# Is relativity of simultaneity measurable?

Discussion in 'Physics & Math' started by Pete, May 8, 2013.

1. ### OnlyMeValued Senior Member

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This line of discussion threatens to generate even another split thread. A hazard of attempting to use controversial positions in argument for an only tangentially associated discussion.

Here Tach is technically correct in direct reference to the question he was answering. Both time dilation and length contraction are experimentally "observable". They are not both experimentally measureable or proven, in any direct sense. While clocks preserve the affects of time dilation, as they move between frames, the same is not true of rulers. In addition length contraction, within the context of high energy particle physics, is only observable as an interpretation of downstream data, and then.., only as that data is interpreted based on the underlying theory.

But, again.., and as Pete has mentioned earlier, if this subject is to be pursued, it should be in a thread of its own.

3. ### ash64449Registered Senior Member

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when we draw space-time diagrams we find that time dilation is not observed, instead relativistic doppler is observed.

5. ### ash64449Registered Senior Member

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Onlyme: ""They are not both experimentally measureable or proven, in any direct sense. ""
when we say that something is observed,we need to see them in the direct sense.

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8. ### eramSciengineerValued Senior Member

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I've just thought of a simple test of RoS using a radar gun. Very difficult to achieve with current technology though.

9. ### Neddy BateValued Senior Member

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So your argument is that RoS is not measurable, for the same reasons that time dilation and length contraction are not measurable. That is not much of an argument, especially considering that time dilation and length contraction ARE measurable.

:bugeye:

Tell me which part of the following three lines of text you disagree with:

The ground clocks are synchronized in the ground frame. The ground clocks MEASURE the same time for two events. Therefore the events are MEASURED TO BE simultaneous in the ground frame.

The rail clocks are synchronized in the rail frame. The rail clocks MEASURE different times for those same two events. Therefore the events are MEASURED TO BE non-simultaneous in the rail frame.

Bringing the measurement data together in one place allows comparison. We find that the two events in question were simultaneous in one frame, but non-simultaneous in the other frame. RoS is therefore evident in the MEASUREMENTS.

10. ### OnlyMeValued Senior Member

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I am unsure what you mean as it relates to my post....

In lay terms "observed" can refer to seeing. In a scientific context it would include measurement, which could be either direct or indirect.

What I was saying was assuming an interpretation of the word "observed" in the context of science.

Time dilation has certainly been measured—(or scientifically observed)... And is no longer a theoretical component of SR or GR (though there are some who may still debate the cause...)

Length contraction has only been indirectly indicated to occur with particles and ions in high energy accelerators.., and that is only a conclusion derived from the aftermath of collisions... And even then there remains some debate about whether it is a Lorentz contraction or some other cause.

11. ### TachBannedBanned

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There is no debate about it.

12. ### PeteIt's not rocket surgeryRegistered Senior Member

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Excellent, now we're getting somewhere! It is certainly true that my setup explicitly relies on a uniform one-way speed of light, which is part of the Einstein synchronization procedure.

So, let's look more closely at the results, using the original setup where the events are rigged to be simultaneous in the lab frame.

We agree that:
As ground-clock A passes rail-clock A, ground-clock A reads $t_0$ and rail-clock A reads $t'_0$.
Agreed?
As ground-clock B passes rail-clock B, ground-clock B reads $t_0$ and rail-clock B reads $t'_0 + v\gamma L/c^2$.
Agreed?

The point you rightly raise is that this is as much a test of the synchronization process as it is of simultaneity, and the synchronization process relies on the untestable assumption that the one-way speed of light is frame independent.

Is that a fair summary?

13. ### OnlyMeValued Senior Member

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No with you there is only argument.

However, I have seen the ion packet bunching you spoke of, explained as a function of the accelerator mechanism. (Figure that out for yourself, a little homework.)... And all conclusions about the pancaking of ions is based on observations of the aftermath of collisions. No one, I repeat no one, has claimed to directly measure the shape of an ion to be a pancake.., that is as length contracted.

You want to discuss this further start another thread.

14. ### TachBannedBanned

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There is a lot more than that in post 95. You need to read both articles. Taken together, they explain why you can never achieve a valid setup for your attempt at measuring RoS.

15. ### TachBannedBanned

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This is outright false, both references I gave have explained the results as an effect of length contraction. The authors are true scientists, not some relativity-denying fringers.

16. ### UndefinedBannedBanned

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And they are true scientists because they do not claim to be describing anything except as "interpretations from theory", not actual direct measurements before and after acceleration and collision. The links you gave had simulations from theory assumptions input to theory algorithms, not actual direct empirical measurements of all the forces involved and their effects. So they are true scientists because they do not claim to "explain" but only "interpret theoretically" something which may well be truly explained by other forces and effects involved. Debate with "priests" on the other hand is always impossible, because they are convinced and believe blindly in the "inerrancy" of the theory mantra they learned as acolytes but have not tried to check fully themselves with open mind.

17. ### TachBannedBanned

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False, the links point at explanations of the effects measured experimentally. The visual simulations are built based on measurements, not the other way around. This is the second time I corrected your false claims, why do you persist in this lie?

18. ### UndefinedBannedBanned

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What was "measured"?

What claims? You have that the wrong way around. It is your claims and links about SR theory "contraction" that are being questioned by me and some other people.

19. ### PeteIt's not rocket surgeryRegistered Senior Member

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Fundamentally it all comes down to RoS relying on choice of synchronization, as I said. The test I propose explicitly relies on the assumption of Einstein synchronization.

Since we're stepping into philosophy now, I'm interested in why you say RoS is real, given that it can't be rigorously confirmed by experiment.

Is relativity of simultaneity real?
How do you know?

20. ### TachBannedBanned

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The websites tell you. Have you read them?

21. ### UndefinedBannedBanned

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Yes. You have too, haven't you? Then tell us what they "measured" since it is your claim that these measurements are the "proof" you claim them to be. And then explain exactly what and how and why these "measured effects" are what you claim.

22. ### TachBannedBanned

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...and the second article I linked for you explains why you cannot build a valid test. It doesn't matter if you use Einstein synchronization or slow clock transport, you can't build a test for RoS. Additionally, the explanation that I gave you lists the type of tests that you could build, the ones restricted to the RMS parameters $a,b,d, \frac{c}{c'}$. On the other hand, as explained, $e$ is off limits. (and I explained to you why).

We don't know, scientists are divided on the subject as per the first article I linked for you. Instead of arguing, you should read it.

23. ### TachBannedBanned

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Sure, I have. It appears that you don't know, so rather than me teaching you, you should go back and read the two articles.

It is not my claim, it is the claim of the professional physicists who ran the actual experiments.