I never said models matching observations was the only requirement, just that it is a requirement and I can't see why anyone would be bothered by it. Your original question to me seemed to indicate that you are bothered by it, so I'm trying to understand why. Nothing you have said addresses that at all.hutchphd said:
Not really. The basic argument is that we live in a time asymmetric solution to the underlying laws, which (with a few exceptions that don't seem like they should matter for most of what we observe) are time symmetric. There's no need for statistical arguments to show that; we just need to show that there is a time asymmetric solution to the laws that matches what we observe.hutchphd said:
But if the asymmetry matches our observations, why would it be "arbitrary"? It's there in our models because it's there in our observations.hutchphd said:
I think it's a matter of ambition of explanatory value that is bothering? A theory that needs 1000 parameters emprically fixed, adds less explanarory value than one that corroborates after tuning only 100 parameters. Similarly a theory that requires a priori improbable (ad hoc ~ low entropy) initial conditions to fit current observations comes with a bothering less explanatory value than a model that works with less fine tuning.PeterDonis said:
I understand this, but it's a different requirement than the requirement that models should match observations. The requirement you describe here is basically Occam's Razor: given two models that both match the observations equally well, the simpler of the two (which in this case means the one with fewer adjustable parameters) should be preferred.Fra said:
WernerQH said:
It's the same reason SR was preferred to Aether theories like LET, and why these days, many (probably most) explanations of SR are based on symmetry rather than discussions of simultaneity as Einstein originally did. There seems to be an aesthetic filter most physicists/mathematicians have to hone in on the 'simplest' theory. One of the problems I find with discussing physics with lay people is they find it difficult to grasp that the 'aesthetic' filter is based on mathematical formulation. It's part of why I believe our education system has taken a backward step (at least in Australia), with most students not doing calculus in HS. When I went to HS, everyone chose to do it. Surprisingly, the reason guidance councillors gave to encourage students to take it wasn't science but economics. Back in those days, economics was taught using calculus, and in some places like Caltech still is, but that seems to have fallen out of favour although, IMHO, it is easier to understand that way. Of course, every informed citizen needs to know the basics of economics. At a practical level, it would be great if we could refer those interested in QM to Susskind's excellent book, knowing they have done the required calculus. He wrote it for such an audience ie those with dim memories of calculus from school.hutchphd said:
The most fundamental arrow-of-time argument is at the very foundations of all of physics. It assumes that there is causality, i.e., that it makes sense to look for regular patterns in the phenomena in nature to begin with, and the success of physics in describing these phenomena indicates that this is a pretty justified assumption.hutchphd said:
Yes I agree they are different as such.PeterDonis said:
I fear you are at least partly correct regarding the expectation in physics that theories against the current mainstream paradigm have to reach a threshold of rigor to even consider or warrant a level of discussion this probably has to do with a large number of ill formed ideas having been proposed by those without a sufficient background in the subject and the deeper philosophical leanings humans inquiries are focused on but there is work showing that the current means for sharing ideas which are not yet fully formed academic preprints are not reaching a wide enough audience given the high rates of information scientists have to deal with as well as the publish or perish imperative. This was discussed in Physics today earlier this year (I believe? It was either that or late last year time is all blurring together on me)Fra said:
Fascinating and articulate way of addressing the measurement problem,it may not have a practical measurable effect but for progressing to unify Quantum mechanics with General relativity such a thing I had noticed similarities between frame of reference shift like behavior especially in context with when I had been looking into Wolfram's computational physics model and the large scale limit for a system evolving under a simple Turing machine if all possible orders of operations were allowed to be computed simultaneously and resolve through interference,RUTA said:
I think you might get something out of Inhomogenous and anisotropic cosmology by Matthew Kleban and Leonardo Senatorehutchphd said:
Yes, yet it's perfectly natural. ie. You can't blame others for not sharing your thinking, which is an easy insight from turning the situation around. I wouldn't wish for others to be less critical.Dragrath said:
Do you speak of this? https://arxiv.org/abs/2004.08210 ??Dragrath said:
You are welcome to do so. Any specific suggestions? Something along the lines of Wheeler?CoolMint said:
Paul Davies interviews John Wheeler said:
gentzen said:
Paul Davies interviews Rudolf Peierls said:
I have to live with not knowing, independent of whether I can manage it or not. Worse, I have to live with others not knowing. Those others might be engineers, trying to construct the protocols to keep my communication private, or my financial transactions secure. And maybe this "engineering" in the end is the important difference:CoolMint said:
John Stewart Bell saw himself as a Quantum Engineer. Mathematicians indeed do prove that two and two makes four! The logical foundations for such proofs turned out to have an important impact on how computers are constructed and verified. In theory, there is no difference between theory and practice. In practice, there is!vanhees71 said:
Does it? Some people had the excellent idea to replace the balls with strings, essentially without resolving the quantum mystery much. Except possibly a hint with n'th quantization and n-branes, and some interesting dualities, but it has raised more questions than answers IMO, which isn't necessarily bad though.CoolMint said:
"Quantum mechanics is a theory about the physical description of physical systems relative to other systems, and this is a complete description of the world"gentzen said:
String theory is not going to mend the faulty intuition about the world.Fra said:
Dyson was a big supporter of string theory, but he thought it was in the wrong area. It should be part of mathematics, not physics. He could be right. Added later: I forgot to mention Dyson knew little of String Theory, except his friend of many years, Feynman, thought it was the wrong track. But his mathematics colleagues thought it was important mathematics.vanhees71 said:
I have no idea what faulty intuition you mean. I have a certain intuition based on symmetry. But determining if it is faulty or not is beyond me. I rather like Feynman's view where physics makes progress using all sorts of ways - sometimes it can be positivist philosophy, other times symmetry. Who knows where the next leap will come from?CoolMint said:
Why do we need a special word for it? I'd call them correlations. These correlations are special only if you think that physics is about particles (or "quantum objects"). If you think of QFT as a statistical theory describing the correlations between events in space-time there's no need for an extra word.CoolMint said:
Exactly. Every physicist should know what QFT is about. Maxwell thought that electrodynamics is about the aether. Our view of electrodynamics was much clarified after Einstein and Minkowski had done away with the aether. I think QED is easier to understand if you stop talking quantum objects, and turn to their interactions instead.CoolMint said:
Reality is what physics is about, and the view of what is "real" has undergone considerable evolution over the course of centuries. To say it "simply means determinism" is an arbitrary and completely unjustified restriction on the space of possible theories to be considered. You may think that QFT has reached its final form (it certainly is mature), but it is possible that it carries similar metaphysical baggage as burdened electrodynamics before 1905. We no longer think of the aether as real, have abandoned the search for mechanical models of the aether, and have arrived at a much more satisfactory theory. (Though at heart it is, of course, still Maxwell's theory.) And this process took more than four decades!vanhees71 said:
Many people, including many physicists, would not agree with this. They would say physics is about constructing models that make accurate predictions, without considering whether the entities in the models are "real" or not, and leaving matters like "reality" to philosophers.WernerQH said:
I too disagree with this. Perhaps commonality is what physics is about. We agree to certain common "truths" and how to define them so that we have a defined field of play. I think reality is much too strong a word in this context. I do not know your reality at all.WernerQH said:
There is an excellent text on the subject:PeterDonis said:
I like what I think is a classic textbook charicature of in particular theoretical physics - how an observer sits outiside a black box and trying to infer what is inside, using only interactions as a tool? Opening it, or peeking inside, just isn't possible. Or as Bohr put famously and wisely puy it "It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we say about Nature"WernerQH said:
I repeat myself, because people also repeat again and again statements which contradict the mathematics of relativistic QFT.WernerQH said:
I'm not interested in metaphysics but only physics. Reading Bell's papers makes clear that what Bell means by "realistic" is the assumption that all observables always take determined values, which is the very difference between his local realistic hidden-variable theories and QT.WernerQH said:
The photon is not a massless point particle but the quantum of the massless spin-1-field, called electromagnetic field, and indeed in QT there's nothing discrete since everything is described by differential equations. Of course photons are very specific asymptotic free states of the electromagnetic field and nothing else, and these special states imply that one registers "the photon" either as a whole or nothing. That's the distinctive feature of these states and the probability interpretation of quantum states a la Born resolves the space-particle duality contradiction of old quantum mechanics entirely.WernerQH said:
Yes, "my" reality is not the elusive kind of Reality that only philosophers can conceive. Rather, it's what ordinary physicists have in mind when discussing what their theories are about, the inventory of those theories so to speak. And inventory does not mean the mathematical apparatus, but what the mathematical formalism is supposed to describe. Isn't it embarrassing if, what a theory was supposed to be about, turns out to be non-existent, like the aether?hutchphd said:
Of course, this attitude (philosophy?) is well known, not to say wide-spread: instrumentalism ("saving the phenomena"). In most cases it looks bad in retrospect.PeterDonis said:
I also have no interest in metaphysics. But theory space is much larger than hidden-variable theories and conventional QT. And Bell would never claim to have considered all possibilities.vanhees71 said:
It's not embarassing but a triumph of the scientific method, which is the only method to overcome our philosophical prejudices about Nature. Math is used as a language to talk about our observations of nature, because it's the only language that is precise enough to do so.WernerQH said:
But what you call "instrumentalism" is precisely what you demand above, namely to define what is described by the mathematical models (or even theories). An observable is defined by concrete measurement procedures.WernerQH said:
Of course not, but the EPR hypothesis, as far as this vague philosophical non-mathematical writing can be made rigorous as Bell has done, is ruled out by all experiments and "conventional QT" confirmed.WernerQH said:
Sure. But not all contemporaries of Einstein saw it that way. He did not win his Nobel prize for relativity.vanhees71 said:
If we were to take this seriously, physics should be considered part of linguistics, or, more precisely, socio-linguistics. ;-)Fra said:
Those things are not "hand-waving". They are a reasonable description in ordinary language of the QFT concept of "photons" (or indeed of any "particles"). You are getting very close to a warning here.WernerQH said:
What I described is not "instrumentalism". It's a recognition that all models in physics are just that: models. And a recognition that models are not reality. Confusing the map with the territory is a fundamental mistake.WernerQH said:
If you have a valid reference to another theory that describes quantum entanglement, post it.WernerQH said:
Since quantum field theory does not describe the world "in terms of objects moving about", I don't know what you are getting at here.WernerQH said:
If we are to take it litteraly perhaps. Buy I am pretty sure that wasn't what Bohr meant. Inference as an abstraction is the general term for induction, deductiion or abduction and it has as much to do with linguistics as "observer" has todo with conscioussness. I suspect the same people are responsible for both misunderstandings. Unlike mathematics, words should not be interpreted litteraly. It has both pros and cons.WernerQH said:
So you wouldn't call quantum fields (or their excitations) objects? And aren't they subject to equations of motion?PeterDonis said:
Quantum fields, no. One might say that "objects" are made of excitations of quantum fields, but calling the excitations themselves "objects" is problematic.WernerQH said:
No.WernerQH said:
One solution is to choose to recognize the description as primary only and ask how the dynamics of the description itself is expected to change and what happens when two such descriptions are compared. After some time the description and what it describes is indistinguishableWernerQH said:Quantum theory provides a description that makes these objects hard to recognize.
Hornbein said:
A small addition to your point. I think it should be remembered that classical quantities can be handled within a quantum theory.vanhees71 said:
There's recent work showing more quantities than one would think are superselected in QFT.vanhees71 said:
