PF’s policy on Lorentz Ether Theory and Block Universe
What is the PF’s policy on Lorentz Ether Theory and Block Universe?
Debates about the superiority or “truth” of modern Lorentz Ether Theory (LET) and the Block Universe (BU) concept are outside the scope of PF because:
- There is little or no debate among professional physicists about these issues (as opposed to e.g. interpretations of quantum mechanics)
- Positions on these issues are based on personal philosophical preferences and cannot be addressed (even in principle) by experiment.
The core of a scientific theory is a mathematical model which can be used to predict the outcome of experiments, i.e. in addition to the model, there is a mapping between elements of the model and outcomes of experiments. This mapping is sometimes called the “minimal interpretation”. Scientifically, theories are judged on how complicated their mathematical models are and on how well they predict the outcomes of experiments, with the best models being both simple and applying to a wide variety of phenomena.
There is often a desire by the philosophical community to add more structure to a scientific theory than what is represented by the “mathematical model and minimal interpretation” described above. These structures are also generically called “interpretations”, and are most prolific in the field of quantum mechanics. Interpretations typically include some postulates which can be used to justify the mathematical model, as well as some statements about which items in the derived model are “real” and which are measurement artifacts or limitations on our knowledge.
Often a single theory is compatible with many different philosophical interpretations. There is no possible way to resolve a dispute between different philosophical interpretations through appeal to experiment because all of them make the same predictions for all experiments. The choice between philosophical interpretations is therefore entirely a matter of personal philosophical preference.
For special relativity (SR), the mathematical model is the Minkowski space, a four-dimensional pseudo-Euclidean affine manifold. The symmetry group determining this structure is the proper orthochronous Poincaré (or inhomogeneous Lorentz) group which includes the Lorentz transform.
There are two primary philosophical interpretations: the Block Universe (BU) and Lorentz Aether Theory (LET). The BU considers the universe to exist as a single fixed 4D geometric structure that is not dynamically evolving over time since time is one of the dimensions of the structure. The LET considers the universe to be a 3D world evolving over time and with a single undetectable “true” rest frame.
Both BU and LET use the Lorentz transform, etc., to make all of their experimental predictions, and therefore they are scientifically indistinguishable, making the same experimental predictions in all cases. Because of this experimental equivalence, there is little if any serious ongoing debate between the two in professional physics circles (although the philosophy literature does have ongoing debate). Professional physicists are generally content with minimal interpretation and uninterested in philosophical interpretations.
Because there is little debate among modern scientists on this topic, and because such debates cannot be settled by appeal to experiment, and because such debates tend to degenerate into acrimonious and repetitive shouting matches, and because discussions of LET tend to attract crackpots, it is the policy of the PF Mentors who moderate the relativity forum that threads attempting to argue the superiority or veracity of either BU or LET will be closed with reference to this FAQ.
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[QUOTE=”Ilja, post: 5319377, member: 4997″]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?[/QUOTE]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.
[QUOTE=”Ilja, post: 5319184, member: 4997″]Discussed them? Well understood? Give an example where it has been discussed,[/QUOTE]That is a good suggestion, thank you. I will add some references to the insights article. Hopefully next week.
[QUOTE=”Ilja, post: 5319184, member: 4997″]And, by the way, if it has been discussed, and well understood, why ban it?[/QUOTE]The reasons are already mentioned in the article.
[QUOTE=”Ilja, post: 5319184, member: 4997″]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.[/QUOTE]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.
[QUOTE=”Ilja, post: 5319184, member: 4997″]Then I derive, using Bell’s theorem, that the BU predicts Bell’s inequality[/QUOTE]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.
[QUOTE=”Ilja, post: 5319385, member: 4997″]I prefer the variants based on Reichenbach’s principle[/QUOTE]
Can you give a reference? I’ve never seen one of these variants.
[QUOTE=”Ilja, post: 5319385, member: 4997″]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.[/QUOTE]
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.)
[QUOTE=”PeterDonis, post: 5319349, member: 197831″]No. The classical prediction is that Bell’s inequality should hold. [/QUOTE]
Ups, sorry. Of course.
[QUOTE=”PeterDonis, post: 5319349, member: 197831″]
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.
[/QUOTE]
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.
[QUOTE=”PeterDonis, post: 5319349, member: 197831″]
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).
[/QUOTE]
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.
[QUOTE=”PeterDonis, post: 5319235, member: 197831″]
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.
[/QUOTE]
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?
[QUOTE=”PeterDonis, post: 5319235, member: 197831″]
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.[/QUOTE]
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.
[QUOTE=”Ilja, post: 5319303, member: 4997″]BU + Reichenbach’s principle gives a physical prediction, the violation of Bell’s inequality.[/QUOTE]
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.
[QUOTE=”Ilja, post: 5319303, member: 4997″]QM is not even mentioned in the proof of Bell’s theorem.[/QUOTE]
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.
[QUOTE=”PeterDonis, post: 5319228, member: 197831″]
Why would you assume that? That’s a philosophical principle, not a physics principle. Can you give a physics reference?
[/QUOTE]
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?
[QUOTE=”PeterDonis, post: 5319228, member: 197831″]
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.[/QUOTE]
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.
[QUOTE=”Ilja, post: 5319206, member: 4997″]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.[/QUOTE]
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.
[QUOTE=”Ilja, post: 5319206, member: 4997″]Another field-theoretic interpretation, where temperature was simply a field, was possible too[/QUOTE]
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.
[QUOTE=”Ilja, post: 5319184, member: 4997″]I assume that above interpretations accept Reichenbach’s principle of common cause.[/QUOTE]
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.
[QUOTE=”DaleSpam, post: 5319162, member: 43978″]
I am not sure what you’re talking about. These interpretations are well known and well understood by the scientific community. There is no ignorance involved. The community has proposed them, thought about them, worked with them, discussed them, and moved on.
[/QUOTE]
Discussed them? Well understood? Give an example where it has been discussed, and well understood, about such a simple question as if above interpretations can be extended to gravity, and how.
And, by the way, if it has been discussed, and well understood, why ban it? The readers of this forum may have not discussed, and not understood it. 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.
[QUOTE=”DaleSpam, post: 5319162, member: 43978″]
This is incorrect. Pick any experiment and pick either interpretation. Use the Lorentz transform to determine the prediction for that interpretation. Then switch to the other interpretation, and you will use the same Lorentz transform and therefore get the same prediction.[/QUOTE]
Ok. I use the prediction that Bell’s inequality holds. I assume that above interpretations accept Reichenbach’s principle of common cause. Then I derive, using Bell’s theorem, that the BU predicts Bell’s inequality, but LET does not (because it does not forbid hidden causal influences).
If Bell’s inequality holds or not is Lorentz invariant, thus, switching to other frames changes nothing. The prediction remains different. BU predicts Bell’s inequalities, LET remains silent about this.
[QUOTE=”Ilja, post: 5319149, member: 4997″]But is simple ignorance of the theory an argument to ban a discussion here?[/QUOTE]I am not sure what you’re talking about. These interpretations are well known and well understood by the scientific community. There is no ignorance involved. The community has proposed them, thought about them, worked with them, discussed them, and moved on.
[QUOTE=”Ilja, post: 5319149, member: 4997″]The two interpretations of SR lead to different physical predictions in the case of the violation of Bell’s inequality.[/QUOTE]This is incorrect. Pick any experiment and pick either interpretation. Use the Lorentz transform to determine the prediction for that interpretation. Then switch to the other interpretation, and you will use the same Lorentz transform and therefore get the same prediction.
“There is little or no debate among professional physicists about these issues (as opposed to e.g. interpretations of quantum mechanics)”
Does that mean that PF is intended to follow fads of actual mainstream physics instead of discussing physics?
What I would think: If some alternative theory is published, in a peer-reviewed journal, then it should be allowed to discuss it in a physics forum. If the author follows general scientific rules, and publishes his theory only once it has been finished, there will be one publication, and not 100 or so. If it is nonsense, which has somehow made it through peer review, there will be two publications – the original, and a refutation by somebody who has found what the peer-review has not seen. But is simple ignorance of the theory an argument to ban a discussion here? Ignorance would reduce the number of articles to one: The author would violate basic principles if he would publish the same theory many times, because a new publication should contain new results. The mainstream ignores the theory, so, there will be only one. But is ignorance an argument? And, even more, a sufficiently strong one to ban discussions in a physics forum?
“Positions on these issues are based on personal philosophical preferences and cannot be addressed (even in principle) by experiment.”
Wrong. The two interpretations of SR lead to different physical predictions in the case of the violation of Bell’s inequality. The BU interpretation reduced all causal influences to the light cone (Einstein causality). The causality of the Lorentz ether is classical causality, it allows FTL causal influences if they are not backward in true time. Adding only Reichenbach’s common cause principle, the BU allows to prove Bell’s inequality, but the Lorentz ether is not sufficient for this. If Bell’s inequality is violated or not can be addressed by experiment.
[QUOTE=”Smattering, post: 5287439, member: 576347″]But that statement was not limited to BU and LET, was it?[/QUOTE]Yes, it was. The article explicitly states that the situation is different for QM interpretations.
[QUOTE=”PeterDonis, post: 5288097, member: 197831″]At least one of your examples, Penrose’s Road to Reality, doesn’t meet this criterion. It does, at least, make it clear what is established science vs. what is his own speculations or opinions. But it does contain references to “esoterical ideas”.[/QUOTE]
Even Tegmark’s “Mathematical Universe” makes this distinction. And that one contains way more esoterical ideas than anyone here would be willing to tolerate.
[QUOTE=”vanhees71, post: 5287790, member: 260864″]there are indeed some very good books of this kind, where great scientists write about science as it is without any reference to esoterical ideas[/QUOTE]
At least one of your examples, Penrose’s Road to Reality, doesn’t meet this criterion. It does, at least, make it clear what is established science vs. what is his own speculations or opinions. But it does contain references to “esoterical ideas”.
[QUOTE=”vanhees71, post: 5287790, member: 260864″]Well, but one should write about science when writing popular science books,[/QUOTE]
I would love to discuss this further, but here it seems off topic. Should we create a separate thread for this?
[QUOTE]Even a very high-level math book like Penrose’s “Road to Reality” made it to the bestseller lists.[/QUOTE]
I have that standing in my book shelf, but honestly, it seems very unlikely to me that most of the buyers have read more than 20% of it.
[QUOTE=”Orodruin, post: 5287300, member: 510075″]Why do you think these scientists have become highly regarded writers of popular science? It is not only because of their scientific contributions, but also because it is giving these philosophical interpretations which to a large extent is what sells in popular science and hence these are the people who gain more visibility. There are many highly regarded physicists who are experts in their fields who would make absolutely awful pop-sci writers. I am not saying the other kind does not exist, but there are people interested in different things – just as in all populations. Some physicists will be interested in philosophy, others will like playing board games or doing sports.[/QUOTE]
Well, but one should write about science when writing popular science books, and there are indeed some very good books of this kind, where great scientists write about science as it is without any reference to esoterical ideas. Science in itself is exciting enough so that you can write about it without such nonsense. My favorite examples are Weinberg’s “First Three Minutes”, Ledermann’s “The God Particle” (which is marvelous despite its idiosyncratic title), and Close’s “The Infinity Puzzle”. There are also great biographies like Gleick’s “Genius” about Feynman. Even a very high-level math book like Penrose’s “Road to Reality” made it to the bestseller lists. Writing for a non-expert audience is very difficult, but one should not discredit serious science by including non-scientific (sometimes even counterscientific) ideas just to sell these books a bit better.
[QUOTE=”Smattering, post: 5287336, member: 576347″]The ones I am referring had earned their merits even before they began writing pop science books. Thus, the question is rather why they began writing those books. And I think it was due to the fact that they are really interested in such philosophical interpretations.[/QUOTE]
Yes, I am not arguing that. I am arguing that those individuals who are interested in philosophy make better pop-sci in the sense that it will sell better and therefore be more successful, which will lead to recognition not only by peers but also the general public.
[QUOTE=”DaleSpam, post: 5287408, member: 43978″]If most physicists had a professional interest in the block universe or LET interpretations then there would be active discussion on the topic in the physics literature written by professional physicists to professional physicists. There is not.[/QUOTE]
But that statement was not limited to BU and LET, was it?
Anyway, the main reason that such ideas are not discussed in physics literature is simply that these are not physical questions.
[QUOTE=”Smattering, post: 5284901, member: 576347″]Is this statement really correct?
My impression is rather that many professional physicists are indeed interested in philosophical interpretations. Most of them however, try to make a clear distinction between the minimal intrepretation and the philosophical or metaphysical interpretations.
But to say that professional physicists are generally uninterested in philosophical interpretations does not comply with all the speculative and controversial hypotheses that highly regarded physicists have written down in their pop science books.[/QUOTE]If most physicists had a professional interest in the block universe or LET interpretations then there would be active discussion on the topic in the physics literature written by professional physicists to professional physicists. There is not.
The fact that such comments only occur in pop-sci works is telling. Their usual audience is not interested, and they have to look outside of that community to find interest.
I think that the comment is accurate. Without a survey on the topic the only evidence of current professional interest is the current professional literature. That supports the comment.
[QUOTE=”Orodruin, post: 5287300, member: 510075″]Why do you think these scientists have become highly regarded writers of popular science?[/QUOTE]
The ones I am referring had earned their merits even before they began writing pop science books. Thus, the question is rather why they began writing those books. And I think it was due to the fact that they are really interested in such philosophical interpretations.
To presume that they do it primarily for economic reason although they are not really interested in it, seems a bit too negative to me.
[QUOTE]I am not saying the other kind does not exist, but there are people interested in different things – just as in all populations. Some physicists will be interested in philosophy, others will like playing board games or doing sports.[/QUOTE]
This is certainly true, but I was replying to the presumption that physicists are generally not interested in philosophical interpretations.
So Block Universe is outside the scope of PF, but Mark Stuckey gave us a wonderful 5-part insight on the block world model. [URL]https://www.physicsforums.com/insights/blockworld-foundational-implications-part-5-delayed-choice-no-counterfactual-definiteness/[/URL]
I highly recommend reading all 5 parts.
Is not block world the same thing as block universe?
[QUOTE=”Smattering, post: 5284901, member: 576347″]But to say that professional physicists are generally uninterested in philosophical interpretations does not comply with all the speculative and controversial hypotheses that highly regarded physicists have written down in their pop science books.[/QUOTE]
Why do you think these scientists have become highly regarded writers of popular science? It is not only because of their scientific contributions, but also because it is giving these philosophical interpretations which to a large extent is what sells in popular science and hence these are the people who gain more visibility. There are many highly regarded physicists who are experts in their fields who would make absolutely awful pop-sci writers. I am not saying the other kind does not exist, but there are people interested in different things – just as in all populations. Some physicists will be interested in philosophy, others will like playing board games or doing sports.
[QUOTE=”PF’s policy on Lorentz Ether Theory and Block Universe”]
Professional physicists are generally content with the minimal interpretation and uninterested in philosophical interpretations.
[/QUOTE]
Is this statement really correct?
My impression is rather that many professional physicists are indeed interested in philosophical interpretations. Most of them however, try to make a clear distinction between the minimal intrepretation and the philosophical or metaphysical interpretations.
But to say that professional physicists are generally uninterested in philosophical interpretations does not comply with all the speculative and controversial hypotheses that highly regarded physicists have written down in their pop science books.
Comments on that thread have been disabled. We should not use this thread as a way to get around that.
As with all interpretations, no interpretation can lay claim to being uniquely correct.
Nevertheless, the search for a theory of quantum gravity pits the philosophy of Relativity against that of Quantum Mechanics, especially as to eternalism versus presentism and the definite against the indefinite, so here is a chance for the philosophy that usually precedes science to have a rare opportunity to come back in at the ground floor, which can be done at other forums.
Moderators note: a bunch of posts either about QM interpretations, QM books, or about philosophy in general have been removed. I believe that the thread is now more focused on the BU vs LET topic.
[QUOTE=”JDoolin, post: 5238232, member: 268035″]I have no idea how this model compares to the Block Universe model, or the LET models.[/QUOTE]
It doesn’t. The Block Universe and LET models are interpretations of SR, i.e., flat spacetime. The “standard cosmological model” is a model of a curved spacetime (a solution of the Einstein Field Equation in GR) that describes our universe to a reasonable approximation.
As an example of a situation where the philosophy behind the mathematics is important, consider introductory college physics classes, where several chapters may be devoted to kinematics, then Newton’s Second Law, then to Conservation of Energy, then to the Impulse Momentum law. They are all mathematically equivalent, yet they all come at things from a different “philosophical” perspective. Newton’s second law puts you in a mode of thinking about forces. Conservation of energy has you thinking about different types of energy. Impulse Momentum Law has you thinking in terms of momentum.
They all come from different directions, but all of them are equivalent and may each lead to a “best approach” for a particular sort of question or problem.
But imagine if you didn’t know that these were all equivalent and valid constructions of the same ideas. Imagine the arguments that would occur if three physicists got together and were all talking about Force, but one of them was really talking about Impulse, one was talking about Energy, and one was talking about what we actually call force. They could all be correct, yet end up banning each other from speaking for fear of confusing their students.
Ok, if an alternative model makes the same observable predictions as SR, it’s a mere reinterpretation of SR, and thus not a different physical model. If you have a model that makes predictions that subtly differ from GR, one can test one model against the other, and then that’s science.
[QUOTE=”vanhees71, post: 5238978, member: 260864″] The question is, whether the BU or Lorentz aether theory are really different physical models or mere philosophical interpretations of (special or general) relativity. [..][/QUOTE]
It is our consensus that no mismatch can be found between either interpretation and SR. However, such models become subtly testable (in the sense of possible to reject) in general physics, as one tries to fuse SR with QM in way that makes sense. At first sight (Bell and later commentators) QM is incompatible with “BU”, but apparently some recent papers that I don’t understand still managed to make the BU concept fit with the “instant action at a distance” concept. Similarly other papers that I don’t fully understand claim that the “LET” concept cannot be matched to GR except when making subtle but in principle testable differences in predictions (see for example Ilja’s contributions).
In other words, I would say that while SR and tests of SR cannot give an answer, such interpretations definitely belong to physics.