# Time dilation #3

## Main Question or Discussion Point

I seek information in relation to my attempts to understand an aspect of special theory.

I recently read the comment - "SR says that the measured speed of light is constant."

In his book 'An Introduction to the Special Theory of Relativity' Robert Katz asks (36, Affiliated East-West, 1964) -

"Is the moving rod really contracted in its direction of motion? Is time really dilated? These questions depend on what is meant by 'really'. In physics what is real is identical with what is measured."

In his article 'The Twin Paradoxes of Special Relativity: Their resolution and Implications' S J Prokhovnik wrote (548, Foundations of Physics, Vol 19, No 5, May 1989) that (in space) light travels isotropically away from its source but that if an observer is moving past that source it's emissions will not be isotropic relative to him however on page 550 Simon points out "It is well known that the contraction effect is sufficient to conceal the light-speed anisotropy [from that observer].

Is this correct? Does the idea that his rule is contracted conceal the light's anisotropy relative to the moving observer ergo he measures it to be c?

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atyy
I'm not sure specifically about anisotropy, but the constancy of the speed of light in different inertial reference frames has 2 interpretations
(i) matter contracts, etc in strange ways to make it so
(ii) spacetime itself has strange properties

Variations of the first point of view are nowadays often called "Lorentzian", and you can find an exposition of it in John Bell's book "Speakable and Unspeakable". Variations of the second point of view are often called "Einsteinian", and are descended from Minkowski. If I remember right, Clifford Will's book, for example, usually takes the second point of view. For established theory, one just uses the point of view most congenial to one's mode of thinking, and the problem at hand. There are no differences in experimental predictions.

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JesseM
In a "Lorentz ether" interpretation of SR, there's some preferred frame (often called the 'ether frame' although it's not necessary to believe in an actual physical ether), and rulers moving relative to this frame shrink objectively, and clocks moving relative to this frame slow down objectively. So in this interpretation, light "really" only moves at c in the ether frame, while observers moving relative to the ether frame only think light is moving at c relative to themselves because of their distorted rulers and clocks.

The thing is, all the known fundamental equations of physics are Lorentz-symmetric, which means that they're guaranteed to obey exactly the equations in every inertial coordinate system (general relativity is locally Lorentz-symmetric in the neighborhood of every point in spacetime, although it isn't possible to define inertial frames in a global sense in GR). So, any possible experiment you do in different inertial frames will give identical results in all these frames, according to the known laws of physics. This means even if there is a preferred ether frame, there is no possible way for any observer to determine which frame this is experimentally, so the idea of such a frame is more like a metaphysical speculation than a physics theory.

I'm not sure specifically about anisotropy, but the constancy of the speed of light in different inertial reference frames has 2 interpretations
(i) matter contracts, etc in strange ways to make it so
(ii) spacetime itself has strange properties

Variations of the first point of view are nowadays often called "Lorentzian", and you can find an exposition of it in John Bell's book "Speakable and Unspeakable". Variations of the second point of view are often called "Einsteinian", and are descended from Minkowski. If I remember right, Clifford Will's book, for example, usually takes the second point of view. For established theory, one just uses the point of view most congenial to one's mode of thinking, and the problem at hand. There are no differences in experimental predictions.
Thanks for that input but I would prefer it if we could only talk about Einsteinian applications and not refer in any way to Lorentzian ideas which, in my opinion, only tends to confuse matters and is not relevant to Prokhovnik's or Katz's presentations as they both only refer to STR.

An observer is stationary some distance from a light source and, (hypothetically - using a rule and two clocks) measures the speed of light emitted by that source to be c; he accelerates then moves past that source with uniform velocity.

Is his (1 meter) rule then shorter than it was before he started moving or is it merely measured by an observer alongside the source to be shorter than his (1 meter) rule?

I.e. does the traveler's rule physically incur length contraction?

Or as Katz put it "Is the moving rod really contracted in its direction of motion?"

JesseM
Thanks for that input but I would prefer it if we could only talk about Einsteinian applications and not refer in any way to Lorentzian ideas which, in my opinion, only tends to confuse matters and is not relevant to Prokhovnik's or Katz's presentations as they both only refer to STR.
The difference between the Einstein interpretation and the Lorentz interpretation is purely a matter of how relativity is interpreted conceptually, both make exactly the same experimental predictions in all cases. But the Einstein interpretation says all inertial frames are on equal footing, and that there is no single "real truth" about frame-dependent questions. And of course the laws of physics obey the same equations in all inertial frames (this is true regardless of which interpretation you use), including the fact that in any frame, a ruler moving relative to that frame will be shrunk relative to a ruler at rest relative to that frame.
cos said:
Is his (1 meter) rule then shorter than it was before he started moving or is it merely measured by an observer alongside the source to be shorter than his (1 meter) rule?

I.e. does the traveler's rule physically incur length contraction?

Or as Katz put it "Is the moving rod really contracted in its direction of motion?"
It depends what you mean by "really" or "physically". The rod is contracted relative to the observer's ruler in the coordinates of the observer's rest frame, but it's not contracted in any frame-independent sense, there'd be another frame where the observer's ruler is contracted relative to the rod, and in Einstein's interpretation all inertial frames are considered equally valid.

jtbell
Mentor
I.e. does the traveler's rule physically incur length contraction?
"Physical" is a slippery word. There have been many debates on this forum that ultimately reduce to disagreements about its meaning. You need to define very carefully and very explicitly, in operational terms, what you mean by "physical," for the purposes of this thread.

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jtbell
Mentor
"Sniping" type posts have been deleted. Let's give this thread a chance, and not jump to conclusions about its outcome. If it does end up going round in circles like certain other threads, then it will be locked.

atyy
I.e. does the traveler's rule physically incur length contraction?

Or as Katz put it "Is the moving rod really contracted in its direction of motion?"
Perhaps the most famous toy problem to do with this is Bell's spaceship paradox. I've got to go quickly, and actually I've never studied it myself, so I'm outlining my guess as to what happens, and relying on the usual experts to correct my guess.

Does the string really break? Yes.
Did the string really get shorter or did the distance between the spaceships increase? The string really got shorter with respect to one particular lattice of rods and clocks (reference frame), but the distance between the spaceships really increased with respect to another lattice of rods and clocks.

Al68
Thanks for that input but I would prefer it if we could only talk about Einsteinian applications and not refer in any way to Lorentzian ideas which, in my opinion, only tends to confuse matters and is not relevant to Prokhovnik's or Katz's presentations as they both only refer to STR.

An observer is stationary some distance from a light source and, (hypothetically - using a rule and two clocks) measures the speed of light emitted by that source to be c; he accelerates then moves past that source with uniform velocity.

Is his (1 meter) rule then shorter than it was before he started moving or is it merely measured by an observer alongside the source to be shorter than his (1 meter) rule?

I.e. does the traveler's rule physically incur length contraction?

Or as Katz put it "Is the moving rod really contracted in its direction of motion?"
I think Einstein would say that "the distinction real - unreal is hardly helpful" and "rather than distinguishing between "real" and "unreal" we want to more clearly distinguish between quantities that are inherent in the physical system as such (independent from the choice of coordinate system), and quantities that depend on the coordinate system."

So the "Einsteinian" answer would be that whether or not the rod contracted depends on the choice of coordinate system, ie it's frame dependent.

Edit: Even if there were a preferred reference frame in which measured length is "real" and measurements in other frames were "not real", it would still just be a matter of semantics, since the operational definition of "real" would be "with respect to the preferred frame".

Maybe a better question is - Is "actual length" a different concept than "measured length"? Is there a concept of length that would differ from measured length?

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Hello cos.

Real or unreal, some authors, such as Rindler, comment that it is in principle detectable. The words "real in every sense of the word" are also used. One point to note is that we may not be able "see" such a contraction because of Terrell rotation, an effect more noticeable at high relative velocity but not a relativistic effect, but perhaps for the purposes of deciding on the reality, this effect should be ignored. My personal opinion is probably pretty unhelpful, but it quite common--It depends what you mean by real. Of course this is a discussion whuich has taken place many times and by its nature cannot reach an outcome that will satisfy everybody.

Matheinste.

"Is the moving rod really contracted in its direction of motion? Is time really dilated? These questions depend on what is meant by 'really'. In physics what is real is identical with what is measured."
If some people look at a lamp through a sheet of distorting glass and they are asked to point in the direction of the lamp, they may well point in diverging directions. Who is right ? They all are. Each person's experience is as real as the others. They might argue about the direction of the lamp but only until they discover the glass.

In the case of inertial observers who are not at rest relative to each other, they may experience perceptual distortions relating to distances and clock rates which to them are real ( in the sense that they actually see them ).

The question 'is the rod actually contracted' does not have meaning for any observer who is not at rest wrt to the rod, because 'the length of the rod' has been defined only for someone colocated and at rest wrt to the rod. In order to define the 'length' of the rod for a distant observer who is moving relative to the rod, one must specify exactly what procedures are used to measure the rod. Radar ? Lasers ? How will clocks in different locations be synchronised ? etc.

Until terms like 'length' and 'contraction' are operationally defined, this discussion can't be expected to resolve anything.

I seek information in relation to my attempts to understand an aspect of special theory.

I recently read the comment - "SR says that the measured speed of light is constant."
The 2nd postulate has a long history of experimental verification. The sticky FAQ has one source, and there are others on the internet.

In his book 'An Introduction to the Special Theory of Relativity' Robert Katz asks (36, Affiliated East-West, 1964) -

"Is the moving rod really contracted in its direction of motion? Is time really dilated? These questions depend on what is meant by 'really'. In physics what is real is identical with what is measured."
Real in the context of the science of physics would be phenomena according to the known rules of physics. Perception (conclusions based on sensory input) is real in this sense. Your questions therefore require a distinction between the behavior of matter and the perception of the behavior. If the perception requires phenomena contrary to known rules of physics, then it only appears that way (unless the rare discovery of a new rule).
Perception tends to be incomplete, and can be altered; vertigo, hallucinations, mental disorders, drugs, etc.
Example 1. A coin rotated from a face-on view appears elliptical, yet we know it's still circular, because the subtended angle alone does not determine the rotated dimension, i.e. a case of an incomplete description.
The rod is in uniform motion and in a state of equilibrium. What physics rule would cause the rod to change length?
Time dilation can be explained in terms of matter in motion and the constant speed of light, and has been verified experimentally.

In his article 'The Twin Paradoxes of Special Relativity: Their resolution and Implications' S J Prokhovnik wrote (548, Foundations of Physics, Vol 19, No 5, May 1989) that (in space) light travels isotropically away from its source but that if an observer is moving past that source it's emissions will not be isotropic relative to him however on page 550 Simon points out "It is well known that the contraction effect is sufficient to conceal the light-speed anisotropy [from that observer].

Is this correct? Does the idea that his rule is contracted conceal the light's anisotropy relative to the moving observer ergo he measures it to be c?
If light speed is constant and independent of its source motion, then it has to be anisotropic. Material objects acquire the motion of the parent object, whereas light does not, making it unique and perfectly qualified as a universal measuring tool.
If there is no physical cause for the rule/rod to change, then it must appear to change. The apparent change can be explained in physical terms of non simultaneous emissions from the two ends. If a ruler did in fact change dimensions, so would the observer using it and his ref. frame, so how would he know?
The anisotropy is concealed in the two-way light path, which is what the moving observer measures. The anisotropy is also the reason the moving clock runs slower. A person cannot deny anisotropy and still use it in space-time diagrams or calculations without appearing a little foolish.

In summary, SR tells you it's a theory about transformation of space and time coordinates in each observers description of an event, showing they are in fact describing the same event.
As to why SR requires a length change to the moving length, let's leave that as an open question for the readers.

Hello phyti.

Surely time dilation and length contraction are on a par. If one is "real" so is the other.

Matheinste.

Hello phyti.

Surely time dilation and length contraction are on a par. If one is "real" so is the other.

Matheinste.
evening matheinst

The SR theory has one specific condition in its formation, preserving the constant speed of light. The transformation equations must satisfy this condition, even if it requires altering time, space, mass, etc.
If you form the theory without this condition, only using constant speed of light where necessary, you discover reasons for the transformations. The reasons for each are not the same.

evening matheinst

The SR theory has one specific condition in its formation, preserving the constant speed of light. The transformation equations must satisfy this condition, even if it requires altering time, space, mass, etc.
If you form the theory without this condition, only using constant speed of light where necessary, you discover reasons for the transformations. The reasons for each are not the same.
Your statement does not seem logical or consistent.

If we accept the speed of light as being constant and the same for all observers in relative inertial motion then the transformation equations must reflect this and we must accept the logical consequences whatever they are. If the consequences do not agree with observation then either the light axiom is wrong or the transformations are wrong. I have not come across a probelm with this yet.

We accept the light axiom or we do not. We cannot just choose to accept it when it "where necessary". Perhaps I misinterpret what you meant by this.

-----If you form the theory without this condition, only using constant speed of light where necessary, you discover reasons for the transformations. The reasons for each are not the same-----

I assume you are saying that the reasons for the transformations are not the same for time dilation and light contraction when "only using constant speed of light where necessary ". I will not argue with this because I do not know why you say this. The words "If you form the theory without this condtion" I assume by this that you mean the condition of preserving the constancy of light speed. Could you, or perhaps anyone else, explain the meaning of these words.

Thanks.

Matheinste

Your statement does not seem logical or consistent.

I assume you are saying that the reasons for the transformations are not the same for time dilation and light contraction when "only using constant speed of light where necessary ". I will not argue with this because I do not know why you say this. The words "If you form the theory without this condtion" I assume by this that you mean the condition of preserving the constancy of light speed. Could you, or perhaps anyone else, explain the meaning of these words.

Thanks.

Matheinste
Form the theory using only the constancy of light, and without the condition of total symmetry, and see if the symmetry actually developes. Time dilation is the result of constant light speed. The length contraction is required because the moving observer calculates distances too long by a factor of gamma. This is because the assumed rest frame for the moving observer is not equivalent to a relative rest frame.

JesseM
Form the theory using only the constancy of light, and without the condition of total symmetry, and see if the symmetry actually developes. Time dilation is the result of constant light speed. The length contraction is required because the moving observer calculates distances too long by a factor of gamma. This is because the assumed rest frame for the moving observer is not equivalent to a relative rest frame.
What do you mean by "form the theory"? Can you elaborate on what kind of derivation you're thinking of? For example, are you starting with the light clock thought-experiment?

What do you mean by "form the theory"? Can you elaborate on what kind of derivation you're thinking of? For example, are you starting with the light clock thought-experiment?
You wouldn't believe it if I showed you.

JesseM
You wouldn't believe it if I showed you.
Uh, it's not a matter of "belief", a derivation is either valid or it isn't; if you could show a way for rulers and clocks to behave such that everyone would measure the speed of light to be c but rulers didn't shrink symmetrically in different frames, I'd certainly accept that. And if I didn't accept that I'd have to show a detailed scenario where all observers don't measure the speed of light to be c even if we adopt your assumptions about how rulers and clocks behave.

One possibility that occurs to me is that we might try dropping the assumption that rulers don't change length if they're oriented perpendicular to the direction of motion; if we assume rulers do change length in the perpendicular direction when moving relative to some preferred "aether" frame, then it might be possible to have the first postulate of SR be false but the second be true.

Uh, it's not a matter of "belief", a derivation is either valid or it isn't; if you could show a way for rulers and clocks to behave such that everyone would measure the speed of light to be c but rulers didn't shrink symmetrically in different frames, I'd certainly accept that. And if I didn't accept that I'd have to show a detailed scenario where all observers don't measure the speed of light to be c even if we adopt your assumptions about how rulers and clocks behave.

One possibility that occurs to me is that we might try dropping the assumption that rulers don't change length if they're oriented perpendicular to the direction of motion; if we assume rulers do change length in the perpendicular direction when moving relative to some preferred "aether" frame, then it might be possible to have the first postulate of SR be false but the second be true.
It seems you can't have a discussion about anything wihout defining words!
Anyway here's hint. Referring to the MM experiment, the radial dimension perpendicular to the direction of motion (x) is dg (gamma). The x dimension is dgg. What do you make of it?

JesseM
It seems you can't have a discussion about anything wihout defining words!
Where did I define any words in that comment? I just said it was silly to claim I wouldn't believe you if you had a valid derivation.
phyti said:
Anyway here's hint. Referring to the MM experiment, the radial dimension perpendicular to the direction of motion (x) is dg (gamma). The x dimension is dgg. What do you make of it?
You mean distance shrinks by gamma in the perpendicular direction and gamma^2 in the parallel dimension? In that case if you had a light clock oriented perpendicular to the direction of motion, and it was 0.5 light seconds high in its own frame so it should take one second in its frame for the light to go up and down, in the preferred aether frame it would be 0.5*sqrt(1 - v^2/c^2), so the light travels on the hypotenuse of a right triangle with that as the length of one side and the length of the other side as vt, for a distance of sqrt(v^2*t^2 + 0.25*(1 - v^2/c^2)). And the light should travel at c in the aether frame, so divide that by t and it should equal c. Squaring both sides and multiplying both sides by t^2 gives:

v^2*t^2 + 0.25*(1 - v^2/c^2) = c^2*t^2

Or:

t^2 = 0.25*(1 - v^2/c^2)/(c^2 - v^2) = 0.25*(1/c^2)*(c^2 - v^2)/(c^2 - v^2) = 0.25/c^2

So, t = 0.5/c. And that's just the time for the light to go from the bottom of the light clock to the top, for it to go up and come down again would be twice that, or (1 light second)/c = 1 second. So, this would mean the light clock ticks at the same rate in the aether frame that it does in its own frame, meaning no time dilation.

If the light clock was oriented in the direction parallel to its motion, and it's shrunk by gamma^2 in the aether frame, then it will have a length of 0.5*(1 - v^2/c^2) in the aether frame. So if it's traveling at v, the light will take 0.5*(1 - v^2/c^2)/(c - v) to get from the back end to the front end and 0.5*(1 - v^2/c^2)/(c + v) to get from the front end to the back end, for a total time of:

[0.5*(1 - v^2/c^2)*(c - v) + 0.5*(1 - v^2/c^2)*(c + v)]/(c^2 - v^2) =
c*(1 - v^2/c^2)/(c^2 - v^2) = c*(1/c^2)*(c^2 - v^2)/(c^2 - v^2) = 1/c again. So again the clock will take 1 second to tick in both frames, so no time dilation.

So assuming this would also work for a diagonally oriented clock (which I haven't checked), then yes, this would be an example showing that with a nonsymmetric form of length contraction and no time dilation, you can preserve the second postulate that says all observers should measure light to move at c, while violating the first postulate that says the laws of physics should work symmetrically in different frames.

One little thing I'll note is that this doesn't match up with what it sounded like you were saying before:
Form the theory using only the constancy of light, and without the condition of total symmetry, and see if the symmetry actually developes. Time dilation is the result of constant light speed. The length contraction is required because the moving observer calculates distances too long by a factor of gamma. This is because the assumed rest frame for the moving observer is not equivalent to a relative rest frame.
Here it sounded like you were saying time dilation and length contraction aren't on equal footing because time dilation is inevitable given the assumption of constant c while length contraction is not, but in the above nonsymmetric theory neither time dilation nor length contraction works the same as in SR (in fact there is no time dilation at all), yet c still seems to be constant.

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Where did I define any words in that comment? I just said it was silly to claim I wouldn't believe you if you had a valid derivation.
"Uh, it's not a matter of "belief", a derivation is either valid or it isn't; "
People don't use precisely defined words in common conversations, and frequently use figures of speech or metaphors, where the meanings are usually apparent from the context. Whether Born uses cucumbers or Einstein uses mollusks, the author assumes the reader has the intelligence to know the difference between the subject matter and the verbal imagery. There are also synonyms, and words with multiple meanings, and which words are used depends a lot on the persons background. Forums bring people together with varied educational and employment qualifications, so why expect them to use the formally defined terms of the subject. Also, some only want a general/basic explanation, without a formal in depth study.
In this case, I wasn't asking you to believe without proof. If someone uses a word that's different from your choice of words, so what. That's a good thing, it means we're not just clones. To rephrase what I meant, you're in that group that defends the mainstream popular exposition of SR so vigorously, that it is very unlikely it would allow any other interpretation. The 'believers' of SR look to A. Einstein as an authority figure, therefore he should know, and no one should question his decree. Likewise, two parallel lines never meet, because Euclid said so! Let's not repeat the dark ages, when only a select few could think, and draw conclusions to be dispensed to the multitudes as the truth.

postulates:
My opinion of the first postulate, based on the history of science is, it's a philosophical preference by the author, who believed in a deterministic world, where knowing its current state (in total and all its parts) allows the prediction of its next state. His own theory precludes this because the speed of light is finite, therefore your knowledge of distant objects is historical, not current.

The assumption of consistent rules of physics is preferable but still unknown. By the early 1900's, most scientific research had been confined to the earth, with the exception of astronomical studies. It's a giant leap of faith to extrapolate the known rules of physics to the entire universe based on such a confined sampling. Should we assume extraterrestrial intelligent life forms look like us because that's all we know? Probably not.
It seemed reasonable for Newton to extend gravity beyond the earth, because its predictions appeared to match observation, but that's only one aspect of physics, and in retrospect it requires modification. Based on reason alone, regarding how human concepts are formed, all theories are incomplete because all things aren't perceived, and all definitions are relative. The first part is true because new things are discovered. The second part is true because there is no truly fundamental definition.

The speed of light has been measured under varying conditions, space, air, water, etc., and has a well documented history of factual support. For the foundation of a theory, this would be my choice over the first postulate.
This reply is long enough, so another will cover the remainder of your post.

JesseM
JesseM said:
Where did I define any words in that comment? I just said it was silly to claim I wouldn't believe you if you had a valid derivation.
"Uh, it's not a matter of "belief", a derivation is either valid or it isn't; "
People don't use precisely defined words in common conversations, and frequently use figures of speech or metaphors, where the meanings are usually apparent from the context.
I wasn't quibbling about the meaning of the word "belief", I was saying that your comment "You wouldn't believe it if I showed you" was ridiculous (and also somewhat insulting, portraying me as so close-minded I would refuse to listen to a valid argument) because if you show me, the derivation will either be valid or invalid mathematically, so I'd either have to accept it (which I did!) or I'd have to show you a specific error which if you understood it would convince you it was wrong too. The word "belief" wasn't important to my response, you could have substituted any word or phrase ___ in "You wouldn't ___ it if I showed you" (for example, 'you wouldn't agree with it if I showed you') and I would have thought the comment was equally ridiculous and responded in the same way.
phyti said:
To rephrase what I meant, you're in that group that defends the mainstream popular exposition of SR so vigorously, that it is very unlikely it would allow any other interpretation.
No I'm not, I commented right at the beginning of this thread that you were free to take the Lorentz ether interpretation. What I usually defend on this forum is just the consistency of the theory against people who think they've found internal inconsistencies, which isn't possible because the theory is consistent mathematically. It is possible that the theory itself could be wrong experimentally, though unlikely at this point, but in any case that's not what people who criticize relativity on this forum are usually trying to show.

And of course, in this particular case, when you stopped being paranoid and actually explained what you meant, I agreed that with different postulates about length contraction and time dilation, one could construct a theory in which the speed of light would be measured to be c by all observers, yet the first postulate (symmetry between the laws of physics in different frames) would not hold. Of course this would not just be a differing "interpretation" of SR, this would be a significantly different theory with different experimental predictions that would run into trouble with a large number of experiments that have already been performed (for example, as I mentioned this theory would predict no time dilation, which would make it hard to explain all the particle accelerator experiments which show particle lifetimes increasing as a function of velocity).
phyti said:
The 'believers' of SR look to A. Einstein as an authority figure, therefore he should know, and no one should question his decree.
Not true at all, in fact on cos' previous thread I was saying that he was relying too much on the decrees of Einstein rather than giving any independent rationales for how his claims made sense.
phyti said:
postulates:
My opinion of the first postulate, based on the history of science is, it's a philosophical preference by the author, who believed in a deterministic world, where knowing its current state (in total and all its parts) allows the prediction of its next state.
Then you simply misunderstand the first postulate, it has nothing to do with determinism, taken together with the second postulate it means nothing more than that the equations of the laws of physics should be Lorentz-invariant (invariant under the coordinate transformation given by the Lorentz transformation). It would be quite possible to have probabilistic equations that were Lorentz-invariant, in fact I think the most common interpretation of QM would say that quantum field theory is a probabilistic theory, and it is certainly Lorentz-invariant. All the fundamental equations of physics found so far have been Lorentz-invariant, and there is quite a lot of experimental evidence to support these equations.
phyti said:
His own theory precludes this because the speed of light is finite, therefore your knowledge of distant objects is historical, not current.
Do you think that this fact precludes determinism? Why? Determinism does not say you can actually predict the future with perfect accuracy given your own limited knowledge, it just says there is some objective truth about the complete physical state of the universe at every given moment (which we can imagine being known by an imaginary being like [URL [Broken] Demon[/url] in a thought-experiment), and that the complete physical state at later moments is completely determined by (the complete state at any earlier moment) + (the complete deterministic laws of physics).

Of course I'm only pointing out here that there's no logical conflict between determinism and the finite speed of light, not actually arguing there's any reason to expect determinism is true in the real world.
phyti said:
The assumption of consistent rules of physics is preferable but still unknown.
No one just "assumes" any physical symmetry, whether Lorentz invariance or other symmetries like spatial translation symmetry--they are all experimentally testable aspects of physical theories.

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and also somewhat insulting, portraying me as so close-minded
I don't insult people, and dislike forums where insults and demeaning statements are common, and moderators ignore them. It discourages the inquiring minds, and they go elsewhere. If you are open minded then good for you. I tend to make statements about people in general, and do not target anyone. Some of the forums have posters who insist there is only one way to interpret an idea. If I did respond, it would be with a question that hopefully causes them to think a little deeper.

What I usually defend on this forum is just the consistency of the theory against people who think they've found internal inconsistencies, which isn't possible because the theory is consistent mathematically.
That's why I refer to you as the public defender of postulate 1!

Then you simply misunderstand the first postulate, it has nothing to do with determinism,
I know what it means, and wasn't defining it. I'm just considering his beliefs, because that determines how he thinks. Prior to quantum physics, the mechanistic, cause and effect, deterministic universe was the popular model. The EPR paper was his latest effort to save that view. He did not want to accept a world based on probabilities.

atyy