Another problem is that there is no clear demarcation line, and different contributors (and especially newcomers) will have quite varied views as to what belongs where. Who decides what belongs where? For each thread a majority vote among the mentors?vanhees71 said:What's the problem discussing this simply in another subforum?
This is almost blatantly an assumption, with little to no foundational support, especially when speaking about QT.vanhees71 said:The only thing I think about probability theory, successfully applied in statistics as well as theoretical physics for about 150+/- years, is that it works. That's all I need to justify the use of any specific mathematical concept in the natural sciences.
The problems at the edge of knowledge are actually the only problems really worth worrying about. In this case they are distinctly physical problems, which can only become abundantly clear - i.e. to foundations skeptics such as yourself - once a new theory has actually been developed which manages to supersede the old one in some aspects. The production of any new theory which contains QM as a limit and is falsifiable is one of the major contemporary goals of theoretical physics.vanhees71 said:where all these speculations about apparent problems, which are in fact pseudo-problems, are discussed without confusing people interested in science rather than cargo cult
This might surprise you, but actually no, it isn't as clear cut as it seems as pointed out by many experts. There are several conceptually different notions related to probability, which in the exact sciences are usually immediately interpreted as being probability as described by the standard theory and therefore reduced to standard probability; a few of these concepts are vagueness, uncertainty, likelyhood, possibility and propensity.vanhees71 said:Probability is a clear defined mathematical concept with clear applications in terms of statistics. Completed by information theory and QT it provides objective assignments of probability distributions of real-world systems.
Why not, it can be heard and understood. However, others may legitimately want to go further for their intellectual satisfaction.vanhees71 said:That's all I need to justify the use of any specific mathematical concept in the natural sciences.
Fully agree with this. I think the main value of this forums is to see how other think and reason about open, difficult foundational problems.Auto-Didact said:The problems at the edge of knowledge are actually the only problems really worth worrying about. In this case they are distinctly physical problems, which can only become abundantly clear - i.e. to foundations skeptics such as yourself - once a new theory has actually been developed which manages to supersede the old one in some aspects. The production of any new theory which contains QM as a limit and is falsifiable is one of the major contemporary goals of theoretical physics.
Indeed. What those who complain about threads like these don't seem to understand is that problems in the foundations of physics are always open problems! @vanhees71 such open problems are where contemporary physics simply has no clear answers and they are always with us - usually carefully tucked far away from more practical physics where higher levels of certainty often reign freely.Fra said:Fully agree with this. I think the main value of this forums is to see how other think and reason about open, difficult foundational problems.
I fully agree with this. The long form somewhat personal discussion format of physicsforums - IMO even more so than on stackexchange and far more than Twitter - offers an open platform of free speech, to those interested at all levels and from all walks of life.Fra said:If I have a basic question about something standard, that can be found in textbooks i would go consult the books, not ask people on internet to explain to this me and consider it an authorative answer. So for me, physicsforums is all about exchanging ideas and ways of reasoning and understanding foundations of physics and science.
Feynman said:The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn’t know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is still in some doubt. We have found it of paramount importance that in order to progress we must recognize our ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty — some most unsure, some nearly sure, but none absolutely certain.
Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure, that it is possible to live and not know. But I don’t know whether everyone realizes this is true. Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.
In a way i feel that foundational QM questions (this is explicitly so in my personal perspective) often belongs to BTSM because some aspire not to be "interpretations" but rather proper reconstructions that impact the whole standardmodel.ftr said:I agree with @vanhees71 in his view that maybe a subforum "quantum foundation" can be created, however, I think that might complicate many questions that could be borderline between standard and foundation.
The problem is that even when I try this, also threads starting about "normal" quantum theory turns rapidly into a discussion about "interpretation" and philosophy. See, e.g., the thread about picture dependence, which has nothing to do whatsoever with interpretational (pseudo-)issues but rapidly was turned into a discussion about it and about non-scientific questions concerning subjective and objective meanings or probabilities!A. Neumaier said:What's your problem with simply ignoring threads about foundations (i.e., what you label philosophy)?
I don't see where the thread 'Interpretation of QM in the Heisenberg Picture' degenerated in this way.vanhees71 said:The problem is that even when I try this, also threads starting about "normal" quantum theory turns rapidly into a discussion about "interpretation" and philosophy. See, e.g., the thread about picture dependence, which has nothing to do whatsoever with interpretational (pseudo-)issues but rapidly was turned into a discussion about it and about non-scientific questions concerning subjective and objective meanings or probabilities!
Fra said:I personally never quite understood the pure interpretation discussion which aim to make no difference to open issues.
vanhees71 said:My problem is to see the necessity for "completions", as long as there are no observations hinting at an incompleteness of QT. The problem I have with understanding, why some people are so obsessed with purely philosophical issues that they think the QT is somehow incomplete. The only incompleteness I'm aware of is the pressing issue of the missing quantum theory of gravity (and, in view common of the geometrical interpretation of GR, probably also spacetime).
vanhees71 said:Your problem seems precisely to be that there's no problem. I can't say, which phenomena would indicate an incompleteness of QT since there are none known today.
Concerning the incompleteness of QT with regard of describing the gravitational interaction (or spacetime geometry) the problem is that the only hint are the singularities of GR (black holes, big bang/crunch etc.), where obviously something is wrong, but whether this is cured by some future quantum formulation or not I can't say. As far as I know there are no hints about phenomena related to quantum features of gravity either.
Concerning supersymmetry, it's a purely theoretical construct which in some sense look mathematically natural and predicts some interesting features like the coupling constants of the SM merging in a closer region (maybe 1 point) hinting at some unification of all known forces. It also may provide dark-matter candidates. The trouble here is that it's with today technology impossible to look for the entire SUSY-extension landscape of the SM. Only the minimal extensions are under test at the LHC and so far it hints at more and more regions of the landscape of the minimal extension are ruled out.
It seems that you do not shy away from philosophical statements when you want to heighten importance of QFT.vanhees71 said:This is a science forum (at least that's what I thought) and not about philosophy (even not about philosophy of science). However the QM-section more and more is deformed to a discussion forum about this off-topic subject, and I find this a pity. Particularly even threads where a student asks some scientific question about introductory QM it's soon turned to discussions about some quibbles with the standard minimal interpretation.
I still think, and I hope finally the mentors here agree, that one should split the QM section into a strictly scientific part, where standard QM is discussed and another philosophy-of-science part, where all these speculations about apparent problems, which are in fact pseudo-problems, are discussed without confusing people interested in science rather than cargo cult!
vanhees71 said:Ironically for photons you come very far with just thinking about them not as classical particles (which is far from their true nature which is only describable in QED) but as classical electromagnetic waves.
It is a philosophical statement IF you mean that the current description of the photon given by QFT is fully sufficient such that no future possible deeper underlying mathematical theory - of which QFT might one day turn out to be an approximation - will ever meaningfully modify the core mathematical properties of the description of a photon.vanhees71 said:It's not a philosophical statement to say that QFT provides the only correct description of what a "photon" is. It's a scientific statement based on observational facts.
And statistics are more fundamental than individual events, right?vanhees71 said:It's not a philosophical statement to say that QFT provides the only correct description of what a "photon" is. It's a scientific statement based on observational facts.
I disagree that this is irrelevant; this is literally encouraging bad scientific practice by focusing too much on the short term instead of the long term. Experiment has limits, the goal of theory is inherently to go beyond these limits; this is why experiments are done in the first place i.e. in order to select the (most) correct theory from the set of extent theories.vanhees71 said:Again, we are in this spiral to irrelevant discussions. Any natural-science statement is putative. If one day one finds a contradiction to QT we have to think about a new theory.