
This new experiment could finally unite the two biggest theories in physics - joeyespo
https://sciencealert.com/quantum-mechanics-unify-general-relativity-gravitational-field-experiment-proof
======
auntienomen
This is about quantum Newtonian gravity, not general relativity. The headline
is misleading hype.

Quantum Newtonian gravity has been investigated before. It's even discussed in
standard textbooks like Sakurai.

~~~
jessriedel
Re:Sakurai, are you just talking about neutron interferometry in a
gravitational field? That is a completely different effect and not relevant.

~~~
auntienomen
It's the same regime, obviously not the same effect. Very far from any
situation where you need anything like the effective field theory of GR. The
title's claim that this is a unification of gravity and quantum physics is
quite overblown.

------
randomdrake
Study: Spin Entanglement Witness for Quantum Gravity

Citation: Sougato Bose, Anupam Mazumdar, Gavin W. Morley, Hendrik Ulbricht,
Marko Toroš, Mauro Paternostro, Andrew A. Geraci, Peter F. Barker, M. S. Kim,
and Gerard Milburn Phys. Rev. Lett. 119, 240401 – Published 13 December 2017.

Link:
[https://doi.org/10.1103/PhysRevLett.119.240401](https://doi.org/10.1103/PhysRevLett.119.240401)

DOI: 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.

\---

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

Citation: C. Marletto and V. Vedral Phys. Rev. Lett. 119, 240402 – Published
13 December 2017.

Link:
[https://doi.org/10.1103/PhysRevLett.119.240402](https://doi.org/10.1103/PhysRevLett.119.240402)

DOI: 10.1103/PhysRevLett.119.240402

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.

