Is relativity of simultaneity measurable?

[OnlyMe]

You are mixing up two different effects:

1. OWLS isotropy (this is NOT what the experiments are about)

2. OWLS (in)dependence of source-detector relative speed (this IS what the experiments are about, such experiments do not measure OWLS but its independence of the relative speed between source and detector, as the website teaches you).

You are making the same exact mistake as OnlyMe in his post above by mixing up two different classes of experiments:

a. One measures OWLS independence wrt direction, the other measures OWLS independence wrt source-detector speed.

b. Neither is TWLS, neither measures the OWLS value (because, indeed , such a measurement is impossible).

The bottom line is that the experiments measuring the light speed independence of the source-detector relative speed are NOT two-way light speed, contrary to your earlier claim. This is what the website is telling you.

Tach, this is perhaps one of the few, of your posts, where your intent seems clear. That's good.

There is nothing wrong with your descriptions of the reference. I assume that last statement was directed at me, but I have no recollection of having claimed that, "the experiments measuring the light speed independence of the source-detector relative speed" were measurements of, "two-way light speed". What I was saying is that those experiments were either comparing two legs of light path as in the interferometer based experiments or they rely on synchronized clocks.., even at times relying on assumptions about the starting and ending points of the light path, as in the gamma ray based experiments.

Either way that is a distraction from the real issue.

You seem at this point to be applying a dual standard, relative to discussions, on this forum, and references you use to support your case, not just in the case of this thread. The constancy of OWLS, is an assumption that affects conclusions made in almost all of your references across any thread dealing with SR and many dealing with GR. If Pete's experimental design is flawed based on your current objections, then most if not all of the conclusions drawn from, any SR hypothetical, to particle physics and high energy colliders, is also flawed. Even the GPS system and GP-B experiments "assume" the OWLS to be equal to the measured TWLS.

If that is what your argument boils down to, you seem to be arguing for the sake of argument. Instead of proof reading posts as if they were on their way to the press, try to look for the author's intent. Personnally, I throw a post together on the fly most of the time. But even where it appears that others, like Pete put some greater thought into it, you seem to be focussing on minutia, rather than the intent.

 

[Tach]

Tach, your link goes to section, "3.3 Tests of Light Speed from Moving Sources", which refers to astronomical data, based on the underlying assumption(s).

The previous section, "3.2 One-Way Tests of Light-Speed Isotropy", lists a number of experiments with limits on the anisotrophy of c (sometimes listed as one way anisotrophy) from 100 m/s to at best the refrence quoted below of 0.13 m/s.

from sec 3.2 One-Way Tests of Light-Speed Isotropy from Tach's link
Ragulsky, “Determination of light velocity dependence on direction of propagation”, Phys. Lett. A, 235 (1997), pg 125.
A “one-way” test that is bidirectional with the outgoing ray in glass and the return ray in air. The interferometer is by design particularly robust against mechanical perturbations, and temperature controlled. The limit on the anisotropy of c is 0.13 m/s.​

P.S. to correct the first part of my post above section 3.3 does include several terrestrial experiments, but they all either include similar limitations on the accuracy or are not attempting to measure a one way speed of light... Example — the following measures the effect of a moving glass plates on the measured speed of light.

Babcock and Bergmann, Journal Opt. Soc. Amer. Vol. 54, pg 147 (1964).
This repeat of Kantor's experiment in vacuum shows no significant variation in the speed of light affected by moving glass plates. Optical Extinction is not a problem. k < 0.02.
​

You are commingling two different classes of experiments:

1. Experiments that constrain light speed anisotropy (paragraph 3.2)

2. Experiments that constrain light speed dependence on the source-detector relative speed (paragraph 3.3)

The subject of discussion was 3.3 , not 3.2, mixing the two together produces only confusion. The link I gave points to 3.3, 3.2 is a totally different, unrelated subject, ok?

There is no one way speed of light experiment that approaches the accuracy of two way speed of light experimental data. And you can see from the variety of experiments referenced that they have not reached agreement. There is always that "within the limit of" disclaimer, attached.

Adding (incorrect) claims of the differences in precision between the two different classes of experiments further confuses the issue.

 

[RJBeery]

Hmm, 200+ posts and I feel the discussion is on the wrong key word.

1. Define a series of "simultaneous events" for a given frame.
2. Switch to another frame, and determine if those events are "simultaneous" using the same definition.
3. Conclude that simultaneity is RELATIVE.

It isn't about proving or disproving SIMULTANEITY, it's about defining the term and then determining if that definition is ABSOLUTE or RELATIVE.

 

[Tach]

2. Switch to another frame, and determine if those events are "simultaneous" using the same definition.

Therein lies the problem, RJ. Mainstream physics teaches you that there is no way to "determine if those events are simultaneous" through any experiment. You should stop mixing physics with "natural philosophy", they are different fields. Last I checked, "natural philosophy" wasn't science, actually, it is quite the opposite.

 

[RJBeery]

Therein lies the problem, RJ. Mainstream physics teaches you that there is no way to "determine if those events are simultaneous" through any experiment. You should stop mixing physics with "natural philosophy", they are different fields. Last I checked, "natural philosophy" wasn't science, actually, it is quite the opposite.

The concept of simultaneity doesn't need to be verified, it is defined. It can't be "invalidated" as a definition unless it is logically contradictory. We can apply simultaneity for a given frame with a lattice of synced clocks; when an event occurs a local camera takes a picture of the event along with the local lattice clock; two space-like separated events are simultaneous according to this definition if the respective pictures show the same time.

We can have more than one set of lattice clocks, each of which represent a given frame of reference. Now we can determine whether or not both sets of clocks concur on the simultaneity of two events. Whether or not they concur on the simultaneity of those events says nothing about the validity of our definition of simultaneity. It simply proves that simultaneity is not absolute.

 

[Tach]

.

We can have more than one set of lattice clocks, each of which represent a given frame of reference. Now we can determine whether or not both sets of clocks concur on the simultaneity of two events.

Mainstream physics teaches you that you cannot "determine whether or not both sets of clocks concur on the simultaneity of two events. ", RJ. Once again, you are confusing physics with your (natural) philosophy.

Whether or not they concur on the simultaneity of those events says nothing about the validity of our definition of simultaneity.

The definition of simultaneity is not under debate.

It simply proves that simultaneity is not absolute.

This is not what the thread is all about. What is the thread about, RJ? What does the title say?
As an aside, in physics one cannot prove anything, one can only disprove and this is done via experiment. In the case of RoS , no experiment can be run for reasons already explained early on, in post 95.

 

[RJBeery]

Mainstream physics teaches you that you cannot "determine whether or not both sets of clocks concur on the simultaneity of two events. ", RJ. Once again, you are confusing physics with your (natural) philosophy.



The definition of simultaneity is not under debate.



This is not what the thread is all about. What is the thread about, RJ? What does the title say?
As an aside, in physics one cannot prove anything, one can only disprove and this is done via experiment. In the case of RoS , no experiment can be run for reasons already explained early on, in post 95.

But the "hotly debated topic", as you put it, is resolved by convention (aka definition):

First published Mon Aug 31, 1998; substantive revision Thu Jul 15, 2010
In his first paper on the special theory of relativity, Einstein indicated that the question of whether or not two spatially separated events were simultaneous did not necessarily have a definite answer, but instead depended on the adoption of a convention for its resolution. Some later writers have argued that Einstein's choice of a convention is, in fact, the only possible choice within the framework of special relativistic physics, while others have maintained that alternative choices, although perhaps less convenient, are indeed possible.

To debate whether or not we can "prove" RoS is equivalent to debating whether or not we can "prove" Galilean Invariance. We can only make the postulate, and then accept it based upon our inability to disprove it. Other than that, you aren't stating anything profound.

 

[OnlyMe]

This is not what the thread is all about. What is the thread about, RJ? What does the title say?

So why did you not just answer my earlier question(s) directly?

Is this current argument about the SR hypothetical or a scientifically acceptable experimental proof of RoS? (Understanding that is a rare thing that any experiment is accurate to a certainty.)... Or is this a semantic objection to the use of "experimentally measure", rather than "experimentally confirm"?

Yes, RoS cannot be measured. The difference in the observed timing of events which are simultaneous in one frame and not simultaneous in another can be measured, to within the accuracy of currently available measuring devices.

The simultaneity of two events as observed in one frame can be determined.., again to within the accuracy of the measuring devices available. The absolute simultaneity, of two events, can even be established with currently available technology, as observed from one frame.., again to within the accuracy and design limitations, of available measuring devices and methods.... AND yes Tach, no experiment can at this time be constructed that will meet the standards defined in hypotheticals.., where ideal clocks, rulers and synchronization are assumed.

All of this does not amount to a measurement of RoS, in any literal sense. Any experiment, even hypotheticals, is intended to confirm RoS, by recording or measuring the timing of events as observed from two different frames. That is a comparrison, of measurements.., not a direct measurement.

Pete can correct me if I am wrong, but I do not believe he intended the title to be interpreted literally, as you seem to be. If he had I don't believe there would have been as much confussion and the need for as RJ says 200+ posts.

 

[RJBeery]

So why did you not just answer my earlier question(s) directly?



Yes, RoS cannot be measured. The difference in the observed timing of events which are simultaneous in one frame and not simultaneous in another can be measured, to within the accuracy of currently available measuring devices.

The simultaneity of two events as observed in one frame can be determined.., again to within the accuracy of the measuring devices available. The absolute simultaneity, of two events, can even be established with currently available technology, as observed from one frame.., again to within the accuracy and design limitations, of available measuring devices and methods.... AND yes Tach, no experiment can at this time be constructed that will meet the standards defined in hypotheticals.., where ideal clocks, rulers and synchronization are assumed.

All of this does not amount to a measurement of RoS, in any literal sense. Any experiment, even hypotheticals, is intended to confirm RoS, by recording or measuring the timing of events as observed from two different frames. That is a comparrison, of measurements.., not a direct measurement.

Pete can correct me if I am wrong, but I do not believe he intended the title to be interpreted literally, as you seem to be. If he had I don't believe there would have been as much confussion and the need for as RJ says 200+ posts.

I'm not even sure I agree with this, OnlyMe (or perhaps I don't understand your point). It seems like you are saying that Simultaneity is an infinitely-precise concept that can never be measured in the real world; I don't think that is what Tach is saying.

Anyway, we can define Simultaneity by convention, then we can measure for the Absoluteness of it. In the absence of Absoluteness, we are left with Relativity. In other words, the Relativity is the negative result. Arguing about the Simultaneity itself is pointless because we defined it. We could expand our definition of Simultaneity to include an error term that lies within our capability to measure, for example.

 

[OnlyMe]

I'm not even sure I agree with this, OnlyMe (or perhaps I don't understand your point). It seems like you are saying that Simultaneity is an infinitely-precise concept that can never be measured in the real world; I don't think that is what Tach is saying.

Anyway, we can define Simultaneity by convention, then we can measure for the Absoluteness of it. In the absence of Absoluteness, we are left with Relativity. In other words, the Relativity is the negative result. Arguing about the Simultaneity itself is pointless because we defined it. We could expand our definition of Simultaneity to include an error term that lies within our capability to measure, for example.

What I was saying is that, technically RoS is a comparison of measurements made from two different frames, which measure of the order of two events. The RoS comes in in the comparrison of the two frames measurements. It is not a measurement in and of itself.

In Einstein's hypotheical he went to great lengths to establish that the two events (the lightning strikes) were simultaneous in the embankment frame, but that is not really even necessary. It is just as valid if the two events have no common frame, but are observed to occur simultaneously, in one frame and sequentially in another. In any case RoS was/is defined by a comparrison of measurements made in separated frames. It is not itself a direct measurement.

When Tach referred to the thread title, Is relativity of simultaneity measurable? it seemed to me that he was interpreting the wording literally. In a literal sense the only things that are measured are the order of the two events as observed in two frames.., and perhaps the difference in those measurements.

Tach's objection seems to have wandered, over the course of the thread. But since he does not often fully explain his own position, some of that may be my inability to understand him.

 

[Tach]

Anyway, we can define Simultaneity by convention, then we can measure for the Absoluteness of it.

Who is "we" in "we can measure"? No one in the physics field agrees with the above.

 

[Tach]

Yes, RoS cannot be measured. The difference in the observed timing of events which are simultaneous in one frame and not simultaneous in another can be measured, to within the accuracy of currently available measuring devices.

You are contradicting yourself. Your first sentence is correct, your second one is false.

 

[RJBeery]

Who is "we"? No one in the physics field agrees with the above.

Um, what? I don't even know how to respond to this. Newtonian Physics presumed that Simultaneity was Absolute; any and all experiments which validate SR over Newton are measurements for Absoluteness...and the negative result lead us to conclude that Simultaneity is Relative.

 

[Tach]

Um, what? I don't even know how to respond to this. Newtonian Physics presumed that Simultaneity was Absolute; any and all experiments which validate SR over Newton are measurements for Absoluteness...and the negative result lead us to conclude that Simultaneity is Relative.

Post 95 explains why mainstream physicists, as opposed to natural philosophers, know why you cannot measure the "Absoluteness" of simultaneity any more than you can measure "relativity" of simultaneity. If you still think otherwise, you should try to describe such an "experiment". It would be intriguing to see how you "can measure the Absoluteness of it". Please go ahead and describe the "experiment".

 

[RJBeery]

Post 95 explains why mainstream physicists, as opposed to natural philosophers, know why you cannot measure the "Absoluteness" of simultaneity any more than you can measure "relativity" of simultaneity. If you still think otherwise, you should try to describe such an "experiment". It would be intriguing to see how you "can measure the Absoluteness of it". Please go ahead and describe the "experiment".

If we can neither measure the absoluteness nor the relativity of simultaneity then how can we proclaim SR over Newtonian physics?

 

[OnlyMe]

You are contradicting yourself. Your first sentence is correct, your second one is false.

Falling back into old habits! Explain yourself Tach. What is wrong with the second sentence?

Are you suggesting that observers who are not collocated cannot measure the same events and then compare the measurements?

The added, "within the accuracy of measuring devices", only refers to the fact that all measurements in any frame are within the accuracy of the measuring devices.

 

[OnlyMe]

Post 95 explains why mainstream physicists, as opposed to natural philosophers, know why you cannot measure the "Absoluteness" of simultaneity any more than you can measure "relativity" of simultaneity. If you still think otherwise, you should try to describe such an "experiment". It would be intriguing to see how you "can measure the Absoluteness of it". Please go ahead and describe the "experiment".

Even though, Einstein's hypothetical represents an ideal case, what it was intended to demonstrate is that simultaneity is relativity!

So now you add the "absolute" card and begin to sound like a crank. There is very little in science that is measured in an absolute manner. We just don't have access to the ideal, clocks and rulers, of hypotheticals.

 

[Pete]

This tangle of misinterpretation and diversion is why it's so hard to make progress.

Tach, one-way light speed isotropy is what is relevant to this thread.

I concede that relativity of simultaneity is not measurable, only because the setup relies on synchronizing separated clocks using the Einstein synchronization method, which relies on the isotropy of the one-way speed of light, as you said in post 95.

The above explains why measuring RoS has proven an elusive as measuring OWLS. In fact, the two are inextricably connected, you cannot measure OWLS because it requires two synched clocks that turn out to be synched based on measuring .... OWLS.

So in this philosophical hole you've found, you have potentially non-isotropic light speed, you allow the existence of a preferred but not experimentally detectable reference frame, you can't rely on Lorentz transforms, and "synchronized" doesn't actually mean anything physical at all.

If that makes you happy, so be it.

 

[Fednis48]

Even though, Einstein's hypothetical represents an ideal case, what it was intended to demonstrate is that simultaneity is relativity!

So now you add the "absolute" card and begin to sound like a crank. There is very little in science that is measured in an absolute manner. We just don't have access to the ideal, clocks and rulers, of hypotheticals.

OnlyMe, I think you're getting confused about Tach's objection. I get the impression you think the problem is practical limitations on measurement precision, or maybe the ability of two observers in different frames to compare results. The problem is actually much deeper and more fundamental than that.

If we make only the bare minimum set of initial assumptions, we arrive at a whole class of theories that differ in how they define synchronization for spatially separated clocks, but predict identical results for all possible experiments. If we add the assumption the the one-way speed of light is the same as the two-way speed of light, we arrive at SR. But unless we make that assumption, there is in principle no way to choose a "correct" theory from this class. Even in a given frame, these various theories can disagree on whether two events are simultaneous. So Tach's objection is that relativity of simultaneity is not measurable because simultaneity itself is not measurable.

RJBeery has a good point, though, when he says that we can measure RoS for a given definition of simultaneity. For example, eram's radar-gun experiment from a few pages back would experimentally demonstrate relativity of simultaneity-as-defined-by-Einstein-synchronized-clocks. It is important to keep in mind that eram's experiment (or any other experiment) cannot prove that simultaneity-as-defined-by-Einstein-synchronized-clocks is "true" simultaneity, whatever that would mean. But in contexts where we take the correctness of SR as an initial assumption and want to explore its consequences (like, say, the three threads that came before this one), it is definitely possible to measure RoS.

 

[Tach]

I concede that relativity of simultaneity is not measurable, only because the setup relies on synchronizing separated clocks using the Einstein synchronization method,

I already pointed out to you that RoS cannot be measured no matter what synchronizing scheme is being used. The Mansouri-Sexl papers deal with both E-synch and slow clock transport. This explains why there is no "experimental test for RoS" to date and why no mainstream experimentalist will ever attempt undertaking such a fool's errand. The theory precludes it.

In this quote, are you talking about one-way light speed isotropy?

No, "measuring OWLS" and "light speed anisotropy" are different subjects in experimental physics. The former is impossible, the latter is dealt with routinely in thousands of experiments. They are not the same thing.