Gravity/Quantum mechanics Reconciliation Possibilities:

[beecee]

https://phys.org/news/2018-03-gravity-quantum-mechanics.html

A possible experiment to prove that gravity and quantum mechanics can be reconciled:

Two teams of researchers working independently of one another have come up with an experiment designed to prove that gravity and quantum mechanics can be reconciled.

excerpt:

The experiment essentially involves attempting to entangle two particles using their gravitational attraction as a means of confirming quantum gravity. In practice, it would consist of levitating two tiny diamonds a small distance from one another and putting each of them into a superposition of two spin directions. After that, a magnetic field would be applied to separate the spin components. At this point, a test would be made to see if each of the components is gravitationally attracted. If they are, the researchers contend, that will prove that gravity is quantum;

Read more at: https://phys.org/news/2018-03-gravity-quantum-mechanics.html#jCp

the papers: 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.240402

Gravitationally Induced Entanglement between Two Massive Particles is Sufficient Evidence of Quantum Effects in Gravity:

 

ABSTRACT

All existing quantum-gravity proposals are extremely hard to test in practice. Quantum effects in the gravitational field are exceptionally small, unlike those in the electromagnetic field. The fundamental reason is that the gravitational coupling constant is about 43 orders of magnitude smaller than the fine structure constant, which governs light-matter interactions. For example, detecting gravitons—the hypothetical quanta of the gravitational field predicted by certain quantum-gravity proposals—is deemed to be practically impossible. Here we adopt a radically different, quantum-information-theoretic approach to testing quantum gravity. We propose witnessing quantumlike features in the gravitational field, by probing it with two masses each in a superposition of two locations. First, we prove that any system (e.g., a field) mediating entanglement between two quantum systems must be quantum. This argument is general and does not rely on any specific dynamics. Then, we propose an experiment to detect the entanglement generated between two masses via gravitational interaction. By our argument, the degree of entanglement between the masses is a witness of the field quantization. This experiment does not require any quantum control over gravity. It is also closer to realization than detecting gravitons or detecting quantum gravitational vacuum fluctuations.

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https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.240401

ABSTRACT

Understanding gravity in the framework of quantum mechanics is one of the great challenges in modern physics. However, the lack of empirical evidence has lead to a debate on whether gravity is a quantum entity. Despite varied proposed probes for quantum gravity, it is fair to say that there are no feasible ideas yet to test its quantum coherent behavior directly in a laboratory experiment. Here, we introduce an idea for such a test based on the principle that two objects cannot be entangled without a quantum mediator. We show that despite the weakness of gravity, the phase evolution induced by the gravitational interaction of two micron size test masses in adjacent matter-wave interferometers can detectably entangle them even when they are placed far apart enough to keep Casimir-Polder forces at bay. We provide a prescription for witnessing this entanglement, which certifies gravity as a quantum coherent mediator, through simple spin correlation measurements.

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Questions.....Why specifically diamonds?

In the Abstract of the first paper, it says, " By our argument, the degree of entanglement between the masses is a witness of the field quantization." When they speak of the "the degree of entanglement"  are they referring to how far the masses are apart before entanglement ceases? If so, I was always of the opinion that this entanglement process, extended to infinity?

In the second paper, it says, "We show that despite the weakness of gravity, the phase evolution induced by the gravitational interaction of two micron size test masses in adjacent matter-wave interferometers can detectably entangle them even when they are placed far apart enough to keep Casimir-Polder forces at bay." So again I understand that "Casimir forces only act over very short distances of less then the wavelengths of vacuum fluctuations or your average virtual particle that pops into and out of existence. So what has this to do with entanglement? Or more properly, what am I misunderstanding?

And finally, when will we have a verifiable QGT? Will we ever really have the tools and methodology of measuring at those quantum/Planck levels to validate or otherwise?

 

 

Edited March 12, 2018 by beecee

[beecee]

No one having an attempt at this? 

[Strange]

On 12/03/2018 at 8:11 PM, beecee said:

In the Abstract of the first paper, it says, " By our argument, the degree of entanglement between the masses is a witness of the field quantization." When they speak of the "the degree of entanglement"  are they referring to how far the masses are apart before entanglement ceases?

This is a measure of how entangled they are (entanglement is not an either-or thing): https://en.wikipedia.org/wiki/Quantum_entanglement#Entropy

On 12/03/2018 at 8:11 PM, beecee said:

In the second paper, it says, "We show that despite the weakness of gravity, the phase evolution induced by the gravitational interaction of two micron size test masses in adjacent matter-wave interferometers can detectably entangle them even when they are placed far apart enough to keep Casimir-Polder forces at bay." So again I understand that "Casimir forces only act over very short distances of less then the wavelengths of vacuum fluctuations or your average virtual particle that pops into and out of existence. So what has this to do with entanglement? Or more properly, what am I misunderstanding?

I assume this is referring to the need to  keep the masses far enough apart to eliminate other interactions (e.g. Casimir-Polder) that could cause entanglement but still allow measurable gravitational interaction.

On 12/03/2018 at 8:11 PM, beecee said:

And finally, when will we have a verifiable QGT?

Not sure. But it will probably be a Thursday.

On 12/03/2018 at 8:11 PM, beecee said:

Why specifically diamonds?

No idea. Maybe because they can be made small, with high purity, and a regular and stable crystal structure that can tweaked in the right way ?

More background on the proposed experiment here: https://www.quantamagazine.org/physicists-find-a-way-to-see-the-grin-of-quantum-gravity-20180306/