We know about some events that happen very quickly. For example, the dielectric relaxation time is about $10^{-14}\, \mathrm{seconds}$.
I'm interested in other processes that switch extremely fast or or could be use as a very short tick in a clock.
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2 Answers
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The fastest fully localized process is the evaporation of the smallest black hole worth the time - it takes one Planck time or so, $10^{-43}$ seconds. There are other characteristic processes in quantum gravity that take a Planck time - the shortest time scale for which the usual spacetime geometry works.
However, if you allow changes in collective properties of large objects, there are much shorter times. For example, the mass of the visible Universe is $3\times 10^{52}$ kilograms or so. The corresponding energy, via $E=mc^2$, is $10^{61}$ Joules. The periodicity of the corresponding quantum wave, via $E=\hbar\omega$, is about $10^{-95}$ seconds. So the wave function of the Universe periodically changes its phase $10^{95}$ times every second.
I guess that you mean local processes, and moreover some processes accessible experimentally. That's a question with no permanent answer. The whole field of particle physics may be classified according to the time scale we can resolve. The time scale you mention is that of atomic physics; the time scales in nuclear physics are up to 10 orders of magnitude shorter, $10^{-24}$ seconds or so. The LHC is probing time scales that are 4 orders of magnitude shorter than that. In principle, this progress could continue. The "higher energy" we have, the shorter times (and distances) we may resolve.
answered May 5, 2011 at 17:05
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$\begingroup$ If a microblackhole is so unstable, it can hardly be created then. $\endgroup$ Commented May 5, 2011 at 17:54
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1$\begingroup$ Aren't decoherence times of macroscopic objects typically much shorter than the Planck time? $\endgroup$– dbraneCommented May 5, 2011 at 18:55
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$\begingroup$ The mass of the Universe does not belong to one particle! Similarly the mass of a macroscopic body does not belong to any particle so it is useless in your example. $\endgroup$ Commented May 5, 2011 at 22:09
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3$\begingroup$ @Vladimir something doesn't have to be a single particle to have a quantum wave. In fact, people have observed de Broglie interference of C60: nature.com/nature/journal/v401/n6754/abs/401680a0.html $\endgroup$ Commented May 6, 2011 at 16:36
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$\begingroup$ @Spencer Nelson You are right but this something should be in a quantum state which is not so easy to achieve for macroscopic bodies. The larger body, the harder to prepare a quantum state. $\endgroup$ Commented May 6, 2011 at 16:45
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a photon traveling a planck length.
answered May 6, 2011 at 16:22
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6$\begingroup$ What about a photon traveling half a Planck length? $\endgroup$– FabianCommented May 6, 2011 at 19:59
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1$\begingroup$ At this rate it will end up covering an infinite number of half distances! $\endgroup$ Commented Sep 5, 2011 at 21:55
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2$\begingroup$ hmm, I'm being a planck here, I think $\endgroup$ Commented Sep 7, 2011 at 13:57