What sort of an experiment can refute QM or QFTs?

[MathematicalPhysicist]

I assume most people when they refer to Quantum Theory, they sort of referring to QFT.

So my question boils down to, what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)?

 

[CoolMint]

Any experiment(s) which can demonstrate that classical mechanics is sufficient to explain the micro world in detail.
Was it not the Nazis who tried to refute QT by labeling it 'Jewish physics"? Did they manage to explain quantum phenomena in some novel way?

 

[MathematicalPhysicist]

Any experiment(s) which can demonstrate that classical mechanics is sufficient to explain the micro world in detail.
Was it not the Nazis who tried to refute QT by labeling it 'Jewish physics"? Did they manage to explain quantum phenomena in some novel way?

Why is that? couldn't both classical mechanics and quantum theory be wrong?

I mean Dark Matter was suggested by Fritz Zwicky since Newtonian gravity cannot explain the discrapancy.

 

[phinds]

Why is that? couldn't both classical mechanics and quantum theory be wrong?

Sure, they COULD be, but the point is that if classical mechanics is sufficient then whether it is right or wrong, quantum theory is definitely wrong.

 

[CoolMint]

Why is that? couldn't both classical mechanics and quantum theory be wrong?

I mean Dark Matter was suggested by Fritz Zwicky since Newtonian gravity cannot explain the discrapancy.

There will be better theories but it's very unlikely that anything very significant will change wrt to what QT already implies(that nature is not classical at its core).

 

[PeterDonis]

I assume most people when they refer to Quantum Theory, they sort of referring to QFT.

I'm not sure why you would assume that, since non-relativistic QM is sufficient for many if not most problem domains.

Also, the term "quantum theory" can be used to describe not any particular theory, but a general framework for constructing theoretical models. "Quantum field theory" in this usage would then be one possible family of applications of this general framework, used in problem domains where relativistic phenomena are significant.

what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)?

Any particular theoretical model can be refuted by experimental results that do not match its predictions. You can't refute a general theoretical framework with experiments since a general theoretical framework does not make any particular predictions; all you can do is make the framework less useful in practice by refuting particular models that are built using that framework.

 

[ohwilleke]

I assume most people when they refer to Quantum Theory, they sort of referring to QFT.

So my question boils down to, what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)?

The evidence is overwhelming that some sort of quantum field theory accurately explains reality, which does not behave in the manner of classical physics. One could conceivably show that the Standard Model of Particle Physics needs a tweak or two, but it is hard to imagine any evidence that could refute the overwhelming observations to date that the laws of physics are quantum in nature.

 

[MathematicalPhysicist]

I'm not sure why you would assume that, since non-relativistic QM is sufficient for many if not most problem domains.

Also, the term "quantum theory" can be used to describe not any particular theory, but a general framework for constructing theoretical models. "Quantum field theory" in this usage would then be one possible family of applications of this general framework, used in problem domains where relativistic phenomena are significant.Any particular theoretical model can be refuted by experimental results that do not match its predictions. You can't refute a general theoretical framework with experiments since a general theoretical framework does not make any particular predictions; all you can do is make the framework less useful in practice by refuting particular models that are built using that framework.

In the red book of Muller's pQCD it stated that one can look at QCD in non-relativistic speeds.
So I guess that QFTs can also be looked at speeds less than ultra-relativistic.

I guess I am not sure what is the general framework of QT (quantum theory)?

 

[PeterDonis]

I guess that QFTs can also be looked at speeds less than ultra-relativistic.

Yes, one can have non-relativistic quantum field theories. These are often used, for example, in condensed matter physics.

what is the general framework of QT (quantum theory)?

A good starting point might be the 7 Basic Rules that we use as guidelines in this forum:

https://www.physicsforums.com/threads/the-7-basic-rules-of-quantum-mechanics.971724/

Rules 1, 2, 4, and 5 in particular will, I think, be the case in any quantum model. Rules 3, 6, and 7 are somewhat more specialized and might have to be modified in some cases (for example, Rule 3 is a non-relativistic rule and "time evolution" in QFT is treated differently).

 

[MathematicalPhysicist]

There will be better theories but it's very unlikely that anything very significant will change wrt to what QT already implies(that nature is not classical at its core).

So do you mean the "moon when not looked at ceases to exist"?

 

[CoolMint]

So do you mean the "moon when not looked at ceases to exist"?

There is always someone(something) looking. Knowing.
If there were no life in the reality, the way we perceive reality might just not be the same as how it fundamentally is. Could life be the elusive fundamental constituent of reality? Well, it is too far into the metaphysics.

 

[Paul Colby]

I guess I am not sure what is the general framework of QT (quantum theory)?

Weinberg‘s “The Quantum Theory of Fields” Vol. I chapter 2 Starts from QT as spelled out 1925-26. Relativity appears as a symmetry. It’s a nice readable development of the subject.

 

[physika]

but it is hard to imagine any evidence that could refute the overwhelming observations to date that the laws of physics are quantum in nature.

𝗠𝗮𝘆𝗯𝗲 𝗻𝗼𝘁 𝗮𝘁 𝗺𝗮𝗰𝗿𝗼𝘀𝗰𝗮𝗹𝗲.

.

 

[Nugatory]

So do you mean the "moon when not looked at ceases to exist"?

”Not classical at its core” does not imply that macroscopic objects like the moon only exist when observed, nor that they behave differently in any way when we’re not looking. Quantum mechanics is weird, but not that weird.

The historical perspective is important here: Einstein made that famous comment about the moon long ago, when our understanding of how to apply QM to macroscopic systems was less well developed. There are indeed real foundational questions that can be shoved into the general category of “the measurement problem”, but the putative non-existence of an unobserved moon is not an effective starting point for taking on these questions.

 

[phinds]

There is always someone(something) looking. Knowing.

Utterly irrelevant. Do you think the moon did not exist prior to their being observers to observe it and then it just popped into being?

 

[CoolMint]

Utterly irrelevant. Do you think the moon did not exist prior to their being observers to observe it and then it just popped into being?

Observers can indeed be relevant in some interpretations. That you don't agree with them is also irrelevant.

 

[phinds]

Observers can indeed be relevant in some interpretations. That you don't agree with them is also irrelevant.

You didn't answer my question.

 

[CoolMint]

You didn't answer my question.

Because this is not a philosophy forum. Science concerns itself with observable facts

 

[PeterDonis]

Because this is not a philosophy forum. Science concerns itself with observable facts

Your post #11 looks more like philosophy to me than what @phinds is asking.

For a better response to what you were responding to in post #11, see post #14 by @Nugatory or below.

do you mean the "moon when not looked at ceases to exist"?

QM doesn't say that objects don't exist when they are not being "looked at" (a better term would be "interacted with", which is much more general--see further comments on decoherence below). Quantum systems always exist, although they don't always behave the way our classical intuitions would expect.

For the moon, however, even the latter caution doesn't really apply. The moon is not a simple quantum system; it is composed of something like $10^{50}$ atoms, and it is constantly being decohered by interactions both with its environment (photons from the rest of the universe are always interacting wtih it) and within itself (as those $10^{50}$ atoms are constantly interacting with each other). So non-classical quantum effects are negligible for the moon.

 

[Vanadium 50]

I am amused that this discussion is going on using devices that verify the predictions of QM literally billions of times every second.

 

[Nugatory]

So my question boils down to, what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)?

To answer the question in the thread title (“What sort of experiment could refute QM?”):
First we would need some candidate theory that agrees, within the limits of experimental accuracy, with QM everywhere that QM has been tested. (A candidate theory that fails this requirement is already dead - it doesn’t match existing experimental evidence).

Second that candidate theory would have to make a different prediction than QM in some way that has not yet been tested. (Otherwise there is no possibility of suggesting an experiment that might falsify QM).

And then it has to be possible, at least in principle, to design an experiment that will determine whether the quantum mechanical or the new theory prediction is more accurate. If it is…. then it’s the sort of experiment that could in principle falsify QM.

I will not be holding my breath….

 

[CoolMint]

Your post #11 looks more like philosophy to me than what @phinds is asking.

For a better response to what you were responding to in post #11, see post #14 by @Nugatory or below.QM doesn't say that objects don't exist when they are not being "looked at" (a better term would be "interacted with", which is much more general--see further comments on decoherence below). Quantum systems always exist, although they don't always behave the way our classical intuitions would expect.

For the moon, however, even the latter caution doesn't really apply. The moon is not a simple quantum system; it is composed of something like $10^{50}$ atoms, and it is constantly being decohered by interactions both with its environment (photons from the rest of the universe are always interacting wtih it) and within itself (as those $10^{50}$ atoms are constantly interacting with each other). So non-classical quantum effects are negligible for the moon.

Fair point but since I have not seen a consensus or a peer-reviewed resolution to these Schrodinger's cat questions about what exists between observations/interactions, Phinds and MathematicalPhysicist should probably not be asking them in this particular forum.

 

[CoolMint]

Wouldn't a cat attached to a vial with poison gas that is constantly making cat noises resolve the 'paradox' when the cat suddenly stops mewing and reveals the atom emitting an alpha particle and cat getting killed? Even with the lid closed. Has this been performed?
I will open a separate thread if this question requires more than a brief answer.

 

[vanhees71]

In the red book of Muller's pQCD it stated that one can look at QCD in non-relativistic speeds.
So I guess that QFTs can also be looked at speeds less than ultra-relativistic.

I guess I am not sure what is the general framework of QT (quantum theory)?

QFT is the most comprehensive mathematical formulation of all kinds of quantum theories. It's not limited to relativistic QT. Also what's usually taught first, the so-called "first-quantization formalism" of non-relativistic quantum theory (or quantum mechanics), is a special case of the more general "second-quantization formalism" for cases where one deals with a fixed number of particles, which are not destroyed and/or created in the processes under consideration. In this sense QFT is simply the most general mathematical description of QT.

 

[Lord Jestocost]

what exists between observations/interactions

The formalism of quantum mechanics is related to the experiential reality:
If you have a set of parameters describing a system in state A, you can calculate the probability that an observer will find it in state B after a certain time. But there is nothing which tells you what is actually going on in between the preparation of the system and your observation at a certain time later.

 

[Nullstein]

You can falsify all relativistic quantum field theories at once by finding a violation of CPT symmetry. You can falsify quantum theory in general by finding correlations that exceed Tsirelson's bound.

Generally, if you want to falsify a whole class of theories, you must falsify a prediction that is true for the whole class, i.e. derivable from the axioms alone.

 

[CoolMint]

The formalism of quantum mechanics is related to the experiential reality:
If you have a set of parameters describing a system in state A, you can calculate the probability that an observer will find it in state B after a certain time. But there is nothing which tells you what is actually going on in between the preparation of the system and your observation at a certain time later.

Give it a few hours. Many people will rush into explain to you what is really going on.

 

[PeterDonis]

since I have not seen a consensus or a peer-reviewed resolution to these Schrodinger's cat questions about what exists between observations/interactions, Phinds and MathematicalPhysicist should probably not be asking them in this particular forum.

It is a valid point that discussions of QM interpretations is off topic for this thread and this forum; those discussions belong in the interpretations forum.

Moderator's note to all participants: please keep discussion in this thread focused on the OP question, which is about experiments, not interpretations.

 

[bob012345]

I assume most people when they refer to Quantum Theory, they sort of referring to QFT.

So my question boils down to, what sort of an experiment could potentially refute QFTs (its plural because there are QF theories)

If experimental results proved the existence of something such as particle or an energy state for example which QM says cannot exist. I would think that such new knowledge would just modify QM to include it especially if by QM one means everything beyond the Classical world.

 

[PeterDonis]

I could give a hypothetical example but I might be banned for mentioning it.

If you're not going to give an example, then don't give it. Hints like this are a good way to get a warning. Please take heed.

 

[bob012345]

If you're not going to give an example, then don't give it. Hints like this are a good way to get a warning. Please take heed.

I was just trying to avoid a potential controversy. My example then is if experiments proved the existence of the so-called Hydrino state, the hypothetical state below the ground state of Hydrogen, that might be considered a refutation of QM as currently understood.

 

[Nullstein]

I was just trying to avoid a potential controversy. My example then is if experiments proved the existence of the so-called Hydrino state, the hypothetical state below the ground state of Hydrogen, that might be considered a refutation of QM as currently understood.

It woudn't. One would just modify the Hamiltonian so it predicts the modified energy spectrum. However, this theory seems to be pseudo-science anyway.

 

[PeterDonis]

I was just trying to avoid a potential controversy.

The way to do that is to not mention the potentially controversial thing at all. Hinting at it and then saying you can't give more detail because it might get you banned is not avoiding controversy, it's inviting a warning for yourself. Again, please take heed.

 

[PeterDonis]

One would just modify the Hamiltonian so it predicts the modified energy spectrum.

That might still be problematic because you can't just arbitrarily modify the Hamiltonian. The standard Hamiltonian for the electron in the hydrogen atom is not just taken from thin air; it is derived from the standard non-relativistic kinetic energy and the Coulomb potential of the nucleus. (There are additional fine and hyperfine structure terms as well, but those don't matter for this discussion.)

 

[Nullstein]

That might still be problematic because you can't just arbitrarily modify the Hamiltonian. The standard Hamiltonian for the electron in the hydrogen atom is not just taken from thin air; it is derived from the standard non-relativistic kinetic energy and the Coulomb potential of the nucleus. (There are additional fine and hyperfine structure terms as well, but those don't matter for this discussion.)

That's right, but if this didn't produce the correct results, it would just show that the Coulomb potential wasn't the full story. As you noted, there is also e.g. fine structure, but we didn't take its discovery as an argument to reject quantum theory. We just added some higher order terms to account for the discrepancy.