I have already pointed out the mistakes you have made in the "eram experiment". Correct application of SR demonstrates that the RoS in "eram's experiment" is precisely....zero.
Is relativity of simultaneity measurable?
- Thread starter Pete
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I have already pointed out the mistakes you have made in the "eram experiment". Correct application of SR demonstrates that the RoS in "eram's experiment" is precisely....zero.
I'd forgotten that post since it came right before the thread closure - my bad. I don't think I quite get your argument, though. Objects $$A$$ and $$B$$ arrive simultaneously at the AND gate in all frames. Using that fact, the post-launch speeds of the objects as measured by the radar guns, and the fact that the AND gate is midway between the objects pre-launch, we can deduce that the objects must have launched at different times in the radar gun frame. This demonstrates RoS of the launches. What's the problem there?
It is hard to get Tach to state his position clearly. You can throw different interpretations of what he says at him asking, "Is this what you mean?", and just get back a.., "No you're wrong!".
What I suspect is the real problem.., is confusing the measurement of two events as simultaneous in a frame common to both events and the RoS. While it is accurate to say that we cannot with certainty measure two events to have occurred simultaneously, in any absolute manner, RoS is not limited in application to events which are simultaneous, in any absolute manner.
Yes, Einstein's hypothetical did include such a construction, but that specific construction is not required to meet the conditions of RoS. All one needs is, using one clock in one frame, measure two events to be simultaneous as observed from that frame.., and another clock in another frame measuring the same events occurring sequentially, rather than simultaneously. For RoS it is not as important that two clocks measure events as occurring at different times, as it is that two clocks measure two events to occur in a different order... ideally one clock records the events to be simultaneous and the other sequential, but even that is not really necessary. Though the ideal hypothetical is a better teaching tool.
The implications and impact of RoS is not limited to conditions requiring two events be simultaneous in a shared frame of reference. It contributes to an understanding that all inertial frames are equivalent.
The above calculation is incorrect. Here is the correct calculation:
$$T'_A=\gamma(t_A+\frac{vx_G}{c^2})$$
$$T'_B=\gamma(t_B+\frac{vx_G}{c^2})$$
where $$x_G$$ is the position of the AND gate and $$t_A=t_B$$ by the way you defined the experiment.
So, $$T'_A=T'_B$$, contrary to your claim above.
On a higher level note, do you understand why theory precludes any RoS measurement? I saw you writing relatively good prose on the subject, meaning that you have some basic understanding of the theory presented in post 95, why isn't your math at the same level as your prose? After all, the language of physics is math.
OnlyMe, the issue is still more basic than that. Case in point:
This is already impossible. Without making assumptions about the one-way speed of light, it is impossible to show that two events are simultaneous in a given frame. More generally, given two space-like separated events, there is no completely rigorous way to measure the order in which they occur.
This is already impossible. Without making assumptions about the one-way speed of light, it is impossible to show that two events are simultaneous in a given frame. More generally, given two space-like separated events, there is no completely rigorous way to measure the order in which they occur.
Almost correct, the correct sentence is: Given two space-like separated events, there is no way to measure their time separation. Theory precludes any such experiment from being constructed.
In my calculation, I used $$T$$ to denote the "flight time" between an object launching and it hitting the AND gate. That's as opposed to the time component of the four-position, $$t$$, which is what you correctly calculate above. Looking back, I really should have made that more clear - sorry. Since the objects hit the gate at the same time but their flight times were different, they must have launched at different times.
I do understand, thanks to this thread actually. What I'm trying to say at this point is the following: "Making no unproven assumptions, RoS is impossible to measure. Assuming that the one- and two-way speeds of light are the same, RoS is easy to measure."
(Edit: Maybe not easy in practice. But easy in principle.)
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This is exactly what I was referring to. What you are arguing about is the measurement of two events separated in space ocurring simultaneously in an absolute manner. That was part of Einstein's hypothetical and cannot be measured.
RoS is not limited to those hypothetical conditions. It is one of the foundation stones of the larger context of SR.
The idealized conditions of the hypothetical are teaching tools. The fact that they cannot be duplicated in a practical experiment, does not lessen the impact RoS has on our understanding of the world...
The one way speed of light is already a fundamental assumption incorporated in everything that relies on or incorporates SR. As long as you accept and discuss physics in the context of SR, you by default accept the assumption that the one way speed of light is equal to the two way speed of light, along with any number of other, as yet unproven assumptions.
This is an SR exercise. Unless that assumption is the issue of discussion, it is disingenuous to use the fact that it is assumed as argument.
Again this is a sidetrack from RoS itself, which serves to demonstrate that what is simutaneous for one observer is not simutaneous for all observers.., or more generally the order that one observer records two events to occur is not the same as the order all observers record the same two events to occur... And that is experimentally measurable.
Do you really need to know that the one way speed of light is constant, to prove this?
...a time difference that nor you nor anyone else can measure. Ever.
Correction: RoS is impossible to measure. Independent of assumptions.
False, the theory of measurement has nothing to do with the above, if you read and understand RMS, you will find out that RoS cannot be measured independent of the clock synch scheme being used.
By contrast, light speed anisotropy, parameters $$a,b,d$$ can and are being routinely measured. This contradicts directly your claim.
Eh, maybe. I don't think Pete actually specified SR in his original post for this thread. The fact that RoS is actually the only (I think?) un-measurable prediction of SR seems kind of cool to me, and I didn't know that until I read this thread. I definitely agree that the other three threads that spawned this one are SR exercises, which is why I want to convince Tach that RoS can be measured in those contexts (ie. when SR is assumed to be true) before we close this thread and get back to the others.
Yeah, actually, you do. You talk about "the order that one observer records two events to occur", but if the events are space-like separated (which is a prerequisite for RoS), there is no way for an observer to measure the order in which they occur. And I don't mean in some absolute sense, either. Even the question "Which event happened first according to my frame of reference?" is in principle unanswerable.
On the Wikipedia page Tach linked to in post 95, it mentions that the authors of the paper that described all this considered several particular theories from the class of theories that is experimentally indistinguishable from SR. One of those theories defines simultaneity in all frames according to the rest frame of the cosmic microwave background. If this theory is true (and remember, there is in principle no way to disprove it), RoS isn't just impossible to measure; it's actually wrong.
Of course, most scientists accept that SR is the correct theory from this class, because all the others introduce bizarre asymmetries with no real justification. But it's important to know the difference between what we assume to be true and what is experimentally demonstrable. Weirdly enough, RoS is in the former category.
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Ok, I agree. But if we say the OWSL is equal to the TWSL, doesn't that imply the validity of Einstein clock synchronization? That was the impression I got from the Wikipedia page and related links. If not, my bad, and I'd love to see a reference that explains why not. Either way, though, I'd argue that RoS is easy to measure if we choose a correct clock synchronization scheme. Which SR does, so it's definitely correct to say that RoS can be observed in the context of an SR hyptothetical.
The validity of Einstein clock synch is not under discussion. Besides, all the experiments that constrain light speed anisotropy are valid confirmations as being the case (OWLS=TWLS).
You are arguing a false and indefensible position reflecting the fact you you do not yet understand the RMS papers. They tell you that regardless of the clock synch scheme you cannot construct a RoS measuring experiment. A more sophisticated test theory, SME, produces the same conclusion. The net result is, no "RoS test", i.e. no way to measure it, something that you found on your own, with the failure of the "eram test".
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Here again, you are talking about an absolute sense of which occurred first. For any observer events occur, in their frame of reference, when they are measured. If you have more information than the time of observation measurement, you can account for time of light delays. But that is getting away from what RoS demonstrates. Which is that, the order that events are recorded to have occurred in, is frame dependent. Different observers will disagree on the timing and even order of events.
Einstein went to a great deal of trouble to establish that the two, lightning strikes did in fact occur at the same time, in the same frame of reference and an observer halfway between the two strikes, observed the flashes at the same instant. That is not what RoS is about. What RoS is about is that once he establish simultaneous flashes (lightning strikes) and an observer recording them to be simultaneous.., (which establishes the assumed constancy of the one way speed of light... The distance between A and M, and M and B being equal), a second observer records the events as sequential... Simutaneity of events, even if you could know they are absolutely simultaneous is relative. It is a frame dependent observation.
RoS is not about two events happening at the same time. It is about the observation of simutaneity being frame dependent.
You cannot prove that two spatially separate events were infact simultaneous, but you can prove that two spatially or inertially separated observers, will record the same two events with different timing and/or order.
Again: RoS is not about two events happening at the same time. It is about the observation of simutaneity being frame dependent.
You realize that the two sentences contradict each other, right? The first one is false, the second one is true.
Write4U
Valued Senior Member
This may be only indirectly connected to the topic, but IMO, the demonstration reveals aspects of the properties and permutations of waves and wavelike actions.
To me this simple demonstration confirms the theories that support a Universal wavelike action such as Bohm's Holomovement.
Get ready to be astounded,
http://sciencedemonstrations.fas.ha...ram_name=indepth.html#a_icb_pagecontent341734
To me this simple demonstration confirms the theories that support a Universal wavelike action such as Bohm's Holomovement.
Get ready to be astounded,
http://sciencedemonstrations.fas.ha...ram_name=indepth.html#a_icb_pagecontent341734
Wait, what? Now I'm really confused. Are you saying now that OWLS$$=$$TWLS is a testable prediction? Because according to your own link (the third link in post 95): "Note that while these experiments clearly use a one-way light path and find isotropy, they are inherently unable to rule out a large class of theories in which the one-way speed of light is anisotropic." The un-measurability of OWLS is what leads to this issue in the first place.
I will admit that I haven't read the RMS papers; link them and I'll do so. But everything I've read so far goes against what you're saying here. According to the third link in post 95, regarding the theories that are indistinguishable from SR: "These theories share the property that the round-trip speed of light is isotropic in any inertial frame, but the one-way speed is isotropic only in an aether frame." This one-way anisotropy leads to differences in how clocks are synchronized, and it's impossible to measure simultaneity without synchronized clocks. But I challenge you to find a source anywhere that says given a clock synchronization scheme, we can't demonstrate relativity of simultaneity-as-defined-by-that-scheme.
Let's try again: There is a very large tests that constrain light speed anisotropy, thus effectively constraining OWLS to be equal to TWLS. This is different from claiming that we can measure OWLS. Do you see the difference?
This is because you haven't read the papers meaning that you do not understand them.
As explained above, light speed anisotropy has been constrained to incredible precision, something of the order of $$10^{-8}$$. Therefore, light speed anisotropy is not the obstacle in measuring RoS.
You keep ignoring (willfully) the fact that was pointed to you that RMS contains both E-synch (based on light speed isotropy) and slow clock transport synch (which has nothing to do with light speed isotropy). You are also ignoring the point that the RMS papers specifically explain how to test (constrain) parameters $$a,b,d$$ and light speed anisotropy $$\frac{c}{c'}$$ but expressly forbid testing parameter $$e$$ , the parameter that is representing RoS.
Thirdly, you refuse to acknowledge the total absence of any "RoS test" in the list of tests of SR.
What does all this tell us? That anyone claiming to be able to measure RoS is going against mainstream physics, just embarking on a fool's errand, pretty much like "eram's test".
We're talking past each other. If you don't know whether the one- and two-way speeds of light are the same, you can't account for time of light delays. There is really no way to measure simultaneity - even relative simultaneity - without first making some assumptions.
Again, this isn't true! Check out that Wikipedia page. It points out that there's a theory in the aforementioned class in which the cosmic microwave background defines the absolute rest frame. There is no experiment that could prove that theory false, and if it's true, there is no RoS.
WHAT?! So you say that we can show OWLS$$=$$TWLS, but we can't measure OWLS? By extension, wouldn't that mean we can't measure TWLS? Unless you mean that we can determine OWLS but we can't measure it directly, in which case you're just being pedantic.
I find this doubtful, actually. Links please? (Apologies if you already gave some, but I can't find them.)
If you'd actually link these RMS papers, that'd be great. Until you give me a specific reason to think otherwise, I maintain the following:
1. The un-testability of RoS, the un-measurability of e, the choice of clock synchronization, and the potential anisotropy of OWLS are all interrelated.
2. Once we specify one of these things by assumption, the rest fall into place, and relativity of simultaneity-by-a-given-convention becomes testable.
Edit: Missed the bit about slow clock transport. As far as I can tell, if SR is wrong, slow clock transport is not a valid synchronization method. Again, I'd love a reference proving me wrong.
You obviously do not understand the difference between measuring OWLS (experimentally impossible) and proving that OWLS is isotropic (routinely done , experimentally). Confirmation that OWLS is isotropic is sufficient to infer that it is equal to TWLS without actually having to measure OWLS.
What gives you this bright idea? twice I have already explained to you how mainstream experimentalists arrive to the conclusion that OWLS is equal to TWLS.
Nope, I am just explaining how experimental physicists deal with the issue <shrug>.
You need to start learning about the SR tests . Here
It doesn't matter what you claim, mainstream science cares very little about the claims you made.