The Relativity of Simultaneity

[Emil]

The concept of an absolutely synchronised clock implies the concept of an absolute interval of time to synchronise it, synchronisation is a process, so the concept leaves the question: how was the first clock synchronised "absolutely"? (??).

There is no such thing as an absolute interval of time, but there are arbitrary intervals of time--for instance, the interval it takes a particle such as a muon to decay.

Currently are used two standards. Coordinated Universal Time (UTC) and International Atomic Time (TAI)

Also defined here. http://physics.nist.gov/cuu/Units/second.html

Unit of time (second)

The unit of time, the second, was defined originally as the fraction 1/86 400 of the mean solar day. The exact definition of "mean solar day" was left to astronomical theories. However, measurement showed that irregularities in the rotation of the Earth could not be taken into account by the theory and have the effect that this definition does not allow the required accuracy to be achieved. In order to define the unit of time more precisely, the 11th CGPM (1960) adopted a definition given by the International Astronomical Union which was based on the tropical year. Experimental work had, however, already shown that an atomic standard of time-interval, based on a transition between two energy levels of an atom or a molecule, could be realized and reproduced much more precisely. Considering that a very precise definition of the unit of time is indispensable for the International System, the 13th CGPM (1967) decided to replace the definition of the second by the following (affirmed by the CIPM in 1997 that this definition refers to a cesium atom in its ground state at a temperature of 0 K):

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

 

[origin]

Emil, these really have no bearing on the notion of absolute time.

 

[quantum_wave]

You are completely missing the points. In science it is very significant to acknowledge observations and data. It is particularly important if that very data is used to develope a theory. MD is not doing this. He is ignoring that actual measurements and data because it refutes his beliefs.

He is essentially saying - "I chose to reject reality and substitute my own." This is not science and it is not even rational.

Like I said, I came in at the end. I understand MD to have a postulate and I have been following to see how the members falsify it.

To say that he can't prove his postulate shouldn't be the point so I assume you are not insisting that he do that? Has anyone said how to measure the speed of a ray of light, the same ray or expanding light sphere as we he is calling it, from its point of origin and from a frame of reference that is in motion relative to the point of origin?

 

[DonQuixote]

Hi DonQuixote, thank you for the encouragement.

I think it's not so much that the train observer has the right to consider himself at rest, but that his measurements are consistent with him being at rest, and that he is frustrated by the rules of the universe that prevent him from measuring his absolute velocity, and also that the embankment observer similarly can not prove that the embankment is at rest.

Yes, in this exercise I'm starting with the assumptions of time dilation and length contraction, without explanation. They're fundamental features of this model. I find it an interesting contrast to the historical approach, where Einstein started from the assumption of the frame independence of the speed of light, and derived time dilation and length contraction.

The synchronizing of clocks by slow separation was examined in [post=2753794]post #393[/post]. The result was that the train observer's clocks were not actually synchronized according to embankment clocks. In fact, it gave him the same result as Einstein's synchronization method would have.

I have exams coming up in a few weeks, so I can't afford to dedicate any more time to this at the moment. I might arrange a more formal discussion with MD in the debates forums afterward.

Hi Pete. Thank you for responding.
Of course your exams are the most important (What are you studying?). If you do arrange a discussion later, I would like to be able to follow it.
I just felt that this discussion is less entrenched than almost any other I have found.

I believe I fully appreciate the train observers predicament. The relativity of meassurement is of course a curse that was acknowledged long before Einstein, and as far as I can understand, it is this curse that he ventures to deliver us from, using the postulate of the constancy of the speed of light as leverage.

I must admit that I don't understand why you include length contraction and time dillation among your axioms (or postulates), if they can be derived anyway. It somewhat weakens your argument, I think.

I believe that what I proposed is a bit different from what you discussed in post #393. I am not concerned with whether or not the clocks can be considered to be synchronised from the other frame's point of view. Nor is actually the method of synchronisation a big deal to me. I just thought that MD might object to using light for synchronisation, while - as far as I know - a relativist would not object to a symmetrical movement of clocks, as any relativistic effects on the clocks should be the same if the clocks moved to the left or to the right.

I take it that you agree with Einstein that clocks can be synchronised within one frame of reference? After all, he spends a bit of time establishing this...

Given that we have a way of synchronising clocks in one frame of reference, I propose to outfit the clocks in the embankment frame with a counter that increments by one per "tick". Each clock records at its position the tick number and whether or not a lightning stroke takes place. Two lightning strokes are said to be simultaneous in that reference frame if the clocks have recorded the same "tick number" for the two events.

Again, I don't know if any of you would agree to such a setup.

Don Quixote

 

[Emil]

Emil, these really have no bearing on the notion of absolute time.

Perhaps you have not noticed but arfa brane has used the notion "interval of time" and not "time", as you use.

 

[origin]

Like I said, I came in at the end. I understand MD to have a postulate and I have been following to see how the members falsify it.

To say that he can't prove his postulate shouldn't be the point so I assume you are not insisting that he do that? Has anyone said how to measure the speed of a ray of light, the same ray or expanding light sphere as we he is calling it, from its point of origin and from a frame of reference that is in motion relative to the point of origin?

It really is very simple - elementary actually. MD says that the velocity of observer affects the relative speed of light. IF that were true then his analysis would be right.

Lets test it. Mesure the speed of light from the star Sirius when the earth's orbit is moving us towards the star. 6 months later measure the speed of light again from the star. If the MD was correct then there should be a large difference in the speed of light measured due to the motion of the earth.

Guess what, there isn't any differerence. The speed of light is not affected by the motion of the observer. That is one of many reasons that people are so exhasperated with MD, if there is data that conflicts with his beliefs then he ignores it.

Another thing makes him such a fun punching bag is that he will purposely distort or misinturpret a post so that he can dodge and weave around information that shows he is wrong.

In short he is wrong, hard data shows he is wrong and nothing anyone can say or show him will cause him to admit that. He is a lost ball in high weeds.:shrug:

 

[origin]

Perhaps you have not noticed but arfa brane has used the notion "interval of time" and not "time", as you use.

Nope, he used the term "ABSOLUTE interval of time" that is different than simply saying interval of time. ABSOLUTE interval of time implies that a time interval is independent of the reference frame. The exact terminology and agreement on definitions is vital when discussing science.

 

[arfa brane]

Perhaps you have not noticed but arfa brane has used the notion "interval of time" and not "time", as you use.

Perhaps you have not noticed, but your post above describes "units" of time and not "absolute intervals".

What you posted doesn't appear to distinguish between units and intervals. It doesn't describe, or mention, any "absolute" time or "absolute intervals" of time. This is quite probably because there is no such thing (note the italics), there never has been.

 

[Motor Daddy]

Perhaps you have not noticed, but your post above describes "units" of time and not "absolute intervals".

What you posted doesn't appear to distinguish between units and intervals. It doesn't describe, or mention, any "absolute" time or "absolute intervals" of time. This is quite probably because there is no such thing (note the italics), there never has been.

When light traveled 299,792,458 meters from a point in space, how much time elapsed?

 

[quantum_wave]

It really is very simple - elementary actually. MD says that the velocity of observer affects the relative speed of light. IF that were true then his analysis would be right.

Lets test it. Mesure the speed of light from the star Sirius when the earth's orbit is moving us towards the star. 6 months later measure the speed of light again from the star. If the MD was correct then there should be a large difference in the speed of light measured due to the motion of the earth.

Guess what, there isn't any differerence. The speed of light is not affected by the motion of the observer. That is one of many reasons that people are so exhasperated with MD, if there is data that conflicts with his beliefs then he ignores it.

Another thing makes him such a fun punching bag is that he will purposely distort or misinturpret a post so that he can dodge and weave around information that shows he is wrong.

In short he is wrong, hard data shows he is wrong and nothing anyone can say or show him will cause him to admit that. He is a lost ball in high weeds.:shrug:

Normally that would be a practical way to test if the speed of light is affected by the motion of the observer. But you are characterizing MD's postulate differently than he characterized it to me.

He is describing a situation where an expanding light sphere has a continuing presence in space and a constant speed relative to the point of origin. Because the light sphere is traveling at c in the original frame, he is saying that to an observer in motion relative to that existing light sphere it will appear that the existing light sphere is traveling at c+/-.

Your test measures new expanding light spheres from a moving frame but the whole point is that from the point of origin and from another moving point, the same light ray is not being measured in your example. The difference seems subtle but the implications are not so subtle.

 

[Emil]

Perhaps you have not noticed, but your post above describes "units" of time and not "absolute intervals".

What you posted doesn't appear to distinguish between units and intervals. It doesn't describe, or mention, any "absolute" time or "absolute intervals" of time. This is quite probably because there is no such thing (note the italics), there never has been.

Maybe you should read about International System of Units (SI)

 

[Motor Daddy]

Normally that would be a practical way to test if the speed of light is affected by the motion of the observer. But you are characterizing MD's postulate differently than he characterized it to me.

He is describing a situation where an expanding light sphere has a continuing presence in space and a constant speed relative to the point of origin. Because the light sphere is traveling at c in the original frame, he is saying that to an observer in motion relative to that existing light sphere it will appear that the existing light sphere is traveling at c+/-.

Your test measures new expanding light spheres from a moving frame but the whole point is that from the point of origin and from another moving point, the same light ray is not being measured in your example. The difference seems subtle but the implications are not so subtle.

quantum_wave, I appreciate your help in explaining my position. Some people don't understand the concept, and then go on to say things that are not even representative of my concept, and then go on to use that misinterpretation to say I'm incorrect.

I'm pretty sure you have a firm grasp of the concept, and I appreciate your help.

 

[origin]

He is describing a situation where an expanding light sphere has a continuing presence in space and a constant speed relative to the point of origin.

Which is exactly what will happen with the 'light sphere' moving out from the point of origin, Sirius.

Because the light sphere is traveling at c in the original frame, he is saying that to an observer in motion relative to that existing light sphere it will appear that the existing light sphere is traveling at c+/-.

Measurements such as the one I presented show this postulate to be false.

Your test measures new expanding light spheres from a moving frame

That is meaningless. There is no absolute motion so when MD says that his light sphere is emitted from a spot and an observer is in motion it is exactly the same as saying the origin of the light sphere is moving and the obsever is motionless relative to the light. There is no 'real' way to say who is moving.

but the whole point is that from the point of origin and from another moving point, the same light ray is not being measured in your example.

Really? How so? Are you saying the photon emitted from Sirius is not the photon measured?

The difference seems subtle but the implications are not so subtle.

I think the difference is nonexistent.

 

[quantum_wave]

quantum_wave, I appreciate your help in explaining my position. Some people don't understand the concept, and then go on to say things that are not even representative of my concept, and then go on to use that misinterpretation to say I'm incorrect.

I'm pretty sure you have a firm grasp of the concept, and I appreciate your help.

No problem, I find the idea interesting. You didn't answer my question about your view on time dilation and the tests that show clocks measure time to pass a different rates from different frames. I think it was James R who said you took some alternative view?

 

[quantum_wave]

Which is exactly what will happen with the 'light sphere' moving out from the point of origin, Sirius.

Measurements such as the one I presented show this postulate to be false.


That is meaningless. There is no absolute motion so when MD says that his light sphere is emitted from a spot and an observer is in motion it is exactly the same as saying the origin of the light sphere is moving and the obsever is motionless relative to the light. There is no 'real' way to say who is moving.

Really? How so? Are you saying the photon emitted from Sirius is not the photon measured?

I think the difference is nonexistent.

whatever you say. I said my piece and you said yours. We don't agree. All I would be doing is repeating myself and you are too .

 

[arfa brane]

When light traveled 299,792,458 meters from a point in space, how much time elapsed?

If you know where the source of the light that traveled 299,792,458 (metres or whatever) is, and you know where the leading edge of the light (i.e. a wavefront) is, by detecting it with something rather than just claiming it's 299,792,458 (metres, or arm-lengths) from the source, then you have measured an interval of time, exactly like using a clock to measure an interval of time.

The definition could be based on any measurement you like, for instance the time it takes for an object dropped from a certain height to reach the ground.
That light is used 'precisely' by also counting a number of wavelengths which are at a fixed frequency, is really only a matter of preference, in the case of science the preference is for precision. But this is also a completely arbitrary notion, it corresponds to our anthropocentric narrative. As far as we can tell using precise measurements, there is no smallest interval of time.

OK?

 

[Motor Daddy]

No problem, I find the idea interesting. You didn't answer my question about your view on time dilation and the tests that show clocks measure time to pass a different rates from different frames. I think it was James R who said you took some alternative view?

Again, if light travels at a constant speed in space, from its point of origin in space, it is physically impossible for all frames to measure the speed of light to be the same in their own frame, using the standard meter and second.

Einstein has no way of determining the absolute velocity of a frame, so in order to say the speed of light is constant in all frames, he invents time dilation and length contraction, as ways to get around using the standard meter and second, so that his numbers don't lead to contradictions.

So he HAS TO assume length contraction and time dilation in order for his numbers to work.

If one uses Einstein's methods to see if the numbers match with measurements, the numbers are consistent using time dilation and length contraction. The problem is that Einstein still doesn't know the absolute velocity of the frame, relative to the constant speed of light in space.

So in my method, I don't need time dilation and length contraction, because I know the absolute velocity of the frame, and I know the speed of light is constant in space, and I know that the speed of light is measured to be different in every frame because of the absolute velocity of the frame.

 

[Motor Daddy]

If you know where the source of the light that traveled 299,792,458 is, and you know where the leading edge of the light (i.e. a wavefront) is, by detecting it with something rather than just claiming it's 299,792,458 from the source, then you have measured an interval of time, exactly like using a clock to measure an interval of time.

The definition could be based on any measurement you like, for instance the time it takes for an object dropped from a certain height to reach the ground. That light is used 'precisely' by also counting a number of wavelengths which are at a fixed frequency is really only a matter of preference, in the case of science the preference is for precision. But this is also a completely arbitrary notion, it corresponds to our anthropocentric narrative. As far as we can tell, using precise measurements, there is no smallest interval of time.

OK?

Many words and no understanding.

The distance and time that light travels are inseparable. If light traveled 299,792,458 meters, the time light traveled is 1 second. You seem to have a problem with that???

 

[arfa brane]

Again, if light travels at a constant speed in space, from its point of origin in space, it is physically impossible for all frames to measure the speed of light to be the same in their own frame, using the standard meter and second.

It might be physically impossible, but it's what we measure with instruments, because we don't just trust our ideas because they sound logical.

Since the speed of light is measured physically to be the same in all frames of reference where the speed of light is measured, it cannot be the case that it is physically impossible to measure it. In fact, it IS physically possible for anyone to measure the speed of light.

Well, perhaps we should exclude people who have no idea how to measure the speed of anything, like yourself.

If light traveled 299,792,458 meters, the time light traveled is 1 second. You seem to have a problem with that???

Yes, IF it traveled 299,792,458 metres. But how can you know this is how far it traveled?
Wouldn't you have to measure it?

Didn't the speed of light get measured, by someone, once upon a time?

 

[Motor Daddy]

It might be physically impossible, but it's what we measure with instruments, because we don't just trust our ideas because they sound logical.

Since the speed of light is measured physically to be the same in all frames of reference where the speed of light is measured, it cannot be the case that it is physically impossible to measure it. In fact, it IS physically possible for anyone to measure the speed of light.

Well, perhaps we should exclude people who have no idea how to measure the speed of anything, like yourself.

So are you saying your measurements will not factor in length contraction and time dilation, and come to the correct answer?