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Response to n2doc (Original post)

Sat Jun 8, 2013, 05:34 PM

2. A paper from 2011 disagrees that the size of quantum graininess can be the Planck length.

The article referenced in the OP says:

The Planck length turns out to be a very short distance: about 10[sup]-35[/sup] meters. It is a hundred million trillion times smaller than the diameter of a proton—too small to measure and, arguably, too small to ever be measured.


There is another important aspect of the Planck length. Relativity predicts that distances as measured by an observer in a fast-moving reference frame shrink—the so-called Lorentz contraction. But the Planck length is special—it’s the only length that can be derived from the constants c, G, and h without adding some arbitrary constant—so it may retain the same value in all reference frames, not subject to any Lorentz contraction. But the Planck length is derived from universal constants, so it must have the same value in all reference frames; it can’t change according to a Lorentz contraction. This implies that relativity theory does not apply at this size scale. We need some new scientific explanation for this phenomenon, and stochastic space-time might provide it. The idea that the Planck length cannot be shortened by the Lorentz contraction suggests that it is a fundamental quantum, or unit, of length. As a result, volumes with dimensions smaller than the Planck length arguably don’t exist. The Planck length then, is a highly likely candidate for the size of a space-time “grain,” the smallest possible piece of space-time.

A description of the 2011 paper says:

Einstein’s General Theory of Relativity describes the properties of gravity and assumes that space is a smooth, continuous fabric. Yet quantum theory suggests that space should be grainy at the smallest scales, like sand on a beach.


Some theories suggest that the quantum nature of space should manifest itself at the ‘Planck scale’: the minuscule 10[sup]-35[/sup] of a metre, where a millimetre is 10[sup]-3[/sup] m.

However, Integral’s observations are about 10 000 times more accurate than any previous and show that any quantum graininess must be at a level of 10[sup]-48[/sup] m or smaller.

“This is a very important result in fundamental physics and will rule out some string theories and quantum loop gravity theories,” says Dr Laurent.

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