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An Experiment Could Determine Whether Gravity Is Quantized (forbes.com)
TheAlexKnapp writes: Physicist Brian Koberlein explains an experimental proposal by Großardt et al, which would attempt to determine whether gravity is quantized. "Their idea," explains Koberlein, "is to take a charged disk of osmium with a mass of about a billionth of a gram and suspend it an electric field. This is small enough that its energy levels in the electric field would take on quantum behavior when cooled to temperatures a fraction of a Kelvin above absolute zero, but its also massive enough that its gravitational pull would affect the quantum behavior."
The two primary approaches to a quantum gravity, the "perturbative approach" and "the semi-classical method," predict different results from this type of interaction. So the results of the experiment, could, in principle, elucidate the right approach for developing future theories of quantum gravity.
The two primary approaches to a quantum gravity, the "perturbative approach" and "the semi-classical method," predict different results from this type of interaction. So the results of the experiment, could, in principle, elucidate the right approach for developing future theories of quantum gravity.
Proposed experiment: arXiv:1510.01696.
More detailed theory: arXiv:1510.01262.
See also blog post.
There's a good explanation by a physicist who thinks about experimental validation of quantum gravity here.
Just to be clear, Planck units have no physical significance. They're just a convenient way of doing physics calculations because when you use Planck units, you can treat some fundamental constants as equal to 1.
So Planck time isn't the frame rate of reality, it's just a really small unit that makes some calculations easier.
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Well, electron states being quantized has helped us to (truly) understand chemistry and create transistors as well as LEDs. By realizing that things are only allowed to make certain transitions under certain conditions, you can "cheat" and build up high-energy states that are far more stable than they really should be. I am not saying we would get macroscopic anti-gravity or a "Faraday cage for gravity", but this is kind of the space where we would get more specific explanations for how you might be able to accompish those things in theory. For very delicate experiments (similar to the one described!) and possibly sub-nanoscale manufacturing procedures, an understanding of a quantized nature of gravity influences might be useful, if only for better understanding the noise in measurements and tolerances.
So... a fraction of a Kelvin then.
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Just to be clear, Planck units have no physical significance
False. The Plank length is the smallest length that it could be possible to measure by any method. Classical ideas of size and distance likely fail many orders of magnitude above the Plank length, but it's certain that a distance or length shorter or more precise than Plank length is non-physical.
It's the smallest scale at which a metric (from which concepts like "distance" and "length" come) makes physical sense. And from relativity we know that the Plank time is the same - no concept of "duration" makes physical sense at finer granularity than Plank time.
The Plank mass is likely unimportant, however, unless those String theorists are actually right about something for once. Color me skeptical.
However, none of this should be taken as justifying a view that the universe has a "frame rate" or could be described in terms of voxels. We know from relativity that those ideas also make no physical sense. (Also, anything like that would have a grain that would be totally obvious. There's no "special" directions at right angles to one another, no preferred physical axes.)
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