B Test of the Universality of Free Fall with Atoms

[fresh_42]

I have found an article about an experiment that states that gravity on a small scale doesn't experience quantum effects. Of course the headline has been catchy, so I want to ask about the real importance or relevance of the experiment.

Or for short: Do the results imply any consequences on GUT's.

We report a test of the universality of free fall by comparing the gravity acceleration of the Rb87 atoms in mF=+1 versus those in mF=−1, of which the corresponding spin orientations are opposite. A Mach-Zehnder-type atom interferometer is exploited to alternately measure the free fall acceleration of the atoms in these two magnetic sublevels, and the resultant Eötvös ratio is ηS=(0.2±1.2)×10−7. This also gives an upper limit of 5.4×10−6m−2 for a possible gradient field of the spacetime torsion. The interferometer using atoms in mF=±1 is highly sensitive to the magnetic field inhomogeneity. A double differential measurement method is developed to alleviate the inhomogeneity influence, of which the effectiveness is validated by a magnetic field modulating experiment.

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.023001

 

[mfb]

I have found an article about an experiment that states that gravity on a small scale doesn't experience quantum effects.

That is a misleading description.

The experiment shows that the spin of rubidium atoms does not influence the gravitational acceleration (within the experimental uncertainty, as always). It would have been really weird if it would.

Gravitational fields quantize energy states of particles, this has been demonstrated with neutrons. The gravitational field has the same role as electrostatic fields for experiments with electrons or protons.
Here is an example

 

[ohwilleke]

As far as I know, gravity has only been experimentally tested against predictions of GR at scales as small as about 10^-6 meters (about 1,000 million atomic radii long), where one might expect classical behavior, even if quantum gravity effects are real, because this is far larger than the atomic scale of around 10^-15 meters.