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All undergraduate physics majors are shown how the counterintuitive aspects (“mysteries”) of time dilation and length contraction in special relativity (SR) follow from the light postulate, i.e., that everyone measures the same value for the speed of light c, regardless of their motion relative to the source (see this Insight, for example). And, we can understand the light postulate to follow from the principle of relativity, sometimes referred to as “no preferred reference frame” (NPRF). Simply put, if the speed of light from a source was only equal to ##c=\frac{1}{\sqrt{\epsilon_o \mu_o}}## (per Maxwell’s equations) for one particular velocity relative to the source, that would certainly constitute a preferred reference frame. Borrowing from Einstein [1], NPRF might be stated (see this...

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  • #2
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I enjoyed this, esp the image of other universal constants working the same as c.

it seems like a chicken and egg problem a little (QM superselection rules and NPRF physical constants) but at least they are both chickens.
 
  • #3
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I enjoyed this, esp the image of other universal constants working the same as c.

it seems like a chicken and egg problem a little (QM superselection rules and NPRF physical constants) but at least they are both chickens.

Thnx. Would you mind expanding on that second comment for me? A referee said something similar, so I'm curious what exactly brought that to mind :smile:
 
  • #4
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Which comes first, the partition that provides the correct equivalence relation on average for (c,h,G, b?) or the equivalence relation that dictates partition?
 
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  • #5
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Which comes first, the partition that provides the correct equivalence relation on average for (c,h,G, b?) or the equivalence relation that dictates partition?
Which is the superselection rule as you see it?
 
  • #6
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I’m going to go with “partition”, and venture even further... that is what physical chemistry sort of is.
 
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  • #7
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I’m going to go with “partition”, and venture even further... that is what physical chemistry sort of is.
Let's look at SR. Here is the explanatory hierarchy as we present it in our paper:

NPRF --> everyone measures c --> time dilation and length contraction --> relativity of simultaneity (different partitions of spacetime).

So, NPRF is not the equivalence relation, but it is the ultimate basis for our equivalence relation, which is strictly speaking the synchronized proper time of the comoving observers for either Alice or Bob (or ... ). Here we have NPRF/equivalence relation leading to the partition. Now let's flip it:

Relativity of simultaneity --> time dilation and length contraction --> everyone measures c --> NPRF.

For QM we have:

NPRF --> everyone measures h --> average-only conservation and Bell state correlations --> relativity of data partition (different partitions of Bell state data).

Again, NPRF isn't the equivalence relation, but it is the ultimate basis for it. Now let's flip it:

Relativity of data partition --> average-only conservation and Bell state correlations --> everyone measures h --> NPRF.

If you go with the equivalence relation as fundamental, you have one and the same rule leading to two different consequences. If you go the other way, you have two different rules with the exact same consequence. I think physicists would prefer the former, since they tend to be reductionists (explain more and more with less and less" per Weinberg). The other way makes NPRF look like an amazing coincidence.
 
  • #8
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hmm. I sort of read the table in the article up and down and that's why "at least both are chickens" aha. And I guess I see NPRF as exactly that pretty neat coincidence between relativity of simultaneity and the discrete partitioning of information for Bell observers in different frames.

to me these sound like accurate historical accounts of "what happened"
Relativity of simultaneity --> time dilation and length contraction --> everyone measures c --> NPRF.
Relativity of data partition --> average-only conservation and Bell state correlations --> everyone measures h --> NPRF.

So, I guess I see NPRF as a statement of "connected fact" rather than pejorative "amazing coincidence".
 
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  • #9
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hmm. I sort of read the table in the article up and down and that's why "at least both are chickens" aha. And I guess I see NPRF as exactly that pretty neat coincidence between relativity of simultaneity and the discrete partitioning of information for Bell observers in different frames.

to me these sound like accurate historical accounts of "what happened"

So, I guess I see NPRF as a statement of "connected fact" rather than pejorative "amazing coincidence".
That could be true :smile:
 
  • #10
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Actually, I prefer

“Time dilation and length contraction --> Relativity of simultaneity -->everyone measures c --> NPRF.”

“Average-only conservation and Bell state correlations --> Relativity of data partition --> everyone measures h --> NPRF.”
 
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  • #11
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I bought and am reading the book you recommended, "Universal Constants in Physics". Thnx for pointing that out, Jimster41.
 
  • #12
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And I just bought your book (Kindle) for morning coffee.
 
  • #14
PeterDonis
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I've started a thread in the BSM forum zeroing in only on the subtopic of a discussion of references [23] and [24] in the Insights article. https://www.physicsforums.com/threa...d-dark-energy-with-minor-tweaks-to-gr.994343/

Moderator's note: That thread has been put in moderation for review. On an initial look, it is much too long and much too broad for a single thread discussion; a single thread discussion should be focused on one particular reference, and ideally on one particular question raised by that reference.

Also, that thread is asking for people's "gut check" opinions, which is off topic and doesn't lead to fruitful discussion.
 
  • #15
PeterDonis
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relativity of simultaneity (different partitions of spacetime)

Relativity does not partition spacetime into two regions with respect to a particular event. It partitions spacetime into three regions: the past light cone, the future light cone, and the spacelike separated region. This partitioning, for any given event, is invariant.

It seems to me that the above fact should be taken into account in any attempt to provide an explanation.
 
  • #16
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I only just started chapter two of the book. The chapter is titled “Block Universe from Special Relativity” looking forward to it. My gut reaction to your comments above (FWIW):

There is only ever Alice and Bob.
And
Invariant except for differential aging
(I get that both measure the same second... and yet their seconds aren’t the same)

the first thought leaves me wishing I had a clearer picture of some of the more complicated Bell experiments... ones with more than two detectors etc. What does the math even look like when you are trying to simultaneously resolve three of Schrodinger’s cats? I’m guessing it has to be done pair-wise?
 
  • #17
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Relativity does not partition spacetime into two regions with respect to a particular event. It partitions spacetime into three regions: the past light cone, the future light cone, and the spacelike separated region. This partitioning, for any given event, is invariant.

It seems to me that the above fact should be taken into account in any attempt to provide an explanation.
That is a different partition altogether. I'm talking about partitions per surfaces of simultaneity for any given observer. The partition I'm talking about is therefore observer dependent, which is key to the entire explanation.
 
  • #18
PeterDonis
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I'm talking about partitions per surfaces of simultaneity for any given observer.

Yes, I know that.

The partition I'm talking about is therefore observer dependent

No, it's coordinate dependent. Which means that, according to the standard way that GR is interpreted, it has no physical meaning, since only invariants have physical meaning.
 
  • #19
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No, it's coordinate dependent. Which means that, according to the standard way that GR is interpreted, it has no physical meaning, since only invariants have physical meaning.
The coordinates are associated with the observer here and they certainly do have physical meaning for the observer, they represent what that observer will measure.
 
  • #20
PeterDonis
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The coordinates are associated with the observer here

But there's no unique way of doing that. In SR, if the observer is inertial forever, there is at least a coordinate chart that is picked out by the observer's state of motion--but in our real universe spacetime is not flat and no observer is ever inertial forever.

they certainly do have physical meaning for the observer, they represent what that observer will measure.

Only on the observer's worldline. The coordinates picked by an observer on Earth don't represent what the observer directly measures in the Andromeda galaxy since the observer can't directly measure anything there.
 
  • #21
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But there's no unique way of doing that. In SR, if the observer is inertial forever, there is at least a coordinate chart that is picked out by the observer's state of motion--but in our real universe spacetime is not flat and no observer is ever inertial forever.

Only on the observer's worldline. The coordinates picked by an observer on Earth don't represent what the observer directly measures in the Andromeda galaxy since the observer can't directly measure anything there.
We rarely have to worry about GR corrections. And we do use distant coordinates all the time in making measurements, e.g., probes around distant planets.
 
  • #22
PeterDonis
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We rarely have to worry about GR corrections.

Perhaps in a practical sense this is true for many problem domains. But you are talking about foundations. For foundations, the fact that GR is more accurate than SR is critical.

we do use distant coordinates all the time in making measurements, e.g., probes around distant planets

We use coordinates to describe the results of measurements. We do not use coordinates to make measurements. Measurement results are invariants. Coordinate values are not.
 
  • #23
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Perhaps in a practical sense this is true for many problem domains. But you are talking about foundations. For foundations, the fact that GR is more accurate than SR is critical.

We use coordinates to describe the results of measurements. We do not use coordinates to make measurements. Measurement results are invariants. Coordinate values are not.
The comparison I'm talking about is the relativity principle of SR as applied to c with its application in QM to h. The theoretical structure of GR in no way undermines that relationship and does not add anything to the analysis. The coordinate values can (and usually do) correspond to or directly relate to measured values, e.g., SG magnet angles. The point of a coordinate system is, as the name states, to "coordinate."
 
  • #24
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The theoretical structure of GR in no way undermines that relationship and does not add anything to the analysis.

To me, that's because your analysis is limited in scope, which, as I said, doesn't seem viable if you are talking about foundations. For example, your analysis doesn't cover gravity.
 
  • #25
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To me, that's because your analysis is limited in scope, which, as I said, doesn't seem viable if you are talking about foundations. For example, your analysis doesn't cover gravity.
The relationship between SR and QM that we point out is valid, so de facto it is independent of gravity. Indeed, the principle relating them (relativity principle) and dd = 0 hold across all theories of physics, Newtonian and modern. Thus, it is clear that we don't need a theory of everything to do foundations of physics.
 

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