(Apparent?) paradoxes - Classical/Quantum theory predictions

[davidge]

I want to discuss about two apparent contradictions that are on my mind for awhile.

1st: General Relativity predicts no radiation out of black holes. Quantum Mechanics does. If we perform an experiment and see that say, black holes radiates outwards, does that mean General Relativity is wrong?

2nd: I think this is a classical problem. If (using quantum theory, here) two particles are created according to Heinsenberg uncertainty principle and one of them enters a black hole, the two particles would not obey that time that appears on the Heinsenberg condition anymore. However, for this case, maybe our conclusion should be that the Heinsenberg "existence time" condition for the particles holds if the system is unperturbed. In the case posed here, would there be an interaction with the black hole, which maybe destroy the Heinsenberg condition. So it would not be a contradiction at all. I have not talked about entanglement between the two particles, though. That case would be other candidate for contradiction.

If we agree that when trying to understand nature from one theory, we should not consider what other theories states, and that what determines whether a theory is valid or not are independent experiments which will confirm or not the predictions of a given theory, then we could get rid of a large number of apparent contradictions.

Examples are the "repulsion" between a pair of fermions and "information transmited instantaneously in quantum entagled systems".

For the first case I posed here, however, this line of reasoning doesn't seem to work, because necessarily one of the two theories in question must be wrong, depending on the result of an independent experiment to check out whether black holes emit radiation.

By independent experiment, I mean one that doesn't depend on neither of the theories in question.

 

[PeterDonis]

If we perform an experiment and see that say, black holes radiates outwards, does that mean General Relativity is wrong?

No, it means GR is a classical theory and we've done an experiment that is outside its domain of validity.

the Heinsenberg "existence time" condition for the particles

I have no idea what this means. Do you have a reference?

 

[cosmik debris]

There will be better answers than my naiive one but:

1. No, GR is known to be an incomplete answer but is correct in its domain of applicability.
2. The explanation using virtual particles is heuristic and not an accurate representation of the phenomenon.

Cheers

 

[PeterDonis]

If we agree that when trying to understand nature from one theory, we should not consider what other theories states, and that what determines whether a theory is valid or not are independent experiments which will confirm or not the predictions of a given theory, then we could get rid of a large number of apparent contradictions.

Indeed.

For the first case I posed here, however, this line of reasoning doesn't seem to work, because necessarily one of the two theories in question must be wrong, depending on the result of an independent experiment to check out whether black holes emit radiation.

How does that invalidate your strategy? If two theories don't make different predictions, you can't even test them by experiment in the first place.

By independent experiment, I mean one that doesn't depend on neither of the theories in question.

This is too strong, because most theories will include rules about how experimental results are to be interpreted, and those rules will differ from one theory to another. So it's not really possible to have an experiment that is independent of all theories.

 

[mfb]

If (using quantum theory, here) two particles are created according to Heinsenberg uncertainty principle and one of them enters a black hole

This is not what happens. Pop-science descriptions are not accurate representations of the actual physics.

Edit: Fixed grammar

Heisenberg, by the way, no second n.

 

[davidge]

Thank you all for your responses

I have no idea what this means. Do you have a reference?

I mean $\Delta E \Delta t \leq \hbar / 2$.

This is not what happens. Pop-science description are not accurate representation of the actual physics.

The explanation using virtual particles is heuristic and not an accurate representation of the phenomenon

I should forget about virtual particles, then. But it seems that the problem persists. Check this out from 5:00

 

[davidge]

Heisenberg, by the way, no second n.

Even my english is a shame.

 

[Mentz114]

Even my english is a shame.

Your English is fine.

Have a look at this https://en.wikipedia.org/wiki/Vaidya_metric
https://en.wikipedia.org/wiki/Vaidya_metric
It desciribes a Schwarzschild-like spacetime where the mass is increasing or decreasing because of incoming or outgoing radiation.

 

[PeterDonis]

I mean $\Delta E \Delta t \leq \hbar / 2$.

This is not a valid relation, because $t$ is not an observable, it's a parameter.

it seems that the problem persists.

I still don't understand what problem you are referring to. Pop science videos aren't a good source. Do you have a reference to an actual textbook or peer-reviewed paper?

 

[mfb]

Well, names don't follow rules. A German name in this case.

But it seems that the problem persists.

Sure. We have two different frameworks and we don't know what happens when they are both relevant at the same time.

 

[PeterDonis]

We have two different frameworks and we don't know what happens when they are both relevant at the same time.

That's the general problem of quantum gravity, yes. But it's not a problem relevant to Hawking radiation from black holes. Standard quantum field theory in curved spacetime is already sufficient to solve that problem, by showing that quantum fields in Schwarzschild spacetime near the horizon violate the energy conditions that are essential assumptions in the theorem of classical GR that says that black holes can't lose mass or radiate.

 

[PeterDonis]

Have a look at this https://en.wikipedia.org/wiki/Vaidya_metric

It desciribes a Schwarzschild-like spacetime where the mass is increasing or decreasing because of incoming or outgoing radiation.

This is a good point--it shows that, even in purely classical GR (i.e., without taking any quantum fields into account), there is a solution that contains a horizon but has outgoing radiation.

 

[davidge]

Pop science videos aren't a good source. Do you have a reference to an actual textbook or peer-reviewed paper?

Well, they are university professors/researchers.

They are the guys who usually review papers/textbooks before publication.

 

[OCR]

... no second n.

Heinseberg... ?
Are you certain... ?

Even my english is a shame.

Your English is OK... it's readable, and Heisenberg was a simple spelling mistake... but you should capitalize English.

I asked the doctor to give me my diagnosis in English, not medical jargon.

By the way, almost anybody can make grammatical errors... in this case, the use of plurals.

Pop-science description are not accurate representation of the actual physics.

This should be written as...

Pop-science descriptions are not accurate representations of the actual physics.

Carry on...

 

[PeterDonis]

they are university professors/researchers.

So what? That doesn't make them any less human, or any less prone to human failings like not being sufficiently rigorous unless they're forced to be. Pop science articles and videos aren't good sources for learning science, no matter who writes them or makes them.

They are the guys who usually review papers/textbooks before publication.

Yes, but that's not what they're doing, or the standard they are being held to, when they make pop science videos or write pop science books and articles. Sorry, but that's how it is.

 

[MikeS123]

I want to discuss about two apparent contradictions that are on my mind for awhile.

1st: General Relativity predicts no radiation out of black holes. Quantum Mechanics does. If we perform an experiment and see that say, black holes radiates outwards, does that mean General Relativity is wrong?

2nd: I think this is a classical problem. If (using quantum theory, here) two particles are created according to Heinsenberg uncertainty principle and one of them enters a black hole, the two particles would not obey that time that appears on the Heinsenberg condition anymore. However, for this case, maybe our conclusion should be that the Heinsenberg "existence time" condition for the particles holds if the system is unperturbed. In the case posed here, would there be an interaction with the black hole, which maybe destroy the Heinsenberg condition. So it would not be a contradiction at all. I have not talked about entanglement between the two particles, though. That case would be other candidate for contradiction.

If we agree that when trying to understand nature from one theory, we should not consider what other theories states, and that what determines whether a theory is valid or not are independent experiments which will confirm or not the predictions of a given theory, then we could get rid of a large number of apparent contradictions.

Examples are the "repulsion" between a pair of fermions and "information transmited instantaneously in quantum entagled systems".

For the first case I posed here, however, this line of reasoning doesn't seem to work, because necessarily one of the two theories in question must be wrong, depending on the result of an independent experiment to check out whether black holes emit radiation.

By independent experiment, I mean one that doesn't depend on neither of the theories in question.

I think it's important to recognize the glassy behavior of black holes at the horizon, and possibly in the singularity, along with the nonlinear rules that govern its behavior (similar to how memory in the brain as a hopfield net is considered glassy if disordered). Glasses exhibit a peculiar kind of resonance, that allows cross modulation-like effects to occur in it (in RF and acoustically - and gravitationally).

So, I think once this resonance is properly understood, it will led to a quantum gravity solution, and a resolution of these problems.

 

[PeterDonis]

the glassy behavior of black holes at the horizon

Can you clarify what you are referring to here? Or give a reference that gives more details?

 

[bhobba]

Well, they are university professors/researchers. They are the guys who usually review papers/textbooks before publication.

Yes - but they are trying to explain quite advanced mathematical concepts to lay people. Even the 'experts' (and we have quite a few here - btw I am not one, but have studied actual QFT textbooks) have trouble with this and slip into heuristics to get a feel. This is what they tell lay audiences - but its just heuristics and wrong.

The truth is it is not quite correct to say QM and GR are incompatible - we have a perfectly good theory combining the two that is valid up to about the Plank Scale:
https://arxiv.org/abs/1209.3511

That theory predicts Hawking radiation.

The heuristic explanation is of the electron/positron virtual particles popping in and out of existence at the event horizon one gets sucked in and the other escapes as radiation. It's wrong - it's just an aid to intuition, experts know it, and it would not pass as a properly refereed paper in a physics journal, but it's all they can really tell lay people to get some idea what's going on across. It contains inaccuracies galore eg virtual particles, despite what you may have read do not actually exist, but even some textbooks tell fibs and say they do - not Quantum Field Theory textbooks - they tell the real story - but beginner level books. Again for the same reason - QFT is quite advanced mathematically so instead of simply shrugging their shoulders and say - you don't know enough to understand the real explanation - tell what are at best half truths - and that is being charitable.

Its one of those annoying things about physics - there are others in QM as well - see:
https://arxiv.org/pdf/quant-ph/0609163.pdf

Here you will get the real deal - not half truths.

Thanks
Bill

 

[davidge]

Thank you all!