# Is relativity of simultaneity measurable?

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

1. ### OnlyMeValued Senior Member

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I do tend to ramble. This may be in part an attempt to cover too many side issues without delivering a five or six page analysis. Never the less, it does often get in the way of things...

Your questions, seem to be directed at my comments about experience, as it relates to remote measurements of lengths or distances, which I think are better described as judgements of remote lengths or distances, and the relationship between length contraction and proper lengths, with respect to measurements...

Experience,

I did not mean to say that experience is not based on past measurements, however judgements based on past experience cannot always be considered measurements.

We make judgements about measurements all of the time everyday, when we look across a room and judge an object to be 1 meter or 3 feet long or across. This is consistent with past experience and may be an accurate judgement, but it does not represent a measurement of the dimensions of the object.

We can make no remote measurements of distance or length that are not dependent on assumptions. The most fundamental of which is OWLS. {Going any further into this here would be rambling again and the issue could be a subject of its own.}

Length Contraction and proper lengths,

Length contraction can be confirmed by similar remote judgements about the lengths of moving objects. That is objects moving relative to the point where the judgement is being made. (Again I am using the word judgement here because we cannot use a ruler from one frame to make direct measurements in another frame.)

The problem with experimentally confirming length contraction is that unlike clocks, rulers do not retain any persistent information about any length contraction, they may have undergone while in relative motion. (This assumes that we have some means of identifying that an object has been in motion with respect to some other frame.)...

How this relates to proper lengths is similarly experimentally unprovable. Once again, say you know that an object has experienced acceleration and thus some length contraction relative to a starting and ending frame of reference, any measurements of proper length, which would have been length contracted, have no persistent character. Proper length is always measured from an object's rest frame and thus never differs as an object's velocity changes... And an object's proper length cannot be directly measured from a remote frame of reference.

In almost all cases, within the context of SR these comparrisons involve the use of Lorentz transformations, which are not measurements.

P.S. I often add the "current technology" disclaimer, because even in my own life time I have seen such improvements, that I don't want to suggest that the technology will never exist to experimentally test and prove, many of the theoretical issues discussed.

Last edited: Jun 6, 2013
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3. ### eramSciengineerValued Senior Member

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Ok, I somewhat get it now.

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5. ### Neddy BateValued Senior Member

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Before we can talk about simultaneity, we need a definition of simultaneity. Einstein gives us a definition, and when we use that definition, we can measure RoS. Some folks say that we have not really measured RoS, because we are using an untestable definition. That is fine, but it leaves us with no definition of simultaneity, and no understanding of relativity theory.

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7. ### Neddy BateValued Senior Member

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On that we can agree.

8. ### TachBannedBanned

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Mainstream physics community tells you that you can't but this doesn't seem to stop your fringe claims.

9. ### Neddy BateValued Senior Member

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Oh, look who's back!

Tach, I'm not at all convinced that you even understand what RoS is. Let's start with something simple. Do you agree that Einstein's observer at M' would record the lighting strikes as having occurred non-simultaneously?

10. ### TachBannedBanned

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Like I said, the mainstream community tells you that you can't measure RoS but one can never stop a fool on his errand. You have a very rudimentary understanding of physics, yet this doesn't stop you from making pronouncements (that turn out to be outright crank). I suggest that you set up an earnest experiment for measuring RoS, if you manage to run it, the Nobel Prize awaits you. It would be educational to see your level of understanding of experimental physics, how would you set up such an experiment?

11. ### Neddy BateValued Senior Member

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Of course the two-way (round trip) speed can be measured easily. It is the one-way trip that is much more difficult (some say impossible) to measure. Way back in 1676, Ole Roemer indirectly measured the speed of light traveling from Jupiter to the earth by timing eclipses of Jupiter's moon Io. However, he did not get very accurate results.

http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p_roemer.html

A more modern version of this experiment is to start with two atomic clocks in the same place, synchronise them, and then slowly transport one of the clocks to a remote location. After that, the one-way speed of light can be measured between the clocks. Some folks say this is not really a one-way speed measurement, because "slow transport" is considered to be a clock synchronization scheme which is identical to Einstein synchronization. That argument is also used against Roemer's measurement. It is all in this wikipedia article:

http://en.wikipedia.org/wiki/One-way_speed_of_light

Enjoy!

12. ### Neddy BateValued Senior Member

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I had a very strong feeling you would not answer my simple question. Your evasiveness is one of the reasons I suspect you don't even understand what RoS is. If you'd care to answer my simple question, then we can proceed with the discussion. Otherwise, I'm not interested.

Here is it again:

Do you agree that Einstein's observer at M' would record the lighting strikes as having occurred non-simultaneously?

13. ### LaymanTotally Internally ReflectedValued Senior Member

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I don't see why it would be so difficult to measure the effects of RoS. All you would have to do is determine if two flashes reach the same location at the same time. The RoS predicts that the flashes that are equidistant from a point will not arrive at the same time. But, the thing is that similar experiments have already been done! They found that they actually do reach the center at the same time! Gauge invariance has already been discovered! Imagine that! Wouldn't that be something? The thing is that it is not measurable because the consequences stated in RoS do not exist! If the RoS was measurable then the photon wouldn't be a gauge boson!

14. ### Neddy BateValued Senior Member

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I guess you didn't notice that M and M' are only in the same place at one time, and that is when the lighting strikes OCCUR. By the time the light from the lighting strikes reaches either M or M' they are no longer in the same place.

15. ### TachBannedBanned

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Correction: any person who knows physics will tell you that it is impossible to measure OWLS. Like I said, your knowledge is very rudimentary, somewhere between high school and an unfinished BS.

16. ### Neddy BateValued Senior Member

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I am not claiming OWLS is measurable. I am claiming that RoS is measurable if we operate under Einstein's definition of simultaneity. Sorry this is difficult for you to understand. Maybe if you took a shot at answering my question, you'd start to get it.

Here is it again:

Do you agree that Einstein's observer at M' would record the lighting strikes as having occurred non-simultaneously?

17. ### LaymanTotally Internally ReflectedValued Senior Member

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I have never heard of OWLS, besides the ones that hoot and stay up at night up in trees. Do you have a link that tells about this?

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19. ### LaymanTotally Internally ReflectedValued Senior Member

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The MME has been tested while it is in motion, and then it got the same results. It is taught this way in layman physics. I think that it actually is sufficient in order to determine that the arrival times of the beams reach at the same time or all these scientist wouldn't be writing about it like it is.

20. ### TachBannedBanned

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You just did and I just corrected you. You do not comprehend your own posts.

21. ### LaymanTotally Internally ReflectedValued Senior Member

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Wow, imagine we have discovered the Higgs Boson and the one way speed of light still completely alludes us...

If push comes to shove and you ever find yourself in a situation where you just absolutely have to figure out when things are simultaneous, I would just try to figure the proper time for each frame and then say that the two different values of time you get for each frame is happening at the same time...

22. ### Neddy BateValued Senior Member

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I was not trying to make a claim one way or the other. Perhaps I could have worded that better. Thanks.

23. ### Neddy BateValued Senior Member

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What is the "proper time for each frame" (as you put it) for the lighting strikes in Einstein's thought experiment?

By the way, you are assuming the events would be simultaneous in both frames, (regardless of what the times are), so why do you even need the times?