Relativty of Simultaneity and clock synchronisation

Morbert

roosh wrote: »

Forget about the already extended barrel, and imagine a pole being extended from A; you can picture the barrel of the laser being extended from the top of A out towards the train if its helpful, such that it starts from the top of A and moves towards the train, at whatever speed.

We can imagine that the sides of the train have been designed such that the middle section of each sidewall has been removed, but connected at either end of the train; this means that the pole which is being extended from A can pass right through the train unimpeded and the train can travel on unimpeded.

Now, as the pole approaches the train, it always forms a right angle to the train; as it moves through the first sidewall of the carriage, it forms a right angle to it, and as it proceeds through the other side wall it passes through it at a right angle also. It might be helpful to imagine the barrel of the laser extending through the sidewalls of the train carriage.

Imagine there are two observers at the back of the carriage, one on either side of the aisle, and they see the pole, fully extended through the side walls of the carriage, coming towards them; they won't see the pole coming at them angled towards one of them, they will see the pole approaching them equally, by forming right angles to the sidewalls of the train.

This is true, despite the fact that, as the pole was being launched from A, it appeared to travel towards the train at an angle, and if we use the reference frame S', it would depict the path of the tip of the pole as following an angled line, as well as all subsequent points on the pole; but the pole disects the train perpendicularly; this can clearly be seen by the observers on the train when the pole passes through, still moving relative to the train.

Now consider two additional observes such that the 4 observers trace out two right-angled triangles. The first new observer is rotating at a speed of 6 revolutions per second, while the second new observer blinks at at a rate of 6 times a second so that they always see the same image when looking at the other observer. This observer owns a monkey, sitting at the end of the pole with a compass implanted into his brain that relays the orientation of the earth with respect to his right thumb. But the compass only works if he is stationary with respect to a light clock owned by the revolving observer. This light clock is built on a physically rotated and physically not-rotated tapestry that exhibits monastic illustrations of Chronos. A photon is emitted by Chronos's left nostril that blinds Albert's father in the left eye.

Or I could just point out that your mistake would be glaringly obvious if you just did the relevant Lorentz transformations. You have shown that the orientation of the pole is perpendicular, but the path of the pole tip, like the path of the photon, would not be. If your two new observers were standing opposite each other, and the pole skewered one as it entered the train, it would not skewer the other.

So is that a:
- yes, the radii of the sphere are different lengths
- no, the radii are the same length
- each observer measures the same length of the radius but disagrees about their counterparts measurement
or
- some other explanation?

Ok, I'll make a deal. I will answer your question if you promise not to introduce any more wacky thought experiments.

Except that whether or not an observer measures the photons stiking in order doesn't depends on their previous life experiences, their culture, etc., as the concepts of "boring" and "interesting" do.

It does, however, depend on their velocity with respect to the clocks in question.

I'm not arguing that its not frame dependent; the point is that the statement; "the photons physically strike the clocks on the train in the order of one first, then the other" is a valid statement under relativity.

So too is, "the same photons physically strike the same clocks on the train in a different order".

The point is that, that is not physically possible, and is physically paradoxical.

If it's frame-dependent, it isn't physical.

dlouth15

roosh wrote: »

You may want to watch the video again, but this time imagine two clocks which are back to back in the centre of the train, where the passenger is. According to the observer on the platform, the clock facing the front of the train gets struck first and is started first, while the rear facing clock gets started second; here both observers agree that the clocks are not synchronised.

This is correct. If the two clocks are coincident in space, then they will be unsynchronized in all frames of reference. The clocks being unsynchronized in one frame yet synchronized in another depends on them being separated in space.

Note also that the video depicts the light physically meeting the passenger in the order of one first, then the other.

The position of the passenger in the centre of the carraige is a good substitute for clocks at either end. Because the passenger sees bolts arriving at different times from the center and we know that if we had clocks at either end, those clocks will be unsychronized when viewed in this frame.

EDIT: it might also be worth pointing out that the reason the clocks are supposedly both synchronised and unsynchronised is because the lightning supposedly physically strikes the clocks in the order of one first, then the other, according to one reference frame, but physically strikes them in a different order according to the other.

You use the word "supposedly" here.

According to how you see things, are the clocks synchronized in both frames? Are they unsynchronized in both frames?

roosh

Morbert wrote: »

Or I could just point out that your mistake would be glaringly obvious if you just did the relevant Lorentz transformations. You have shown that the orientation of the pole is perpendicular, but the path of the pole tip, like the path of the photon, would not be. If your two new observers were standing opposite each other, and the pole skewered one as it entered the train, it would not skewer the other.

I can visualise the frames and the plotting of the path, but I was confusing the orientation with the path, my apologies.

Morbert wrote: »

Ok, I'll make a deal. I will answer your question if you promise not to introduce any more wacky thought experiments.

I suppose that depends on what you mean by whacky.

Morbert wrote: »

It does, however, depend on their velocity with respect to the clocks in question.

Indeed, whether or not they measure the photons to physically strike the clocks in a given order.

Morbert wrote: »

If it's frame-dependent, it isn't physical.

Measurements made in the physical world aren't dependent on mathematical co-ordinates; if you mean that the conclusion, that photons physically strike two physical clocks (or an observers retinae) in a given order, depends on the physical motion of the observer relative to the physical events, then yes, it is frame dependent, in the physical sense of the word frame, as opposed to the mathematical.

It doesn't change the fact that, according to the measurements of one observer - measurements of the physical world - the photons physically strike the clocks, and they do so in a given order. If they didn't physically strike the clocks, then the clocks wouldn't be started; if they didn't physically strike the clocks in the given order, then the clocks wouldn't be unsynchronised. His measurements of the physical events might depend on his physical location and physical motion relative to the events, but the strikes are no less physical and, according to his measurements they occur in a certain order.

So, again, according to one observer's measurements, the photons physically strike the clocks in a given order.


EDIT: just try and state it as clearly as possible; the relatively moving observer says that the photons physically strike the clocks; the relatively moving observer says the strikes occur in a given order; therefore, the relatively moving observer says the photons physically strike the clocks in a given order. We can substitute in S' for the relatively moving observer here.

roosh

dlouth15 wrote: »

This is correct. If the two clocks are coincident in space, then they will be unsynchronized in all frames of reference. The clocks being unsynchronized in one frame yet synchronized in another depends on them being separated in space.The position of the passenger in the centre of the carraige is a good substitute for clocks at either end. Because the passenger sees bolts arriving at different times from the center and we know that if we had clocks at either end, those clocks will be unsychronized when viewed in this frame.

Again, bearing in mind that the observer on the train says that the lightning physically struck the clocks in the order of one first, then the other; while the observer on the platform says they physically struck, not in that order, but in a different order.

dlouth15 wrote: »

You use the word "supposedly" here.
According to how you see things, are the clocks synchronized in both frames? Are they unsynchronized in both frames?

Are you asking me what do I think relativity says?

dlouth15

roosh wrote: »

Are you asking me what do I think relativity says?

No, I'm wondering what you think actually happens, specifically with regards to the synchronized status of the clocks as measured in both reference frames. Are the clocks synchronized or not synchronized as measured in a) the reference frame associated with the train and b) the reference frame associated with the platform.

roosh

dlouth15 wrote: »

No, I'm wondering what you think actually happens, specifically with regards to the synchronized status of the clocks as measured in both reference frames. Are the clocks synchronized or not synchronized as measured in a) the reference frame associated with the train and b) the reference frame associated with the platform.

That I couldn't be sure about.

What I would be more sure about is the fact that two physical clocks cannot be physically started in the order of one first, then the other, as well as physically started in a different order.

Morbert

roosh wrote: »

Measurements made in the physical world aren't dependent on mathematical co-ordinates; if you mean that the conclusion, that photons physically strike two physical clocks (or an observers retinae) in a given order, depends on the physical motion of the observer relative to the physical events, then yes, it is frame dependent, in the physical sense of the word frame, as opposed to the mathematical.

It doesn't change the fact that, according to the measurements of one observer - measurements of the physical world - the photons physically strike the clocks, and they do so in a given order. If they didn't physically strike the clocks, then the clocks wouldn't be started; if they didn't physically strike the clocks in the given order, then the clocks wouldn't be unsynchronised. His measurements of the physical events might depend on his physical location and physical motion relative to the events, but the strikes are no less physical and, according to his measurements they occur in a certain order.

So, again, according to one observer's measurements, the photons physically strike the clocks in a given order.

EDIT: just try and state it as clearly as possible; the relatively moving observer says that the photons physically strike the clocks; the relatively moving observer says the strikes occur in a given order; therefore, the relatively moving observer says the photons physically strike the clocks in a given order. We can substitute in S' for the relatively moving observer here.

But that's just it. You're not stating the scenario as clearly as possible. This is a breakdown of what you are saying.

the relatively moving observer says that the photons physically strike the clocks

Here, you apply the adverb "physically" to describe the photons striking the clock. This is fine.

the relatively moving observer says the strikes occur in a given order

This is also fine, as it is not implied that the order is in any way physical.

therefore, the relatively moving observer says the photons physically strike the clocks in a given order

Here is where you make your mistake. Here, you are now applying the adverb "physically" to the photons striking in a given order, which does not follow.

The strikes are physical, the strikes occur in a given order, according to S/S', but the strikes do not physically occur in a given order. Similarly, rainbows are physical. Rainbows are pretty according to me, but this does not mean rainbows are physically pretty.

roosh

Morbert wrote: »

But that's just it. You're not stating the scenario as clearly as possible. This is a breakdown of what you are saying.



Here, you apply the adverb "physically" to describe the photons striking the clock. This is fine.



This is also fine, as it is not implied that the order is in any way physical.



Here is where you make your mistake. Here, you are now applying the adverb "physically" to the photons striking in a given order, which does not follow.

The strikes are physical, the strikes occur in a given order, according to S/S', but the strikes do not physically occur in a given order. Similarly, rainbows are physical. Rainbows are pretty according to me, but this does not mean rainbows are physically pretty.

That depends on what you mean by pretty; what you refer to as pretty quite probably corresponds to specific neuronal activity, that leads to your interpretation of "pretty"; in this sense, the rainbow is physically pretty.

If the strikes are physical, and if the strikes occur, then the strikes necessarily occur physically.

If the strikes occur in a given order, and the strikes are necessarily physical, then the strikes necessarily occur physically and in a given order. If the strikes occur occur in a given order, and the strikes necessarily occur physically, then the strikes necessarily occur, physically, in a given order.

We can look at it another way; if the strikes are necessarily physical, then we can replace the term "strikes" with a more detailed description of them, the "physical strikes"; then we can have "the physical strikes occur in a given order".

dlouth15

roosh wrote: »

That I couldn't be sure about.

What I would be more sure about is the fact that two physical clocks cannot be physically started in the order of one first, then the other, as well as physically started in a different order.

What about the lightning strikes themselves. In the video the observer on the platform sees them as simultaneous yet the observer on the train sees them as non-simultaneous. Do you see that as being impossible?

Morbert

roosh wrote: »

That depends on what you mean by pretty; what you refer to as pretty quite probably corresponds to specific neuronal activity, that leads to your interpretation of "pretty"; in this sense, the rainbow is physically pretty.

The point is "pretty" is not an inherent quality of the rainbow, but rather a statement about my opinion of the rainbow.

If the strikes are physical, and if the strikes occur, then the strikes necessarily occur physically.

That's fine. It's effectively a tautology.

If the strikes occur in a given order, and the strikes are necessarily physical, then the strikes necessarily occur physically and in a given order. If the strikes occur occur in a given order, and the strikes necessarily occur physically, then the strikes necessarily occur, physically, in a given order.

But here, you introduce an extrinsic quality: Ordering. The description of physical strikes occurring in one order or another is a statement about what an observer, hypothetical or otherwise, would measure.

We can look at it another way; if the strikes are necessarily physical, then we can replace the term "strikes" with a more detailed description of them, the "physical strikes"; then we can have "the physical strikes occur in a given order".

There is nothing wrong with the "physical strikes occur in a given order" because that statement is in the context of an observer/frame of reference.

Consider this distilled thought experiment: Albert and Henry are moving with respect to each other. They both observe a physical object. Albert observes the object as moving. Henry observes the object as at rest. Are you analogously arguing that the object must be either physically at rest or physically moving.

roosh

Morbert wrote: »

The point is "pretty" is not an inherent quality of the rainbow, but rather a statement about my opinion of the rainbow.

That's a fair point, but the measurement of the order of photon strikes is markedly different to an observers perception of the beauty of a rainbow; because, while two observers at rest relative to each other might disagree on the beauty of a rainbow, or how entertaining a film was, they should agree on the order in which the photons strike; so the order of events is not observer dependent in the sense that perception of beauty is.

I presume the response you would have to this is that the order is intrinsic to the inertial reference frame, and therefore not physical; but if it is not physical then how is it that we measure the order of events?

Morbert wrote: »

But here, you introduce an extrinsic quality: Ordering. The description of physical strikes occurring in one order or another is a statement about what an observer, hypothetical or otherwise, would measure.

Is it an extrinsic quality though? It's not extrinsic in the sense that you outlined above with the analogy of the perception of beauty, or prettiness. Presumably we can only measure what is physical, and while we measure the physical photon strikes we conclude that they occur in a given order; but the detection of physical photon strikes only allows us to conclude that the photons are physical and the striking events are physical. How do we deduce the order of the strikes, if there is nothing physical about them?

Morbert wrote: »

There is nothing wrong with the "physical strikes occur in a given order" because that statement is in the context of an observer/frame of reference.

That's fine, we don't actually need any more than that for the conclusion. I can plug that into the discussion about Albert and I think we can arrive at the same conclusion.

Morbert wrote: »

Consider this distilled thought experiment: Albert and Henry are moving with respect to each other. They both observe a physical object. Albert observes the object as moving. Henry observes the object as at rest. Are you analogously arguing that the object must be either physically at rest or physically moving.

This could branch into a discussion we've had previously, but it doesn't need to; because, like the "pretty" analogy above, this isn't analogous; the only analogy is with the word "relative", but the relative motion isn't a specific event whose order is the case of disagreement.

Morbert

roosh wrote: »

That's a fair point, but the measurement of the order of photon strikes is markedly different to an observers perception of the beauty of a rainbow; because, while two observers at rest relative to each other might disagree on the beauty of a rainbow, or how entertaining a film was, they should agree on the order in which the photons strike; so the order of events is not observer dependent in the sense that perception of beauty is.

I presume the response you would have to this is that the order is intrinsic to the inertial reference frame, and therefore not physical; but if it is not physical then how is it that we measure the order of events?

The order of events is absolutely observer dependent. That is the whole point. We measure it with clocks and rulers.

Is it an extrinsic quality though? It's not extrinsic in the sense that you outlined above with the analogy of the perception of beauty, or prettiness. Presumably we can only measure what is physical, and while we measure the physical photon strikes we conclude that they occur in a given order; but the detection of physical photon strikes only allows us to conclude that the photons are physical and the striking events are physical. How do we deduce the order of the strikes, if there is nothing physical about them?

We cannot deduce the order of the strikes, as there is no true ordering of the strikes, since the strikes are causally unconnected. All we can do is arbitrarily label the strikes as happening in a given order, using a coordinate system.

That's fine, we don't actually need any more than that for the conclusion. I can plug that into the discussion about Albert and I think we can arrive at the same conclusion.

You definitely need more, as you have been attempting to establish a contradiction between the different labels by different reference frames.

roosh

Morbert wrote: »

The order of events is absolutely observer dependent. That is the whole point. We measure it with clocks and rulers.

Not in the sense that perception of beauty is. If Albert were on the train he would measure the order of events to be different, so it isn't necessarily something inherent in Albert, given that he would still, probably, find the rainbow "pretty" regardless of where he was.

But what is it that we measure? We measure the photons which are physically intrinsic to the event.

Morbert wrote: »

We cannot deduce the order of the strikes, as there is no true ordering of the strikes, since the strikes are causally unconnected. All we can do is arbitrarily label the strikes as happening in a given order, using a coordinate system.

It isn't necessarily an arbitrary process, in the sense that we do "eeny, meeny, miny, moe", to decide which one is first and which is second. Something must occur for one observer to say that the events happen in a given order. As you say above, "we measure it witch clocks and rulers" and detectors. So we must be measuring something physical and then ascribing order on the basis of those measurements of physical properties.

Morbert wrote: »

You definitely need more, as you have been attempting to establish a contradiction between the different labels by different reference frames.

I haven't been trying to establish a contradiction between the labels, I've been trying to establish a contradiction between how those labels apply to the physical world.

Morbert

roosh wrote: »

Not in the sense that perception of beauty is. If Albert were on the train he would measure the order of events to be different, so it isn't necessarily something inherent in Albert, given that he would still, probably, find the rainbow "pretty" regardless of where he was.

But what is it that we measure? We measure the photons which are physically intrinsic to the event.

It isn't necessarily an arbitrary process, in the sense that we do "eeny, meeny, miny, moe", to decide which one is first and which is second. Something must occur for one observer to say that the events happen in a given order. As you say above, "we measure it witch clocks and rulers" and detectors. So we must be measuring something physical and then ascribing order on the basis of those measurements of physical properties.

It is absolutely an arbitrary process. Sure, we have to be consistent, and sure, we have to use standardised clocks and rulers, but once these conditions are met, one coordinate label is no more or less correct than any other. Albert, as you say, will measure a different ordering if he is on the train, because he is now using a different, but equally valid, set of clocks and rulers.

I haven't been trying to establish a contradiction between the labels, I've been trying to establish a contradiction between how those labels apply to the physical world.

I.e. A contradiction between the different labels. You have been trying to argue that what S and S' says cannot both be true, because you are extrinsic coordinate labels with intrinsic properties of the physical events.

roosh

Morbert wrote: »

It is absolutely an arbitrary process. Sure, we have to be consistent, and sure, we have to use standardised clocks and rulers, but once these conditions are met, one coordinate label is no more or less correct than any other. Albert, as you say, will measure a different ordering if he is on the train, because he is now using a different, but equally valid, set of clocks and rulers.

Albert doesn't necessarily us a different set of clocks and rulers; he can take his clocks and rulers with him and, according to him, they will meausure the exact same units as when he was on the platform.

Also, I said, that the measurement of the ordering of events wasn't arbitrary in the sense of doing an "eenie, meenie, miny, moe"; Albert doesn't cover his eyes and stick a pin in the two photons to decide which was first and which was second. The order is determined by making physical measurements of physical properties which are intrinsic to the the original events; that is, measurements are made of the physical photons and the values of these measurements imply a certain order.

The choice of measuring apparatus may be arbitrary, and the units they measure may be arbitrary, but the ascription of order isn't done by flicking a coin to see which one is labled as "first". It is done by making physical measurements.

Morbert wrote: »

I.e. A contradiction between the different labels. You have been trying to argue that what S and S' says cannot both be true, because you are extrinsic coordinate labels with intrinsic properties of the physical events.

I have argued that while they may be mathematically consisitent i.e. no contradiction between the lables; what they say, when applied to the physical world, leads to a paradox. Not necessarily a contradiction between the labels, but the application of the labels to the physical world.

Morbert

roosh wrote: »

Albert doesn't necessarily us a different set of clocks and rulers; he can take his clocks and rulers with him and, according to him, they will meausure the exact same units as when he was on the platform.

Also, I said, that the measurement of the ordering of events wasn't arbitrary in the sense of doing an "eenie, meenie, miny, moe"; Albert doesn't cover his eyes and stick a pin in the two photons to decide which was first and which was second. The order is determined by making physical measurements of physical properties which are intrinsic to the the original events; that is, measurements are made of the physical photons and the values of these measurements imply a certain order.

The choice of measuring apparatus may be arbitrary, and the units they measure may be arbitrary, but the ascription of order isn't done by flicking a coin to see which one is labled as "first". It is done by making physical measurements.

They are a different set of clocks and rulers. Completely. For example, his clocks and rulers previously told him the train was moving at a speed v. Now they tell him it is stationary. They previously told him the time it took for the signals to reach the train was t seconds. Now it's γt seconds. They previously told him the strikes happened at the same time. Now they tell him the strikes didn't. they previously told him the length of the train was L. Now they tell him it's γL. They previously told him the distance between the poles was l. Now they tell him it's l/γ. Which set of labels he uses is entirely arbitrary, as each set refers to what will be measured by some hypothetical observer or other.

What is so hard to understand about the whole situation? Ordering, length, duration, speed, distance, are all labels specific to a set of clocks and rulers, hypothetical or otherwise, that define a coordinate frame. That two coordinate frames order events differently is no more mysterious than two coordinate frames disagreeing over whether or not an object is stationary. The physics is the same.

I have argued that while they may be mathematically consisitent i.e. no contradiction between the lables; what they say, when applied to the physical world, leads to a paradox. Not necessarily a contradiction between the labels, but the application of the labels to the physical world.

And you have not, in the slightest, shown this to be the case. In the end, we have a system with an intrinsic causal structure, consistent between all frames of reference, and extrinsic ordering belonging to the various arbitrary frames of reference.

At most, you have expressed your distaste for the idea that events are Minkowskian rather than Newtonian. Do yourself a favour. Don't open a quantum mechanics book.

roosh

Morbert wrote: »

They are a different set of clocks and rulers. Completely. For example, his clocks and rulers previously told him the train was moving at a speed v. Now they tell him it is stationary. They previously told him the time it took for the signals to reach the train was t seconds. Now it's γt seconds. They previously told him the strikes happened at the same time. Now they tell him the strikes didn't. they previously told him the length of the train was L. Now they tell him it's γL. They previously told him the distance between the poles was l. Now they tell him it's l/γ. Which set of labels he uses is entirely arbitrary, as each set refers to what will be measured by some hypothetical observer or other.

What is so hard to understand about the whole situation? Ordering, length, duration, speed, distance, are all labels specific to a set of clocks and rulers, hypothetical or otherwise, that define a coordinate frame.

So Albert can't take two physical clocks with him as he boards the train, reset them and use them; and he can't take his trusty metre stick with him? Just as he could theoretically lay out clocks all over the universe to define his frame as being at rest relative to the embankment, he can theoretically take those same clocks, reset them, and use them to define his reference frame as being at rest relative to the train.

Morbert wrote: »

That two coordinate frames order events differently is no more mysterious than two coordinate frames disagreeing over whether or not an object is stationary. The physics is the same.

There is no disagreement between the reference frames with regard to the motion of either physical observer relative to the other physical observer; there is a disagreement over the order of one physical strike with the other physical strike.

You're saying also saying that the ordering of events is observer dependent in the manner that an observer's perception of beauty is, when it clearly isn't; an observer doesn't use any measuring instruments to measure the beauty of a rainbow; the order of events is measured by making a physical measurement which involves something which is physically instrinsic to the event, the photon.

Morbert wrote: »

And you have not, in the slightest, shown this to be the case. In the end, we have a system with an intrinsic causal structure, consistent between all frames of reference, and extrinsic ordering belonging to the various arbitrary frames of reference.

Again, we know that observers have ordered experiences of events, despite the fact that order is not an intrinsic property of the system; we know that an observers experience is determined by the physical stimuli which "strike" their sensory organs. The striking of the sensory organs alone doesn't necessitate that an observer will have an ordered experience; what necessitates the ordered experience is the order in which the physical strikes occur. Again, this is despite the fact that the ordering is not an intrinsic, physical characteristic of the system.

S' says that the physical retinae strikes occur in the order of one first, then the other; if they do, then Albert's brain should process them in that order, and generate an ordered experience.

Morbert wrote: »

At most, you have expressed your distaste for the idea that events are Minkowskian rather than Newtonian. Do yourself a favour. Don't open a quantum mechanics book.

I'm sure I'll open one in due course.

Morbert

You are beginning to repeat the same mistakes you are making in this thread:

http://www.boards.ie/vbulletin/showthread.php?t=2056789049

To avoid duplication, I will continue the conversation in that thread.