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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.
Yes. The smallest unit of time is called Planck time. Its sort of the frame rate of reality.
It would open up the possibility of observing the effects of quantization of gravitational interaction in the low field limit. Up to now, no one has observed any quantization of gravity. This is a really tiny effect, so you might argue that you don't care, but it would be a small clue in the big mystery of how to reconcile quantum mechanics and general relativity. In the history of physics, this has happened before. We had quantum mechanics in the 1920s through 1940s, but we didn't know how to quantize the electromagnetic field. We simply used classical interactions between charged particles and quantized their motion since we didn't know how to quantize the electromagnetic fields themselves. Then in the late 1940s and early 1950s, Schwinger, Feynman, and Tomonaga figured out how to quantize the electric and magnetic fields. It made only tiny changes in the predictions of quantum mechanics for atoms, but it has turned out to be critical to modern precision measurement and definition of the units we use. Their Quantum Electrodynamics has proved to be one of the great triumphs of theoretical physics.
Now quantization of gravity is a much much smaller effect in conditions that we can study on earth. This proposes that we might be able to observe some effects. Unfortunately, in this low field limit, I think most physicists expect that perturbative methods will give the right answer. In this case, the experiments will not be much help in building a self-consistent quantum gravity theory because perturbative methods are known to fail in the high field regime where the inconsistency between quantum mechanics and general relativity becomes important. But we definitely should make these measurements to see if the effects can be observed. Precision measurements often yield new insights, often unexpected ones.
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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