Question on Lorentz transforms and relativity of simultaneity

roosh · 28-10-2012 07:26AM

Thanks ceejay, that is certainly a very comprehensive reply. I'll try to address some of the points you raise.

ceejay wrote: »

I think these two paragraphs, and especially the last sentence, highlight an assumption which is where I think you're going wrong. Essentially the moving observer is not you, it is something else which is moving relative to you and has a moving frame of reference relative to you in your rest frame of reference, and it is observing three events: the lightning strikes and you turning 50. So to that observer the three events are not simultaneous, but to you they are.

You cannot be both the observer at rest and the observer moving relative to yourself at the same time!

You see the flashes simultaneously with turning 50 because you are at rest, and someone else moving relative to you would describe the situation differently due to relativity. You cannot be both at rest and moving at the same time, so you cannot experience both descriptions of the events at the same time, and hence there is no way for you to remember both descriptions as you seem to be asserting.

A way of thinking about it which may help clarify it is this:

You are with a friend Alex who is standing still right beside you when you turn 50. At the same time your other friend Brian is speeding past at a significant fraction of the speed of light. You see the two flashes of lightning striking just as you turn 50, and you say "wow did you see that, those flashes of lightning happened just as I turned 50!"

Alex would agree with you and says "yes, amazing!" (if we ignore the very slight difference in when he would perceive the light flashes due to the slight difference in position of him versus you - it would be extremely small and probably not humanly discernible anyway).

Later you talk to Brian after he has finished speeding around the place, and he disagrees with the description that you and Alex agree on, saying that he saw one flash, then you turning 50, and then the second flash. Here I'm assuming there's some external visible manifestation of you turning 50 that Brian can detect - maybe all your hair turned grey at that moment!

Neither you, Alex, or Brian have any set of superimposed memories of both descriptions, since you each experienced the events according to your own frames of reference. However using the Lorenz transformations and Brian's information of the speed he was travelling at relative to you and Alex, you can work out that the two descriptions are actually consistent.

You and Alex would be able to visualise what it must have looked like for Brian, including accurately determining the time between the three events as he perceived them, and Brian would be able to visualise that the events would have appeared as simultaneous for you and Alex.

That last bit is important, and as has been shown in other posts: Brian wouldn't see the events as simultaneous, but he can work out that you would have seen them as simultaneous in your frame of reference. This means that while the first part of your assertion is correct,

(which is true from the perspective of an observer in the moving frame of reference), your next part is incorrect)

since the moving observer can do the transformation in reverse to determine that "50 yr old you" would have seen them as simultaneous.

All the events, objects, individuals, etc. in the scenario are real and happen. However observers moving at significant speeds relative to each other will have different descriptions of when exactly the events occur. No observer can directly experience the sequence events of another observer moving relative to them, but they can work out using the Lorenz transformations what it would be like for them.

Does any of that help?

You mention that we cannot be the observer at rest and the observer moving relative at the same time; but we can represent the observer that is located midway between the lightning rods in both reference frames.

In both reference frames the observer is located midway between the lightning rods, so if light travels at the same speed in both directions, we should be able to conclude that, if the lightning strikes are non-simultaneous, that the light will reach the observer at the midpoint simultaneously.

Instead, as morbert alludes to, when the light strikes the lightning poles it somewho has two centres, one which remains centred over the pole and one which doesn't. The explanation we are given for this is that it is due to the geomety of events. I would have thought, however, that geometry was just our way of mathematically representing the phyiscal events; if it is, then we are left without an explanation for how light can have two centres. Relative motion doesn't really answer the question, because it would require an observes motion to affect the underlying physical structure; but, of course, the underlying physical structure can't be affected because that would necessitate that the same bit of spacetime is both affected and not affected; as an observer can equally be considered at rest in a part of spacetime as he could be considered in motion.

Hopefully the following can make the issue a little clearer.

Laser eye surgery
We may be able to formulate the thought experiment in such a way that it demonstrates the issue better.

Again, we can use the bones of the traditional thought experiment, but just alter it slightly; let's say there is an observer located midway between two rods, A and B; atop the rods are two lasers which will blind the observer if it comes into contact with his eye; the observer is positioned in such a way that his left retina is the same distance from the laser at A, as his right retina is from the laser at B.

In frame S, the lasers on A and B fire simultaneously; the lasers hit each retina simultaneously and can be considered two separate events; the observer is blinded in both eyes simultaneously.

There is a relatively moving observer, who is at rest in S'; performing the Lorentz transform we find that the lasers fire non-simultaneously in S'; we also find that the other two events, of the laser hitting each retina of the observer, occurs non-simultaneously; blinding him in one eye, before the other.

Thus, if both S and S' are equally valid, or accurate, representations of the physical world, the observer should have discordant experiences.

Morbert · 28-10-2012 07:25PM

roosh wrote: »

Laser eye surgery
We may be able to formulate the thought experiment in such a way that it demonstrates the issue better.

Again, we can use the bones of the traditional thought experiment, but just alter it slightly; let's say there is an observer located midway between two rods, A and B; atop the rods are two lasers which will blind the observer if it comes into contact with his eye; the observer is positioned in such a way that his left retina is the same distance from the laser at A, as his right retina is from the laser at B.

In frame S, the lasers on A and B fire simultaneously; the lasers hit each retina simultaneously and can be considered two separate events; the observer is blinded in both eyes simultaneously.

There is a relatively moving observer, who is at rest in S'; performing the Lorentz transform we find that the lasers fire non-simultaneously in S'; we also find that the other two events, of the laser hitting each retina of the observer, occurs non-simultaneously; blinding him in one eye, before the other.

Thus, if both S and S' are equally valid, or accurate, representations of the physical world, the observer should have discordant experiences.

An even more pronounced thought experiment can be carried out. Say the observer has their arms stretched out, and that each arm is 300,000 km long. I.e. Each arm is touching a poll. In one frame, the observer gets shocked by lightning simultaneously. In another, the left arm gets shocked before the right. But, like any arbitrary setup, causality is the same in all reference frames. The information travels through the nerves, and reaches the brain simultaneously for all observers.

Or we can consider the opposite. Let's say each rod has a button and the observer presses them simultaneously in his reference frame. In the other reference frame, the signal from the brain will reach one hand before the other. None of this poses a problem for causality.

You can even consider the brain itself as an extended object, and the structure of which action potentials and neural firings cause others will be preserved, preserving the same consciousness.

roosh · 29-10-2012 12:49AM

Morbert wrote: »

An even more pronounced thought experiment can be carried out. Say the observer has their arms stretched out, and that each arm is 300,000 km long. I.e. Each arm is touching a poll. In one frame, the observer gets shocked by lightning simultaneously. In another, the left arm gets shocked before the right. But, like any arbitrary setup, causality is the same in all reference frames. The information travels through the nerves, and reaches the brain simultaneously for all observers.

Or we can consider the opposite. Let's say each rod has a button and the observer presses them simultaneously in his reference frame. In the other reference frame, the signal from the brain will reach one hand before the other. None of this poses a problem for causality.

You can even consider the brain itself as an extended object, and the structure of which action potentials and neural firings cause others will be preserved, preserving the same consciousness.

Those examples rely on the information traveling parallel to the direction of motion; in the laser eye example, however, the optic nerve would run perpendicular to the direction of motion; or at least, we can construct the thought experiment so that this is the case. When we do this, causality is violated.

krd · 29-10-2012 10:46AM

roosh wrote: »

Those examples rely on the information traveling parallel to the direction of motion;

No they don't. The arms do not have to be parrallel. You could even cross the arms and you'll get the same result.

roosh · 29-10-2012 11:48AM

krd wrote: »

No they don't. The arms do not have to be parrallel. You could even cross the arms and you'll get the same result.

The initial formulation isn't much different in that the information has to travel the same distance, in the same direction, to converge in a single event; that is, the undefined, "light reaching the observer". Crossing the arms seems to have the same effect of leaving the "light reaching the observer" as an undefined singular event.

We can, however, define "the light reaching the observer" as two separate events, that of the light, or the laser, hitting each retina; this is more representative of how the light actually would reach the observer. In frame S, these events are simultaneous, in S' they are non-simultaneous. That means, if we follow the logic of S', the observer should experience blindness in one eye then the other; while following the logic of S, he should experience blindness in both eyes simultaneously.

krd · 29-10-2012 04:42PM

roosh wrote: »

We can, however, define "the light reaching the observer" as two separate events, that of the light, or the laser, hitting each retina; this is more representative of how the light actually would reach the observer. In frame S, these events are simultaneous, in S' they are non-simultaneous. That means, if we follow the logic of S', the observer should experience blindness in one eye then the other; while following the logic of S, he should experience blindness in both eyes simultaneously.

What you're describing is something that happens all the time, and has no influence on causality. Both your eyes will only experience an event as simultaneous if they are absolutely equidistant from the source of the event. In all other positions, the eyes will register the event at different times. This has nothing to do with the Special Relativity, and is because of the speed of light - you can get a compass and draw some circles - the expanding circle from the source is the light. If the eyes are not equidistant from the source, the circle will cross each at different times, this has no effect on the causality.

roosh · 30-10-2012 01:13AM

krd wrote: »

What you're describing is something that happens all the time, and has no influence on causality. Both your eyes will only experience an event as simultaneous if they are absolutely equidistant from the source of the event. In all other positions, the eyes will register the event at different times. This has nothing to do with the Special Relativity, and is because of the speed of light - you can get a compass and draw some circles - the expanding circle from the source is the light. If the eyes are not equidistant from the source, the circle will cross each at different times, this has no effect on the causality.

In the case of the eye lasers we are dealing with two distinct events, not one; namely, the laser from A hitting the left retina, and the laser from B hitting the right retina; each retina is equidistant from the laser it is closest to; that is, the left retina is the same distance from A as the right retina is from B.

In S' the events, of the lasers hitting the observer's retinae, are non-simultaneous, while in S, they are simultaneous. This means that, according to S', the observer will go blind in, say, his right eye first and then his left; while, according to S, he will go blind in both eyes simultaneously.

If both are equally valid representations of the physical phenomena, then seeming paradox arises and causality would seem to be violated.

citrus burst · 30-10-2012 01:43AM

roosh wrote: »

In the case of the eye lasers we are dealing with two distinct events, not one; namely, the laser from A hitting the left retina, and the laser from B hitting the right retina; each retina is equidistant from the laser it is closest to; that is, the left retina is the same distance from A as the right retina is from B.

In S' the events, of the lasers hitting the observer's retinae, are non-simultaneous, while in S, they are simultaneous. This means that, according to S', the observer will go blind in, say, his right eye first and then his left; while, according to S, he will go blind in both eyes simultaneously.

If both are equally valid representations of the physical phenomena, then seeming paradox arises and causality would seem to be violated.

Yeah but in another frame of reference S'' which for argument sake is moving in the opposite direction of S' and moving relative to the rest frame S the chap will go blind in his left eye first.

These events are all related in some way. It just so happens that there is one frame (there could be more) that happens to have the right conditions for the light to blind the guy simultaneous in both eyes. It also just so happens that we have chosen this frame to be our rest frame. You could set up some problem to test is there any frame of reference where two events occur simultaneous. This is in theory no more difficult then finding a point between two charged anythings where the electric field is zero. A fairly basic physics question.

I can't really see how case and effect are influenced by this. I mean in all reference frames the guy will go blind after the laser hits his eye. In no reference frame will he go blind before a laser hits an eye, so I can't see what difference bringing causality into the picture will bring.

roosh · 30-10-2012 08:10AM

citrus burst wrote: »

Yeah but in another frame of reference S'' which for argument sake is moving in the opposite direction of S' and moving relative to the rest frame S the chap will go blind in his left eye first.

These events are all related in some way. It just so happens that there is one frame (there could be more) that happens to have the right conditions for the light to blind the guy simultaneous in both eyes. It also just so happens that we have chosen this frame to be our rest frame. You could set up some problem to test is there any frame of reference where two events occur simultaneous. This is in theory no more difficult then finding a point between two charged anythings where the electric field is zero. A fairly basic physics question.

I can't really see how case and effect are influenced by this. I mean in all reference frames the guy will go blind after the laser hits his eye. In no reference frame will he go blind before a laser hits an eye, so I can't see what difference bringing causality into the picture will bring.

Apologies, it is my reading of the concept of "violation of causality" that is causing some confusion. The issue is more of a paradox than a violation of causality.

The issue is that, if both S and S' are equally valid representations of the physical events, then Albert - the laser eye patient - should have discordant experiences of the same events; that is, he should experience both simultaneous blindness and non-simultaneous blindness, wrt his eyes; this appears to be a paradox.

krd · 30-10-2012 08:14AM

roosh wrote: »

In S' the events, of the lasers hitting the observer's retinae, are non-simultaneous, while in S, they are simultaneous. This means that, according to S', the observer will go blind in, say, his right eye first and then his left; while, according to S, he will go blind in both eyes simultaneously.

If both are equally valid representations of the physical phenomena, then seeming paradox arises and causality would seem to be violated.

There is no paradox, or violation of casuality. A laser beam is made up of photons. The photons that blind the left eye, are not the same photons that blind the right eye.

Special Relativity is rock solid. People have been trying to have a go at it for over a hundred years. No one has beaten it.

roosh · 30-10-2012 08:48AM

krd wrote: »

There is no paradox, or violation of casuality. A laser beam is made up of photons. The photons that blind the left eye, are not the same photons that blind the right eye.

Special Relativity is rock solid. People have been trying to have a go at it for over a hundred years. No one has beaten it.

There is no suggestion that it's the same photons; we are talking about two different lasers blinding two different eyes; according to one reference frame the blinding events are simultaneous, according to the other they're not.

If both reference frames are valid representations of the physical events, then the observer should have discordant experiences of his own blindness - not simply that relatively moving observers will disagree about them.

If we say that the observer experiences the blindness events as simultaneous, as described by S, then we are saying that the physical events, as described by S', are less valid, or don't accurately represent the physical events.

Morbert · 30-10-2012 01:59PM

roosh wrote: »

Those examples rely on the information traveling parallel to the direction of motion; in the laser eye example, however, the optic nerve would run perpendicular to the direction of motion; or at least, we can construct the thought experiment so that this is the case. When we do this, causality is violated.

No. Causality is not violated and I have no idea why you think it is.

The brain is an elaborate computer, at least from a physical perspective. And since the structure of its logic architecture is unchanged across reference frames, all reference frames will agree on what the observer between the rods experiences. To make this easier to understand, replace the observer with a computer and optical detectors.

Even if we treat consciousness as some space-like surface extended through the brain, ignoring the explicit architecture, as you seem to be doing, causality is not violated. In S', not only are the lightning strikes or laser emissions no longer simultaneous, but the ordering of stimuli needed to generate an equivalent experience is also different, since we've extended consciousness through the brain.

roosh · 30-10-2012 03:14PM

Morbert wrote: »

No. Causality is not violated and I have no idea why you think it is.

The brain is an elaborate computer, at least from a physical perspective. And since the structure of its logic architecture is unchanged across reference frames, all reference frames will agree on what the observer between the rods experiences. To make this easier to understand, replace the observer with a computer and optical detectors.

Even if we treat consciousness as some space-like surface extended through the brain, ignoring the explicit architecture, as you seem to be doing, causality is not violated. In S', not only are the lightning strikes or laser emissions no longer simultaneous, but the ordering of stimuli needed to generate an equivalent experience is also different, since we've extended consciousness through the brain.

Yes, apologies, I was reading the term "violation of causality" to mean a difference in the experience of an observer; or, as you eloquently put it that "the ordering of stimuli needed to generate an equivalent experience is [...] different".

The issue isn't a violation of causality, rather a paradox of discordant experiences.

Presumably, given that the structure of the brain is unchanged across reference frames, all reference frames will agree that if Albert is blinded in both eyes non-simultaneously, that he will experience blindness in one eye first and then the other; while, on the other hand, if he is blinded in both eyes simultaneously, that he will experience loss of vision in both eyes simultaneously.

It just becomes a question of whether or not he is blinded simultaneously. According to S' he isn't, while according to S he is; this should lead to discordant experiences, which appears to be a paradox.

I don't think we need to extend consciousness throughout the brain; once the lasers blind Albert it's just a question of how long it takes the information to travel through his brain. If we assume that it takes the same time for each eye, then the simultaneity of events will affect which one loses vision first. If it takes different amounts of time then we can backwards rationalise it to see what the experience should be like given simultaneous blinding, and what it should be like given non-simultaneous blinding. It would still work out to give discordant experiences.

Morbert · 30-10-2012 05:56PM

roosh wrote: »

Yes, apologies, I was reading the term "violation of causality" to mean a difference in the experience of an observer; or, as you eloquently put it that "the ordering of stimuli needed to generate an equivalent experience is [...] different".

The issue isn't a violation of causality, rather a paradox of discordant experiences.

Presumably, given that the structure of the brain is unchanged across reference frames, all reference frames will agree that if Albert is blinded in both eyes non-simultaneously, that he will experience blindness in one eye first and then the other; while, on the other hand, if he is blinded in both eyes simultaneously, that he will experience loss of vision in both eyes simultaneously.

All reference frames won't agree on that. Remember that the brain is an extended object. What you are doing is assuming the detection of light undergoes RoS, but that the brain processing doesn't. In S', the eyes are blinded at different times, but since the brain is an extended object, brain activity will also be different at that time. Hence, what happens is the brain receives the input at different times, but the brain activity generates a conscious experience of being blinded simultaneously.

roosh · 31-10-2012 12:18PM

Morbert wrote: »

All reference frames won't agree on that. Remember that the brain is an extended object. What you are doing is assuming the detection of light undergoes RoS, but that the brain processing doesn't. In S', the eyes are blinded at different times, but since the brain is an extended object, brain activity will also be different at that time. Hence, what happens is the brain receives the input at different times, but the brain activity generates a conscious experience of being blinded simultaneously.

As you have mentioned, Albert's experiences will be determine by his rest frame, because that is the reference frame of his brain. If his eyes are physically blinded non-simultaneously, then this is what his brain will process and his experiecne will reflect this. If his eyes are blinded simultaneously then this is what his brain will process, and his experience will reflect this. It then becomes a question of the phyiscality of the blinding events.

If the non-simultaneous events are physically valid, then his experience should reflect this; if they are simultaneous, then his experience should refelct this. If both are valid, then he should have discordant experiences; and that would seem to be a paradox.

ceejay · 31-10-2012 02:32PM

Both descriptions of the timing of the events are valid and can be transformed between each other using the Lorenz transformations, but your extrapolation of this fact to mean that the observer in the rest frame will also experience the events as described by a different observer in the moving frame is incorrect.

Think of the classic twins example where one twin stays on Earth and is treated as the rest frame, while the other twin sets off at a large fraction of the speed of light and comes back to Earth at a later point in time. For the twin in the rest frame he will experience the time between the two events of the other twin leaving and returning as being much longer than the other twin. The speedy twin will experience the time between the events as much shorter than his stay-at-home twin. Both descriptions are equally valid. Neither twin experiences the other twin's perception of how long it takes between the events. The two descriptions can be transformed between each other using the Lorenz transformations to show that they are mutually consistent in the framework of Special/General Relativity.

My key point again is that your basic assumption that your observer in the rest frame is the same as the observer in the moving frame is just incorrect. You exist in both frames of course, but your conscious experiences are only ever arising from the events as described in the rest frame.

Morbert · 01-11-2012 12:03AM

roosh wrote: »

If his eyes are physically blinded non-simultaneously, then this is what his brain will process and his experiecne will reflect this.

Not in S', for reasons I mentioned in my previous post: "In S', the eyes are blinded at different times, but since the brain is an extended object, brain activity will also be different at that time. Hence, what happens is the brain receives the input at different times, but the brain activity generates a conscious experience of being blinded simultaneously. "

roosh · 01-11-2012 01:15AM

ceejay wrote: »

Both descriptions of the timing of the events are valid and can be transformed between each other using the Lorenz transformations, but your extrapolation of this fact to mean that the observer in the rest frame will also experience the events as described by a different observer in the moving frame is incorrect.

Think of the classic twins example where one twin stays on Earth and is treated as the rest frame, while the other twin sets off at a large fraction of the speed of light and comes back to Earth at a later point in time. For the twin in the rest frame he will experience the time between the two events of the other twin leaving and returning as being much longer than the other twin. The speedy twin will experience the time between the events as much shorter than his stay-at-home twin. Both descriptions are equally valid. Neither twin experiences the other twin's perception of how long it takes between the events. The two descriptions can be transformed between each other using the Lorenz transformations to show that they are mutually consistent in the framework of Special/General Relativity.

My key point again is that your basic assumption that your observer in the rest frame is the same as the observer in the moving frame is just incorrect. You exist in both frames of course, but your conscious experiences are only ever arising from the events as described in the rest frame.

This example is different, because it involves the experience of just one obsevrer, and is a question of the physicality of the events, as described by both reference frames.

You are correct to an extent, that an observers experiences will be processed, by their brain, in the rest frame of their brain. It then becomes a question of the physicality of the events.

If light physically enters Albert's eyes non-simultaneously i.e. through one eye, before the other, then his experience will be of light entering one eye before the other. If light enters both eyes simultaneously, then he will experience light entering both eyes simultaneously.

It is then a question of whether the light physically hits his eye simultaneously, or non-simultaneously.

According to S' the light physically hits his eyes non-simultaneously; according to S, it physically hits his eyes simultaneously. If both are true, then Albert should have discordant experiences.

Only if the light doesn't physically hit his eyes, in the manner of one, or both, of the above, will he not have discordant experiences.

Again, the key point is that Albert's brain processes his experiences in the frame in which it is at rest; the order in which light physically hits his eyes will determine his experience. Are the events as described by S' physical, that is, does light physically hit his eyes non-simultaneously; are the events described by S physical, that is, does the light physically hit his eyes simultaneously? If so he will have discordant experiences.

roosh · 01-11-2012 02:04AM

Morbert wrote: »

Not in S', for reasons I mentioned in my previous post: "In S', the eyes are blinded at different times, but since the brain is an extended object, brain activity will also be different at that time. Hence, what happens is the brain receives the input at different times, but the brain activity generates a conscious experience of being blinded simultaneously. "

Using the term "blinding", or "blinded" might be causing some confusion, because it doesn't distinguish between the laser damaging his eyes and the moment he loses vision; it might be more helpful to speak of photons hitting the retinae and the experience as processed by the brain.

As mentioned, and as per the response to ceejay, Albert's brain will process his experiences in the frame in which it, and he are at rest. If light physically hits his eyes simultaneously, then the experience, as processed by the brain, will be of light hitting both eyes simultaneously; if light physically hits both retinae non-simultaneously, then his brain will process the experience accordingly.

It's just a question of whether the light physically hits his eyes simultaneously, as per S, or non-simultaneously, as per S'; if the light physically hits his eyes as per both, then his brian should process discordant experiences.

citrus burst · 01-11-2012 03:06AM

roosh wrote: »

You are correct to an extent, that an observers experiences will be processed, by their brain, in the rest frame of their brain. It then becomes a question of the physicality of the events.

Why only to an extent? I know we're not really talking about how the brain processes information but I just want to know why he isn't "fully" right.

roosh wrote: »

If light physically enters Albert's eyes non-simultaneously i.e. through one eye, before the other, then his experience will be of light entering one eye before the other. If light enters both eyes simultaneously, then he will experience light entering both eyes simultaneously.

It is then a question of whether the light physically hits his eye simultaneously, or non-simultaneously.

roosh wrote: »

According to S' the light physically hits his eyes non-simultaneously; according to S, it physically hits his eyes simultaneously. If both are true, then Albert should have discordant experiences.

why?

roosh wrote: »

Only if the light doesn't physically hit his eyes, in the manner of one, or both, of the above, will he not have discordant experiences.

But there could then be another frame S'' that light hits his eyes simultaneous.

roosh wrote: »

Again, the key point is that Albert's brain processes his experiences in the frame in which it is at rest; the order in which light physically hits his eyes will determine his experience.

True, this is probably the most important thing you have said all thread. The moment light hits his eyes are his experiences. Every other frame is not his experience but somebody or something else's. This is how his memory is correct and not a mixed stew of the memories of all other reference frames. He was never "in" any of them. He can be "described" by all other reference frames, and all other reference frames will agree that the light hit his eyes simultaneous. They will not however observe the light hitting his eyes simultaneous.

This seems totally against common sense and it should be, but if special relativity is correct then it will be the case.

roosh wrote: »

Are the events as described by S' physical, that is, does light physically hit his eyes non-simultaneously;

yes

roosh wrote: »

are the events described by S physical, that is, does the light physically hit his eyes simultaneously?

yes

roosh wrote: »

If so he will have discordant experiences.

No

citrus burst · 01-11-2012 03:14AM

roosh wrote: »

As mentioned, and as per the response to ceejay, Albert's brain will process his experiences in the frame in which it, and he are at rest and where the event took place, that is reference frame S. If light physically hits his eyes simultaneously, then the experience, as processed by the brain, will be of light hitting both eyes simultaneously; if light physically hits both retinae non-simultaneously, then his brain will process the experience accordingly.

Agreed.

roosh wrote: »

It's just a question of whether the light physically hits his eyes simultaneously, as per S, or non-simultaneously, as per S';

It does both, S just happens to be a special case where it is simultaneous and as such his memories would be affected accordingly. In other frames this wont be the case.

roosh wrote: »

if the light physically hits his eyes as per both, then his brian should process discordant experiences.

Again unless he can "simultaneously" be in the doctors office (S) getting his eyes zapped and in a space ship (S') going 0.5c then he will have discordant memories. Fortunately he can't be.

roosh · 01-11-2012 12:06PM

citrus burst wrote: »

Why only to an extent? I know we're not really talking about how the brain processes information but I just want to know why he isn't "fully" right.
...
why?

He is correct to the extent that an observers brain will process physical events in the reference frame in which it, the brain, is at rest. That is, if you are on the embankment, your brain will do it's processing on the embankment, of any sensory input. When light physically hits the retina it becomes input which the brain will process.

It is just a question of whether the light physically hits your eyes simultaneously, non-simultaneously, or both. According to S the light physically hits your eyes simultaneously; according to S', it physically hits your eyes non-simultaneously.

If both represent real physical events, that is, if the light hitting your retina, as described in S' is a real, physical event, and the light hitting your retina as described by S, is a real, physical event, then your brain should process them as such; the processing will be done by the brain on the embankment.

citrus burst wrote: »

But there could then be another frame S'' that light hits his eyes simultaneous.

Indeed, and there could be another reference frame which has the non-simultaneity, of the physical events, as being different from that in S'; this just represents an additional discordant experience that the observer should have.

citrus burst wrote: »

True, this is probably the most important thing you have said all thread. The moment light hits his eyes are his experiences. Every other frame is not his experience but somebody or something else's. This is how his memory is correct and not a mixed stew of the memories of all other reference frames. He was never "in" any of them. He can be "described" by all other reference frames, and all other reference frames will agree that the light hit his eyes simultaneous. They will not however observe the light hitting his eyes simultaneous.

This seems totally against common sense and it should be, but if special relativity is correct then it will be the case.

Albert's brain does it's processing of physical events in the frame in which it is at rest; that is, the processing occurs in the rest frame i.e. on the embankment. If light physically hits Albert's eyes, then his brain will process the experience accordingly; if light physically hits Albert's eyes non-simultaneously, then his brain will process the experience accordingly; if light physically hits Albert's eyes simultaneously, then his brain will process the experience accordingly

Put another way, Albert's brain will process sensory stimuli according as they are received by the sensory organs; when light physically hits the retina of the eye, that represents the receipt of a sensory stimulus, which the brain will process. The order in which the stimuli are received determines the experience.

According to S' the physical, sensory events - the processing of which takes place in the brains rest frame - that is the light hitting Albert's retinae, occurs non-simultaneously; so if Albert receives physical, sensory stimulation - as he should when light hits his retina - non-simultaneously, his brain will process a non-simultaneous experience.

On the other hand, when the light hits his retinae simultaneously, as it does according to S, his brain will process the simultaneous experience

citrus burst wrote: »

yes

yes

No

If the light physically hits his eyes simultaneously, his brain will process the experience accordingly.

If the light physically hits his eyes non-simultaneously, his brain will process the experience accordingly.

Does the light physically hit his eyes both simultaneously and non-simultaneously?

Bearing in mind that his brain will do the processing, in the frame in which it is at rest, of all physical events, of light hitting his eyes; and that Albert is physically on the embankment, not physically in the mathematical reference frame labelled S, or S'; where S and S' are mathematical representations, or descriptions, of physical events.

citrus burst wrote: »

Agreed.
...
It does both, S just happens to be a special case where it is simultaneous and as such his memories would be affected accordingly. In other frames this wont be the case.

While you may agree with your amendment to the statement, I don't necessarily agree with it. The event takes place on the embankment, where Albert is physically located; S and S' are mathematical representations of the events and, as such, physical events cannot take place in those mathematical reference frames. It is simply a question of whether the mathematical representations correspont to actual, physical events.

Again, according to the description given by S', the light physically hits Albert's retinae - while Albert is standing on the embankment - non-simultaneously; if this is an accurate representation of physical events, then Albert's brain will process the non-simultaneous events while he is at rest on the embankment.

Only if the light doesn't physically hit Albert's retinae non-simultaneously, while he is physically on the embankment, will his brain not process them as non-simultaneous. If it doesn't physically hit his retinae non-simultaneously, while he is standing on the embankment, then the description of events given by the mathematical reference frame S' - which says that light physically hits his retinae non-simultaneously, while he is standing on the embankment - must not pertain to real, physical events.

citrus burst wrote: »

Again unless he can "simultaneously" be in the doctors office (S) getting his eyes zapped and in a space ship (S') going 0.5c then he will have discordant memories. Fortunately he can't be.

Indeed, there is no suggestion that Albert is physically in two places; in this case, he is standing on the embankment only, not on the train whizzing by at relative velocity of 0.98c.

The mathematical reference frame S says that light physically hits his retinae simultaneously, while he is physically standing on the embankment. S' says that, while he is physically standing on the embankment, the light hits his eyes non-simultaneously.

If light hits his eyes simultaneously, while he is standing on the embankment, then his brain will process the simultaneous experience; if light hits his eys non-simultaneously, while he is standing on the embankment, then his brain will process a non-simultaneous experience.

If both mathematical representations, of light physically hitting his retinae, while he is physically standing on the embankment, are valid, correct, true, or whatever term we care to use, then his brain will process discordant experiences of what are, supposedly, the same phenomenon.

Only if the light doesn't physically hit his eyes, non-simultaneously (for arguments sake), while he is physically standing on the embankment, will his brain not process discordant experiences.

roosh · 01-11-2012 01:14PM

We can idealise the observer, can't we, to make the effect more noticeable; we can make Albert into "Giant Albert", or like Gulliver in the land of Liliput?

ceejay · 01-11-2012 02:57PM

Look at this again:

Morbert wrote: »

Try the transformations explicitly yourself. Let's say the rods a and b are each 1 lightsecond (ls) away from the observer in the middle. In the reference frame of the observer, we have:

Time of strikes is Ta =Tb = 0 s
Position of rod a is Xa = 1 ls
Position of rob b is Xb = -1 ls
Time strike a is witnessed is ta = 1 s
Time strike b is witnessed is tb = 1 s
The strikes are both witnessed at position x = 0 ls

Now let's transform the coordinates to a reference frame travelling at v relative to the observer. We'll use natural units, so that c = 1.

The time of strikes are

Ta' = γ(Ta-vXa) = -γv
Tb = γ(Tb-vXb) = γv

But the strikes are witnessed at

ta' = γ(ta-vx) = γ
tb' = γ(tb-vx) = γ

So you see that, even though the strikes are not simultaneous, all reference frames will agree that you witness both strikes simultaneously. Hence, causality is preserved.

Morbert uses the mathematics to describe the situation generically but also exactly. What the maths above shows is that in the rest frame the lightning strikes at points A and B happen simultaneously at t = 0 seconds, and that you see them simultaneously at t = 1 seconds because you are standing in the middle at a distance of 1 light second away from each rod.

From the maths above again using the results of the transformations, these show that in the moving frame the lightning strikes at A and B are no longer simultaneous - the strike at A happens at t = -γv seconds, and the strike a B happens at t = γv seconds, instead of them both happening at t = 0 seconds. In the moving frame of reference there is 2γv seconds between the two lightning strikes.

More significantly: even in the moving frame of reference the light from both lightning strikes still arrive at your position in the middle simultaneously though it is measured in the moving frame of reference as happening at t = γ seconds instead of at t = 1 seconds.

As you vary the chosen speed for the moving reference frame the separation in time between the two lightning flashes will change, and the precise moment when they simultaneously arrive at you standing in the middle will change, but the maths show that the light will always arrive simultaneously at you standing in the middle no matter what reference frame you use!

So there is no discordant memory situation to worry about

I must admit that I had missed the significance of this when I first read Morbert's post.

Morbert · 01-11-2012 03:41PM

roosh wrote: »

As mentioned, and as per the response to ceejay, Albert's brain will process his experiences in the frame in which it, and he are at rest. If light physically hits his eyes simultaneously, then the experience, as processed by the brain, will be of light hitting both eyes simultaneously; if light physically hits both retinae non-simultaneously, then his brain will process the experience accordingly.

You keep saying this, and it will not be true no matter how many times you do. In S', the experience processed by the brain is still of being blinded in both eyes simultaneously. This is because in S', brain activity itself exhibits RoS. You are consistently ignoring this point.

roosh · 01-11-2012 04:13PM

ceejay wrote: »

Look at this again:

Morbert uses the mathematics to describe the situation generically but also exactly. What the maths above shows is that in the rest frame the lightning strikes at points A and B happen simultaneously at t = 0 seconds, and that you see them simultaneously at t = 1 seconds because you are standing in the middle at a distance of 1 light second away from each rod.

From the maths above again using the results of the transformations, these show that in the moving frame the lightning strikes at A and B are no longer simultaneous - the strike at A happens at t = -γv seconds, and the strike a B happens at t = γv seconds, instead of them both happening at t = 0 seconds. In the moving frame of reference there is 2γv seconds between the two lightning strikes.

More significantly: even in the moving frame of reference the light from both lightning strikes still arrive at your position in the middle simultaneously though it is measured in the moving frame of reference as happening at t = γ seconds instead of at t = 1 seconds.

As you vary the chosen speed for the moving reference frame the separation in time between the two lightning flashes will change, and the precise moment when they simultaneously arrive at you standing in the middle will change, but the maths show that the light will always arrive simultaneously at you standing in the middle no matter what reference frame you use!

So there is no discordant memory situation to worry about

I must admit that I had missed the significance of this when I first read Morbert's post.

This assumes that the photons converge at the same point; the point being made is that the retina are not located at the same point, there is a distance between them such that, according to S', the light will hit the retina non-simultaneously.

roosh · 01-11-2012 04:23PM

Morbert wrote: »

You keep saying this, and it will not be true no matter how many times you do. In S', the experience processed by the brain is still of being blinded in both eyes simultaneously. This is because in S', brain activity itself exhibits RoS. You are consistently ignoring this point.

Albert's brain isn't in S'; Albert's brain is with him on the embankment. Albert's brain will do its processing on the embankment, not in a relatively moving train. Albert's brain will process physical stimuli according as they are received.

S' says that the photons will hit Albert's retina, on the embankment, non-simultaneously; that is, S' says the physical stimuli will enter his retinae non-simultaneously, on the embankment. If senosry input enters Albert's retinae non-simultaneously, on the embankment, then his brain will process a non-simultaneous experience, on the embankment.

S says that the sensory stimuli will be received simultaneously, on the embankment; that is, S says the physical stimuli will enter his retinae simultaneously, on the embankment. If senosry input enters Albert's retinae simultaneously, on the embankment, then his brain will process a simultaneous experience, on the embankment.

It's just a question of whether he receives the physical, sensory stimuli simultaneously, non-simultaneously, or both, on the embankment; S says he will receive them simultaneously, on the embankment; S' says non-simultaneously, on the embankment. If both are valid representations of the physical, sensory stimuli, then his brain should produce discordant experiences of the received photons, on the embankment.

Morbert · 01-11-2012 04:45PM

roosh wrote: »

Albert's brain isn't in S'; Albert's brain is with him on the embankment. Albert's brain will do its processing on the embankment, not in a relatively moving train. Albert's brain will process physical stimuli according as they are received.

S' says that the photons will hit Albert's retina, on the embankment, non-simultaneously; that is, S' says the physical stimuli will enter his retinae non-simultaneously, on the embankment. If senosry input enters Albert's retinae non-simultaneously, on the embankment, then his brain will process a non-simultaneous experience, on the embankment.

S says that the sensory stimuli will be received simultaneously, on the embankment; that is, S says the physical stimuli will enter his retinae simultaneously, on the embankment. If senosry input enters Albert's retinae simultaneously, on the embankment, then his brain will process a simultaneous experience, on the embankment.

It's just a question of whether he receives the physical, sensory stimuli simultaneously, non-simultaneously, or both, on the embankment; S says he will receive them simultaneously, on the embankment; S' says non-simultaneously, on the embankment. If both are valid representations of the physical, sensory stimuli, then his brain should produce discordant experiences of the received photons, on the embankment.

You still clearly don't understand how reference frames are applied. S and S' are two different sets of labels in which we consider the relevant events. What you are doing is considering the lights striking the eyes in S', but refusing to consider the brain activity in S' at each strike. This is a blatantly inconsistent use of coordinate labels. I do not know how to make this point any simpler.

Take this simplification: Instead of eyes, consider two synchronised clocks separated by an arbitrary distance, each equally close to a respective rod. In S, both clocks are struck by the respective lasers simultaneously, and register this. In S', the clocks are struck at different times, but they are also no longer synchronous. The clock struck first is a little ahead of the other. Thus, both clocks register the same time, even though they were struck at different times. You are saying "oh but the clocks aren't in S', they're in S." which is a nonsensical statement.

[edit]- Removed confusing sentence.

roosh · 05-11-2012 01:19AM

Morbert wrote: »

You still clearly don't understand how reference frames are applied. S and S' are two different sets of labels in which we consider the relevant events. What you are doing is considering the lights striking the eyes in S', but refusing to consider the brain activity in S' at each strike. This is a blatantly inconsistent use of coordinate labels. I do not know how to make this point any simpler.

Take this simplification: Instead of eyes, consider two synchronised clocks separated by an arbitrary distance, each equally close to a respective rod. In S, both clocks are struck by the respective lasers simultaneously, and register this. In S', the clocks are struck at different times, but they are also no longer synchronous. The clock struck first is a little ahead of the other. Thus, both clocks register the same time, even though they were struck at different times. You are saying "oh but the clocks aren't in S', they're in S." which is a nonsensical statement.

[edit]- Removed confusing sentence.

I understand how reference frames are applied; this line of questioning, in part, questions the validity of how they are applied. What we are looking at here is the physicality of the events, as represented by the mathematical reference frames, and how Albert's brain processes physical stimuli which hit his retinae.

We can stick with the thought experiment as is, considering Albert's eyes and brain; we can augment it to say that Albert is in the army and is awaiting instructions as to whether or not to blow up a bridge; his instructions are, if you receive the signals simultaneously, blow up the bridge, if you receive the signals non-simultaneously, do not blow up the bridge.

Albert is physically standing on the embankment; he's not in either S or S'; S and S' are simply mathematical representations of physical events. Albert's brain will process any physical stimuli received by his retinae from its location on the embankment; his brain doesn't process his experiences by viewing itself from a relatively moving reference frame. That is, as soon as physical stimulae enter Albert's retinae, his brain processes as though it is not subject to relativistic effects, because, as far as it is concerned, it isn't.

So, picture Albert standing on the embankment; now picture two photons hitting his retinae simultaneously; his brain will process the sensory stimuli and produce the simultaneous experience which informs him to blow up the bridge.

Again, picture Albert standing on the embankment; now, picture two photons hitting his retinae non-simultaneously; his brain will process the sensory stimuli and produce the non-simultaneous experience, which informs him not to blow up the bridge.

According to relativity, Albert receives the sensory information both simultaneously and non-simultaneously; from there it follows that his brain should produce discordant experiences and he should both blow up the bridge and not blow up the bridge.

EDIT: essentially the point you are making, by saying that Albert's brain undergoes relativistic effects, is that Albert's brain will process physical stimuli which are received through his retinae, from the perspective of a relatively moving observer; in other words, that Albert will process his experiences from the perspective of a relatively moving observer.

We might say that, from the perspective of a relatively moving observer, Albert's brain is measured to undergo relativistic effects, but Albert's won't process his experiences from the relatively moving observers perspective; if we say that the photons are only measured to hit Albert's retinae non-simultaneously, by a relatively moving observer, then we open the question as to whether or not the photons physically hit Albert's retinae simultaneously, or if there is an anomaly in the relatively moving observers measurements that mean his measurements don't represent the physical events, that is the photons hitting the retinae [non-simultaneously].

If the photons do physically hit the retinae non-simultaneously, then Albert's brain won't process them from the perspective of a relatively moving observer.

Morbert · 05-11-2012 12:27PM

roosh wrote: »

I understand how reference frames are applied; this line of questioning, in part, questions the validity of how they are applied. What we are looking at here is the physicality of the events, as represented by the mathematical reference frames, and how Albert's brain processes physical stimuli which hit his retinae.

We can stick with the thought experiment as is, considering Albert's eyes and brain; we can augment it to say that Albert is in the army and is awaiting instructions as to whether or not to blow up a bridge; his instructions are, if you receive the signals simultaneously, blow up the bridge, if you receive the signals non-simultaneously, do not blow up the bridge.

Albert is physically standing on the embankment; he's not in either S or S'; S and S' are simply mathematical representations of physical events. Albert's brain will process any physical stimuli received by his retinae from its location on the embankment; his brain doesn't process his experiences by viewing itself from a relatively moving reference frame. That is, as soon as physical stimulae enter Albert's retinae, his brain processes as though it is not subject to relativistic effects, because, as far as it is concerned, it isn't.

So, picture Albert standing on the embankment; now picture two photons hitting his retinae simultaneously; his brain will process the sensory stimuli and produce the simultaneous experience which informs him to blow up the bridge.

Again, picture Albert standing on the embankment; now, picture two photons hitting his retinae non-simultaneously; his brain will process the sensory stimuli and produce the non-simultaneous experience, which informs him not to blow up the bridge.

According to relativity, Albert receives the sensory information both simultaneously and non-simultaneously; from there it follows that his brain should produce discordant experiences and he should both blow up the bridge and not blow up the bridge.

EDIT: essentially the point you are making, by saying that Albert's brain undergoes relativistic effects, is that Albert's brain will process physical stimuli which are received through his retinae, from the perspective of a relatively moving observer; in other words, that Albert will process his experiences from the perspective of a relatively moving observer.

We might say that, from the perspective of a relatively moving observer, Albert's brain is measured to undergo relativistic effects, but Albert's won't process his experiences from the relatively moving observers perspective; if we say that the photons are only measured to hit Albert's retinae non-simultaneously, by a relatively moving observer, then we open the question as to whether or not the photons physically hit Albert's retinae simultaneously, or if there is an anomaly in the relatively moving observers measurements that mean his measurements don't represent the physical events, that is the photons hitting the retinae [non-simultaneously].

If the photons do physically hit the retinae non-simultaneously, then Albert's brain won't process them from the perspective of a relatively moving observer.

You continue to blatantly ignore everything I have said. Here is the important point again: In S', the experience processed by the brain is still of being blinded in both eyes simultaneously. This is because in S', brain activity itself exhibits RoS. So even though the Albert isn't struck simultaneously in S', his brain will still register simultaneous strikes for the same reason two clocks would register simultaneous strikes. You are consistently ignoring this point.

So in your new, completely superfluous and irrelevant augmented thought experiment, both reference frames would agree that Albert blows up the bridge.

Question on Lorentz transforms and relativity of simultaneity

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