# Relativity, LET and Reality

Aether
Gold Member
JesseM said:
I'm not talking about a selecting a simultaneity convention, I'm just asking about physical measurements on a physical system of rulers and clocks. How many times do I have to say "you are not obligated to use a coordinate system where the clocks are synchronized" before it sinks in? Again, analyzing a physical situation involving a physical system of rulers and clocks which have been "synchronized" using the physical procedure known as the Einstein synchronization convention does not magically force you to use a coordinate system with a simultaneity convention that says the clocks all read the same time at a given t-coordinate, any more than analyzing the behavior of the physical clocks in the twin paradox would magically force you to use a coordinate system where each twin's clock reads the same time at every t-coordinate (which would be impossible once they reunite anyway).

But I've been saying this over and over and you still don't seem to get it. Can you explain which part of the above is unclear?
It isn't so much that it is unclear, it is that I am unwilling to risk absorbing this while the larger questions of Lorentz symmetry, tensor notation, etc. are still outstanding. When those issues are fully resolved, then I will be in a better position to absorb or reject some of these other notions in an informed way. Let's come back to these lesser issues later.
I'll look around for something like this, although as I said I'm not too knowledgeable about group theory or tensor mathematics. Doing a bit of quick googling, it seems the term "Lorentz covariance" is synonymous with Lorentz symmetry, and this page has a quote by Einstein where he defines Lorentz covariance in terms of the equations of physics being unchanged by a Lorentz transformation (which I hope you'd agree is equivalent to my statement that the laws of physics are measured to work the same in the different inertial systems of rulers and clocks described by Einstein in his 1905 paper, since the two postulates can be used to prove that the positions and times assigned by these systems must be related by the Lorentz transformation): And this page from the Springer Encyclopaedia of Mathematics says: So both these sources define the notion of Lorentz covariance/invariance simply in terms of the laws of physics being unchanged under a Lorentz transformation, which I would think means they are talking about the non-tensor form of the laws, since I had thought that any physical law (including, say, Newton's laws) could be expressed in a "generally covariant" tensor form in which it would work the same way in all coordinate systems (for example, see the last section of this page), although I could be misunderstanding things here.
This is such an important issue that I would like to fully understand it before proceeding with the rest of the discussion. Since Newton's laws are expressed using 3-vectors rather than 4-vectors, I don't see how they could be Lorentz covariant/invariant. Also, if Lorentz covariance/invariance is specifically tied to the Lorentz transforms then it may not be as fundamental of a physical concept as we have given it credit for above (e.g., what about the LET transforms?). I would question whether or not Poincare covariance/invariance isn't the more general physical symmetry; I'm not saying that this is so, but these are questions that I would need to know the answers to before leaving this subject.

Aether said:
It isn't so much that it is unclear, it is that I am unwilling to risk absorbing this while the larger questions of Lorentz symmetry, tensor notation, etc. are still outstanding.
Why? The question of whether the two postulates of relativity can be interpreted as "physical" or not is separate from the question of whether they are equivalent to what is called "Lorentz-symmetry". I think my argument above makes it pretty clear that they are perfectly physical, these "larger questions" that you mention are irrelevant to that argument.
Aether said:
This is such an important issue that I would like to fully understand it before proceeding with the rest of the discussion. Since Newton's laws are expressed using 3-vectors rather than 4-vectors, I don't see how they could be Lorentz covariant/invariant.
They aren't Lorentz covariant, they are generally covariant, which is a separate concept. As I understand it, general covariance basically means the equations work the same way in every possible coordinate system--inertial, non-inertial, whatever--and any law of physics can be expressed in a generally covariant form if you use the right sort of tensor notation, so it is not really a characteristic of the laws of physics like Lorentz covariance is. The link I gave at the end of the last post quotes Michael Friedman's Foundations of Space-Time Theories as saying (and note that when the page refers to 'covariance', they are referring to general covariance rather than Lorentz invariance/covariance):
Looking back on the development of relativity from our present point of view, we can see that there are three distinct notions that have been inadvertently conflated: symmetry, indistinguishability, and covariance. The symmetry group of a space-time theory characterizes the objects of that theory: it tells us which objects are absolute and which dynamical, and the size of the symmetry group is inversely proportional to the number of absolute objects. The indistinguishability group of a space-time theory characterizes the laws of that theory: it determines which reference frames (states of motion) are distinguishable (by a "mechanical experiment") relative to those laws, and in well-behaved theories the indistinguishability group is contained in the symmetry group (indistinguishable models are identical). Covariance, on the other hand, is really a property of formulations of space-time theories rather than space-time theories themselves: it characterizes systems of differential equations ... representing the intrinsic laws of a space-time theory relative to some particular coordinatization .... The covariance group of such a formulation reflects the range of coordinate systems in which that particular system of equations holds good.

In pre-general-relativistic physics these three distinct notions happen to coincide. In well-behaved theories with inertial coordinate systems (flat space-time) the symmetry group = the indistinguishability group = covariance group of the standard formulation (with respect to a subclass of inertial coordinate systems). Thus, for example, in classical electrodynamics the symmetry group = ... = the indistinguishability group = covariance group of the standard formulation .... In relativistic electrodynamics, on the other hand, the symmetry group = the Lorentz group = indistinguishability group = the covariance group of the standard formulation ....

In general relativity, however, our three notions are not interchangeable. As we have seen, we cannot interpret the general principle of relativity as an indistinguishability requirement, for the indistinguishability group of the general theory is just the restricted group of transformations from one local inertial frame to another. Nor can we interpret it as a covariance requirement, for the general theory has no standard formulation in the usual sense, and the covariance group of the theory is the same as the covariance group of every other space-time theory. Hence, in neither of these interpretations is the general principle of relativity any kind of generalization of the special principle of relativity. As Anderson was the first to realize, the only way to interpret the general principle as such is to make it a symmetry requirement. That is, we interpret the general principle of relativity s the requirement that the symmetry group of our theory include all differentiable transformations: in effect, that it be just the group M. This requirement means that our theory can have no absolute objects, for the only geometrical objects invariant under all differentiable transformations are constant-valued scalars. (Friedman 1983, 212-4).
Aether said:
Also, if Lorentz covariance/invariance is specifically tied to the Lorentz transforms then it may not be as fundamental of a physical concept as we have given it credit for above (e.g., what about the LET transforms?).
If you would actually think about my argument above showing why the two postulates are completely physical ones, you would see that the postulates are every bit "as fundamental of a physical concept as we have given it credit for", and from there it is a short step to agreeing that if Lorentz-symmetry is equivalent to the statement that the laws of physics must work the same way in all the physical measuring-systems that Einstein describes in his 1905 paper, as I have claimed and as I think the quotes in my previous post suggest, then Lorentz-symmetry would also be a completely physical statement about the laws of nature. If you are not willing to think about this, but instead insist that we take a course in tensor mathematics and group theory before drawing any conclusions, then this discussion can't go any further.

Aether
Gold Member
JesseM said:
If you are not willing to think about this, but instead insist that we take a course in tensor mathematics and group theory before drawing any conclusions, then this discussion can't go any further.
As always, I appreciate your help; but with all due respect, you do not yourself know the answers to my questions, so you can not possibly know the extent to which they are relevant to this discussion. The fact is that you do not at this time have the answers my questions; that's ok, perhaps someone else who knows the answers will chime in, or after a few days one of us will have the answers. If pervect or Hurkyl advise me that they think this is an unreasonable request, then I will reconsider it. I single them out because I suspect that they already know the answers to these questions.

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Aether said:
With all due respect, you do not yourself know the answers to my questions, so you can not possibly know the extent to which they are relevant to this discussion.
Nonsense, the argument about the two postulates being physical is completely clear, the mathematical details of how "Lorentz-symmetry" is defined could not change this conclusion since the argument doesn't even use that term. You might as well say that because I do not know the answers to questions about the metric of a rotating black hole, I "can not possibly know the extent to which they are relevant to this discussion". Do you have an actual argument as to how you think the definition of Lorentz-symmetry could possibly affect our conclusions as to whether questions about the measurements made by a physical system of rulers and clocks are coordinate-dependent or not, or are you just unwilling to give any thought to the issue until I jump through your hoops?

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Aether
Gold Member
JesseM said:
Do you have an actual argument as to how you think the definition of Lorentz-symmetry could possibly affect our conclusions as to whether questions about the measurements made by a physical system of rulers and clocks are coordinate-dependent or not, or are you just unwilling to give any thought to the issue until I jump through your hoops?
I am not really ready to make an argument, that is why I am asking these questions; but I will give you my thoughts as they are at this moment so that you will know better why I want to examine one issue before another. I think that the definition of Lorentz-symmetry (at least as you have described it above) may well lead to the conclusions that you are making (e.g., if it is specifically linked to the Lorentz transforms and not equally applicable to the LET transforms). If that is true, then I want to know if the statement that "all known physical laws are Lorentz-symmetric" isn't some sort of subset of a more general statement along the lines of "all known physical laws are Poincare symmetric, and Lorentz symmetry is a subgroup of Poincare symmetry" for example. If that is the case, then Lorentz-symmetry itself could be a coordinate-system dependent concept.

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Aether said:
I am not really ready to make an argument, that is why I am asking these questions; but I will give you my thoughts as they are at this moment so that you will know better why I want to examine one issue before another. I think that the definition of Lorentz-symmetry (at least as you have described it above) may well lead to the conclusions that you are making (e.g., if it is specifically linked to the Lorentz transforms and not equally applicable to the LET transforms). If that is true, then I want to know if the statement that "all known physical laws are Lorentz-symmetric" isn't some sort of subset of a more general statement along the lines of "all known physical laws are Poincare symmetric, and Lorentz symmetry is a subgroup of Poincare symmetry" for example. If that is the case, then Lorentz-symmetry itself could be a coordinate-system dependent concept.
OK, but when I asked you if you were willing to think about my argument, I was only talking about the argument which didn't even mention the concept of "Lorentz-symmetry", the one about how the claim that the laws of physics respect Einstein's two postulates is a physical claim which is independent of what coordinate system you choose to use (and therefore independent of how you choose to define simultaneity). Of course once we have addressed this question we can then ask whether "the claim that the laws of physics respect Einstein's two postulates" is identical in meaning to the claim that "the laws of physics are Lorentz-symmetric"; but this is an entirely separate question, you don't need to even touch upon it to address the first one.

Aether
Gold Member
JesseM said:
OK, but when I asked you if you were willing to think about my argument, I was only talking about the argument which didn't even mention the concept of "Lorentz-symmetry", the one about how the claim that the laws of physics respect Einstein's two postulates is a physical claim which is independent of what coordinate system you choose to use (and therefore independent of how you choose to define simultaneity). Of course once we have addressed this question we can then ask whether "the claim that the laws of physics respect Einstein's two postulates" is identical in meaning to the claim that "the laws of physics are Lorentz-symmetric"; but this is an entirely separate question, you don't need to even touch upon it to address the first one.
You said "the only thing I am claiming here, that Einstein's postulates are physical ones which are equivalent to the postulate that the laws of physics should be Lorentz-symmetric", so now I want to know what "Lorentz-symmetric" really means. I think that I am diligently pursuing an examination of "the only thing that [you are] claiming here", but I will look at what you just said above first...tomorrow.

Aether said:
You said "the only thing I am claiming here, that Einstein's postulates are physical ones which are equivalent to the postulate that the laws of physics should be Lorentz-symmetric", so now I want to know what "Lorentz-symmetric" really means.
OK, but in subsequent posts I narrowed down my question after you questioned whether my definition of "Lorentz-symmetric" was the correct one. What I am asking about now is just the claim that "Einstein's postulates are physical ones" (ie that they are postulates about what will be measured by systems of physical rulers and clocks constructed in a specific way, and that they are therefore coordinate-independent postulates). We don't need to bring up the definition of Lorentz-symmetry to address this.

Aether
Gold Member
JesseM said:
What I am asking about now is just the claim that "Einstein's postulates are physical ones" (ie that they are postulates about what will be measured by systems of physical rulers and clocks constructed in a specific way, and that they are therefore coordinate-independent postulates). We don't need to bring up the definition of Lorentz-symmetry to address this.
Would ideal observers in two different inertial frames ever disagree as to "what will be measured by systems of physical rulers and clocks constructed in a specific way" if those measurements were coordinate-system independent? Don't ideal observers in two different inertial reference frames sometimes disagree as to "what will be measured by systems of physical rulers and clocks constructed in a specific way" (e.g., properly constructed in view of Einstein's postulates)?

Aether said:
Would ideal observers in two different inertial frames ever disagree as to "what will be measured by systems of physical rulers and clocks constructed in a specific way" if those measurements were coordinate-system independent?
No, they would never disagree.
Aether said:
Don't ideal observers in two different inertial reference frames sometimes disagree as to "what will be measured by systems of physical rulers and clocks constructed in a specific way" (e.g., properly constructed in view of Einstein's postulates)?
No, for any given ruler-clock system, all observers will agree what it measures. I'm not talking about each observer constructing their own ruler-clock system according to Einstein's procedure, and then looking only at what is measured by their own system; I'm talking about different observers each looking at the same ruler-clock system, regardless of whether it is at rest relative to themselves, and seeing what is measured by that system. You can also construct multiple such ruler-clock systems in relative motion, give them all labels like "system A" and "system B", and then all observers will agree on what was measured by the physical system A (even if its measurements don't correspond to the coordinates assigned by the observers' own chosen coordinate system), all will agree on what was measured by physical system B, etc. The two postulates of SR amount to the idea that each physical measuring-system constructed according to Einstein's procedure will measure the laws of physics to work the same way, including the speed of light as measured by that system.

If there is some event that I observe to happen right next to the 3-meter mark on a given ruler-clock system, with the clock at the 3-meter mark reading 15 seconds at the moment it happened, do you think other observers might observe the event to happen next to a different mark or a different clock-reading on the same ruler-clock system? Relativity doesn't allow disagreements about local physical events like that, if it did you could get totally different physical predictions (suppose the event was an astronaut sending a radio transmission back to earth, and the clock at the 3-meter mark was programmed to explode when it read 15 seconds--different frames shouldn't disagree on whether the transmission would get cut off by the astronaut's unfortunate demise!)

Aether
Gold Member
JesseM said:
No, they would never disagree. No, for any given ruler-clock system, all observers will agree what it measures. I'm not talking about each observer constructing their own ruler-clock system according to Einstein's procedure, and then looking only at what is measured by their own system; I'm talking about different observers each looking at the same ruler-clock system, regardless of whether it is at rest relative to themselves, and seeing what is measured by that system. You can also construct multiple such ruler-clock systems in relative motion, give them all labels like "system A" and "system B", and then all observers will agree on what was measured by the physical system A (even if its measurements don't correspond to the coordinates assigned by the observers' own chosen coordinate system), all will agree on what was measured by physical system B, etc.
Agreed.
The two postulates of SR amount to the idea that each physical measuring-system constructed according to Einstein's procedure will measure the laws of physics to work the same way, including the speed of light as measured by that system.
The one-way speed of light is not "measurable" by this system. Each physical measuring-system constructed according to Einstein's procedure will "measure" the laws of physics to work the same way because they are proportional to the one-way speed of light which is put-in by hand using Einstein's procedure.
If there is some event that I observe to happen right next to the 3-meter mark on a given ruler-clock system, with the clock at the 3-meter mark reading 15 seconds at the moment it happened, do you think other observers might observe the event to happen next to a different mark or a different clock-reading on the same ruler-clock system?
No.
Relativity doesn't allow disagreements about local physical events like that, if it did you could get totally different physical predictions (suppose the event was an astronaut sending a radio transmission back to earth, and the clock at the 3-meter mark was programmed to explode when it read 15 seconds--different frames shouldn't disagree on whether the transmission would get cut off by the astronaut's unfortunate demise!)
Ok. I didn't say that it did. The disagreement that I was referring to was between the two clocks in different frames being in disagreement about the time-stamp to put on a given event.

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Aether said:
Agreed.The one-way speed of light is not "measurable" by this system.
Of course it is, although that doesn't mean the one-way speed of light is itself an objective physical quantity. Similarly, this system can measure the distance of any event from the origin of the system, but that obviously isn't an objective physical quantity either. Still, the measurement itself is physical and objective in the sense that for a given measuring-system, all observers will agree on what that particular system measures for the one-way speed of light in that system, or the distance of an event from the origin in that system.
Aether said:
Each physical measuring-system constructed according to Einstein's procedure will "measure" the laws of physics to work the same way because they are proportional to the one-way speed of light which is put-in by hand using Einstein's procedure.
Not at all, if we lived in a universe with Newtonian laws (and with Maxwell's laws only working exactly in the rest frame of the aether), and you constructed systems according to Einstein's procedure, different systems would measure the laws of physics to work differently. Of course they would each measure the one-way speed of light to be the same in all directions (the simultaneity convention guarantees the propogation of light will be isotropic in each system), but different systems would measure different values for the speed of light itself (in this case I believe a system moving at v relative to the aether would measure the speed of light as $$(c^2 - v^2)/c$$), and many other laws of physics would be measured to obey different equations when in different systems. This would be true even if we artificially shrunk the length of rulers moving at speed v relative to the aether by a factor of $$\sqrt{1 - v^2/c^2}$$, and expanded the length of clock ticks by $$1/\sqrt{1 - v^2/c^2}$$, so that the coordinates of different measuring systems were still related by the Lorentz transform (although I think in this case I think each system would measure the speed of light to be the same).
Aether said:
Ok. I didn't say that it did. The disagreement that I was referring to was between the two clocks in different frames being in disagreement about the time-stamp to put on a given event.
Right, but do you understand now that this has nothing to do with what I was talking about when I said all observers would agree about what each physical measuring-system measures?

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Aether said:
I didn't say that it did. The disagreement that I was referring to was between the two clocks in different frames being in disagreement about the time-stamp to put on a given event.
You mean between the clock in an inertial frame and the other one in a non-inertial frame?

Aether said:
There is a physical difference between objects in relative motion to one another. For example, if two identical atomic clocks are synchronized while co-located and at rest in a first inertial frame; then one clock is moved into a second inertial frame (!!!) for a time; then returned to the starting position
Do you understand what it means to give phony examples? Do you understand the very basic difference between an inertial and a non-inertial frame?

Aether
Gold Member
JesseM said:
Aether said:
The one-way speed of light is not "measurable" by this system.
Of course it is, although that doesn't mean the one-way speed of light is itself an objective physical quantity. Similarly, this system can measure the distance of any event from the origin of the system, but that obviously isn't an objective physical quantity either. Still, the measurement itself is physical and objective in the sense that for a given measuring-system, all observers will agree on what that particular system measures for the one-way speed of light in that system, or the distance of an event from the origin in that system.
Such a quantity is not an objective physical quantity. Such a "measurement" is coordinate-system dependent.
Aether said:
Ok. I didn't say that it did. The disagreement that I was referring to was between the two clocks in different frames being in disagreement about the time-stamp to put on a given event.
Right, but do you understand now that this has nothing to do with what I was talking about when I said all observers would agree about what each physical measuring-system measures?
I see that there is a distinction to be made between who's clock we are referring to when we make such a "measurement". I would rather say that "all observers would agree about what each physical measuring-system indicates". There is a class of measurements for which each physical measuring-system will agree (e.g., fine-structure constant, two-way speed of light, etc.), and there is a class of measuring-system indications for which each physical-measuring system will not agree (e.g., the one-way speed of light, the length of an object, etc.). I do not see you making such a distinction.

Aether
Gold Member
JesseM said:
that doesn't mean the one-way speed of light is itself an objective physical quantity
nakurusil, do you agree with JesseM that the one-way speed of light is not itself an objective physical quantity?

Aether said:
nakurusil, do you agree with JesseM that the one-way speed of light is not itself an objective physical quantity?
This is not the subject of the OP nor is it the subject of the discussion between the two of us. The subject of the discussion between the two of us is your lack of understanding of the differences between inertial and non-inertial frames and how mixing them into your example rendered it irrelevant. Can we get a clear answer from you on this issue?

Aether
Gold Member
nakurusil said:
This is not the subject of the OP nor is it the subject of the discussion between the two of us.
This is the subject of the OP:
Leo.Ki said:
I'm trying to picture various light based experiments as described from a frame that is in motion with respect to the experiment devices.

For instance the reflection of a photon in a light clock: the atoms (and their fields) that constitute the surface of the mirror are squashed. How is the reflected photon adapted to match this reality?
nakurusil said:
The subject of the discussion between the two of us is your lack of understanding of the differences between inertial and non-inertial frames and how mixing them into your example rendered it irrelevant. Can we get a clear answer from you on this issue?
Please answer my question: do you agree with JesseM that the one-way speed of light is not itself an objective physical quantity?

Aether said:
This is the subject of the OP:Please answer my question: do you agree with JesseM that the one-way speed of light is not itself an objective physical quantity?
The subject of the discussion between the two of us is your lack of understanding of the differences between inertial and non-inertial frames and how mixing them into your example rendered it irrelevant. Can we get a clear answer from you on this issue?

Aether
Gold Member
nakurusil said:
The subject of the discussion between the two of us is your lack of understanding of the differences between inertial and non-inertial frames and how mixing them into your example rendered it irrelevant. Can we get a clear answer from you on this issue?
I will ignore you from now on unless and until you answer my question. Please feel free to ignore me as well.

Aether said:
Such a quantity is not an objective physical quantity. Such a "measurement" is coordinate-system dependent.
Irrelevant to my argument. The quantity being measured is coordinate-system-dependent, but all coordinate systems will agree on what a particular physical measuring system will get as a result for that measurement. Do you not see the distinction here?
Aether said:
I see that there is a distinction to be made between who's clock we are referring to when we make such a "measurement". I would rather say that "all observers would agree about what each physical measuring-system indicates".
Fine, use the word "indicates" rather than "measures", although I'm pretty sure it is standard terminology to talk about all the inertial coordinate systems "measuring" the same laws of physics. But anyway, we can say that each physical measuring-system designed according to Einstein's procedure will "indicate" that the laws of physics obey the same equations. And this is a property of the laws of physics themselves--it wouldn't be true if the laws were Newtonian, for example. Do you disagree?
Aether said:
There is a class of measurements for which each physical measuring-system will agree (e.g., fine-structure constant, two-way speed of light, etc.), and there is a class of measuring-system indications for which each physical-measuring system will not agree (e.g., the one-way speed of light, the length of an object, etc.). I do not see you making such a distinction.
Now you're talking about a generalized notion of "physical measuring-systems" which goes beyond the ones constructed according to Einstein's procedure--that's what I've been referring to just as "coordinate systems". You don't even need to physically construct a measuring system whose measurements will correspond to a coordinate system, you could just take some other measuring-system (like the ones described by Einstein), then pick some arbitrary mathematical transformation on that system's coordinates, then call the result "your" coordinate system (in this sense, even the two-way speed of light could be disagreed on, although it would be the same in all coordinate systems if you restrict your allowable coordinate systems to ones where differences in position coordinates would match measurements of physical rulers at rest in that coordinate system and differences in time coordinates between events with the same position-coordinates would match measurements of a physical clocks at rest at that position-coordinate).

Anyway, no matter what coordinate system you choose to work in, local physical facts like "when this event occurred, it was right next to this physical clock, which read 30 seconds at the moment it occurred" will be agreed upon by all coordinate systems. And the fact that all the physical ruler-clock systems constructed according to Einstein's procedure will indicate the same "laws of physics" is itself a statement that can be broken down into a bunch of such local physical facts, so it's a fact that's agreed upon by all coordinate systems as well (including ones whose coordinates don't match any of Einstein's ruler-clock systems).

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Aether said:
This is the subject of the OP
No it isn't, the original post was simply assuming we were using the same types of inertial coordinate systems used in SR, and asking how the same mirror would look in different frames at an atomic level, and why all frames would agree on their predictions about the behavior of light when analyzing things at the atomic level. Your bringing up the whole issue of the "reality" of statements made in SR was irrelevant to the OP, and I think it'd be better if this side-issue were split into a different thread so there'd be a better chance someone would actually address Leo.Ki's question.

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Aether
Gold Member
JesseM said:
Aether said:
This is the subject of the OP
No it isn't, the original post was simply assuming we were using the same types of inertial coordinate systems used in SR, and asking how the same mirror would look in different frames at an atomic level, and why all frames would agree on their predictions about the behavior of light when analyzing things at the atomic level.
The OP didn't specify that we were using the same type of inertial coordinate systems used in SR. More than three days went by with no response to his question before I replied to him with an explanation of precisely what an inertial frame is.
Your bringing up the whole issue of the "reality" of statements made in SR was irrelevant to the OP, and I think it'd be better if this side-issue were split into a different thread so there'd be a better chance someone would actually address Leo.Ki's question.
The OP specifically asked "How is the reflected photon adapted to match this reality?". Nevertheless, I agree that our discussion here may not be exactly what the OP needs to hear in order to answer his question. Would you (or a moderator) care to start a new thread for this side-issue, or do you want me to do it?

Aether said:
The OP didn't specify that we were using the same type of inertial coordinate systems used in SR.
Not in those precise words, but the OP said "a frame that is in motion with respect to the experiment devices", and since it was asked in the context of SR I think we can assume the question was based on the usual SR convention of "frames" rather than some other convention.
Aether said:
The OP specifically asked "How is the reflected photon adapted to match this reality?"
From the context, I don't think "reality" was being used in any deep philosophical sense, just as a way of asking the practical question about how the atoms look in that frame, and how their squashed length affects the way they reflect photons as predicted in that frame.

Anyway, I'm not really blaming you for taking the thread off-topic since you didn't know that your post would lead to such a lengthy discussion, but at this point I do think it would be good if the mods split off the discussion about whether SR is a theory about "reality" into its own thread. Until then, we might as well keep discussing it here, since the mods can split off any new posts we make too if they decide to do a thread split.

Aether
Gold Member
JesseM said:
Doing a bit of quick googling, it seems the term "Lorentz covariance" is synonymous with Lorentz symmetry, and this page has a quote by Einstein where he defines Lorentz covariance in terms of the equations of physics being unchanged by a Lorentz transformation
Actually, I too rather prefer to suppose that "matter is spherically spatially extended, and thus to reject the concept of the particle" in a classical sense at least. Nevertheless, "the Logic of Relativity is founded on, and completely consistent with, an Absolute Space. (Contrary to current opinions)". I am so glad to see that I do not have to justify this position at all, as it has been Einstein's own position all along. Though I may now have to consider changing my name from "Aether", to "Extended Particle" or something. Most profoundly, Lorentz first deduced the foundations of Albert Einstein's Relativity from the assumption of a rigid Space (ether), and that the cause of the electromagnetic field effect that he was using was in fact vibrations in this Space/Ether.

Though Albert Einstein related relative motions of matter only to other matter and not back to an absolute Space like Lorentz did, (which is mathematically simpler) the important point is that the Logic of Relativity is founded on, and completely consistent with, an Absolute Space. (Contrary to current opinions)

From Lorentz's purely mathematical foundation Albert Einstein then developed his Theory of Relativity, which assumed that matter existed as a spherical spatially extended field which changes ellipsoidal shape with motion and thus also with acceleration (which leads to the ellipsoidal geometry which underpins General Relativity and gravitation).

Albert Einstein took one further step than Lorentz though, and assumed (like Leibniz and Mach) that all motion of matter was relative only to other matter, he writes;

"It has, of course, been known since the days of the ancient Greeks that in order to describe the movement of a body, a second body is needed to which the movement of the first is referred." (Albert Einstein, 1919)

By doing this Albert Einstein effectively renounced the concept of a fundamental Space separate from matter (as a field), as he explains below;

"Since the field exists even in a vacuum, should one conceive of the field as state of a 'carrier', or should it rather be endowed with an independent existence not reducible to anything else? In other words, is there an 'aether' which carries the field; the aether being considered in the undulatory state, for example, when it carries light waves? The question has a natural answer: Because one cannot dispense with the field concept, it is preferable not to introduce in addition a carrier with hypothetical properties." (Albert Einstein, 1950)

"Physical objects are not in space, but these objects are spatially extended. In this way the concept 'empty space' loses its meaning. The field thus becomes an irreducible element of physical description, irreducible in the same sense as the concept of matter (particles) in the theory of Newton." (Albert Einstein, 1954)

Albert Einstein had many valid reasons for asserting that matter is spherically spatially extended, and thus to reject the concept of the particle (which always had the problem of explaining action-at-a-distance);

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Aether said:
Actually, I too rather prefer to suppose that "matter is spherically spatially extended, and thus to reject the concept of the particle" in a classical sense at least. Nevertheless, "the Logic of Relativity is founded on, and completely consistent with, an Absolute Space. (Contrary to current opinions)".
Are you quoting yourself?
Are you aware that all attempts in detecting Absolute Space have failed?

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