 1's perspective, the lightning events are equidistant to him (The total distance being ɣL), but they occur at different times. When rod B is struck, it is a distance ɣL/2 away from observer 1. This occurs before both rods are equidistant to observer 1. (I probably should have shown in my last post that there is a length contraction between the rods. They are a distance L/ɣ. The ɣL should be called the distance between lightning strikes.) So by the time observer 1 is passing observer 2, there has already been a bolt of lightning.

This is how I understand it: Observer 1 is moving relative to Observer 2; Observer 2 is moving relative to Observer 1; at a velocity of 0.8c in both cases. The crux of the issue, as far as I can see, is that Observer 1 is also moving relative to the rods, while Observer 2 is at rest, relative to the rods.

So, strictly from the perspective of Observer 1: he is equidistant from rods A and B when the lighning strikes, but he doesn't know that, and he doesn't know that the lightning has struck because he can't see the rods and the the information doesn't reach him instantaneously.

If Observer 1 moves relative to Observer 2, or vice versa, then Observer 1 and the rods also move relative to each other. Observer 1 doesn't know this, because he can't see the rods, but this is what happens.

Given the positions of the rods relative to one another, and the fact that he and the rods are moving relative to each other, when the light from rod B reaches him, he will no longer be equidistant from both rods; likewise when the light from rod A reaches him.

Morbert wrote: »

There is a very important clarification that needs to be made here. It might be the reason for the author's confusion.

He won't "see" the rod closer to him. When the lightning struck, rod B was a distance of ɣL/2 away from him. So the flash of light contains information about a rod of distance ɣL/2 away. At the instant he sees the flash, the rod will be closer, but he won't see a closer rod because that information has not reached him yet. So he sees a rod ɣL/2 away get struck. He knows he is seeing an image from the past, and by considering the speed of light and the distance it travelled, he can work how when, in the past, the lightning struck. He will reach a different conclusion to observer 2.

A common example is the moon. We don't actually see where the moon is. We see where it was about a second ago.

The same goes for rod A. Rod A will be further away, but he will not observe rod A to be further away as that information has not reached him. What he sees is how far away rod A was when it was struck. This allows him to calculate the distance travelled by the light, and deduce when rod A was struck.

Here again is another critical issue I think. You mention that when he sees the lighning strike rod B, rob B will actually be closer but the information contained in the flash will be of a rod further away; similiarly, you say the flash from rod A will contain information showing the rod closer, even though it is now further away. I'm not sure this is actually correct however.

The assumption is that the flash only contains information about the rod, but again, that isn't necessarily true, as it will also contain information about its journey to the observer, and the exact distance it has traversed; in the case of the strike at rod B, the information will show that the distance traversed was shorter compared to the flash form rod A.

You mention that what he is seeing is an image from the past, much as what we see of the moon is an image from a second ago, but, strictly speaking, this isn't the case. What he is actually seeing is the light hitting his retina, having travelled a certain distance - much as what we see of the moon is the light from the moon hitting our retina in the present.

Morbert wrote: »

Now we are getting to the crux of the matter. Observer 1(a) and 1(b) and 1(c) (Assuming 1(c) got on the train with 1(a) ) would intuitively conclude that the train is moving, and that the platform is stationary. But is this true? The earth is rotating, so the ground at the equator is moving at 1000 miles per hour. If the train heads off in the opposite direction, it would be stationary, even though observers would assume the train is moving.

So the train would be stationary with respect to the centre of the earth. But is the earth stationary? It is orbiting the sun at 30 kilometres per second. But is the sun stationary? Our solar system is orbiting the galactic centre at 250 kilometres per second. Is the galactic centre stationary? Is the centre of mass of all the galaxies in the universe stationary? Maybe everything is drifting.

The crux of the issue, as far as I can see, isn't the relative motion of either Observer with respect to the earth, the sun, or our solar system; it is that Observer 1 is moving relative to Observer 2, as well as both rods, A and B, while Observer 2 is at rest relative to the rods.

Morbert wrote: »

This is the core lesson of relativity. No instrument or collection of instruments, no matter how sophisticated, no matter how many frames of reference you consider, can produce an absolute velocity. It must always be measured relative to the velocity of something else. This is similar to the abandonment of absolute time. So you should really be arguing against the author.

With respect to the instruments, would some form of sophisticated laser measurement system not provide relevant information? If each rod was fitted with some form of emitter which was capable of registering lightning strikes; if the emitter sent out a constant pulse to a device monitored by Observer 1, and sent out a single, different pulse when strick by lightning, but then reverted back to its usual signal, could some form of triangulation be set up, which would provide more accurate info?

roosh · 07-09-2011 6:28pm

Morbert wrote: »

Has he gotten back to you? I am interested in hearing his response.

he emailed me back, but I must have another read of what he says, to make sure I understand it.

He asked me not to copy and paste his replies, but if I want, to put it in my own words and reference him - hence the need to re-read.

I'm not sure me being the middle man would be the ideal way to go about questioning him though, but there is a "contact" button on his website which is how I contacted him.

If you do decide to email him, would it be cheeky of me to ask to be ccd on it, as I would be very interested in reading and informed discussion.

Morbert · 07-09-2011 9:33pm

roosh wrote: »

This is how I understand it: Observer 1 is moving relative to Observer 2; Observer 2 is moving relative to Observer 1; at a velocity of 0.8c in both cases. The crux of the issue, as far as I can see, is that Observer 1 is also moving relative to the rods, while Observer 2 is at rest, relative to the rods.

So, strictly from the perspective of Observer 1: he is equidistant from rods A and B when the lighning strikes, but he doesn't know that, and he doesn't know that the lightning has struck because he can't see the rods and the the information doesn't reach him instantaneously.

If Observer 1 moves relative to Observer 2, or vice versa, then Observer 1 and the rods also move relative to each other. Observer 1 doesn't know this, because he can't see the rods, but this is what happens.

Given the positions of the rods relative to one another, and the fact that he and the rods are moving relative to each other, when the light from rod B reaches him, he will no longer be equidistant from both rods; likewise when the light from rod A reaches him.

Again, nobody is disputing that the light will reach him first. The light will reach him at t2 and t4 (from the perspective of oberver 2), and at t2' and t4' from the perspective of observer 1. But since the speed of light is the same for both observers, they must disagree on when the lightning struck. Let my explain why your scenario would mean the speed of light is not the same for all observers:

According to your scenario, rod B is a distance L/2 away when lightning strikes. Both observer 1 and observer 2 are at location x = 0 when this happens. Observer 1 speeds towards the light wave at some velocity v. Let's say he meets the light wave one second after the lightning strikes. So in that second, the wave of light travels at speed c, so that it is a distance of one light-second away from the rod. Both observer 1 and observer 2 would agree that the light was one light-second away from the rod when it met observer 1. Observer 1 would therefore conclude, in agreement with observer 2, that the the lightning struck one second after observer 1 met the wave. The wave would continue on to observer 2 (say 1.5 seconds after the lightning struck). So far so good.

But here is the catch. Observer 1 sees the rod travelling towards him at a speed of v. If the light was able to speed ahead of the rod, so that it was one light-second ahead of the rod after one second, then observer 1 would observe the light travelling at a speed of (c+v)! Otherwise how could it be a light-second ahead of the rod? Observer 1 could do a quick calculation and work out that the speed of light, with respect to its source, is c. But the speed of light is c with respect to all observers, not just the rest-frame of the source.

In other words, if both observers agree about the distance the light travelled before meeting observer 1, and both observers disagree about the motion of the rod, then they cannot agree on the speed of light.

Here again is another critical issue I think. You mention that when he sees the lighning strike rod B, rob B will actually be closer but the information contained in the flash will be of a rod further away; similiarly, you say the flash from rod A will contain information showing the rod closer, even though it is now further away. I'm not sure this is actually correct however.

The assumption is that the flash only contains information about the rod, but again, that isn't necessarily true, as it will also contain information about its journey to the observer, and the exact distance it has traversed; in the case of the strike at rod B, the information will show that the distance traversed was shorter compared to the flash form rod A.

And to reiterate, what is the distance it has traversed? According to observer 2, the rod is stationary, and the light has traversed a distance of one light second to meet observer 1. But according to observer 1, if we follow your train of thought, the rod is observed to be moving towards him at speed v, and the light still traverses a light-second ahead of the rod.

You mention that what he is seeing is an image from the past, much as what we see of the moon is an image from a second ago, but, strictly speaking, this isn't the case. What he is actually seeing is the light hitting his retina, having travelled a certain distance - much as what we see of the moon is the light from the moon hitting our retina in the present.

You are reading to much into my use of the word image. I meant it in the same way a photograph is an "image" of the past. We don't directly see the moon, but instead see an "image" of where it was when the light left it. Likewise, observer 1 sees an image of where the rod was when light left it. I cannot stress enough that, when scientists are talking about time dilation, or the lack of an absolute present, they are not merely talking about the different times of detection of light. That is incorporated into relativity.

The crux of the issue, as far as I can see, isn't the relative motion of either Observer with respect to the earth, the sun, or our solar system; it is that Observer 1 is moving relative to Observer 2, as well as both rods, A and B, while Observer 2 is at rest relative to the rods.

Then what is the absolute "present"? What must we be stationary with respect to in order to determine the true present?

With respect to the instruments, would some form of sophisticated laser measurement system not provide relevant information? If each rod was fitted with some form of emitter which was capable of registering lightning strikes; if the emitter sent out a constant pulse to a device monitored by Observer 1, and sent out a single, different pulse when strick by lightning, but then reverted back to its usual signal, could some form of triangulation be set up, which would provide more accurate info?

We can assume from the start that any postulated observer is using instruments with perfect precision. We can even assume the instruments are better than is physically possible.

finnegann · 08-09-2011 1:15pm

Joycey wrote: »

Sorry for the late reply, ive only just seen this.

Well if you take as your definition of a "now" - a given unchanging arrangement of all the matter in the universe, then there are indeed "nows" in relativity. The snapshot metaphor captures the idea nicely IMO.

I think one of the main attractions to Barbour of his theory is that it makes relativity and quantum physics cohere, at least to some extent, by removing the idea of time from them at all, thus removing a central area of conflict between the two theories.

I like that idea, and undoubtedly this is what time is, however what you have done is simply expressed the truth that cohabitation of space is possible, you have not really explained anything in saying it.

I think you have mixed up cause and effect, like what Joe was saying above, in that rather than "without it nothing would happen as all things would be fixed in place", its more something like this "different arrangements of matter are observed to occur, hence a concept of time arises in us in order to comprehend this difference". Time is not an objective phenomenon which permits this difference, it is the apphrehension of this difference that leads us to believe in time.

A lot of the "philosophers" on this thread seem keen to make the distinction between what "objectively exists" and what "appears to exist" only as some mental construct.
Let's throw time into the second bin but we'll have our consciousness and various phenomena in the first one. On what grounds? With this sort of solipsistic paranoia why stop
at time? Maybe nothing has an objective reality... You can see how this line of reasoning quickly trips up and falls down the stairs of common sense.

If you are interested in the nature of time, my advice would be to put down the dusty old Aquinas and Kant tomes, give eastern mystics a wide birth and listen to what some
physicists have to say. The nature of time is far from an "outdated orthodoxy" but is the subject of intense and exciting debate within many fields of physics. I'll just mention
one that hasn't been discussed here- The arrow of time.

The direction of time is a curious idea in thermodynamics. As the universe moves forward in time it gets more and more disordered. Think of
an ice cube being dropped into a cup of tea... The ice cube will heat up and melt, the energy transaction will never happen backwards with heat suddenly escaping an ice cube
shaped volume in the middle of a cup of tea creating a single floating cube in an otherwise hot cup! Entropy (as this disorder is known) is sometimes fobbed off as a statistical
law, but the fact that it can only happen in one direction means that there is a fundamental link between the mechanics of energy transfer at the smallest measurable scales and
this arrow of time. Some theorists believe that if the universe continues to expand and lose entropy, eventually (trillions of years down the line) there will be no more energy
to dissipate (sometimes called the "heat-death" of the universe) and as such, since entropy will have stopped there will be no more arrow of time, in effect time will end. Seems
hard to get your head around (in the same way as the beginning of time some 14 billion years ago is hard to get your head around).

roosh · 09-09-2011 8:14pm

Morbert wrote: »

Again, nobody is disputing that the light will reach him first. The light will reach him at t2 and t4 (from the perspective of oberver 2), and at t2' and t4' from the perspective of observer 1. But since the speed of light is the same for both observers, they must disagree on when the lightning struck. Let my explain why your scenario would mean the speed of light is not the same for all observers:

According to your scenario, rod B is a distance L/2 away when lightning strikes. Both observer 1 and observer 2 are at location x = 0 when this happens. Observer 1 speeds towards the light wave at some velocity v. Let's say he meets the light wave one second after the lightning strikes. So in that second, the wave of light travels at speed c, so that it is a distance of one light-second away from the rod. Both observer 1 and observer 2 would agree that the light was one light-second away from the rod when it met observer 1. Observer 1 would therefore conclude, in agreement with observer 2, that the the lightning struck one second after observer 1 met the wave. The wave would continue on to observer 2 (say 1.5 seconds after the lightning struck). So far so good.

But here is the catch. Observer 1 sees the rod travelling towards him at a speed of v. If the light was able to speed ahead of the rod, so that it was one light-second ahead of the rod after one second, then observer 1 would observe the light travelling at a speed of (c+v)! Otherwise how could it be a light-second ahead of the rod? Observer 1 could do a quick calculation and work out that the speed of light, with respect to its source, is c. But the speed of light is c with respect to all observers, not just the rest-frame of the source.

In other words, if both observers agree about the distance the light travelled before meeting observer 1, and both observers disagree about the motion of the rod, then they cannot agree on the speed of light.

OK, both observers agree on the speed of light, that is a given from the outset; what they can differ on is either the simultaneity of events, or the distance the light had to travel.

The thought experiment works on the assumption that Observer 1 will measure each rod as being equidistant from him, when he observers their respective flashes. That is the assumption that is being challenged.

To try and demonstrate why it is inaccurate, we need to introduce a few more props. If we introduce a third rod that is located mid-way between A and B, and if we assume that the track on which the train is running is actually graduated, like a measuring stick. Then, if we assume that the Observer on the train is carrying precision photography equipment, which captures exactly what he himself observes.

Picturing the event again, we can make the analogy between the flash of lightning and the flash from a camera, only in reverse. When the light from each rod reaches the photography equipment it registers much like a photo, encoding the information and giving a perfect representation of what the Observer on the train will see.

When the flash from rod B reaches the camera it will not only register the picture of the rod, but also the associated measurement on the graduated track. When the light from rod A reaches the camera, it will do likewise, with one difference, it will also register the rod at the mid-way point.

Comparing the two photographs the Observer on the train should conclude that the light had to travel different distances to him.

The track could also be set up with triggers at each of the three rods, which register with a device on the train, which will allow anyone who checks the Odometer to measure the distance between each rod, and the overall distance between rods A and B.

Morbert wrote: »

And to reiterate, what is the distance it has traversed? According to observer 2, the rod is stationary, and the light has traversed a distance of one light second to meet observer 1. But according to observer 1, if we follow your train of thought, the rod is observed to be moving towards him at speed v, and the light still traverses a light-second ahead of the rod.

the distance traversed is the distance the light has to travel before reaching the Observer, as you indicated above, the Observer on the train will not meet each "beam" of light at the mid-point between the rods.

The issue with the assumption that the Observer on the train will measure both rods as being equidistant, is how does the light - which is carrying the information - get encoded with information it hasn't actually encountered, in the case of the light from rod B, and lose information it has encountered, in the case of the light from rod A.

Morbert wrote: »

You are reading to much into my use of the word image. I meant it in the same way a photograph is an "image" of the past. We don't directly see the moon, but instead see an "image" of where it was when the light left it. Likewise, observer 1 sees an image of where the rod was when light left it. I cannot stress enough that, when scientists are talking about time dilation, or the lack of an absolute present, they are not merely talking about the different times of detection of light. That is incorporated into relativity.

I understood the use of the term "past", but I was just trying to give a more accurate representation of the phenomenon.

Morbert wrote: »

Then what is the absolute "present"? What must we be stationary with respect to in order to determine the true present?

If we go back to your example of the people standing around a radio, you mentioned that each hears the radio at a different decible, so which is the true snapshot? The true snapshot is of both observers and what they hear, not just one persons perpcetption of it; the true snapshot is the room and everything in it at that particular moment, whatever form that takes.

Yahew · 09-09-2011 8:21pm

This conversation is as dull as dishwater.

The fact that observers see light strike them at different times says nothing about the non-existence of time, in the general theory this spacetime time is assumed to be a 4th dimension, which is not a proof of it's non-existance, but the opposite.

And as finnegann suggests, my bedroom doesn't make itself. The universe is trending in the direction of entropy. Thats clear in real life, and it's clear in the general and special theories regardless of when light hits the specific observers.

roosh · 09-09-2011 8:41pm

Yahew wrote: »

This conversation is as dull as dishwater.

The fact that observers see light strike them at different times says nothing about the non-existence of time, in the general theory this spacetime time is assumed to be a 4th dimension, which is not a proof of it's non-existance, but the opposite.

And as finnegann suggests, my bedroom doesn't make itself. The universe is trending in the direction of entropy. Thats clear in real life, and it's clear in the general and special theories regardless of when light hits the specific observers.

In the context of the discussion, time dilation, and the non-simultaneity of events, was being used as evidence to demonstrate the existence of time. That is the point that is being challenged. It doesn't prove that time doesn't exist, it simply attempts to refute any evidence for the existence of time.

As such, the argument is that there is no evidence which, when correctly interpreted, supports the contention that time exists. The assumption that time forms a fourth dimension is not proof that time exists, because it is circular reasoning.

I was going to respond to finnegans post later on, but I'll have a look at it again. Needless to say, I'm going to be asking how the universe tending towards disorder is evidence of the existence of time?

Feel free to offer your thoughts.

roosh · 09-09-2011 8:53pm

finnegann wrote: »

A lot of the "philosophers" on this thread seem keen to make the distinction between what "objectively exists" and what "appears to exist" only as some mental construct.
Let's throw time into the second bin but we'll have our consciousness and various phenomena in the first one. On what grounds? With this sort of solipsistic paranoia why stop
at time? Maybe nothing has an objective reality... You can see how this line of reasoning quickly trips up and falls down the stairs of common sense.

If you are interested in the nature of time, my advice would be to put down the dusty old Aquinas and Kant tomes, give eastern mystics a wide birth and listen to what some
physicists have to say. The nature of time is far from an "outdated orthodoxy" but is the subject of intense and exciting debate within many fields of physics. I'll just mention
one that hasn't been discussed here- The arrow of time.

The direction of time is a curious idea in thermodynamics. As the universe moves forward in time it gets more and more disordered. Think of
an ice cube being dropped into a cup of tea... The ice cube will heat up and melt, the energy transaction will never happen backwards with heat suddenly escaping an ice cube
shaped volume in the middle of a cup of tea creating a single floating cube in an otherwise hot cup! Entropy (as this disorder is known) is sometimes fobbed off as a statistical
law, but the fact that it can only happen in one direction means that there is a fundamental link between the mechanics of energy transfer at the smallest measurable scales and
this arrow of time. Some theorists believe that if the universe continues to expand and lose entropy, eventually (trillions of years down the line) there will be no more energy
to dissipate (sometimes called the "heat-death" of the universe) and as such, since entropy will have stopped there will be no more arrow of time, in effect time will end. Seems
hard to get your head around (in the same way as the beginning of time some 14 billion years ago is hard to get your head around).

Instead of just listening to what some physicists have to say, and blindly accepting it, why not question it for yourself and challenge the assumptions where you meet them, regardless of the authority of the person who holds them.

As the course is changed to give eastern mystics a wide-berth, why not look out the window and see what you pick up on the way. Perhaps this quote attributed to "the Buddha" might be food for thought

Do not believe in anything simply because you have heard it. Do not believe in anything simply because it is spoken and rumored by many. Do not believe in anything simply because it is found written in your religious books. Do not believe in anything merely on the authority of your teachers and elders. Do not believe in traditions because they have been handed down for many generations. But after observation and analysis, when you find that anything agrees with reason and is conducive to the good and benefit of one and all, then accept it and live up to it.

Now, how exactly is the fact that the universe is tending towards disorder, or increased entropy, evidence for anything other than the fact that the universe is tending towards disorder, or increased entropy?

Where, in the smashing of a cup on the floor not happeing in reverse, is time to be seen?

Yahew · 09-09-2011 8:58pm

roosh wrote: »

Now, how exactly is the fact that the universe is tending towards disorder, or increased entropy, evidence for anything other than the fact that the universe is tending towards disorder, or increased entropy?

Where, in the smashing of a cup on the floor not happeing in reverse, is time to be seen?

Um, because it doesn't ever reverse the process, hence the arrow of time moves in the direction of entropy.

By the way, it's interesting that your argument against "authority" - the physicists who can do the hard maths on this - was using an Eastern mystic and was itself an argument to authority.

roosh · 09-09-2011 9:14pm

Yahew wrote: »

Um, because it doesn't ever reverse the process, hence the arrow of time moves in the direction of entropy.

again, how exactly does the "arrow of time" move in the direction of entropy, what you have shown is that the arrow of entropy moves in one direction i.e. that the universe moves from order to disorder - where does time come into it?

Yahew wrote: »

By the way, it's interesting that your argument against "authority" - the physicists who can do the hard maths on this - was using an Eastern mystic and was itself an argument to authority.

except that it wasn't, it was the opposite of an argument from authority because the point being made wasn't, hey accept what this guy says because he is an eastern mystic - which would have been an argument from authority (except that wasn't what was said) - it was don't accept arguments from authority, oh, and here is an eastern mystic who says it too, but hey, don't just accept it because he said it, hold it up to scrutiny.

EDIT: btw, if you are disagreeing with what is said in the quote, then you are advocating arguments from authority

Yahew · 09-09-2011 9:18pm

roosh wrote: »

again, how exactly does the "arrow of time" move in the direction of entropy, what you have shown is that the arrow of entropy moves in one direction i.e. that the universe moves from order to disorder - where does time come into it?

The direction of entropy is the direction of time. I thought I explained that. This isn;t a semantic game, it is the explanation of the direction of time. You might well have noticed this yourself when you put an ice cube in a cup of tea.

except that it wasn't, it was the opposite of an argument from authority because the point being made wasn't, hey accept what this guy says because he is an eastern mystic - which would have been an argument from authority (except that wasn't what was said) - it was don't accept arguments from authority, oh, and here is an eastern mystic who says it too, but hey, don't just accept it because he said it, hold it up to scrutiny.

Yet, you didn't quote Chidyun Nyugen from Nagkik, you quoted Buddha, a figure of authority. I was reminded of a scene from Python, you know the one.

In any case the questioning of authority as a "proof" is not acceptable in and of itself, so lets leave that to wither on the vine.

roosh · 09-09-2011 9:35pm

Yahew wrote: »

The direction of entropy is the direction of time. I thought I explained that. This isn;t a semantic game, it is the explanation of the direction of time. You might well have noticed this yourself when you put an ice cube in a cup of tea.

You may have thought that you explained it, but you didn't explain it at all.

The direction of entropy is the direction of entropy, how can it possibly be the direction of time also?

While I've never put an ice cube in a cup of tea, I can imagine the penomenon you are referring to; again, however, how is a melting ice cube evidence for time? The fact that the process doesn't happen in reverse doesn't show that time exists, it shows that an ice cube won't reform after it is melted.

Again, the imagined arrow of direction applies to entropy and not a separate, existential property called time.

Yahew wrote: »

Yet, you didn't quote Chidyun Nyugen from Nagkik, you quoted Buddha, a figure of authority. I was reminded of a scene from Python, you know the one.

If I was familiar with a quote form the aforementioned I would have quoted it, but I'm not, and even if I had it would still not have made any difference to the fact that it wasn't an argument from authority.

Here:

Quoting something from an "authority" and saying, here, look, this authority says it, therefore, it is true = argument from authority
Saying, don't accept something as true because an authority figure says it is, and then quoting an "authority" figure who says don't accept arguments from authority ≠ argument from authority

EDIT:

Yahew wrote: »

In any case the questioning of authority as a "proof" is not acceptable in and of itself, so lets leave that to wither on the vine.

Indeed

Morbert · 12-09-2011 4:44pm

roosh wrote: »

OK, both observers agree on the speed of light, that is a given from the outset; what they can differ on is either the simultaneity of events, or the distance the light had to travel.

The thought experiment works on the assumption that Observer 1 will measure each rod as being equidistant from him, when he observers their respective flashes. That is the assumption that is being challenged.

Yes, and to clarify: For any one lightning strike, the rods will not be equidistant. I.e. When Rod B is struck, rod A and rod B will not be the same distance from observer 1. But when rod B is struck, it will be a distance of ɣL/2 from observer 1. When rod A is struck, at a later time, it will also be a distance of ɣL/2. This is all from observer 1's perspective of course.

To try and demonstrate why it is inaccurate, we need to introduce a few more props. If we introduce a third rod that is located mid-way between A and B, and if we assume that the track on which the train is running is actually graduated, like a measuring stick. Then, if we assume that the Observer on the train is carrying precision photography equipment, which captures exactly what he himself observes.

Picturing the event again, we can make the analogy between the flash of lightning and the flash from a camera, only in reverse. When the light from each rod reaches the photography equipment it registers much like a photo, encoding the information and giving a perfect representation of what the Observer on the train will see.

Yes. As I mentioned earlier. We can assume the observers have infinitely precise instruments.

When the flash from rod B reaches the camera it will not only register the picture of the rod, but also the associated measurement on the graduated track. When the light from rod A reaches the camera, it will do likewise, with one difference, it will also register the rod at the mid-way point.

Comparing the two photographs the Observer on the train should conclude that the light had to travel different distances to him.

The track could also be set up with triggers at each of the three rods, which register with a device on the train, which will allow anyone who checks the Odometer to measure the distance between each rod, and the overall distance between rods A and B.

the distance traversed is the distance the light has to travel before reaching the Observer, as you indicated above, the Observer on the train will not meet each "beam" of light at the mid-point between the rods.

The issue with the assumption that the Observer on the train will measure both rods as being equidistant, is how does the light - which is carrying the information - get encoded with information it hasn't actually encountered, in the case of the light from rod B, and lose information it has encountered, in the case of the light from rod A.

How is this an issue with relativity?

In post # 54, I derived the times of the lightning strikes.

Morbert wrote:

Now let's look at the times. Lightning strikes Rod A at

t' = ɣ(t - vxA/c^2) = ɣ(0 - vxA/c^2) = -ɣvxA/c^2

It strikes Rod B at

t' = ɣ(t - vxB/c^2) = ɣ(0 - vxB/c^2) = -ɣvXB/c^2.

xA is -L/2 and xB is +L/2, so the times for rod A and B are +ɣvL/2c^2 and -ɣvL/2c^2 respectively. Notice that the time for rod A is positive and rod B is negative. This means rod B is struck before observer 1 passes the midpoint, and rod A is struck after observer 1 passes the midpoint. So the light wave from rod A passes the midpoint, and hence the new rod, on its way to observer 1.

The graduated ruler between the rods would be a distance L in observer 2's frame of reference, and L/ɣ in observer 1's frame of reference.

None of this is an issue for relativity and I am wondering why you would think it is. If this is the reasing the author has given you, then he should know better. In short, he is neglecting length contraction, which will account for the rod positions.

If we go back to your example of the people standing around a radio, you mentioned that each hears the radio at a different decible, so which is the true snapshot? The true snapshot is of both observers and what they hear, not just one persons perpcetption of it; the true snapshot is the room and everything in it at that particular moment, whatever form that takes.

But I didn't ask for the true snapshot of the radio. I asked for the true decibel level of the radio. Do you believe there is a single 'true' decibel level?

In the context of the discussion, time dilation, and the non-simultaneity of events, was being used as evidence to demonstrate the existence of time. That is the point that is being challenged. It doesn't prove that time doesn't exist, it simply attempts to refute any evidence for the existence of time.

This isn't what they were being used for. They were being used to demonstrate that there is no single "present", and how Julian Barbour's timeless universe is consistent with relativity and very different to what you are proposing, which contradicts relativity.

finnegann · 12-09-2011 5:10pm

Ok, first of all- No serious scientist (bar a mathematician) would ever try to "PROVE" the existence of something. As a side project- perhaps you'd like to pick your favourite existent phenomena or object and apply the same ridiculous rigor in an attempt to prove it exists as you seem to be demanding of time.
Now, as for "blindly following" some physicists opinions... I pointed out that the concept of time is the subject of intense and exiting debate. Scientists disagree with one another more than anybody else over questions like this! Try to get beyond this idea of the old dogmatic orthodoxy of scientists blindly swallowing what their superiors have thought them and poisoning the minds of the rest of us. That's not how science works. In fact that's exactly the opposite of what happens. As for the Buddha quote- Nice quote. I think the last sentence captures the scientific ethos perfectly.
Finally, to return to the first point- the "entropy definition" of time (again this is one of many theories) like any other theory can only be said to explain the true nature of time in as much as it's predictions and experimental observations conform and coincide with more and more evidence. My point was that these lines of inquiry are out best attempt at grasping the true picture of reality.

roosh · 16-09-2011 2:46pm

I'll separate the response to your post into that specifically dealing with Special Relativity, and the shorter point on the "true present".

OK, I can see now that I haven't entirely understood the whole notion of the length contraction. To a certain extent is appears as though you are assuming your conclusion, but I know that length contraction is a direct consequence of the Michelson Morley experiment (MMX) - so I've been trying to get a better grasp of that; incidentally, the author of the webite (who I by no means accept as being definitively correct) offers an alternative reason for the null result of the MMX.

It could be, and to your mind quite probably is, down to my lack of understanding of Special Relativity and Length contraction, but, as mentioned, it appears as though there is circular reasoning involved, or perhaps more pointedly that the reasoning involves smoke and mirrors - I'm not saying that you are, or anyone else is, deliberately attempting to deceive, because I don't think that, it just appears - to my mind - that that there is faulty reasoning in there somewhere, which is difficult to pin down because of the different reference frames; again, this could quite easily be down to my misunderstanding of SR.

If you have the inclination to continue then we might either tease that circular reasoning out, or I will learn where I am going wrong in my understanding of Special Relativity and length contraction.

If not, the separate point on the "true present" might be a prefarable point of continuation.

roosh · 16-09-2011 4:28pm

Morbert wrote: »

Yes, and to clarify: For any one lightning strike, the rods will not be equidistant. I.e. When Rod B is struck, rod A and rod B will not be the same distance from observer 1. But when rod B is struck, it will be a distance of ɣL/2 from observer 1. When rod A is struck, at a later time, it will also be a distance of ɣL/2. This is all from observer 1's perspective of course.

In post # 54, I derived the times of the lightning strikes.

xA is -L/2 and xB is +L/2, so the times for rod A and B are +ɣvL/2c^2 and -ɣvL/2c^2 respectively. Notice that the time for rod A is positive and rod B is negative. This means rod B is struck before observer 1 passes the midpoint, and rod A is struck after observer 1 passes the midpoint. So the light wave from rod A passes the midpoint, and hence the new rod, on its way to observer 1.

None of this is an issue for relativity and I am wondering why you would think it is. If this is the reasing the author has given you, then he should know better. In short, he is neglecting length contraction, which will account for the rod positions.

The emboldened sentences above I think capture where my lack of understanding of length contraction is, and probably ɣ.

Firstly - and this may seem like a silly question - but does the distance ɣL/2 (from

equal the distance ɣL/2 (from A) - or is there something in the calculation of ɣ that means that they are not the same distance.

I've been assuming that the both distances are equal, and represent the distance from the midpoint to both A & B, from the perspective of Observer 1 (on the train).

It is this assumption which has lead me to question how, if Rod B is struck before Observer 1 passes it, can the distance be ɣL/2?
-I'm assuming here you mean at a point before the midpoint and not before he has passed it, as in, as he is passing it

Also, if Rod A is struck after Observer 1 passes the midpoint, how can the distance to Observer 1 be ɣL/2?

Morbert wrote: »

The graduated ruler between the rods would be a distance L in observer 2's frame of reference, and L/ɣ in observer 1's frame of reference.

Just on this point: it isn't so much that there is a graduated ruler for each Observer, it is more that the track along which the train is running is graduated like a ruler.

The issue is that the track forms part of Observer 2's reference frame, because the [graduated] train track and Oberver 2 are stationary with respect to each other, while Observer 1 is moving relative to both.

Am I right in saying that Observer 1's reference frame [should] consist of solely him and the train; and that the length of the train tracks should contract from his perspective [particularly between the rods]?

roosh · 16-09-2011 5:04pm

Morbert wrote: »

But I didn't ask for the true snapshot of the radio. I asked for the true decibel level of the radio. Do you believe there is a single 'true' decibel level?

This isn't what they were being used for. They were being used to demonstrate that there is no single "present", and how Julian Barbour's timeless universe is consistent with relativity and very different to what you are proposing, which contradicts relativity.

I'll take these two points together, because they relate to the idea of a "true present".

Seeing as thought experiments are a bit of theme in this discussion, I'll propose, again, the idea of a "universal pause button", a button which, when pushed, pauses the entire universe; it pauses the planets in their orbits; it pauses trains travelling at 80% the speed of light; it pauses light waves, sound waves and the waves in the ocean; it pauses the neural activity of every brain in the universe; it pauses every single sub-atomic particle in their relative positions; it pauses the membrane in 11-dimensional space (if that is indeed an accurate representation of reality)

Now, if we take the room with the radio as a microcosmic view, and imagine that this pause button is pushed and everything freezes where it is, then that is the "true present" - whatever form that is, but not necessarily from any one persons perspective.

There isn't necessarily a "single 'true' decibel level", there is the [frozen] sound wave which has arrived at more than the ears of a single person; there is the corresponding brain activity in each individual, which gives rise to their interpretation of the sound; there are the atoms of everything in the room frozen in their relative positions.

In the case of Observers 1 & 2, if the universal pause button is hit, then the "true present" would be all the sub-atomic particles frozen in their relative positions; the neural activity of the observers (which gives rise to their persepectives) frozen; the photons frozen in their relative positions; the fold in spacetime (or whatever it is that happens to give rise to length contraction between two connected reference frames).

Again, the "true present" isn't necessarily seen from any one persons perspective, just imagine the entire universe being paused, and whatever the "state of play" is, that is the "true present".

Whatever form it takes, that would be the true present.

Morbert · 16-09-2011 6:23pm

roosh wrote: »

The emboldened sentences above I think capture where my lack of understanding of length contraction is, and probably ɣ.

Firstly - and this may seem like a silly question - but does the distance ɣL/2 (from equal the distance ɣL/2 (from A) - or is there something in the calculation of ɣ that means that they are not the same distance.

I've been assuming that the both distances are equal, and represent the distance from the midpoint to both A & B, from the perspective of Observer 1 (on the train).

It is this assumption which has lead me to question how, if Rod B is struck before Observer 1 passes it, can the distance be ɣL/2?
-I'm assuming here you mean at a point before the midpoint and not before he has passed it, as in, as he is passing it

Also, if Rod A is struck after Observer 1 passes the midpoint, how can the distance to Observer 1 be ɣL/2?

It's not a silly question. ɣ is a scaling factor. A constant. The best way is by illustration.

Here is the situation from observer 2's frame of reference. Very straightforward.

Here is observer 1's frame of reference when the first rod is struck. Note that these pictures are of when the lightning actually strikes, not when an observer detects the strikes.

From this reference frame, it is the rods (and observer 2) that are moving. Notice that first rod is struck before observer 2 passes observer 1. The distance between the rods is shortened to L/ɣ. But observer 1 is not equally distant from both rods. So the distance between the lightning strike and him is not L/2ɣ, but rather ɣL/2 (a longer distance than L/2).

Then, the other rod is struck.

Here, observer 1 has passed the midpoint. Again I stress that these are not detection times. These are the actual strikes, calculated by the observers if the speed of the flashes are the same in both reference frames.

Just on this point: it isn't so much that there is a graduated ruler for each Observer, it is more that the track along which the train is running is graduated like a ruler.

The track itself, everything along the direction of travel, will be contracted.

The issue is that the track forms part of Observer 2's reference frame, because the [graduated] train track and Oberver 2 are stationary with respect to each other, while Observer 1 is moving relative to both.

Am I right in saying that Observer 1's reference frame [should] consist of solely him and the train; and that the length of the train tracks should contract from his perspective [particularly between the rods]?

Both reference frames contain everything. The difference is the train is moving according to observer 2, and the tracks and rods are moving according to observer 1. Relativity say neither is more correct. You can interpret the tracks as stationary, or as moving due to the rotation of the earth, or the solar system, or the galaxy, or the universe etc. No reference frame is more physically meaningful than any other.

Morbert · 16-09-2011 6:40pm

roosh wrote: »

There isn't necessarily a "single 'true' decibel level", there is the [frozen] sound wave which has arrived at more than the ears of a single person; there is the corresponding brain activity in each individual, which gives rise to their interpretation of the sound; there are the atoms of everything in the room frozen in their relative positions.

Bingo. There isn't a single present. There is instead a 4-dimensional set of all events. It is the reference co-ordinates adopted which give rise to a "present, past, and future". Different co-ordinate systems mean different "present"s. This point was raised to show that relativity does not suppose each reference frame is a separate universe, but rather each frame is a different co-ordinate system applied to the same physical reality. Physics is largely about identifying what is the same for all observers. I.e. The structure of causal relationships, the speed of light, and the laws of physics are the same in all reference frames. "Past, present, and future" are not.

In the case of Observers 1 & 2, if the universal pause button is hit, then the "true present" would be all the sub-atomic particles frozen in their relative positions; the neural activity of the observers (which gives rise to their persepectives) frozen; the photons frozen in their relative positions; the fold in spacetime (or whatever it is that happens to give rise to length contraction between two connected reference frames).

Again, the "true present" isn't necessarily seen from any one persons perspective, just imagine the entire universe being paused, and whatever the "state of play" is, that is the "true present".

Whatever form it takes, that would be the true present.

Let's push the pause button when observer 1 passes observer 2. According to observer 2, the lightning strikes would be frozen at the moment they strike the poles. But according to observer 1, there would be no lightning strikes in the present, since one has already happened, and the other is yet to happen. Which is the true present?

roosh · 20-09-2011 4:26pm

@Morbert - I am mindful of the probability that trying to explain some of the finer points of SR to someone who doesn't fully understand it, and who is actively trying to find fault with it - which, it must be said, will have the effect of either actually finding fault with it, or developing a better understanding of it (for me) - will become a nuisance, so again, I have to enquire if you are are content enough to continue with the "remedial class" on SR, or if you would prefer that a separate thread be started elsewhere (in the appropraite forum).

As it is more beneficial for me, than I imagine it is for you, I am content to continue.

Morbert · 20-09-2011 8:33pm

roosh wrote: »

@Morbert - I am mindful of the probability that trying to explain some of the finer points of SR to someone who doesn't fully understand it, and who is actively trying to find fault with it - which, it must be said, will have the effect of either actually finding fault with it, or developing a better understanding of it (for me) - will become a nuisance, so again, I have to enquire if you are are content enough to continue with the "remedial class" on SR, or if you would prefer that a separate thread be started elsewhere (in the appropraite forum).

As it is more beneficial for me, than I imagine it is for you, I am content to continue.

Feel free to continue. A good command of our current physical theories about time can only help any philosophical positions you might take.

roosh · 21-09-2011 1:26pm

@Morbert - to try and understand the explanation of SR better, I have gone back over our discussion and tried to see if there are things I've misinterpreted - such as reading ɣL/2 as L/2ɣ. In so doing I came across a few things that I am having trouble reconciling; these could indicate where I am having trouble.

I am not entirely sure of the significance of the points.

Observer 2 perspective: Basic Fractions

Morbert wrote: »

According to observer 2: The rods are a distance L apart (Rod A is at location xA. Rod B is at location xB. Observer 2 is at x = 0). Let's say, for simplicity, that according to observer 2, the strikes both occur at t = 0. I.e. Observer 2 will detect both flashes simultaneously, at t = L/2c (Or t3 to use you name), and deduce that they occurred at t = 0. In this same reference frame, the light from rods A and B will reach observer 1 at times L/2(c+v) and L/2(c-v) respectively (or t2 and t4 to use your names).

On this point, I don't really understand how the times, that the light from rods A and B will reach observer 1, are worked out as L/2(c+v), for A, and L/2(c-v), for B.

I think it is down to how I undertand the inofrmation in the equations. How I understand the formulae is as follows:
L/2(c+v): basically, from the perspective of Observer 2 (on the platform), the time the light from Rod A will reach observer one is: the time it takes the light to travel from Rod A to the midpoint (L/2c), plus the length of time it takes Observer 1 to travel the same distance (L/2v).

I'm presuming I'm making a very basic error with regard to fractions, as I am reading L/2(c+v) as L/2c + L/2v

Observer 2 perspective: measurement

This isn't, I don't think, down to a basic error in mathematics, but there may be an error in comprehension there somewhere.

Morbert wrote: »

The short, handwavey answer to this is the author is not treating observer 1 correctly. Observer 1 would not say the distance the light has to travel is L/2 - distance travelled by the train. From observer 1's perspective, he is stationary, and instead the light has to travel a distance of ɣL/2.

Morbert wrote: »

From observer 1's perspective, the lightning events are equidistant to him (The total distance being ɣL), but they occur at different times. When rod B is struck, it is a distance ɣL/2 away from observer 1. This occurs before both rods are equidistant to observer 1. (I probably should have shown in my last post that there is a length contraction between the rods. They are a distance L/ɣ. The ɣL should be called the distance between lightning strikes.) So by the time observer 1 is passing observer 2, there has already been a bolt of lightning.

Morbert wrote: »

It's not a silly question. ɣ is a scaling factor. A constant. The best way is by illustration.

Here is the situation from observer 2's frame of reference. Very straightforward.

Here is observer 1's frame of reference when the first rod is struck. Note that these pictures are of when the lightning actually strikes, not when an observer detects the strikes.

From this reference frame, it is the rods (and observer 2) that are moving. Notice that first rod is struck before observer 2 passes observer 1. The distance between the rods is shortened to L/ɣ. But observer 1 is not equally distant from both rods. So the distance between the lightning strike and him is not L/2ɣ, but rather ɣL/2 (a longer distance than L/2).

Then, the other rod is struck.

OK, from this I understand that the distance from Observer 1 to each event, at their respective times, is ɣL/2.

Morbert wrote: »

The same goes for rod A. Rod A will be further away, but he will not observe rod A to be further away as that information has not reached him. What he sees is how far away rod A was when it was struck. This allows him to calculate the distance travelled by the light, and deduce when rod A was struck.

Morbert wrote: »

He won't "see" the rod closer to him. When the lightning struck, rod B was a distance of ɣL/2 away from him. So the flash of light contains information about a rod of distance ɣL/2 away. At the instant he sees the flash, the rod will be closer, but he won't see a closer rod because that information has not reached him yet. So he sees a rod ɣL/2 away get struck. He knows he is seeing an image from the past, and by considering the speed of light and the distance it travelled, he can work how when, in the past, the lightning struck. He will reach a different conclusion to observer 2.

From the above I understand that Observer 1 will measure the distance of each event as ɣL/2.

An issue, as I see it
Observer 1 won't measure the distance of either strike as ɣL/2; because Observer 1 is travelling relative to "distance" also.

That may seem like a strange statement, but if we consider what the distance actually is, we can see that it can be expressed as the length of track between Observer 1 and the rods; as this is the information which will be encoded by the light.

If Observer 1 is ɣL/2 from Rod B at the time of the strike, by the time the light reaches Observer 1 the track will have moved relative to him, and so the light will not have to traverse as much of the track, thus encoding a distance shorter than ɣL/2.

Would it be [roughly] a distance of 5ɣL/18?

I'm not sure if this calculation is correct, but I am basing it on the ratio of the velocity of the track to the speed of light, so that 4/9 of the ɣL/2 length of track will have passsed underneath Observer 1 when the light meets him.

Similarly, if Rod A is ɣL/2 away from Observer 1, when it is struck, when it eventually reaches Observer 1 it will have travelled a length of track longer than ɣL/2, to reach Observer 1, and thus will have a distance of greater than ɣL/2 encoded. I'm not entirely sure what the calculation for that would be - it would probably require a rounding up to avoid invoking Zeno's paradox.

I'm not entirely sure what the implications would be; is there any significance to the idea that the Observer on the train would measure a distance of ɣL/2 to both rods?

Time: t=0
This is just something else I have a question on, because I'm having trouble with the arbitrary designation of t=0, as the occurence of the lightning events at A & B in Observer 2's reference frame. Would it make a difference if t=0 was set as the time that the lightning first manifested from the clouds i.e. the first spark arising from the friction which travels downwards to the earth?

I'm just wondering would both observers disagree on the simultaneity of the flash of lightning travelling towards the earth, before it strikes the rods - as in, would there be a length contraction that would lead them to disagree, or is the flash of lightning not travelling in the direction of motion and therefore there is no length contraction?

roosh · 21-09-2011 1:43pm

Morbert wrote: »

Bingo. There isn't a single present. There is instead a 4-dimensional set of all events. It is the reference co-ordinates adopted which give rise to a "present, past, and future". Different co-ordinate systems mean different "present"s. This point was raised to show that relativity does not suppose each reference frame is a separate universe, but rather each frame is a different co-ordinate system applied to the same physical reality. Physics is largely about identifying what is the same for all observers. I.e. The structure of causal relationships, the speed of light, and the laws of physics are the same in all reference frames. "Past, present, and future" are not.

Morbert wrote: »

Let's push the pause button when observer 1 passes observer 2. According to observer 2, the lightning strikes would be frozen at the moment they strike the poles. But according to observer 1, there would be no lightning strikes in the present, since one has already happened, and the other is yet to happen. Which is the true present?

I'll respond to the latter of the two points, because I think it goes more to the heart of the argument, and it is a more tangible representation of the preceding point.

It is the idea that either frame of reference represents the "true present"; because the "true present" consists of both reference frames; just as with SR, no one reference frame is preferable to the other.

If we push the button at the time Observer 1 passes Observer 2, then the lightning strikes would be frozen at the rods, but neither would see them, because the light wouldn't have travelled to Observer 2 yet, and the second bolt wouldn't have hit in Observer 1's reference frame.

Given that both referenc frames are connected, because they are in the same universe, and if we assume that it is the same lightning i.e. the same photons, which both Observers witness, then the lightning must be located somewhere in the universe, in some form - there may be some quantum effects at play.

The "true present" would be the flashes of lightning in one reference frame, but not the other, together with the relative locations of all the atoms and photons that make it possible for that to happen. If there is a fold in the spacetime continuum, that results from an Observer travelling at 80% the speed of light, and the light has to travel through that fold, then the true present includes that manipulation of spacetime and the location of the light along it's path.

roosh · 21-09-2011 2:22pm

finnegann wrote: »

Ok, first of all- No serious scientist (bar a mathematician) would ever try to "PROVE" the existence of something. As a side project- perhaps you'd like to pick your favourite existent phenomena or object and apply the same ridiculous rigor in an attempt to prove it exists as you seem to be demanding of time.
Now, as for "blindly following" some physicists opinions... I pointed out that the concept of time is the subject of intense and exiting debate. Scientists disagree with one another more than anybody else over questions like this! Try to get beyond this idea of the old dogmatic orthodoxy of scientists blindly swallowing what their superiors have thought them and poisoning the minds of the rest of us. That's not how science works. In fact that's exactly the opposite of what happens. As for the Buddha quote- Nice quote. I think the last sentence captures the scientific ethos perfectly.

I'm not for a second suggesting that the existence of time needs to be "proven", my position is more akin to that of an atheists position on the existence of God, I'm saying that there is no evidence to support the contention that time exists; and that any such evidence, of which I am aware, is the result of a misinterpretation of the evidence.

Equally, the impression that I have of scientists is not the "idea of the old dogmatic orthodoxy of scientists blindly swallowing what their superiors have thought them and poisoning the minds of the rest of us"; on the contrary, I see scientists as humans and prone the self-same pitfalls of the human condition as the rest of us, with attachment to conditioned beliefs and attachment to things they have invested their entire lives and carreers in - just like the rest of us. Scientists certainly espouse the right ideal, but such is the human condition that they may not always achieve it.

Perhaps something Max Planck recognised when he famously said

A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it

I don't see it as a necessarily deliberate and conscious process, but rather, much like the human condition, the result of sub-conscious conditioning

finnegann wrote: »

Finally, to return to the first point- the "entropy definition" of time (again this is one of many theories) like any other theory can only be said to explain the true nature of time in as much as it's predictions and experimental observations conform and coincide with more and more evidence. My point was that these lines of inquiry are out best attempt at grasping the true picture of reality.

I don't question the value of empirical enquiry, I do sometimes challenge the assumptions on which some of that enquiry is based - not that I am, in any way, alone in that.

Ultimately, the conclusion that entropy is evidence for the existence of time is a philosophical one, because it involves the interpretation of evidence, and the attempt to draw a conclusion from that evidence. It is that conclusion that is open to question.

And the question remains, how is entropy evidence for the existence of time.

Morbert · 21-09-2011 6:35pm

roosh wrote: »

@Morbert - to try and understand the explanation of SR better, I have gone back over our discussion and tried to see if there are things I've misinterpreted - such as reading ɣL/2 as L/2ɣ. In so doing I came across a few things that I am having trouble reconciling; these could indicate where I am having trouble.

I am not entirely sure of the significance of the points.

Observer 2 perspective: Basic Fractions

On this point, I don't really understand how the times, that the light from rods A and B will reach observer 1, are worked out as L/2(c+v), for A, and L/2(c-v), for B.

I think it is down to how I undertand the inofrmation in the equations. How I understand the formulae is as follows:
L/2(c+v): basically, from the perspective of Observer 2 (on the platform), the time the light from Rod A will reach observer one is: the time it takes the light to travel from Rod A to the midpoint (L/2c), plus the length of time it takes Observer 1 to travel the same distance (L/2v).

I'm presuming I'm making a very basic error with regard to fractions, as I am reading L/2(c+v) as L/2c + L/2v

It's not really important, but it doesn't equal L/2c + L/2v. I can go through the derivation if you really want, but what it's basically saying is The order of events is lightning strikes - observer 1 meets first flash - observer 1 meets second flash.

An issue, as I see it
Observer 1 won't measure the distance of either strike as ɣL/2; because Observer 1 is travelling relative to "distance" also.

That may seem like a strange statement, but if we consider what the distance actually is, we can see that it can be expressed as the length of track between Observer 1 and the rods; as this is the information which will be encoded by the light.

If Observer 1 is ɣL/2 from Rod B at the time of the strike, by the time the light reaches Observer 1 the track will have moved relative to him, and so the light will not have to traverse as much of the track, thus encoding a distance shorter than ɣL/2.

Would it be [roughly] a distance of 5ɣL/18?

I'm not sure if this calculation is correct, but I am basing it on the ratio of the velocity of the track to the speed of light, so that 4/9 of the ɣL/2 length of track will have passsed underneath Observer 1 when the light meets him.

Since causality and coincident events must be the same in all reference frames, both observer 1 and observer 2 would agree about what the track ruler would register. Namely, (4/9)(L/2) = 4L/18, so you were close.

Similarly, if Rod A is ɣL/2 away from Observer 1, when it is struck, when it eventually reaches Observer 1 it will have travelled a length of track longer than ɣL/2, to reach Observer 1, and thus will have a distance of greater than ɣL/2 encoded. I'm not entirely sure what the calculation for that would be - it would probably require a rounding up to avoid invoking Zeno's paradox.

Zeno's paradox isn't an issue for modern calculus, as mathematicians have shown that infinite series can converge to a finite value.

You would simply need to solve the simultaneous equations

distance = v * time
distance + L/2 = c * time

The values you end up with are

time = L/2(c-v)
distance = Lv/2(c-v)

I'm not entirely sure what the implications would be; is there any significance to the idea that the Observer on the train would measure a distance of ɣL/2 to both rods?

Observer 1 would say the ruler on the track is wrong, since it is moving. If you want to measure the distance a ball is thrown, you wouldn't move the ruler with respect to the ball. So if you want to measure the distance a photon has travelled, you would not use a moving ruler. Observer 1, if he used his own ruler (say, if the train had graduated marks on its side, would measure the distance to be ɣL/2).

This touches on the issue of light aberration. Light from objects moving relative to the observer will make the objects appear distorted (Note that this is an optical effect, unlike simultaneity, which would be an inherent effect.). It doesn't directly impact this discussion, but it is worth mentioning.

https://www.youtube.com/watch?v=JQnHTKZBTI4

Time: t=0
This is just something else I have a question on, because I'm having trouble with the arbitrary designation of t=0, as the occurence of the lightning events at A & B in Observer 2's reference frame. Would it make a difference if t=0 was set as the time that the lightning first manifested from the clouds i.e. the first spark arising from the friction which travels downwards to the earth?

I'm just wondering would both observers disagree on the simultaneity of the flash of lightning travelling towards the earth, before it strikes the rods - as in, would there be a length contraction that would lead them to disagree, or is the flash of lightning not travelling in the direction of motion and therefore there is no length contraction?

t = 0 is just a label and doesn't affect any of the physics. It just makes some calculations easier. Similarly, when we say lightning strikes, we simply mean the event of the lightning co-incident with the event of the rod. The movement of the storm, the rods, or the lightning is arbitrary.

Morbert · 21-09-2011 6:51pm

roosh wrote: »

I'll respond to the latter of the two points, because I think it goes more to the heart of the argument, and it is a more tangible representation of the preceding point.

It is the idea that either frame of reference represents the "true present"; because the "true present" consists of both reference frames; just as with SR, no one reference frame is preferable to the other.

If we push the button at the time Observer 1 passes Observer 2, then the lightning strikes would be frozen at the rods, but neither would see them, because the light wouldn't have travelled to Observer 2 yet, and the second bolt wouldn't have hit in Observer 1's reference frame.

Given that both referenc frames are connected, because they are in the same universe, and if we assume that it is the same lightning i.e. the same photons, which both Observers witness, then the lightning must be located somewhere in the universe, in some form - there may be some quantum effects at play.

The "true present" would be the flashes of lightning in one reference frame, but not the other, together with the relative locations of all the atoms and photons that make it possible for that to happen. If there is a fold in the spacetime continuum, that results from an Observer travelling at 80% the speed of light, and the light has to travel through that fold, then the true present includes that manipulation of spacetime and the location of the light along it's path.

The bold sentence is the important one. We don't need to worry about quantum effects, as relativity says nothing about them. You are right. It needs to exist in some form in both reference frames. It exists in the present, according to one observer, and the future according to another. This is precisely the point I have been trying to illustrate. Events in the past and future must be just as real as events in the present. To say "only the present exist" would lead to contradictions, as the present is different, depending on which co-ordinate system you use.

What Julian Barbour has done is to frame the universe as the set of all possible configurations, and the notion of "time" or "change" emerges from this structure.

roosh · 22-09-2011 5:49pm

Morbert wrote: »

It's not really important, but it doesn't equal L/2c + L/2v. I can go through the derivation if you really want, but what it's basically saying is The order of events is lightning strikes - observer 1 meets first flash - observer 1 meets second flash.

Cheers, but there's hopefully no need to go through the derivation of it. I just did a quick refresher course on basic fractions on Kahn academy, and I [think I] see where I was going wrong with the basic multiplication of fractions, but I'm still having trouble understanding the information in the formula L/2(c+v).

It is basically (L/2)(1/[c+v]), isn't it? which says that the time it will take the light from Rod A to reach Observer 1 is given as the distance from Rod A to the midpoint divided by the sum of the speed of light plus the relative velocity.

Should it not be though, L/2c + the distance from the midpoint to the Observer, divided by the speed of light, or more pointedly, the overall distance from the rod to the Oberver (when the light reaches him) divided by the speed of light?

Morbert wrote: »

Since causality and coincident events must be the same in all reference frames, both observer 1 and observer 2 would agree about what the track ruler would register. Namely, (4/9)(L/2) = 4L/18, so you were close.

I have a question below about the encoding of information, by the light, which I think this issue is somewhat dependent on.

Morbert wrote: »

Zeno's paradox isn't an issue for modern calculus, as mathematicians have shown that infinite series can converge to a finite value.

It makes intuitive sense, but I had never heard it stated before.

Morbert wrote: »

Observer 1 would say the ruler on the track is wrong, since it is moving. If you want to measure the distance a ball is thrown, you wouldn't move the ruler with respect to the ball. So if you want to measure the distance a photon has travelled, you would not use a moving ruler. Observer 1, if he used his own ruler (say, if the train had graduated marks on its side, would measure the distance to be ɣL/2).

If the ball is at rest, however, and the ruler is moving relative to the ball, to find how much the ruler has moved relative to the ball you could see how much of the ruler has been displaced, no?

Morbert wrote: »

This touches on the issue of light aberration. Light from objects moving relative to the observer will make the objects appear distorted (Note that this is an optical effect, unlike simultaneity, which would be an inherent effect.). It doesn't directly impact this discussion, but it is worth mentioning.

It's probably related to the question of the information encoded by the light, asked below.

Morbert wrote: »

t = 0 is just a label and doesn't affect any of the physics. It just makes some calculations easier. Similarly, when we say lightning strikes, we simply mean the event of the lightning co-incident with the event of the rod. The movement of the storm, the rods, or the lightning is arbitrary.

Doesn't the movement of the lightning from the clouds to the rod affect the co-incident events? If the bolt of lightning moves perpendicular to the direction of motion, would that not mean that no legnth contraction occurs and both Observers would agree on the simultaneity up until the point of the strike?

Consequences
I'm just trying to follow the logical conclusions of this, and there's another issue that I am having trouble getting my head around, and it relates specifically to how light encodes information, and what information it would encode, in the thought experiment.

In order for Observer 1 to measure a distance of ɣL/2 to the pole (or the point of strike), the centre of the expanding sphere of light would have to remain localised a distance of ɣL/2 from Observer 1*, while the expanding sphere moves towards him. If the centre, of the expanding sphere of light, remains localised at the Rod*, then Observer 1 would measure the distance of 5ɣL/18, given that the distance would be displaced at a ratio of 4:5.

*we can install another stationary observer at the point of contact between lightning & rod to portray the idea of the localised centre at ɣL/2; we can also install an observer on the pole to demonstrate the localised centre moving with the pole.

If Observer 1 is ɣL/2 away from the rod when it is struck, then how does the light encode that information? I would have thought it would encode the inforamation as it moved along its path, from the rod to the Observer, which would have included the track and the other elements that made up the scenery; but it can't include the ɣL/2 length of track, because the light won't travel the length of it, as some of the track will have passed beneath Observer 1 by the time the light reaches him - unless the light travels instantly to Observer 1, which we know isn't the case. Can the light encode any information from the moving track, and what information would it encode?

If Observer 1 bases his measurement on the information encoded by the light, how does he do this?

roosh · 22-09-2011 7:15pm

Morbert wrote: »

The bold sentence is the important one. We don't need to worry about quantum effects, as relativity says nothing about them. You are right. It needs to exist in some form in both reference frames. It exists in the present, according to one observer, and the future according to another. This is precisely the point I have been trying to illustrate. Events in the past and future must be just as real as events in the present. To say "only the present exist" would lead to contradictions, as the present is different, depending on which co-ordinate system you use.

What Julian Barbour has done is to frame the universe as the set of all possible configurations, and the notion of "time" or "change" emerges from this structure.

That brings us into the realm of "clock time" and "psychological time", where psychological time exists only as a concept; "past" and "future" fit into the category of psychological.

There is no actual "past" or "future" in any of the reference frames, each reference frame only exists in the "present"; the "past" or "future" in any reference frame only exists as an abstraction.

While 1 observer may say that something happened in his "past", it will only exist as a memory, while it [possibly] manifests in the present of another observer.

roosh · 23-09-2011 5:05pm

We probably don't need to wait for the results of this FTL neutrino experiment, for the purpose of the discussion, as it could be continued on the theoretical basis it has progressed on thus far.

Morbert · 23-09-2011 6:05pm

roosh wrote: »

Cheers, but there's hopefully no need to go through the derivation of it. I just did a quick refresher course on basic fractions on Kahn academy, and I [think I] see where I was going wrong with the basic multiplication of fractions, but I'm still having trouble understanding the information in the formula L/2(c+v).

It is basically (L/2)(1/[c+v]), isn't it? which says that the time it will take the light from Rod A to reach Observer 1 is given as the distance from Rod A to the midpoint divided by the sum of the speed of light plus the relative velocity.

Should it not be though, L/2c + the distance from the midpoint to the Observer, divided by the speed of light, or more pointedly, the overall distance from the rod to the Oberver (when the light reaches him) divided by the speed of light?

L/2(c+v) is the time observer 1 meets the 1st lightwave. L/2(c-v) is the time observer 1 meets the second light wave. It can be derived from "L/2c + the distance from the midpoint to the Observer, divided by the speed of light".

If the ball is at rest, however, and the ruler is moving relative to the ball, to find how much the ruler has moved relative to the ball you could see how much of the ruler has been displaced, no?

Yes, but that would only tell you how much the ruler was displaced. Furthermore, observer 1 would say the ruler is incorrectly calibrated, as the intervals between markings would be too short.

It's probably related to the question of the information encoded by the light, asked below.

Doesn't the movement of the lightning from the clouds to the rod affect the co-incident events? If the bolt of lightning moves perpendicular to the direction of motion, would that not mean that no legnth contraction occurs and both Observers would agree on the simultaneity up until the point of the strike?

That wouldn't matter. An event is just something with three spatial co-ordinates (x,y,z) and a time label (t).

Consequences
I'm just trying to follow the logical conclusions of this, and there's another issue that I am having trouble getting my head around, and it relates specifically to how light encodes information, and what information it would encode, in the thought experiment.

In order for Observer 1 to measure a distance of ɣL/2 to the pole (or the point of strike), the centre of the expanding sphere of light would have to remain localised a distance of ɣL/2 from Observer 1*, while the expanding sphere moves towards him. If the centre, of the expanding sphere of light, remains localised at the Rod*, then Observer 1 would measure the distance of 5ɣL/18, given that the distance would be displaced at a ratio of 4:5.

*we can install another stationary observer at the point of contact between lightning & rod to portray the idea of the localised centre at ɣL/2; we can also install an observer on the pole to demonstrate the localised centre moving with the pole.

This is an important point. The speed of light must be the same for all observers. If the rod is moving, (which it is according to oberver 1) the sphere cannot be centred on the rod, because that would mean the front of the sphere would be travelling at a speed of (c+v), and the back of the sphere would be travelling at a speed of c-v. But the speed must be c. So the incoming rod is actually closer to the observer than the centre. Hence, he sees where it was rather than where it is.

This is somewhat similar to the sound waves from an ambulance speeding towards you. The ambulance is not at the centre of the waves. Or take the more extreme case of a jet travelling faster than sound.

If Observer 1 is ɣL/2 away from the rod when it is struck, then how does the light encode that information? I would have thought it would encode the inforamation as it moved along its path, from the rod to the Observer, which would have included the track and the other elements that made up the scenery; but it can't include the ɣL/2 length of track, because the light won't travel the length of it, as some of the track will have passed beneath Observer 1 by the time the light reaches him - unless the light travels instantly to Observer 1, which we know isn't the case. Can the light encode any information from the moving track, and what information would it encode?

If Observer 1 bases his measurement on the information encoded by the light, how does he do this?

As the sphere of light crosses the track, it gathers information about different sections of the track at different times, and since the track is moving, you get a warping effect like the ones discussed in the video.

Morbert · 23-09-2011 11:03pm

roosh wrote: »

That brings us into the realm of "clock time" and "psychological time", where psychological time exists only as a concept; "past" and "future" fit into the category of psychological.

There is no actual "past" or "future" in any of the reference frames, each reference frame only exists in the "present"; the "past" or "future" in any reference frame only exists as an abstraction.

While 1 observer may say that something happened in his "past", it will only exist as a memory, while it [possibly] manifests in the present of another observer.

But it's the same universe. It cannot be an both real and "just an abstraction". Either an event is real, or it is not. It can't be real for one person, and an abstraction for another.

There is an issue of the psychological "arrow" of time, but that is a separate issue to relativity, and would only add confusion if it were brought up now. Also remember that our "observers" are infinitely precise instruments, and not beings with psychological considerations.

We probably don't need to wait for the results of this FTL neutrino experiment, for the purpose of the discussion, as it could be continued on the theoretical basis it has progressed on thus far.

Yes. While it is certainly an exciting story, we should wait until systematic errors are ruled out as a possible explanation.

roosh · 24-09-2011 11:06am

@Morbert - cheers for taking the time to go through this, I think I'm getting a much clearer visual understanding of it, which unfortunately often leads to more questions.

Morbert wrote: »

L/2(c+v) is the time observer 1 meets the 1st lightwave. L/2(c-v) is the time observer 1 meets the second light wave. It can be derived from "L/2c + the distance from the midpoint to the Observer, divided by the speed of light".

Cheers, I had understood the part in bold already; I suppose it is just the derivation of it that I am having trouble with, but there's no need to go into it.

Morbert wrote: »

Yes, but that would only tell you how much the ruler was displaced. Furthermore, observer 1 would say the ruler is incorrectly calibrated, as the intervals between markings would be too short.

If Observer 1 knew how much the markings would be contracted by, could he not calculate how much of the ruler had been displaced i.e. how much the ball has moved relative to the ruler, and vice versa?

Morbert wrote: »

That wouldn't matter. An event is just something with three spatial co-ordinates (x,y,z) and a time label (t).

Would that make the lightning bolt, on it's path from the clounds to the pole a series of events then? If so, would it be travelling perpendicular to the direction of motion and so not be contracted, until it strikes the pole? I'm just wondering would that lead to a disconnect in Observer 1's reference frame, between the lightning bolt and it's striking of the pole?

Morbert wrote: »

This is an important point. The speed of light must be the same for all observers. If the rod is moving, (which it is according to oberver 1) the sphere cannot be centred on the rod, because that would mean the front of the sphere would be travelling at a speed of (c+v), and the back of the sphere would be travelling at a speed of c-v. But the speed must be c. So the incoming rod is actually closer to the observer than the centre. Hence, he sees where it was rather than where it is.

This is somewhat similar to the sound waves from an ambulance speeding towards you. The ambulance is not at the centre of the waves. Or take the more extreme case of a jet travelling faster than sound.

How does Observer 1 reconcile the fact that there must also be an expanding sphere of light centred on the pole? Does that mean that there are two distinct sphere's of expanding light?

Morbert wrote: »

As the sphere of light crosses the track, it gathers information about different sections of the track at different times, and since the track is moving, you get a warping effect like the ones discussed in the video.

The sphere of light centred at ɣL/2 won't cross ɣL/2 length of track, it will only cross about (ɣL/2)(v/c) = ɣL/10 length of track. This is probably the wrong deduction, and therefore the wrong question but is that the expected contraction; that ɣL/2 should contract to ɣL/10 at 0.8c?

EDIT: how does the roation and orbit of the earht affect the length contraction for both observers?

roosh · 24-09-2011 2:05pm

@Morbert - as I've mentioned, thanks for taking the time to go through all of this with me. I was thinking that there would be some "chink in the armour" of the thought experiment, but I don't think there is, when allowing the assumption of length contraction; for that I think the Michelson Morely experiment would have to be challenged.

For that I'd need to develop a better understanding of both the MMX and the author's critique of it. I'm currently trying to do that on another forum, so you'll be glad to hear you won't be subjected to providing another remedial physics lesson.

I still have a few questions on SR if you are content to continue with those; there are still a few things I am trying to get my head around - as per some of the questions above.

roosh · 24-09-2011 2:11pm

Morbert wrote: »

But it's the same universe. It cannot be an both real and "just an abstraction". Either an event is real, or it is not. It can't be real for one person, and an abstraction for another.

There is an issue of the psychological "arrow" of time, but that is a separate issue to relativity, and would only add confusion if it were brought up now. Also remember that our "observers" are infinitely precise instruments, and not beings with psychological considerations.

It isn't the event that is an abstraction, it's the designation of it as being in "the past" that is. Events can only happen in the present and all reference frames only exist in the present, just as the ifinitely precise instruments can only take measurements in the present.

If the universe were to cease to exist now, then all reference frames would cease to exist in their respective present moments.

roosh · 24-09-2011 5:03pm

Just wondering what the case would be if, in the thought experiment, a cable was connected to the train when Rod A passes by Observer, with part of the cable being coiled on the ground, meaning that the cable is moving relative to itself. Would part of the cable be in the present, while part of it be in the past?

Where would the part of the cable that is accelerating be? If it was fitted with light detectors along its entire length which sphere of light would be detected?

I'm just trying to get a better understanding of the interface between reference frames.

Morbert · 24-09-2011 6:50pm

roosh wrote: »

If Observer 1 knew how much the markings would be contracted by, could he not calculate how much of the ruler had been displaced i.e. how much the ball has moved relative to the ruler, and vice versa?

He could. But this would not tell him whether the ball moved or not. "Relative to the ruler" means the ruler could have moved, the ball could have moved, or a combination of the two.

Would that make the lightning bolt, on it's path from the clounds to the pole a series of events then?

Yes. Any location with a time label is an event.

If so, would it be travelling perpendicular to the direction of motion and so not be contracted, until it strikes the pole? I'm just wondering would that lead to a disconnect in Observer 1's reference frame, between the lightning bolt and it's striking of the pole?

All causal relationships and coincident events are preserved. If lightning strikes a pole in one frame of reference, it will do so in all frames of reference. All that would happen is the series of events that is the lightning strike (x,y,z,t), would appear in the other observers reference frame at (x'.y',z',t').

How does Observer 1 reconcile the fact that there must also be an expanding sphere of light centred on the pole? Does that mean that there are two distinct sphere's of expanding light?

All he has to do is accept that his co-ordinate system will label locations and times differently to other observers' co-ordinate systems. Under his co-ordinate system, the rod is moving, so it will not remain at the centre of the light wave. Under observer 2's co-ordinate system, the rod is not moving, so it will remain at the centre of the light wave.

The sphere of light centred at ɣL/2 won't cross ɣL/2 length of track, it will only cross about (ɣL/2)(v/c) = ɣL/10 length of track. This is probably the wrong deduction, and therefore the wrong question but is that the expected contraction; that ɣL/2 should contract to ɣL/10 at 0.8c?

As stated earlier: "Since causality and coincident events must be the same in all reference frames, both observer 1 and observer 2 would agree about what the track ruler would register. Namely, (4/9)(L/2) = 4L/18, so you were close."

But the track will be warped such that the marking of 4L/18 on the track, when measured with his proper ruler, will actually be a distance of ɣL/2 from the lightning strike on the rod. He can take into account the optical effects due to the motion of the track (his image of the track ruler is effectively made up of different sections at different times), and calculate when the lightning struck. He and observer 2 will not agree on this "when".

EDIT: how does the roation and orbit of the earht affect the length contraction for both observers?

The calculations can be carried out from any frame of reference, such as the centre of the earth, the sun, the galaxy Etc. and the transformations will always preserve causality, the speed of light Etc. Though a complete treatment of rotating frames of reference requires us to move from special to general relativity. When you spin around, from your perspective, you are stationary and everything is moving. The stars all rotate above you at speeds far faster than C. But that is for anther day, and would only confuse matters more.

It isn't the event that is an abstraction, it's the designation of it as being in "the past" that is. Events can only happen in the present and all reference frames only exist in the present, just as the ifinitely precise instruments can only take measurements in the present.

If the universe were to cease to exist now, then all reference frames would cease to exist in their respective present moments.

The present is just as much an abstraction as the past or the future. If an event happens in the present of one frame of reference, has yet to happen in the future of another frame of reference, and has already happened in the past of a third frame of reference, which present is real and which is an abstraction?

roosh · 24-09-2011 8:16pm

Morbert wrote: »

He could. But this would not tell him whether the ball moved or not. "Relative to the ruler" means the ruler could have moved, the ball could have moved, or a combination of the two.

but what if, from the perspective of the observer, the ball is at rest?

Morbert wrote: »

All causal relationships and coincident events are preserved. If lightning strikes a pole in one frame of reference, it will do so in all frames of reference. All that would happen is the series of events that is the lightning strike (x,y,z,t), would appear in the other observers reference frame at (x'.y',z',t').

does it not matter then if other events are not moving in the direction of motion?

Morbert wrote: »

All he has to do is accept that his co-ordinate system will label locations and times differently to other observers' co-ordinate systems. Under his co-ordinate system, the rod is moving, so it will not remain at the centre of the light wave. Under observer 2's co-ordinate system, the rod is not moving, so it will remain at the centre of the light wave.

But the moving rod moves through his co-ordinate system, and he will know that there must be an expanding sphere centred on the rod also, so regardless of how another observer labels it, the two spheres should be connected, no?

Morbert wrote: »

As stated earlier: "Since causality and coincident events must be the same in all reference frames, both observer 1 and observer 2 would agree about what the track ruler would register. Namely, (4/9)(L/2) = 4L/18, so you were close."

But the track will be warped such that the marking of 4L/18 on the track, when measured with his proper ruler, will actually be a distance of ɣL/2 from the lightning strike on the rod. He can take into account the optical effects due to the motion of the track (his image of the track ruler is effectively made up of different sections at different times), and calculate when the lightning struck. He and observer 2 will not agree on this "when".

but the light will only have crossed a length of track measuring ɣL/10, which doesn't equal 2L/9, so the information encoded by the light won't include a marking of 4L/18.

Morbert wrote: »

The calculations can be carried out from any frame of reference, such as the centre of the earth, the sun, the galaxy Etc. and the transformations will always preserve causality, the speed of light Etc. Though a complete treatment of rotating frames of reference requires us to move from special to general relativity. When you spin around, from your perspective, you are stationary and everything is moving. The stars all rotate above you at speeds far faster than C. But that is for anther day, and would only confuse matters more.

No bother, I'll try and get my head around that as well cheers. I was just wondering how it would affect our Observers, as you mentioned that even if Observer 1 concluded that it was he that was moving and not Observer 2, that it wouldn't strictly speaking be true due to the rotation of the earth, the solar system, the galaxy, etc.

Morbert wrote: »

The present is just as much an abstraction as the past or the future. If an event happens in the present of one frame of reference, has yet to happen in the future of another frame of reference, and has already happened in the past of a third frame of reference, which present is real and which is an abstraction?

"The "past" of a reference frame is an abstraction, as is "the future"; each reference frame only exists in the present; so it is the "yet to happen" and the "already happened" that are the abstractions. Whatever is happening in each reference frame when the "universal pause button" is pushed; that collection of present reference frames would represent the overall present, no one reference frame is superior to another, so no single reference frame is more true than another.

Morbert · 24-09-2011 8:59pm

roosh wrote: »

but what if, from the perspective of the observer, the ball is at rest?

Then the ball is at rest from the perspective of the observer.

does it not matter then if other events are not moving in the direction of motion?

No.

But the moving rod moves through his co-ordinate system, and he will know that there must be an expanding sphere centred on the rod also, so regardless of how another observer labels it, the two spheres should be connected, no?

Why must there be an expanding sphere centred on the rod? The expanding sphere of sound from an ambulance is not centred on the ambulance.

but the light will only have crossed a length of track measuring ɣL/10, which doesn't equal 2L/9, so the information encoded by the light won't include a marking of 4L/18.

I think you're losing track of what it is you're trying to argue.

The light will have crossed a track length of L/2 - 2L/9 = 5L/18. But this will not be an indication of the distance light has travelled, since the track is moving, and the track markings are too small. When observer 1 uses a non-moving, proper ruler, he will measure a distance of ɣL/2. Observer 2 will be of the opinion that the track ruler is correct, and the train ruler is incorrect, so light has only travelled a distance of 5L/18 according to him. But neither is more correct than the other.

No bother, I'll try and get my head around that as well cheers. I was just wondering how it would affect our Observers, as you mentioned that even if Observer 1 concluded that it was he that was moving and not Observer 2, that it wouldn't strictly speaking be true due to the rotation of the earth, the solar system, the galaxy, etc.

This is what is meant by there is no absolute "true" reference frame. Any reference frame is just as accurate as any other. Just as there is no "true" loudness of a radio.

"The "past" of a reference frame is an abstraction, as is "the future"; each reference frame only exists in the present; so it is the "yet to happen" and the "already happened" that are the abstractions. Whatever is happening in each reference frame when the "universal pause button" is pushed; that collection of present reference frames would represent the overall present, no one reference frame is superior to another, so no single reference frame is more true than another.

So when the pause button is pressed, is the event "happening", "yet to happen", or "already happened"? Each reference frame has a different present. This means what is in the future and abstract according to one frame of reference, is real according to another. Which present is more real?

In fact, different reference frames will not even agree on when the pause button is pushed. The pushing of the pause button must obviously occur in the "present". But one frame's present is another's future, and another's past. The paused button is pushed "now", but according to which "now"?

roosh · 25-09-2011 1:31am

Morbert wrote: »

Then the ball is at rest from the perspective of the observer.

OK, so it wouldn't be a case of not knowing whether the ball has moved a little and/or the ruler has moved a little? Measuring the displacement of the ruler should show how much relative movement there was.

Morbert wrote: »

Why must there be an expanding sphere centred on the rod? The expanding sphere of sound from an ambulance is not centred on the ambulance.

If there is an observer standing at the rod when the lightning strikes, and is at rest relative to the rod, won't there have to be an expanding sphere of light centred on that Observer, who Observer 1 will see passing through his reference frame.

Morbert wrote: »

I think you're losing track of what it is you're trying to argue.

The light will have crossed a track length of L/2 - 2L/9 = 5L/18. But this will not be an indication of the distance light has travelled, since the track is moving, and the track markings are too small. When observer 1 uses a non-moving, proper ruler, he will measure a distance of ɣL/2. Observer 2 will be of the opinion that the track ruler is correct, and the train ruler is incorrect, so light has only travelled a distance of 5L/18 according to him. But neither is more correct than the other.

I think I'm losing sight of who will measure what, plus my maths might be a bit off.

I might be wrong in this, but if the front of the sphere of light, centred ɣL/2 from Observer 1, travels out from the pole at the speed of light, but the pole follows behind the front of the sphere at a ratio of 4:5, or 4/5, wouldn't that mean that the light will only ever be 1/5 of the overall distance [travelled] ahead of the pole, which would be ɣL/10, or whatever the corresponding distance would be when translated into terms of L?

The 5L/18 would represent the distance travelled by the sphere of light if it was centred at the pole.

Morbert wrote: »

This is what is meant by there is no absolute "true" reference frame. Any reference frame is just as accurate as any other. Just as there is no "true" loudness of a radio.

With regard to the radio, it depends here on what you mean by loudness. It's correct that no one observer can claim rights to the "true" loudness of the radio, but the expanding sphere of sound (if that is how it propagates) exists throughout the room, not just in the ear drum of one listener. Each listener makes up just part of the true state of the room, without any listener being able to claim ownership of the true state.

Morbert wrote: »

So when the pause button is pressed, is the event "happening", "yet to happen", or "already happened"? Each reference frame has a different present. This means what is in the future and abstract according to one frame of reference, is real according to another. Which present is more real?

In fact, different reference frames will not even agree on when the pause button is pushed. The pushing of the pause button must obviously occur in the "present". But one frame's present is another's future, and another's past. The paused button is pushed "now", but according to which "now"?

No one present is more real than the other, they are all equally real; there is no future in any reference frame, as every reference frame exists in the present. To talk about the future or the past of any reference frame is to talk about an abstract concept. The "now" in which the button is pushed is all of their nows, as they all exist in the present; it is right across the universe. It doesn't matter that they don't agree on the content of the present, because all of them only exist in the present and will only measure the present when the button is pressed.

Morbert · 25-09-2011 4:52am

roosh wrote: »

OK, so it wouldn't be a case of not knowing whether the ball has moved a little and/or the ruler has moved a little? Measuring the displacement of the ruler should show how much relative movement there was.

It would be a case of not knowing whether the ball has moved and/or the ruler has moved. But yes, it would show how much relative movement there was. I.e. It would show observer 1 what observer 2 would measure.

If there is an observer standing at the rod when the lightning strikes, and is at rest relative to the rod, won't there have to be an expanding sphere of light centred on that Observer, who Observer 1 will see passing through his reference frame.

In the frame of reference of observer 3, the sphere will be centred on the rod. It will be centred on the rod in any frame of reference with stationary rods. In any frame of reference with moving rods, the sphere will not be centred on the rod. This is not a contradiction, and is no more significant than two observers disagreeing on the loudness of a radio.

I think I'm losing sight of who will measure what, plus my maths might be a bit off.

I might be wrong in this, but if the front of the sphere of light, centred ɣL/2 from Observer 1, travels out from the pole at the speed of light, but the pole follows behind the front of the sphere at a ratio of 4:5, or 4/5, wouldn't that mean that the light will only ever be 1/5 of the overall distance [travelled] ahead of the pole, which would be ɣL/10, or whatever the corresponding distance would be when translated into terms of L?

We were using the markings on the track (which would not be accurate in observer 1's frame of reference). If we are talking about the actual distance measured by observer 1's own ruler, then you would be right. Yes the light will be a distance of 1/5 ahead of the pole. So when the light reaches observer 1, the pole will be ɣL/10 from the observer.

In short, both observers must agree on what each ruler says. But they will disagree on which ruler is correct.

With regard to the radio, it depends here on what you mean by loudness. It's correct that no one observer can claim rights to the "true" loudness of the radio, but the expanding sphere of sound (if that is how it propagates) exists throughout the room, not just in the ear drum of one listener. Each listener makes up just part of the true state of the room, without any listener being able to claim ownership of the true state.

The conclusion is even stronger. It's not just that no one can claim rights to the "true loudness". It's that there is no "true loudness". The state of the expanding sphere of sound does not have a loudness associated with it. So by analogy, no one observer can claim rights to the "true" present because there is no true present. The true state of the universe is the set of all events with no past, present, or future, and different users will place different events in the categories of their own co-ordinate system's past, present, and future.

No one present is more real than the other, they are all equally real; there is no future in any reference frame, as every reference frame exists in the present. To talk about the future or the past of any reference frame is to talk about an abstract concept. The "now" in which the button is pushed is all of their nows, as they all exist in the present; it is right across the universe. It doesn't matter that they don't agree on the content of the present, because all of them only exist in the present and will only measure the present when the button is pressed.

But the present events of one reference frame will have the future events of another reference frame. Are these events real or abstract? If they are real, it means events that are in the future of reference frames are real. If they are abstract, then events that are in the present of reference frames are abstract. They cannot be both real and abstract.

roosh · 25-09-2011 3:06pm

Morbert wrote: »

It would be a case of not knowing whether the ball has moved and/or the ruler has moved. But yes, it would show how much relative movement there was. I.e. It would show observer 1 what observer 2 would measure.

but if we stipulate that the either/or is at rest, then we should know which one is moving, no?

Morbert wrote: »

In the frame of reference of observer 3, the sphere will be centred on the rod. It will be centred on the rod in any frame of reference with stationary rods. In any frame of reference with moving rods, the sphere will not be centred on the rod. This is not a contradiction, and is no more significant than two observers disagreeing on the loudness of a radio.

but if Observer 3 passes through Observer 1's reference frame, Observer 1 would know that there must be a sphere of light centred on Observer 3/rod B as well.

I think the difference between this and the loudness of the radio is that there is just one sphere of sound centred at the radio, as opposed to the same sphere having two different centres.

Morbert wrote: »

We were using the markings on the track (which would not be accurate in observer 1's frame of reference). If we are talking about the actual distance measured by observer 1's own ruler, then you would be right. Yes the light will be a distance of 1/5 ahead of the pole. So when the light reaches observer 1, the pole will be ɣL/10 from the observer.

In short, both observers must agree on what each ruler says. But they will disagree on which ruler is correct.

but would both Observers agree on what the track ruler says? I'm not sure if my reasoning here is correct.

In Observer 1's reference frame, with the light only ever making it 1/5 of the overall distance ahead of the rod, it will only encode the graduation of the track corresponding to a distance of (1/5)(ɣL/2).

In Observer 2's reference frame, with the expanding sphere centred on the rod, the light will travel a lenght of track measuring 5L/18 and will encode that graduated length.

If both observers must agre on what the track ruler says, then ɣL/10 should equal 5L/18.

ɣL/10 = 5L/18

(180) ɣL/10 = (180)5L/18

18ɣL = 50L

As ɣL < L, the above is incorrect.

Morbert wrote: »

The conclusion is even stronger. It's not just that no one can claim rights to the "true loudness". It's that there is no "true loudness". The state of the expanding sphere of sound does not have a loudness associated with it. So by analogy, no one observer can claim rights to the "true" present because there is no true present. The true state of the universe is the set of all events with no past, present, or future, and different users will place different events in the categories of their own co-ordinate system's past, present, and future.

That there is no "true loudness" or that no one observer can claim rights to the "true present" is not in dispute. "Loudness" is dependent on the observer's loaction with resepct to the sound; but there is a true sphere of sound which is not localised to one point in the room, but spreads throughout the room.

No one observer can claim rights to the true present, because the present state of the universe is not localised to their reference frame, it covers all reference frames in existence.

Morbert wrote: »

But the present events of one reference frame will have the future events of another reference frame. Are these events real or abstract? If they are real, it means events that are in the future of reference frames are real. If they are abstract, then events that are in the present of reference frames are abstract. They cannot be both real and abstract.

The present events of any reference frame are real, "the future events of another reference frame" are abstract, not because the events themselves aren't real but because the notion of "the future of another reference frame" is abstract.

Morbert · 25-09-2011 4:48pm

roosh wrote: »

but if we stipulate that the either/or is at rest, then we should know which one is moving, no?

Yes. So the track ruler is moving in one frame of reference, and therefore not accurately measuring the distance light travelled with respect to observer 1. The ruler is stationary in another frame of reference, and therefore accurately measuring the distance light travelled with respect to observer 2. The train ruler, likewise, accurately measures the distance light travelled with respect to observer 1, but not observer 2.

but if Observer 3 passes through Observer 1's reference frame, Observer 1 would know that there must be a sphere of light centred on Observer 3/rod B as well.

There is no passing through reference frames. This would only happen if observer 3 adopted the same velocity of observer 1.

I think the difference between this and the loudness of the radio is that there is just one sphere of sound centred at the radio, as opposed to the same sphere having two different centres.

The sphere has two different "loudnesses", and sphere of light has different centres. The rod, in other words, has two different locations. Just as your computer is "near" in your frame of reference, but "far" in my frame of reference.

but would both Observers agree on what the track ruler says? I'm not sure if my reasoning here is correct.

Yes they would. They would both also agree on what the train ruler says. Observer 2 would say the track ruler is correct. Observer 1 would say the train ruler is correct.

In Observer 1's reference frame, with the light only ever making it 1/5 of the overall distance ahead of the rod, it will only encode the graduation of the track corresponding to a distance of (1/5)(ɣL/2).

In Observer 2's reference frame, with the expanding sphere centred on the rod, the light will travel a lenght of track measuring 5L/18 and will encode that graduated length.

If both observers must agre on what the track ruler says, then ɣL/10 should equal 5L/18.

ɣL/10 = 5L/18

(180) ɣL/10 = (180)5L/18

18ɣL = 50L

As ɣL < L, the above is incorrect.

The above is incorrect because you are conflating the two rulers. We will only consider the track ruler.

Observer 1 passes the 0 mark on the ruler (The midpoint) at t' = 0 and meets the light at t2' = ɣt2(1 - v^2/c^2) (This was derived in post # 54).

t2' = ɣt2(1 - v^2/c^2) = t2/ɣ = 5L/18cɣ

In this time, the track has travelled a distance of

5L/18cɣ * v = 5Lv/18cɣ = 5L/18ɣ(c/v) = 5L/18ɣ(4/5) = 4L/18ɣ

But since the track is contracted, it will measure the larger distance of ɣ4L/18ɣ = 4L/18.

This is in agreement with observer 2.

A similar calculation can be performed to show that both observers will agree with what the train ruler says.

That there is no "true loudness" or that no one observer can claim rights to the "true present" is not in dispute. "Loudness" is dependent on the observer's loaction with resepct to the sound; but there is a true sphere of sound which is not localised to one point in the room, but spreads throughout the room.

No one observer can claim rights to the true present, because the present state of the universe is not localised to their reference frame, it covers all reference frames in existence.

The present events of any reference frame are real, "the future events of another reference frame" are abstract, not because the events themselves aren't real but because the notion of "the future of another reference frame" is abstract.

Your first birthday is a present event of a reference frame. You typing a response yesterday is a present event of a reference frame. You reading this is a present event of a reference frame. If you accept that all these events are real (not just you reading this), then there is no major dispute.

roosh · 26-09-2011 2:36pm

Morbert wrote: »

Yes. So the track ruler is moving in one frame of reference, and therefore not accurately measuring the distance light travelled with respect to observer 1. The ruler is stationary in another frame of reference, and therefore accurately measuring the distance light travelled with respect to observer 2. The train ruler, likewise, accurately measures the distance light travelled with respect to observer 1, but not observer 2.

But in the specific instance of determining whether both observers will read the same measurement on the track ruler what we are interested in is not how much the light has travelled with repsect to Observer 1, but rather how much the light has travelled with respect to the track, to see how much of the track has been illuminated by the light.

Morbert wrote: »

There is no passing through reference frames. This would only happen if observer 3 adopted the same velocity of observer 1.

"passing through reference frames" may be the wrong way to phrase it, but Observer 2 makes up part of Observer 1's reference frame, just as the rods do, and vice versa.

Morbert wrote: »

The sphere has two different "loudnesses", and sphere of light has different centres. The rod, in other words, has two different locations. Just as your computer is "near" in your frame of reference, but "far" in my frame of reference.

with regard to the sphere(s), if it is the same sphere, with different centres, then it won't necessarily be a sphere - I picture it to be somewhat like how a wormhole is traditionally depicted.

Also, to say that the computer (or the rod) has two locations is somewhat of a misnomer, I think, because it blurs the lines between what is meant by "location"; just because we are standing different distances from it, it doesn't mean it has two locations. If you superimpose a theoretical, mathematical co-ordinate system on reality, and I do likewise, then we might argue that it has two locations, but that isn't actually the case because neither of us owns the "true" co-ordinate system.

Morbert wrote: »

Yes they would. They would both also agree on what the train ruler says. Observer 2 would say the track ruler is correct. Observer 1 would say the train ruler is correct.

The above is incorrect because you are conflating the two rulers. We will only consider the track ruler.

Observer 1 passes the 0 mark on the ruler (The midpoint) at t' = 0 and meets the light at t2' = ɣt2(1 - v^2/c^2) (This was derived in post # 54).

t2' = ɣt2(1 - v^2/c^2) = t2/ɣ = 5L/18cɣ

In this time, the track has travelled a distance of

5L/18cɣ * v = 5Lv/18cɣ = 5L/18ɣ(c/v) = 5L/18ɣ(4/5) = 4L/18ɣ

But since the track is contracted, it will measure the larger distance of ɣ4L/18ɣ = 4L/18.

This is in agreement with observer 2.

A similar calculation can be performed to show that both observers will agree with what the train ruler says.

I'm inclined to put more trust in your own mathematical ability - simply because I am familiar with my own

but my initial impression, and this could quite easily be down to an error in my reasoning, is that saying that Observer 1 passes the 0, mark on the ruler at, t'=0 looks like a bit of a red herring - not in the sense that you are deliberately trying to mislead, but because when Observer 1 passes the 0 mark both the light and the track have already been travelling.

In Observer 1's reference frame, with the rod following behind the light, at 4/5 of its speed, the light will only ever have moved ahead of the rod by 1/5 of the overall distance travelled by the light, thus it will only have illuminated a length of track measuring 1/5 of that distance, and hence that graduation on the track - by the time it reaches Observer 1.

On the other hand Observer 2 will see a sphere of light centred on the rod, and so it will illuminate 5/9 of the distance by the time it reaches Oberver 1. Even allowing for contraction, it appears as though they will see different lengths of track illuminated.

All that being said, with respect to the derivation in post #54, the conclusion appears to be assumed in saying that t' = ɣ(t - vx/c^2). The derivation of ɣ as per the video you posted is something which the author also challenges.

Morbert wrote: »

Your first birthday is a present event of a reference frame. You typing a response yesterday is a present event of a reference frame. You reading this is a present event of a reference frame. If you accept that all these events are real (not just you reading this), then there is no major dispute.

In this reference frame none of those events are real any longer, but that would just be in this reference frame. My first birthday, with respect to this reference frame, is now an abstraction; but if that reference frame actually exists then it has it's own present i.e. if me as a one year old exists, the [he] is currently having [his] first birthday (according tho him). So if the entire universe is paused then the present is made up of all those present reference frames.

What would be the case thought if one of the presents was chosen as the moment to pause the universe; where that present is "the past" of another reference frame?

Oberver in motion
This is related to the point above about the "true present"; it might appear to be going back over old ground, but, through my own fault, there was an inherent assumption which was never addressed; the assumption relates to the notion of "past" and "future" reference frames.

Yhe point raised was:

roosh wrote: »

The crux of the issue, as far as I can see, isn't the relative motion of either Observer with respect to the earth, the sun, or our solar system; it is that Observer 1 is moving relative to Observer 2, as well as both rods, A and B, while Observer 2 is at rest relative to the rods.

and the reply:

Morbert wrote: »

Then what is the absolute "present"? What must we be stationary with respect to in order to determine the true present?

The notion of the "universal pause button" was raised after this, while allowing the assumption of "past" and "future" reference frames; "past" and "future" reference frames are however challenged by the notion that Observer 1 would conclude that it is he that is moving relative to the rods and the "beam" of light.

To address the issue: "What must we be stationary with respect to in order to determine the true present?"

Our ability to determine the true present has no bearing on its existence, but in the context of Observers 1 & 2, if Observer 1 correctly [in my opinion] concludes that it is he that is in motion, with repsect to the rods and Observer 1, then he would come to the same conclusion - that the lightning strikes occured at the same time - as Observer 2.

Again, the issue of how Observer comes to the conclusion might need to be addressed, but you would imagine that if he arrives to the train station before his train departs and instead of boarding the train immediately he stands on the platfrom and watches the train start to pull out before boarding it, then he would conclude that it is, in fact, he that is in motion relative to the rods.

Alternatively, if he were to wait with Observer 2 until the train was approaching and then walked a distance to get picked up by the train (using it's sophisiticated device for picking up passengers while in motion), which allowed him to reach the inertial velocity of 0.8c before reaching the rods, he would surely conclude that it was he that was in motion and not the passing countryside.

Does time exist?

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