How Einstein's equivalence principle extends to the quantum world

[beecee]

https://phys.org/news/2018-08-einstein-equivalence-principle-quantum-world.html

How Einstein's equivalence principle extends to the quantum world has been puzzling physicists for decades, but a team including a University of Queensland researcher has found the key to this question.

UQ physicist, Dr. Magdalena Zych from the ARC Centre of Excellence for Engineered Quantum Systems, and the University of Vienna's Professor Caslav Brukner have been working to discover if quantum objects interact with gravity only through curved space-time.

"Einstein's equivalence principle contends that the total inertial and gravitational mass of any objects are equivalent, meaning all bodies fall in the same way when subject to gravity," Dr. Zych said.

"Physicists have been debating whether the principle applies to quantum particles, so to translate it to the quantum world we needed to find out how quantum particles interact with gravity.

Read more at: https://phys.org/news/2018-08-einstein-equivalence-principle-quantum-world.html#jCp

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the paper:

https://www.nature.com/articles/s41567-018-0197-6

Quantum formulation of the Einstein equivalence principle:

Abstract:

The validity of just a few physical conditions comprising the Einstein equivalence principle (EEP) suffices to ensure that gravity can be understood as spacetime geometry. The EEP is therefore subject to ongoing experimental verification, with present-day tests reaching the regime in which quantum mechanics becomes relevant. Here we show that the classical expression of the EEP does not apply in such a regime. The EEP requires equivalence between the rest mass-energy of a system, the mass-energy that constitutes its inertia, and the mass-energy that constitutes its weight. In quantum mechanics, the energy contributing to the mass is given by a Hamiltonian operator of the internal degrees of freedom. Therefore, we introduce a quantum expression of the EEP—equivalence between the rest, inertial and gravitational internal energy operators. Validity of the classical EEP does not imply the validity of its quantum formulation, which thus requires independent experimental verification. We propose new tests as well as re-analysing existing experiments, and we discuss to what extent they allow quantum aspects of the EEP to be tested.

[StringJunky]

If you fired two neutrally-charged quantum particles, say neutrons, on a parallel but usefully close path, they should eventually converge if gravity still had an effect at the quantum level, wouldn't they?

Edited August 17, 2018 by StringJunky

[jajrussel]

On 8/17/2018 at 7:39 PM, StringJunky said:

If you fired two neutrally-charged quantum particles, say neutrons, on a parallel but usefully close path, they should eventually converge if gravity still had an effect at the quantum level, wouldn't they?

I actually have started to learn something because of this question. I learned that I need to pay more attention to the question... Once I figured out that you spoke of neutrons rather than neutrinos. It got easier to understand the question. I'm still clueless, but I did learn something.

[StringJunky]

24 minutes ago, jajrussel said:

I actually have started to learn something because of this question. I learned that I need to pay more attention to the question... Once I figured out that you spoke of neutrons rather than neutrinos. It got easier to understand the question. I'm still clueless, but I did learn something.

I was hoping someone knowledgeable would respond to that to clarify.

[jajrussel]

If you had been speaking of neutrinos, I was wondering how long you were willing to wait for an answer. Since what I read indicated that there had never been a weak interaction observed. So it clicked maybe I should re-read the question, but sorry I couldn't help. Well once again I can't seem to tell a joke without messing up the punch line because while trying to locate the non interaction reference I found this whiich seems to indicate they kind of do. So I will humbly move back to my clueless status.

https://physics.stackexchange.com/questions/110107/weak-interaction-and-neutrino

Edited September 9, 2018 by jajrussel

[StringJunky]

11 hours ago, jajrussel said:

If you had been speaking of neutrinos, I was wondering how long you were willing to wait for an answer. Since what I read indicated that there had never been a weak interaction observed. So it clicked maybe I should re-read the question, but sorry I couldn't help. Well once again I can't seem to tell a joke without messing up the punch line because while trying to locate the non interaction reference I found this whiich seems to indicate they kind of do. So I will humbly move back to my clueless status.

https://physics.stackexchange.com/questions/110107/weak-interaction-and-neutrino

I hope you didn't take my post as implying any negativity towards your post because none was intended. I know you are learning, just like I am. I was just putting it out there to those that are likely to know.  

[Strange]

On 18/08/2018 at 12:39 AM, StringJunky said:

If you fired two neutrally-charged quantum particles, say neutrons, on a parallel but usefully close path, they should eventually converge if gravity still had an effect at the quantum level, wouldn't they?

I think the answer would be yes, unless it turns out that gravity doesn't work the same way at that scale (eg the breakdown of the equivalence principle as suggested in that paper).

But, of course, neutrons would decay before they converged!

Edited September 10, 2018 by Strange

[StringJunky]

1 hour ago, Strange said:

I think the answer would be yes, unless it turns out that gravity doesn't work the same way at that scale (eg the breakdown of the equivalence principle as suggested in that paper).

Cheers.

[swansont]

On 8/17/2018 at 4:32 PM, beecee said:

 "Physicists have been debating whether the principle applies to quantum particles, so to translate it to the quantum world we needed to find out how quantum particles interact with gravity.

We know that individual atoms are affected by the gravity of the earth. You can get atoms cold and gently toss them up, and they come back down. Or you just drop them. Slow atomic beams deflect under gravity. That's been demonstrated  (I've done all of those things)

Interact with gravity and interact with each other via gravity are two different things, though. Since you're probably at 30 or more orders of magnitude smaller for e.g. neutrons