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

March 12, 2018 by Bob Yirka, Phys.org report
A possible experiment to prove that gravity and quantum mechanics can be reconciled
Credit: G. W. Morley/University of Warwick and APS/Alan Stonebraker

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. The first team is a pairing of Chiara Marletto of the University of Oxford and Vlatko Vedral of National University of Singapore. The second is an international collaboration. In the papers, both published in Physical Review Letters, the teams describe their experiment and how it might be carried out.

Gravity is a tough nut to crack, there is just no doubt about it. In comparison, the strong, weak and electromagnetic forces are a walk in the park. Scientists still can't explain the nature of , though how it works is rather well understood. The current best theory regarding gravity goes all the way back to Einstein's general theory of relativity, but there has been no way to reconcile it with quantum mechanics. Some physicists suggest it could be a particle called the graviton. But proving that such a particle exists has been frustrating, because it would be so weak that it would be very nearly impossible to measure its force. In this new effort, neither team is suggesting that their experiment could reconcile gravity and . Instead, they are claiming that if such an experiment is successful, it would very nearly prove that it should be possible to do it.

The experiment essentially involves attempting to entangle two particles using their gravitational attraction as a means of confirming . 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; if they are not, then it will not. The experiment would have to run many times to get an accurate assessment. And while a first look might suggest such an experiment could be conducted very soon, the opposite is actually true. The researchers suggest it will likely be a decade before such an experiment could be carried out due to the necessity of improving scale and the sensitivity involved in such an experiment.

Explore further: Physicists propose test of quantum gravity using current technology

More information: C. Marletto et al. Gravitationally Induced Entanglement between Two Massive Particles is Sufficient Evidence of Quantum Effects in Gravity, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.240402 , https://arxiv.org/abs/1707.06036

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.

Sougato Bose et al. Spin Entanglement Witness for Quantum Gravity, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.240401 , https://arxiv.org/abs/1707.06050

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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Emptycell
4 / 5 (4) Mar 12, 2018
Would they be able to use the same technology that was used to measure gravitational waves. As that would have the sensitivity. It would also be used to count out interference from gravity waves.
antialias_physorg
3.4 / 5 (5) Mar 12, 2018
In comparison, the strong, weak and electromagnetic forces are a walk in the park.

Please put the "in comparison" in italics, bold, underlined. Thx.

Would they be able to use the same technology that was used to measure gravitational waves.

Gravitational waves are measured a differential (when the spacetime warp travels through the detector arms). Here they'd half to measure the force direct. Two different critters (also a lot different in orders of magnitude)
granville583762
3 / 5 (2) Mar 12, 2018
Proof gravity is a particle, when a quark attracts another quark the force on the quark is in the direction the graviton was going when it interacts with the quark. The force is in the direction the quark was going when it emitted the graviton. There is no force on the emitting quark, the force is only on the receiving quark, so there's goes Isaac Newton's 3rd law there's no equal and opposite reaction on the emitting quark. I'm surprised nobody has taken this vital up point up seeing as gravity interacts in the quantum world. For a force that operates in the quantum world, there appears to be very little research being carried out. Theoretical mathematics is not research proved by the anomaly of Newton's 3rd.
javjav
4.2 / 5 (5) Mar 12, 2018
Granville that's not correct. QM is not defined in terms of Newton laws. In QM what is conserved is the Momentum, and that's true both for attractive and repulsive interactions when you consider the direction before & after of both particles. Also please note that QM and uncertainty principle allow virtual particles / force carriers to push the target particle "from the other side". In other words, as long as the final Momentum is conserved it does not matter from which direction are they really pushed, as they do not even have a defined position anyway. You can only know the states of the system "before" and "after" the interaction , not "during" the interaction
granville583762
1 / 5 (1) Mar 12, 2018
The macro world and the quantum world is scale, the quantum world is in our macro world, the force of gravity interacts on the femto scale which is the force we feel when we climb a hill, the quantum world is not uncertain, it is just a state of mind, there's plenty of examples of everyday activities that we have been used to for millennia which now with explanations do not appear to match are experiences the quantum world is the same. we over millennia become accustomed to our world and written formulas to explain our world which matches our experiences so our world is written to match common sense, where we have gone wrong is we have devised formulas that do match common sense for the quantum world to explain the same bazaar experiences, so our intellect looks at the quantum explanations and to our minds they do not make sense. We have to write formulas that make common sense. Difficult as it sounds
Granville
granville583762
1 / 5 (1) Mar 12, 2018
A quark experiences gravity and reacts to force of gravity exactly as a rock rolling down a hill, all the quarks contained are a sum total of mass of the rock and the gravitational force of rock. Newton's laws of gravity are equally applicable to the rock as they are to constituent quarks. Gravity does not distinguish between scale of size and scale of mass, the gravity interacts on the femto scale for obvious reasons, because of the of the femto size of the quarks.
Osiris1
not rated yet Mar 12, 2018
Love to see that done. Every particle that we have found has an anti-particle. This graviton, when found, will be no different, even if it is a fundamental mirror matter or 'negative matter' particle
Spaced out Engineer
not rated yet Mar 12, 2018
How do they explain away a super-deterministic account? Can we assume quantum completeness from gravity?
A looper might suggest the magnetic field is a feature of downselecting from some prior spin-2's evolution, perhaps feature prior in thermal time. Fatalistic. (Maybe even regardless of the outcome....)
Is the universe deterministic since the first fracturing, is it still happening, or is that some aspect of the constraints of a representational theory?
A stringer might say the bodies attraction is an emergent behavior and has the appearance of attraction, but the underlying vibrational pattern is not distorted.
Mimath224
3.7 / 5 (3) Mar 13, 2018
'...If they are, the researchers contend, that will prove that gravity is quantum; if they are not, then it will not...'
Logical fallacy in there somewhere, that is if I am reading it correctly Are they they saying 'if A then B, Not A therefore not B.' ? Denying the antecedent?
Da Schneib
5 / 5 (2) Mar 13, 2018
@Emptycell, gravitational wave observatories can't observe tiny diamonds. It would be like trying to use a truck scale to measure the weight of an atom.
Da Schneib
5 / 5 (1) Mar 13, 2018
'...If they are, the researchers contend, that will prove that gravity is quantum; if they are not, then it will not...'
Logical fallacy in there somewhere, that is if I am reading it correctly Are they they saying 'if A then B, Not A therefore not B.' ? Denying the antecedent?
No, that would be saying it would *prove* it's not, which they don't. The experiment will either provide evidence that militates toward quantum gravity or not provide such evidence, nothing more.
Da Schneib
5 / 5 (1) Mar 13, 2018
In comparison, the strong, weak and electromagnetic forces are a walk in the park.

Please put the "in comparison" in italics, bold, underlined. Thx.
First thing caught my attention was the implicit assumption we know all about the color force. We don't. We don't even really quite fully understand the weak force, though we know a lot more about it (analytically) than the color force.

I also kinda wish they'd stop calling the color force the "strong force." The strong nuclear force is not a fundamental force; it has much the same relation to the color force that van der Waals forces have to electromagnetism.
Whydening Gyre
not rated yet Mar 13, 2018
@Emptycell, gravitational wave observatories can't observe tiny diamonds. It would be like trying to use a truck scale to measure the weight of an atom.

I'd like to see THAT scale setup...:-)
NoStrings
1 / 5 (4) Mar 14, 2018
Impossible experiment to prove that gravity and quantum mechanics can be reconciled.
Steelwolf
not rated yet Mar 14, 2018
@WG, technically it is actually do-able if you have a long enough arm and can control/negate the noise in the system. The Long 12 beam scale, (100M beam) should be in Amazon within the next couple centuries, eh? But ye are right, that would be Something to See.
milnik
1 / 5 (1) Mar 19, 2018
Quantum mechanics is a misunderstanding of determining the minimum or matter or energy that occurs in the universe in all phenomena.
Gravity is for science completely unreachable for understanding, because science did not understand the structure of the universe. Most scientists have turned their heads into thinking that what is unknown to them is defined using "tools" chosen from the domain of wrong and unnatural theories. If the true cause of the emergence of gravity would be found, which would deal with so many millions of people who want to put themselves above those who formed them and they awaken the "giants" who have understood something that is never clear to them or will be, because they have turned off the path that leads to finding out the true causes of the phenomenon.
milnik
not rated yet Mar 19, 2018
We all have to understand the meaningful law of nature: everything visible, measurably observant to our senses, must be formed from a substance. If science does not know that substance, then it invents various fatamagers with whom they ignore both themselves and those who want to find out the truth.
This substance, from which matter is formed, is the "parent" of everything existing from that substance. So, too, we have inseparable family ties with our parents, who is in the series of processes, who formed our ancestors? Why is it necessary to know, before knowing who our parents are and what our relationships are and relationships with these parents.
SHUT, ONE, IT IS TIME, IN THE UNIVERSE ALL OF MATERIAL AND ENERGY FORMERS FROM ASTHER SUBSTANCE, FILLING INFINITE UNIVERSITY !! !!
That Aether is the "parent" and the matter and its properties, such as gravity and magnetism.
milnik
not rated yet Mar 19, 2018
Gravity with the help of Aether attracts particles of 3KG (3 quarks and 3 bonds of gluon), which we can call the "solid" state of matter. Any other explanation leads to a dead end of ignorance.
Magnetism also has a property obtained as a "relational" relation of the "liquid" state of matter (free gluons) to Aether. This is absolutely clear and with it all the attempts to find out the causes of various phenomena in the universe can be explained. This is the simplest, and also the most dangerous method for science. For if this is confirmed and accepted, how many hundreds of thousands of "scientists" are left unemployed and how they will repay debts for scams where they earned everything that the present poor person does not possess, and they have it.
RESPECT THIS MY COPYRIGHT, WHICH IT WILL BE ACCEPTED !!
granville583762
not rated yet Mar 23, 2018
The uncertainty principal is not a god

The uncertainty principal is a state of mind, what is uncertain to one person is certainty to another. The statement "In quantum mechanics the uncertainty principal can allow virtual particals to exist" this statement is incorrect, it is not for formula's to dictate the workings of the structure and creation of the atomic world you can see it's not up to the "uncertainty principal" what is and is not allowed because the uncertainty principal is not a god!

javjav:- Granville that's not correct. Also please note that QM and uncertainty principle allow virtual particles

milnik
not rated yet Mar 23, 2018
The principle of indeterminacy is the conclusion that the behavior of the particle can not be established. However, particles must possess their own behavior stemming from the laws by which particles are formed. And why can not we stop it? Because we will immediately bring in a "rule" by which everything that we do not have a play is accomplished. By what can the position of the electron around the nucleus be established? If the number of electrons is around the nucleus, millions of billions per second, and its radius of rotation, a few thousand millionths of a meter. For an observer, this electron looks like a ring-an electric conductor with a charge of an electron. Can the photon enter into that ring without affecting the motion of the electron and what will it do and how will it affect?

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