Relativity of simultaneity and one-way speed of light

[Andromacus]

Going back to my original question in post #1 and leaving aside the confusing discussions about distant simultaneity(that don't have empirical solution so they are quite useless) , maybe I can formulate it in a way that is easier to understand and get specific answers.

 

My first post highlighted the fact that Einstein used the same time and distance used in galilean transformations for the distance travelled by a light ray in vacuum from spacetime point1 to spacetime point 2, both points measured with global time t i the equation d=ct, to derive the null interval and from it the general minkowskian interval and the Lorentz transformations that leave it invariant.

 

Only using the Einstein synchronization can this be done. So much for conventionality of clock sync. postulated by Einstein himself. The very idea of a standard synchronization establishes the existence of a global time valid at a distance from the clock one has locally.

So the contradiction lies in that Einstein needs both to use a single standard synchronization or global time to derive the Lorentz transformations with his postulates, and at the same time declare his choice a convention because he is promoting a local time that is different from frame to frame, from spacetime point (event) to spacetime point.

The contradiction would be that it is necessary to have the Einstein sync as conventional and not conventional at once for the arguments of Einstein seminal 1905 paper to hold.

 

If we could just center on this, I would appreciate any input.

Edited September 8, 2015 by Andromacus

[david345]

1. My previous calculations already showed global time is not used for the speed of light. If you could count you would see that for frame 1 light was emitted at t=1it reached b at t=2 time of travel 1.

For frame 2 it was emitted at t=.57735 and reached b at t=1.1547 time of travel=.57735. If global time was used the time would be the same for both observers. My calculations show time was not the same for both observers contradicting your unfounded claims. The same is true for distance.

2. In response to your nonsense about frames inside of frames. We do not see the universe picture in picture. We do not see other frames within our own. My math already showed the math works. If you disagree then post a Minkowski diagram done the correct way along with your calculations. Do not respond with another word salad.

3. Conventionality of simultaneity says you can choose a convention within a certain limit. Einstein made his choice. If you wan't to use relativity then you have to deal with his choice. If you don't want to use relativity then choose another convention. You can't say "You can choose but you can't make a choice because that would be a contradiction." Einstein made his choice. Everyone who isn't a crackpot agrees with his choice. If you don't like it then choose something else.

 

I will not respond to another one of your word salads. I have wasted far too much time on you and all your sock puppets. ( please do not steal Facebook photos. It is immoral.)

Edited September 9, 2015 by david345

[Andromacus]

1. My previous calculations already showed global time is not used for the speed of light. If you could count you would see that for frame 1 light was emitted at t=1it reached b at t=2 time of travel 1.

For frame 2 it was emitted at t=.57735 and reached b at t=1.1547 time of travel=.57735. If global time was used the time would be the same for both observers. My calculations show time was not the same for both observers contradicting your unfounded claims. The same is true for distance.

2. In response to your nonsense about frames inside of frames. We do not see the universe picture in picture. We do not see other frames within our own. My math already showed the math works. If you disagree then post a Minkowski diagram done the correct way along with your calculations. Do not respond with another word salad.

3. Conventionality of simultaneity says you can choose a convention within a certain limit. Einstein made his choice. If you wan't to use relativity then you have to deal with his choice. If you don't want to use relativity then choose another convention. You can't say "You can choose but you can't make a choice because that would be a contradiction." Einstein made his choice. Everyone who isn't a crackpot agrees with his choice. If you don't like it then choose something else.

 

I will not respond to another one of your word salads. I have wasted far too much time on you and all your sock puppets. ( please do not steal Facebook photos. It is immoral.)

1. Yeah, if you could read you'd realize that I'm refering to the t used by Einstein to derive the null interval for a ray of light in one frame, not the one used in the Lorentz transformation between the obserber in the train and the observer in the embankment.

3. You obviously are not grasping the simple explanation in my last post.

 

Your last paragraph is just hilarious if it weren't because it might mean you are unstable, or simply a psycho, none of the alternatives is funny. I reported you to the moderators without response so far, but I see you have already been suspended once.

[david345]

Your absolutely right. I'm the unstable one. Just as you say.

[Phi for All]

I will not respond to another one of your word salads. I have wasted far too much time on you and all your sock puppets. ( please do not steal Facebook photos. It is immoral.)

Your last paragraph is just hilarious if it weren't because it might mean you are unstable, or simply a psycho, none of the alternatives is funny. I reported you to the moderators without response so far, but I see you have already been suspended once.

!

Moderator Note

Everyone please refrain from attacking individuals, and save your attacks for ideas.

 

Also, if there is a dispute over stolen FB pics, this is NOT the venue for it.

 

If a discussion is no longer productive for you (anyone), you can always opt to stop posting in it. Discussing not posting in it is posting in it.

 

There's no need to respond to this note, but you can report it if you object.

[swansont]

Going back to my original question in post #1 and leaving aside the confusing discussions about distant simultaneity(that don't have empirical solution so they are quite useless) , maybe I can formulate it in a way that is easier to understand and get specific answers.

 

My first post highlighted the fact that Einstein used the same time and distance used in galilean transformations for the distance travelled by a light ray in vacuum from spacetime point1 to spacetime point 2, both points measured with global time t i the equation d=ct, to derive the null interval and from it the general minkowskian interval and the Lorentz transformations that leave it invariant.

 

Only using the Einstein synchronization can this be done. So much for conventionality of clock sync. postulated by Einstein himself. The very idea of a standard synchronization establishes the existence of a global time valid at a distance from the clock one has locally.

So the contradiction lies in that Einstein needs both to use a single standard synchronization or global time to derive the Lorentz transformations with his postulates, and at the same time declare his choice a convention because he is promoting a local time that is different from frame to frame, from spacetime point (event) to spacetime point.

The contradiction would be that it is necessary to have the Einstein sync as conventional and not conventional at once for the arguments of Einstein seminal 1905 paper to hold.

 

If we could just center on this, I would appreciate any input.

 

It's only a time that works in that one frame. Within one's own frame, there is nothing wrong with using the Galilean equation; there is no Lorentz transformation used. And since c is invariant, there's nothing wrong with using d = ct.

[Andromacus]

 

It's only a time that works in that one frame. Within one's own frame, there is nothing wrong with using the Galilean equation; there is no Lorentz transformation used. And since c is invariant, there's nothing wrong with using d = ct.

Very good point, thanks. (.At least somebody is following my reasoning even if in disagreement, I was about to get really pessimistic) This is sensible and in accordance with how Einstein referred to this issue, which he clearly contemplated.

Let me use an excerpt of the book by Einstein "The meaning of relativity", where he addresses precisely my point in 101#:

 

"Before we draw any conclusions from these two principles

we must first review the physical signicance of the concepts

"time" and "velocity." It follows from what has gone before, that

co-ordinates with respect to an inertial system are physically

defined by means of measurements and constructions with the

aid of rigid bodies. In order to measure time, we have supposed

a clock, U, present somewhere, at rest relatively to K. But

we cannot fix the time, by means of this clock, of an event

whose distance from the clock is not negligible; for there are no

"instantaneous signals" that we can use in order to compare the

time of the event with that of the clock. In order to complete the

definition of time we may employ the principle of the constancy

of the velocity of light in a vacuum. Let us suppose that we

place similar clocks at points of the system K, at rest relatively

to it, and regulated according to the following scheme. A ray

of light is sent out from one of the clocks, Um, at the instant

when it indicates the time tm, and travels through a vacuum a

distance rmn, to the clock Un; at the instant when this ray meets

the clock Un the latter is set to indicate the time tn = (tm+

rmn)/c.

The principle of the constancy of the velocity of light then states

that this adjustment of the clocks will not lead to contradictions.

With clocks so adjusted, we can assign the time to events which

take place near any one of them. It is essential to note that this

denition of time relates only to the inertial system K, since

we have used a system of clocks at rest relatively to K. The

assumption which was made in the pre-relativity physics of the

absolute character of time (i.e. the independence of time of the

choice of the inertial system) does not follow at all from this

definition."

 

Einstein felt the need to stress in the last paragraph that the absolute character of time doesn't follow from his definition because it relates only to one rest inertial frame K, just like you argue in your reply.

So maybe you could help me with the questions that could prompt these reasoning or perhaps indicate me where I'm not using the right premises.

Einstein justified the absence of contradiction in his sync method and his not really using a global time in the fact that the distant spacetime point where he set his second clock(ray arrival clock) was in the same rest inetial frame K as the local departure clock.

 

But how exactly can one ascertain that the distant clock is in the same inertial frame as the local clock?, it seems like the same reasoning Einstein used to justify the use of his synchronization: "In order to measure time, we have supposed a clock, U, present somewhere, at rest relatively to K. But we cannot fix the time, by means of this clock, of an event

whose distance from the clock is not negligible; for there are no "instantaneous signals" that we can use in order to compare the time of the event with that of the clock.", that he solves by using the second postulate, would be needed here to declare the distant event to be in the same inertial frame. Certainly the same solution is given since the reason it is assumed to be in the same frame is the second postulate, that c is invariant in any frame.

 

 

So we see we can use the same second postulate to solve the issue of the sync of distant clocks, and to rest assure that to assume that the distant clock is in the same frame as the local clock is a non-issue and therefore there is no problem with the Galilean equation that uses newtonian time.

 

Another problem that I see with Einstein's argument is that all this refers to a light ray wich is by definition not supposed to have a rest frame neither at departure nor at arrival points. It seems that for the purposes of deriving the null interval and the Lorentz transformations from Einstein postulates it is alright to consider light has rest frame. For any other purposes is forbidden.

Edited September 9, 2015 by Andromacus

[swansont]

So maybe you could help me with the questions that could prompt these reasoning or perhaps indicate me where I'm not using the right premises.

Einstein justified the absence of contradiction in his sync method and his not really using a global time in the fact that the distant spacetime point where he set his second clock(ray arrival clock) was in the same rest inetial frame K as the local departure clock.

 

But how exactly can one ascertain that the distant clock is in the same inertial frame as the local clock?, it seems like the same reasoning Einstein used to justify the use of his synchronization: "In order to measure time, we have supposed a clock, U, present somewhere, at rest relatively to K. But we cannot fix the time, by means of this clock, of an event

whose distance from the clock is not negligible; for there are no "instantaneous signals" that we can use in order to compare the time of the event with that of the clock.", that he solves by using the second postulate, would be needed here to declare the distant event to be in the same inertial frame. Certainly the same solution is given since the reason it is assumed to be in the same frame is the second postulate, that c is invariant in any frame.

 

The assumption that the distant clock is in the same frame in an independent assumption. It relies on nothing other than he has assumed the clock is in the same frame. The synchronization depends on c being a constant.

 

Further, in this exercise, you don't need to determine that the clock is in the same frame. It is assumed to be true — no other justification is necessary. It is a prerequisite for what follows. In practice you would have to worry about this, but not in terms of defining the process.

 

So we see we can use the same second postulate to solve the issue of the sync of distant clocks, and to rest assure that to assume that the distant clock is in the same frame as the local clock is a non-issue and therefore there is no problem with the Galilean equation that uses newtonian time.

 

As I said, the second postulate doesn't come into play in being assured that the clock is in the same frame.

 

Another problem that I see with Einstein's argument is that all this refers to a light ray wich is by definition not supposed to have a rest frame neither at departure nor at arrival points. It seems that for the purposes of deriving the null interval and the Lorentz transformations from Einstein postulates it is alright to consider light has rest frame. For any other purposes is forbidden.

 

Where does he use the rest frame of light?

[Andromacus]

The assumption that the distant clock is in the same frame in an independent assumption. It relies on nothing other than he has assumed the clock is in the same frame. The synchronization depends on c being a constant.

 

Further, in this exercise, you don't need to determine that the clock is in the same frame. It is assumed to be true — no other justification is necessary. It is a prerequisite for what follows. In practice you would have to worry about this, but not in terms of defining the process.

 

 

 

I know it is assumed. My point is that by the same logic that with Einstein's new concepts of time and velocity he considerered that he needed to define a certain synchronization based on the second postulate for the distant clock because we cannot "fix the time, by means of this clock, of an event whose distance from the clock is not negligible; for there are no "instantaneous signals" that we can use in order to compare the time of the event with that of the clock", it seems we should not be able to "fix" by assumption the state of motion, the frame of a distant event unless we use the light potulate that assumes c is invariant in all frames. I mean frames have time coordinates so they involve time.

 

 

 

 

Where does he use the rest frame of light?

Well a lightlike geodesic interval made of events in that interval is being analyzed here using rest frames as literally called in the text, the local clocks that measures the departure time is at rest and the distant clock is supposed to be in the same frame at rest with K.

[swansont]

I know it is assumed. My point is that by the same logic that with Einstein's new concepts of time and velocity he considerered that he needed to define a certain synchronization based on the second postulate for the distant clock because we cannot "fix the time, by means of this clock, of an event whose distance from the clock is not negligible; for there are no "instantaneous signals" that we can use in order to compare the time of the event with that of the clock", it seems we should not be able to "fix" by assumption the state of motion, the frame of a distant event unless we use the light potulate that assumes c is invariant in all frames. I mean frames have time coordinates so they involve time.

But how does that matter in regard to a position being fixed? Would coordinates spontaneously move if c were not invariant? They don't under Galilean physics.

 

 

Well a lightlike geodesic interval made of events in that interval is being analyzed here using rest frames as literally called in the text, the local clocks that measures the departure time is at rest and the distant clock is supposed to be in the same frame at rest with K.

The clock is at rest, as you say. How does that morph into light being at rest?

[Andromacus]

But how does that matter in regard to a position being fixed? Would coordinates spontaneously move if c were not invariant? They don't under Galilean physics.

 

 

 

 

I don't remember talking about position being fixed, don't understand this bit.

 

 

The clock is at rest, as you say. How does that morph into light being at rest?

 

 

Wait, you are morphing now having a rest frame into light being at rest whatever that means. When we have an observer in a train moving relative to the embankment we say this observer is at rest with respect to the train's frame regardless of the speed of the train and we consider it the rest frame of the train. The local clock measuring the departure time of the ray of light in the galilean equation d=c(t2-t1) seems to imply a rest frame, In any case galilean equations involving time and velocity always have an implicit absolute rest frame. This is usually not allowed for light.

Edited September 9, 2015 by Andromacus

[swansont]

I don't remember talking about position being fixed, don't understand this bit.

You don't remember asking "But how exactly can one ascertain that the distant clock is in the same inertial frame as the local clock?"

It was just a few posts back. Then you followed up on it. An object is in the same inertial frame if it's position is fixed relative to the other location. Not moving. This has nothing to do with c being invariant.

 

Wait, you are morphing now having a rest frame into light being at rest whatever that means. When we have an observer in a train moving relative to the embankment we say this observer is at rest with respect to the train's frame regardless of the speed of the train and we consider it the rest frame of the train. The local clock measuring the departure time of the ray of light in the galilean equation d=c(t2-t1) seems to imply a rest frame, In any case galilean equations involving time and velocity always have an implicit absolute rest frame. This is usually not allowed for light.

So? There is no case here where an inertial frame (or rest frame) for light is being used. The local clock is in an inertial frame. That's all.

[Andromacus]

 

You don't remember asking "But how exactly can one ascertain that the distant clock is in the same inertial frame as the local clock?"

It was just a few posts back. Then you followed up on it. An object is in the same inertial frame if it's position is fixed relative to the other location. Not moving. This has nothing to do with c being invariant.

 

Not only its position, a frame includes its time(a frame includes the state of motion so both spatial and time coordinates i.e. both rods and clocks), we saw that Einstein was concerned with determining distant times and he used the second postulate to introduce his synchronization procedure. But as you say he instead stipulates that the frame of the second event is the same as the first to make clear he is not using an absolute time. But it seems clear he is using his synchronization to decide this (because the frame includes time and clocks), and therefore the second postulate.

 

 

 

So? There is no case here where an inertial frame (or rest frame) for light is being used. The local clock is in an inertial frame. That's all.

 

So it is the second postuate of invariance of c what prevents us from considering this ray of light to have a rest frame, And yet we have two clocks at rest measuring a speed c according to the newtonian equation c=d/t, where c is an absolute speed, d is an absolute distance and t a global time and that implies there exists a rest frame.

[swansont]

Not only its position, a frame includes its time(a frame includes the state of motion so both spatial and time coordinates i.e. both rods and clocks), we saw that Einstein was concerned with determining distant times and he used the second postulate to introduce his synchronization procedure. But as you say he instead stipulates that the frame of the second event is the same as the first to make clear he is not using an absolute time. But it seems clear he is using his synchronization to decide this (because the frame includes time and clocks), and therefore the second postulate.

To be in the same inertial frame means one is not moving with respect to anything else in the frame. No motion means the time coordinate is irrelevant.

 

 

So it is the second postuate of invariance of c what prevents us from considering this ray of light to have a rest frame, And yet we have two clocks at rest measuring a speed c according to the newtonian equation c=d/t, where c is an absolute speed, d is an absolute distance and t a global time and that implies there exists a rest frame.

The clocks are where the measurements are made. We are in that frame, not the frame of the photon. No assumption about being in a photon's frame is made.

 

Your objections here seem to be completely manufactured.

[Andromacus]

To be in the same inertial frame means one is not moving with respect to anything else in the frame. No motion means the time coordinate is irrelevant.

 

We are discussing precisely why can one assert that they are in the same frame, that is, not moving, at a distance without making any mention of the distant synchronization of the second clock.

 

Einstein wrote:"It is essential to note that this definition of time relates only to the inertial system K, since we have used a system of clocks at rest relatively to K." And this assured that " The

assumption which was made in the pre-relativity physics of the absolute character of time does not follow at all from this definition."

What he doesn't say is that only local frames can be considered at rest a priori unless we use the pre-relativity absolute character of time.

 

To apply a Lorentz transformation of timelike paths the distant frame is always assumed to be different, but for lightlike paths they must be assumed to be the same frame,.There is no logical justification for this double standard other than for the principle of relativity for inertial frames and the second postulate to be compatible. This is arbitrary.

 

 

The clocks are where the measurements are made. We are in that frame, not the frame of the photon. No assumption about being in a photon's frame is made.

 

Your objections here seem to be completely manufactured.

Ok, I won't insist, as this is collateral to my main argument, I just was under the impression that to measure something you have to be in the frame where that something is, but you claim a measurement is made (in a rest frame of the clock), of a ray light (moving at c by the second postulate) if I understand what you are saying?

Edited September 10, 2015 by swansont
fix quote tags

[swansont]

 

We are discussing precisely why can one assert that they are in the same frame, that is, not moving, at a distance without making any mention of the distant synchronization of the second clock.

 

 

We can assert it because it is an assumed condition of the whole discussion. It is, by the structure of the discussion, true. When one makes an argument of the form "If X, then Y", X is a given. There is no further discussion of X. If one can establish that X isn't true, then one can properly say the conditional argument does not apply.

 

Einstein wrote:"It is essential to note that this definition of time relates only to the inertial system K, since we have used a system of clocks at rest relatively to K." And this assured that " The

assumption which was made in the pre-relativity physics of the absolute character of time does not follow at all from this definition."

What he doesn't say is that only local frames can be considered at rest a priori unless we use the pre-relativity absolute character of time.

 

Because it's not necessary. If the distant clock is at rest it is by definition in the same frame, and vice-versa. It is also a given (an assumption), meaning no further discussion or justification is necessary. dx/dt = 0, and as such, the character of whether it's relative or absolute time is moot. It will still be zero.

 

To apply a Lorentz transformation of timelike paths the distant frame is always assumed to be different, but for lightlike paths they must be assumed to be the same frame,.There is no logical justification for this double standard other than for the principle of relativity for inertial frames and the second postulate to be compatible. This is arbitrary.

 

We only have one frame. There are no transformations.

Ok, I won't insist, as this is collateral to my main argument, I just was under the impression that to measure something you have to be in the frame where that something is, but you claim a measurement is made (in a rest frame of the clock), of a ray light (moving at c by the second postulate) if I understand what you are saying?

 

That's obviously incorrect. How could we ever measure motion (or other properties of moving objects), at all? Moving objects are not in our frame.

[Andromacus]

 

We can assert it because it is an assumed condition of the whole discussion. It is, by the structure of the discussion, true. When one makes an argument of the form "If X, then Y", X is a given. There is no further discussion of X. If one can establish that X isn't true, then one can properly say the conditional argument does not apply.

 

Because it's not necessary. If the distant clock is at rest it is by definition in the same frame, and vice-versa. It is also a given (an assumption), meaning no further discussion or justification is necessary. dx/dt = 0, and as such, the character of whether it's relative or absolute time is moot. It will still be zero.

 

We only have one frame. There are no transformations.

 

Ok, that amounts to saying that it's an assumption arbitrarily postulated, but as it is not explicitly either of the well known postulates of SR, you either adscribe it to any of them(I say it is the second postulate in disguise) or add it as a new postulate

 

That's obviously incorrect. How could we ever measure motion (or other properties of moving objects), at all? Moving objects are not in our frame.

Hmm, you are the one that says we have one frame by definition for light. So I'm not sure what other frame you mean by "not in our frame".

 

On the other hand we usually measure properties of moving objects by being at rest in their frame. For instance we make measurements on the earth(an approximate inertial frame), being at rest in its frame, we make measurement on the uniform velocity train by being at rest with its frame. Being at a frame at rest with respect to something doesn't mean that something is not moving. I'd say this is quite clear.

And we don't "measure motion", we compute it from measures of time and lengths for wich we need clocks and rods at rest in the frame where we want to perform that measurement. Remember the equivalence of inertial frames, we cannot distinguish motion from rest of our own frame without external references.

Maybe you should reconsider if the assertion "to measure something you have to be in the frame where that something is" is so obviosly incorrect after all.

Edited September 10, 2015 by Andromacus

[swansont]

Ok, that amounts to saying that it's an assumption arbitrarily postulated, but as it is not explicitly either of the well known postulates of SR, you either adscribe it to any of them(I say it is the second postulate in disguise) or add it as a new postulate

 

It's a definition, or protocol. It only depends on how we define an inertial frame, and there's nothing "relative" about it. It doesn't need to be a postulate — you need to define your terminology in order to have the discussion, and that's what Einstein was doing. As discussed at the outset of this thread, you are, in principle, free to define some other protocol. Or at least try to build a model based on one. (That gets into the discussion I wasn't having, on the topic of conventionality)

 

But as it happens in a single frame, there is nothing "relative" about it.

Hmm, you are the one that says we have one frame by definition for light.

 

Where did I say that?

So I'm not sure what other frame you mean by "not in our frame".

 

I don't know how else to say it. An object that is moving relative to an observer is not in the same frame of reference as the observer.

On the other hand we usually measure properties of moving objects by being at rest in their frame. For instance we make measurements on the earth(an approximate inertial frame), being at rest in its frame, we make measurement on the uniform velocity train by being at rest with its frame. Being at a frame at rest with respect to something doesn't mean that something is not moving. I'd say this is quite clear.

Even if we usually do this, (and I don't agree), it doesn't matter, because your original claim was that "to measure something you have to be in the frame where that something is" (emphasis added) i.e. it's an absolute statement, and only one counter-case is necessary to rebut it. But there are lots of examples.

 

And we don't "measure motion", we compute it from measures of time and lengths for wich we need clocks and rods at rest in the frame where we want to perform that measurement. Remember the equivalence of inertial frames, we cannot distinguish motion from rest of our own frame without external references.

Maybe you should reconsider if the assertion "to measure something you have to be in the frame where that something is" is so obviosly incorrect after all.

Will that work in court for a speeding ticket? A cop stationary with respect to the earth, measuring my speed as I move relative to the earth. Are you actually going to argue that the cop didn't measure my speed?

 

That a mass spectrometer, which sorts atoms or molecules with E and B fields, does so while the particles are at rest?

 

Who is riding along with Usain Bolt to be in his frame as he runs the 100m dash? (from which we can deduce v from d/t)

 

When you measure a current with a clamp am-meter, are you in the frame of the electrons? Or the flow a fluid with a venturi meter?

 

We can, and do, use the clocks and rods in our frame to do the measurement. I think "obviously incorrect" is apropos. It's trivial to find examples where you measure things that are in a different frame from the observer.

[Andromacus]

 

It's a definition, or protocol. It only depends on how we define an inertial frame, and there's nothing "relative" about it. It doesn't need to be a postulate — you need to define your terminology in order to have the discussion, and that's what Einstein was doing. As discussed at the outset of this thread, you are, in principle, free to define some other protocol. Or at least try to build a model based on one. (That gets into the discussion I wasn't having, on the topic of conventionality)

 

But as it happens in a single frame, there is nothing "relative" about it.

Don't you agree those defintions are free in as much as they are consistent with the rest of the postulates?

 

Where did I say that?

"We only have one frame." said by you at the end of 116#.

 

I don't know how else to say it. An object that is moving relative to an observer is not in the same frame of reference as the observer.

And this hasn't entered the discussion nor I said otherwise.

 

Even if we usually do this, (and I don't agree), it doesn't matter, because your original claim was that "to measure something you have to be in the frame where that something is" (emphasis added) i.e. it's an absolute statement, and only one counter-case is necessary to rebut it. But there are lots of examples.

 

Will that work in court for a speeding ticket? A cop stationary with respect to the earth, measuring my speed as I move relative to the earth. Are you actually going to argue that the cop didn't measure my speed?

 

That a mass spectrometer, which sorts atoms or molecules with E and B fields, does so while the particles are at rest?

 

Who is riding along with Usain Bolt to be in his frame as he runs the 100m dash? (from which we can deduce v from d/t)

 

When you measure a current with a clamp am-meter, are you in the frame of the electrons? Or the flow a fluid with a venturi meter?

 

We can, and do, use the clocks and rods in our frame to do the measurement. I think "obviously incorrect" is apropos. It's trivial to find examples where you measure things that are in a different frame from the observer.

 

If you are not able to distinguish measurements from computations, I'm not sure what kind of a physicist you are.

Take a radar gun, it just clocks (in its rest frame) the reflected signals he sent to the moving object, he measures time differences with the radar's clock of signals that reach him wherever the cop is. Then he uses this measures together with the inferred distances to compute a speed(well the computer in the radar does it).

 

 

 

[studiot]

swansont,

 

+1 for stamina

[swansont]

Don't you agree those defintions are free in as much as they are consistent with the rest of the postulates?

 

Consistency is not the issue. Clock synchronization does not depend on the invariance of c, since you never leave the frame where you are synching the clock. It's independent of that.

 

"We only have one frame." said by you at the end of 116#.

 

It's the inertial frame where we are synchronizing the clock. I never said that it was a frame for light.

 

If you are not able to distinguish measurements from computations, I'm not sure what kind of a physicist you are.

 

Personal attacks generally mean one can't address the substance of the argument.

 

Take a radar gun, it just clocks (in its rest frame) the reflected signals he sent to the moving object, he measures time differences with the radar's clock of signals that reach him wherever the cop is. Then he uses this measures together with the inferred distances to compute a speed(well the computer in the radar does it).

Yes, precisely. The clock in the radar gun is in the rest frame, not in the moving frame of the car. Glad you agree. The measurement of the interval (both time and distance) is made in the rest frame. We do not have to be in the moving frame to measure that interval, which falsifies your claim "to measure something you have to be in the frame where that something is"

[Andromacus]

 

 

Consistency is not the issue.

Well, it is ultimately the issue I am trying to debate here.

 

 

 

 

Clock synchronization does not depend on the invariance of c, since you never leave the frame where you are synching the clock. It's independent of that.

I take it you refer to Einstein synch. So how do you interpret these word by Einstein again:"The principle of the constancy of the velocity of light then states that this adjustment of the clocks will not lead to contradictions." Or: "IIn order to complete the definition of time we may employ the principle of the constancy of the velocity of light in a vacuum."? Are you making a distinction between constancy and invariance of light here?

 

 

It's the inertial frame where we are synchronizing the clock. I never said that it was a frame for light.

Agreed, because it is stipulated in relativity that light simply does not have an inertial frame, otherwise none of the postulates of SR would work in all inertial frames, besides inertial frames are defined physically in terms of rods and clocks at rest in the frame and surely clocks and rods cannot be accelerated to the speed of light. But I'm actually trying to show how mathematical inconsistency sneaks in with light not having inertial frame, as null paths must satisfy an equation for the null interval in arbitrary inertial coordinates and arbitrary coordinate time and yet not qualify to have an inertial frame

 

 

Personal attacks generally mean one can't address the substance of the argument.

I didn't mean to attack, just to show puzzlement, but I withdraw that comment if it bothers you, and while I'm at it I want to thank you again for being basically the only one around here that addresses my arguments, and in a fair way so far.

Also for those reading this, make no mistake about it, I am not a so called "relativity denier" whatever that means, I've worked in relativity related projects and have great respect for Einstein. Just to avoid confusions.

Yes, precisely. The clock in the radar gun is in the rest frame, not in the moving frame of the car. Glad you agree. The measurement of the interval (both time and distance) is made in the rest frame. We do not have to be in the moving frame to measure that interval, which falsifies your claim "to measure something you have to be in the frame where that something is"

 

Ok, I probably misunderstood, and I wouldn't want to deviate from the central issue.

Edited September 11, 2015 by Andromacus

[swansont]

Well, it (consistency) is ultimately the issue I am trying to debate here.

OK, that's easy. If a theory is not internally consistent, it is doomed to fail. Our experience with nature is that from a set of initial conditions only one result happens, and everyone agrees on that result (e.g. an object does not hit its target in one frame and miss it in another). So you can't have a model that gives two (or more) answers.

 

Given that, consistency does not necessarily have further implications about whether one part of a model depends on another part. So the definitions used in SR, and the synchronization protocol, and the postulates all have to be consistent with each other — it's a requirement if the theory is going to work — but that in no way implies that any one of them depend on or follow from any other of them.

[Andromacus]

Well, it (consistency) is ultimately the issue I am trying to debate here.

 

OK, that's easy. If a theory is not internally consistent, it is doomed to fail. Our experience with nature is that from a set of initial conditions only one result happens, and everyone agrees on that result (e.g. an object does not hit its target in one frame and miss it in another). So you can't have a model that gives two (or more) answers.

 

I disagree. A lack of mathematical consistency depending on its kind, doesn't necessarily lead to such heavy-handed consequences. You are missing that there are degrees of inconsistency and certain inconsistencies allow to have incredible approximations to nature. Take for example quantum theory, that is agreed by most not to have complete or rigurous mathematical consistency. Or to go back in time, theories so mathematically inconsistent as Ptolomeus epicycles obtained results that were very close to the newtonians. Newtonian phsics itself is not free from mathematical inconsistency (think of the diverging integrals for mass density at spatial infinity in newtonian gravitation) and yet it is a great approximation.

[swansont]

I disagree. A lack of mathematical consistency depending on its kind, doesn't necessarily lead to such heavy-handed consequences. You are missing that there are degrees of inconsistency and certain inconsistencies allow to have incredible approximations to nature. Take for example quantum theory, that is agreed by most not to have complete or rigurous mathematical consistency. Or to go back in time, theories so mathematically inconsistent as Ptolomeus epicycles obtained results that were very close to the newtonians. Newtonian phsics itself is not free from mathematical inconsistency (think of the diverging integrals for mass density at spatial infinity in newtonian gravitation) and yet it is a great approximation.

 

Epicycles are just Fourier components of rotational systems. Not a good example of inconsistencies. That they are an expansion of a function is precisely why they worked, and the math is internally consistent. A diverging integral is not an example of an inconsistency, it's merely a limit of where the math doesn't work. With what is it inconsistent? I don't see any contradictions arising, such as I had described.

 

Regardless, we had been discussing that the parts of relativity are consistent, and that still does not imply any sort of dependence. Einstein clock synchronization works just fine under Galilean physics, so how can it depend on any postulates of relativity that cause deviations from Galilean physics?