# How Einstein's equivalence principle extends to the quantum world

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.

"We realised that to do this we had to look at the mass."

Mass is dynamic quantity and can have different values, and in quantum physics, mass of a particle can be in a quantum 'superposition' of two different values.

According to the famous equation E=MC2, the mass of any object is held together by energy.

In a state unique to quantum physics, energy and mass can exist in a 'quantum superposition' â€“ as if they consisted of two different values 'at the same time'.

"We realised that we had to look how particles in such quantum states of the mass behave in order to understand how a quantum particle sees gravity in general," she said.

"Our research found that for quantum particles in quantum superpositions of different masses, the principle implies additional restrictions that are not present for classical particlesâ€”this hadn't been discovered before.''

"It means that previous studies that attempted to translate the principle to quantum physics were incomplete because they focused on trajectories of the particles but neglected the mass."

The study opens a door for new experiments that are necessary to test if quantum particles obey the additional restrictions that have been found.

The study has been published in *Nature Physics*.

Explore further

**More information:**Magdalena Zych et al. Quantum formulation of the Einstein equivalence principle,

*Nature Physics*(2018). DOI: 10.1038/s41567-018-0197-6

**Citation**: How Einstein's equivalence principle extends to the quantum world (2018, August 17) retrieved 22 July 2019 from https://phys.org/news/2018-08-einstein-equivalence-principle-quantum-world.html

## User comments

Bugsbunny67antialias_physorgOh, I dunno...Like every double slit experiment, ever?

Mimath224Bugsbunny67GigelWhart1984Da SchneibThe most accurate measurements in all of science come from Heisenberg uncertainty. And the theory they confirm assumes superposition.

Whart1984Mimath224Really, you think so? Going to violated here, Ha, you are in for some flak for certain!

antialias_physorgThis statement is technically true...because Uncertainty can't be violated (just like any other physical principle)

Whart1984TorbjornLarssonIn general, in the weak field approximation they work in, a superposition of mass would be expected for the (approximate) quantum field theory of (linearized) general relativity, at a guess.

@What1984: Those references (at least the first one) are making aap's point.

State squeezing does not violate uncertainty principles, which is why the first link is titled that scientists "evade" it because it is still the operating constraint. Also, this is many years old physics I think, it was curious to first read about it but also "ah, so this is how uncertainty works (in this case)".

Whart1984Captain Stumpy1- just because you don't know what *is* being researched doesn't mean you know what is not being researched

2- strawman built on a false claim

3- your "illustration" doesn't support your strawman (See #1)

4- just because you can't get your pseudoscience legitimized because it's debunked ( https://www.natur...omms9174 ) doesn't mean mainstream science doesn't investigate or research legitimate science

5- your arguments for debunked pseudoscience is like going to a physics convention and asking why they don't validate the bible as legitimate science because of the Ark model build by Hamm as it's obviously built and it doesn't leak when it rains

Bugsbunny67Da Schneibsavvys84Oh really? GRT is bollox

Captain SkipThis actually is another situation that proves that GRT is a bad sequel. The gravitational constant and the so called curvature of space-time is utter bunk.

Long Live Hubble

knowphiself:. what is the relationship to the blackbody effect and time?

Pt_ of InterestI believe that one would be very hard pressed to explain the success of at least the 7-BIT Caltech quantum computer experiment in 2004 without it, among other things. It would be like saying that the digits on your calculator were stuck at a certain random digits whenever you turned on your calculator, only pressing the equal sign sent power to them, so that those states would be revealed. However, they "just happened" to be the answer to the arithmetic problem you keyed in. -- Not very likely...

Pt_ of InterestOff-hand, pit would seem that the greater mass possibility will win and as there is no interaction with spacetime prior to the onset of collapse, the mass of the quantum particle will at least generally be equal to that of the largest possible mass.

savvys84Quite right there, mate

Whart1984Whart1984Whart1984Whart1984Whart1984savvys84thats kind of nutty for sure

humyPLEASE Explain to us in your own words exactly what YOU personally think "dense aether mode" IS.

Please provide us with a (ANY) specific weblink explaining what IS "dense aether mode" and also provide us with a (ANY) specific weblink (the same one or any different one will do) that also explains how it relates to relativity in the way YOU think it does....

If you only just try and do this (shouldn't be difficult if what you say isn't bull****), I believe you might learn something new.

Whart1984Whart1984humyWhy do you want me to suddenly waste my time and change the subject completely to something totally irrelevant to what you were saying ("dense aether mode")?

OBVIOUSLY, its because you have absolutely NO IDEA what you mean by "dense aether mode". Why else? You are obviously just being evasive and you fool nobody here.

Your two links don't even merely mention "aether" let alone "dense aether mode"; which confirms you don't know what you are talking about.

+ the "dense aether mode", whatever that is supposed to mean, clearly is NOT a "widespread concept and trend in contemporary physics". It is just some CRAP you made up.

humyBut, no matter, it is still just some made up CRAP either way.

Captain Stumpyyep

and a word of caution: do not, under any circumstances, go to any reddit link he sends with "AWT" in the link

I would also suggest not going to any shortened link

the "journal" links he may provide are his attempts to link the pseudoscience with a credible science because he actually believes that his aether model is legit and can be justified by comparing his beliefs he states with the science

granville583762with this einsteinion fact it is known a mass falling 1metre and 1m+1femyo-metre can be calculated with the same accuracy as can a mass falling 1 femto-metre be calculate with Newton's law of gravity, as the quantum world starts at 1nano-metre Einstein's equivalence principle holds at any dimension

Mimath224I am not AWT supporter but I do purchase books on alternative theories just to see for myself why this & that. Buying several Aether model books among them two by Steven Rado. In one (kinematics) he talks of the finding the Aether density (via Aetherons) and later gives a 'bulk modulus'. This, or something like it, is probably the origin of the term 'dense Aether Model' Just a thought, that's all.

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