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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.
Physicists are quantized, so they want everything else to be quantized.
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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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Even if mass would be quantized, the Newtonian equation is m1m2/r^2. Even with discrete mass quanta (which is also false, see other replies), you would get a continuous spectrum of resulting forces. Inserting relativity here changes the expressions, but it would really just muddle things. So, no, there is no specific reason to believe gravity to be quantized - outside of an actual theory of quantum gravity.
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.
Does Time come in quanta?
Nope. Cubes.
Faster! Faster! Faster would be better!
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.
Same thing with all of my computers and browsers. Ohh wait... I just went to their home page, forbes.com, then clicked on the link in /. and it suddenly worked. Probably a broken cookie or something.
So... a fraction of a Kelvin then.
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There is a huge difference between something being smaller than any single event and it being quantized by that amount. Even if you can't find an event quicker than that, it is possible time is continuous in such a way that the spacing between events is not an integer number of Planck time. In fact, there isn't really anything in quantum mechanics that says that time behaves that way at all, unless you want to tack on additional hypotheses (and it makes a mess of things).
The Planck units are just multiplying fundamental constants together so that you get some value with the right units, and the significance of that is not necessarily quantization, but limits where extreme gravity and quantum mechanics would be present in the same setup. This either means we can speculate that such situations would require an understanding of quantum gravity, or would do something based on GR instead of quantum mechanics. The Planck mass is nothing extremely large or small for example, at a couple nanograms, although could be the largest mass a point particle can have before being a black hole (with some speculation).
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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This post is a good example of what happens when someone thinks the current model is absolutely true. The map is the territory!
The current model will be wrong in ways that are consistent with existing observations. That doesn't leave room for a "graph-paper universe", nor for energy densities above which a black hole forms.
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It's not a matter of not having a small enough ruler. The problem is that there can be no measurement smaller. There can be no way to infer anything smaller. It's the absolute smallest.