Insights PF's policy on Lorentz Ether Theory and Block Universe - Comments

[Ilja]

" The choice between philosophical interpretations is therefore entirely a matter of personal philosophical preference."

I disagree. What was the atomic theory during the 19th century? Essentially, it was only an interpretation, which has given some observed fields, like the temperature, an interpretation in terms of atomic theory. Another field-theoretic interpretation, where temperature was simply a field, was possible too, and there have been known opponents of the atomic interpretation like Mach.

But would you really like to deny that atomic theory was part of physics? An important one? Even if at that time there was no experiment which would have allowed to decide if it is correct or not?

 

[PeterDonis]

I assume that above interpretations accept Reichenbach's principle of common cause.

Why would you assume that? That's a philosophical principle, not a physics principle. Can you give a physics reference?

Also, Bell's inequalities are really off topic for this discussion, since, as DaleSpam has already noted, the policy under discussion refers to BU/LET as interpretations of classical SR. Quantum mechanics is a separate issue.

 

[PeterDonis]

What was the atomic theory during the 19th century? Essentially, it was only an interpretation, which has given some observed fields, like the temperature, an interpretation in terms of atomic theory.

It did more than that. It predicted observables like the ratios of volumes of gases in chemical reactions, which had to be taken as ad hoc empirical quantities with no theoretical explanation under other theories of matter.

Another field-theoretic interpretation, where temperature was simply a field, was possible too

This wasn't really a theory so much as a lack of a theory; the "temperature was simply a field" model made no predictions about how temperature should behave relative to other thermodynamic variables like pressure and volume. But it was well known by the 19th century that there were definite relationships between these variables. The atomic theory made predictions about these relationships.

 

[Ilja]

Why would you assume that? That's a philosophical principle, not a physics principle. Can you give a physics reference?

There is no such clear-cut subdivision. BU + Reichenbach's principle gives a physical prediction, the violation of Bell's inequality. BU alone gives no such thing. Once a principle allows to make empirical predictions, it is a legitimate part of physics. Not?

This is, by the way, a quite general situation. Theory A, taken alone, makes no empirical predictions. Theory B, taken alone, makes no empirical prediction too. Theory A and theory B, taken together, allow nontrivial empirical predictions. So, are above theories purely philosophical, once, taken alone, they do not make empirical predictions?

Also, Bell's inequalities are really off topic for this discussion, since, as DaleSpam has already noted, the policy under discussion refers to BU/LET as interpretations of classical SR. Quantum mechanics is a separate issue.

Sorry, Bell's inequalities are an empirical claim, something which can be empirically tested, and has been tested. So, it is not an issue of QM interpretation. QM is not even mentioned in the proof of Bell's theorem.

 

[PeterDonis]

BU + Reichenbach's principle gives a physical prediction, the violation of Bell's inequality.

No. The classical prediction is that Bell's inequality should hold. The actual experimental result is that it is violated--but that shows that the classical theory cannot be correct.

Also, the derivations based on classical theory make no mention of Reichenbach's principle, nor of the Block Universe or any other interpretation of SR. In fact they don't even mention SR except as a motivation for the various versions of the locality assumption (basically that spacelike separated events should not be causally connected). The most straightforward derivation, due to, IIRC, a later paper of Bell's than the original one, only assumes factorizability of the conditional probabilities involved, which is an even simpler version of locality/causality than other derivations. There are other related results that make predictions about experiments where no probabilities are involved at all--they predict that certain results should never be observed, whereas QM predicts that they should. IIRC these related results have not (yet) been experimentally tested.

QM is not even mentioned in the proof of Bell's theorem.

No, but it is the only theory we know of that predicts that Bell's inequalities should be violated--which, of course, they are in the actual experiments.

 

[Ilja]

It did more than that. It predicted observables like the ratios of volumes of gases in chemical reactions, which had to be taken as ad hoc empirical quantities with no theoretical explanation under other theories of matter.

So, if a modern ether theory would explain, say, some properties of the Standard Model of particle physics, it would be allowed to discuss it here? As far as I understand, it would be forbidden, not?

This wasn't really a theory so much as a lack of a theory; the "temperature was simply a field" model made no predictions about how temperature should behave relative to other thermodynamic variables like pressure and volume. But it was well known by the 19th century that there were definite relationships between these variables. The atomic theory made predictions about these relationships.

Of course, a field theory also postulates some equations. Like the SM, which also postulates some equations for the fields. To name the SM "lack of a theory" is, IMHO, also an appropriate description.

 

[Ilja]

No. The classical prediction is that Bell's inequality should hold.

Ups, sorry. Of course.

Also, the derivations based on classical theory make no mention of Reichenbach's principle, nor of the Block Universe or any other interpretation of SR.

There are, of course, different variants. I prefer the variants based on Reichenbach's principle, instead of, say, realism, because realism is much more diffuse. Reichenbach's principle is, in comparison, much more clear, it is clear what you need to apply it - a correlation - and it is clear what it gives you - the requirement of a a causal explanation.

In fact they don't even mention SR except as a motivation for the various versions of the locality assumption (basically that spacelike separated events should not be causally connected).

Correct. But this is the place which requires the BU. The Lorentz ether assumes classical causality in the preferred frame. It forbids causal influences into the past, where the past is defined by true time. It does not forbid faster than light causal influences of the future, defined by true time.

You need the BU, with all allowed times being equal in all aspects, thus, with all of them forbidding causal influences into their own past, to have Einstein causality.

 

[PeterDonis]

I prefer the variants based on Reichenbach's principle

Can you give a reference? I've never seen one of these variants.

The Lorentz ether assumes classical causality in the preferred frame. It forbids causal influences into the past, where the past is defined by true time. It does not forbid faster than light causal influences of the future, defined by true time.

I've never seen a version of "Lorentz ether" that does this either. All the versions I'm aware of make exactly the same predictions for all experiments as standard SR, so they predict that spacelike separated events cannot be causally connected, since that's what standard SR predicts. (Btw, this prediction does not require the BU interpretation; it just requires the standard postulates of SR.)

 

[Dale]

Discussed them? Well understood? Give an example where it has been discussed,

That is a good suggestion, thank you. I will add some references to the insights article. Hopefully next week.

And, by the way, if it has been discussed, and well understood, why ban it?

The reasons are already mentioned in the article.

The wrong prejudice that the Michelson-Morley experiment has falsified the ether in general is very common. It is false, the Lorentz ether is a counterexample. But once the Lorentz ether is banned, this common error cannot be corrected.

That common error can still be corrected in the way you mention.

What is what is not allowed is any assertion that either BU or LET is true. The existence of either interpretation and their experimental equivalence can be used to disprove the assertion that experiments prove the other one.

Then I derive, using Bell's theorem, that the BU predicts Bell's inequality

This is a nonsensical claim. Bells theorem is not part of BU. This is like saying "I derive using Maxwells equations that GR predicts ..."

The BU portion of the derivation would use the Lorentz transform. As would the LET portion of the derivation. It is impossible to come out with a different prediction.

Anyway, the repetitiveness of this discussion with you already shows why the policy is good.

 

[Dale]

So, if a modern ether theory would explain, say, some properties of the Standard Model of particle physics, it would be allowed to discuss it here?

Yes. This point has already been made in posts 19, 20, 22, and 25.

This line of discussion has quickly become repetitive and unproductive, a good example of why these discussions are not permitted. Further repetition will be deleted.

 

[OJ Bernander]

The OP comes across as setting up BU as an alternative to LET. I always thought of BU as an alternative to Presentism (a sliding "now"). LET, meanwhile posits the existence of a medium, a different issue altogether, as it can exist (or not) in but BU and Presentism.

 

[Nugatory]

The OP comes across as setting up BU as an alternative to LET. I always thought of BU as an alternative to Presentism (a sliding "now"). LET, meanwhile posits the existence of a medium, a different issue altogether, as it can exist (or not) in but BU and Presentism.

Fair enough, but both present the same moderation challenge so are covered by the same policy - and this thread is about the policy.