B 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.

 

[PeterDonis]

if this didn't produce the correct results, it would just show that the Coulomb potential wasn't the full story.

But then you would have to show where the additional potential was coming from, and explain why it wasn't showing up in any other experiments. Unless in this hypothetical we are also saying that lots of other experiments would also have to have come out differently.

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.

Exactly: these additional terms were due to interactions we already knew were there, just of smaller magnitude so the initial model didn't include them. We added them as measurements became more accurate and we began to see the effects of the higher order terms.

That's very different from having to add a whole new interaction to the model. That might be possible, but it would be very difficult.

 

[bob012345]

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.

I am sorry. I used poor judgement saying that and I apologize.

 

[bob012345]

But then you would have to show where the additional potential was coming from, and explain why it wasn't showing up in any other experiments. Unless in this hypothetical we are also saying that lots of other experiments would also have to have come out differently.

I agree completely with the first sentence but I'm not sure I understand what you mean in the second sentence?

 

[PeterDonis]

I'm not sure I understand what you mean in the second sentence?

Just that if, hypothetically, we imagine that the results of many experiments we have already done were different, then those results might support a different theory. But that sort of hypothetical might not be what the OP intended.

 

[Paul Colby]

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.

It’s even a little better than that. Equation 14.1.1 in Weinberg vol I is a relativistic Lagrangian bit taken straight from the standard model. The coulomb central potential is the usual one, of course, but the Dirac equation is used for the electron. Adding the em field back in for the Lamb shift is straight forward. Always been impressed by how cleanly this works out.

 

[vanhees71]

Sure, there's not the slightest hint for any violation of the standard-model prediction for the hydrogen atom, although it's among the most accurately measured and theoretically calculated phenomena ever. The reason for this effort is that one always looks for violations of the predictions of the Standard Model and physics beyond it, because (a) one still looks for possible new particles that could make up the "dark matter" in the cosmological standard model needed to explain the velocity curves of stars in most galaxies and also the structure formation in the evolution of the universe in the big-bang model and (b) to overcome the fine-tuning problem.

The theoretical foundation for alternative theories (like SUSY extensions of the Standard Model) is, however, still standard QFT (including SUSY extensions of course). There are very few generic features that are valid for any local relativistic QFT. One is the relation between spin and statistics (half-integer-spin fields have to be quantized as fermions those of integer spin as bosons) and the invariance under the CPT transformation. Both predictions are tested thoroughly as well with no contradictions found (while all the symmetries, P, T, C, CP, etc. are observed to be violated by the weak interaction).

 

[Nullstein]

But then you would have to show where the additional potential was coming from, and explain why it wasn't showing up in any other experiments. Unless in this hypothetical we are also saying that lots of other experiments would also have to have come out differently.

Sure, I don't deny that. As I said, this "hydrino" is pseudo-science anyway. But we can still discuss what the reaction of the physics community to such an unlikely discovery would have been.

Exactly: these additional terms were due to interactions we already knew were there, just of smaller magnitude so the initial model didn't include them. We added them as measurements became more accurate and we began to see the effects of the higher order terms.

That's very different from having to add a whole new interaction to the model. That might be possible, but it would be very difficult.

Of course it would be hard, I don't deny that either. Luckily, no such thing as a hydrino was ever discovered. But in the unlikely event that it is discovered, the reaction of the physics community would likely not be the rejection of quantum theory. Instead, we would take this as an indication of beyond standard model physics and try to add new terms to the Lagrangian. There would probably immediately be lots of papers on the arXiv in this direction. Rejection of QT would likely be the very last resort.

 

[MathematicalPhysicist]

Sure, I don't deny that. As I said, this "hydrino" is pseudo-science anyway. But we can still discuss what the reaction of the physics community to such an unlikely discovery would have been.

Of course it would be hard, I don't deny that either. Luckily, no such thing as a hydrino was ever discovered. But in the unlikely event that it is discovered, the reaction of the physics community would likely not be the rejection of quantum theory. Instead, we would take this as an indication of beyond standard model physics and try to add new terms to the Lagrangian. There would probably immediately be lots of papers on the arXiv in this direction. Rejection of QT would likely be the very last resort.

So do you say the rather disturbing thing:"you cannot falsify Quantum Theory"?

 

[Nullstein]

So do you say the rather disturbing thing:"you cannot falsify Quantum Theory"?

Where did you get that from? I said the opposite in post #26.

 

[bob012345]

Sure, I don't deny that. As I said, this "hydrino" is pseudo-science anyway. But we can still discuss what the reaction of the physics community to such an unlikely discovery would have been.

Of course it would be hard, I don't deny that either. Luckily, no such thing as a hydrino was ever discovered. But in the unlikely event that it is discovered, the reaction of the physics community would likely not be the rejection of quantum theory. Instead, we would take this as an indication of beyond standard model physics and try to add new terms to the Lagrangian. There would probably immediately be lots of papers on the arXiv in this direction. Rejection of QT would likely be the very last resort.

Why would you say Luckily, no such thing as a hydrino was ever discovered? If such a thing existed it might be a boon to science and technology. Why would you not want it to be true?

 

[MathematicalPhysicist]

Where did you get that from? I said the opposite in post #26.

From what you wrote here:" But in the unlikely event that it is discovered, the reaction of the physics community would likely not be the rejection of quantum theory. Instead, we would take this as an indication of beyond standard model physics and try to add new terms to the Lagrangian. There would probably immediately be lots of papers on the arXiv in this direction. Rejection of QT would likely be the very last resort."

I guess you cannot falsify a dogma which states that the world is not classic.
Either it's classic or it's not, but if it's not classical, then is this reality depends on a specific observer?
Who is he?

 

[Nullstein]

Why would you say Luckily, no such thing as a hydrino was ever discovered? If such a thing existed it might be a boon to science and technology. Why would you not want it to be true?

Luckily, because our best theories remain valid and we don't have to deal with these pseudo-science models. I don't see how it would benefit science and technology. Most likely, matter, as we know it, would have very different properties then and human life would be impossible.

From what you wrote here:" But in the unlikely event that it is discovered, the reaction of the physics community would likely not be the rejection of quantum theory. Instead, we would take this as an indication of beyond standard model physics and try to add new terms to the Lagrangian. There would probably immediately be lots of papers on the arXiv in this direction. Rejection of QT would likely be the very last resort."

I guess you cannot falsify a dogma which states that the world is not classic.
Either it's classic or it's not, but if it's not classical, then is this reality depends on a specific observer?
Who is he?

If you drop a ball and it goes upwards, you have falsified gravity, but not quantum theory. Similarly, you cannot just pick any arbitrary experiment to falsify quantum theory. You must design the experiment in a way so it tests an actual prediction of quantum theory. Quantum theory doesn't predict that balls have to fall down. Gravity does. These "hydrinos" are just not in direct contradictions with quantum theory, so their discovery would not falsify quantum theory. I told you in post #26 what kind of experiments are needed to falsify quantum theory. It's possible to conduct such experiments, so I don't see the problem. QT is not a dogma.

 

[Vanadium 50]

dogma

Puh-lese.

Any successor to quantum theory needs to explain everything QM does. Which means it needs to make very, very similar predictions over the range its been tested.

 

[bob012345]

Luckily, because our best theories remain valid and we don't have to deal with these pseudo-science models. I don't see how it would benefit science and technology. Most likely, matter, as we know it, would have very different properties then and human life would be impossible.

That makes little sense to me. If something turned out to be experimentally true that was currently considered pseudo-science, do you not think it could and would then become the domain of legitimate science? Are physicists incapable with dealing with a surprise discovery outside the current widely accepted mainstream?

As far as utility goes, hypothetical transitions to lower energy levels of Hydrogen should be an energy source that could benefit humanity if it were true.

 

[bob012345]

Puh-lese.

Any successor to quantum theory needs to explain everything QM does. Which means it needs to make very, very similar predictions over the range its been tested.

Yes but candidate theories might take decades or even centuries to get to that point. For example SED theory or Stephen Wolfram's ideas as depicted in A New Kind of Science.