Sean Carroll
Let's conjure some science up in here. Science is good for the soul. Today: what are "quantum fluctuations," anyway? #qf
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The *macro*state of a system can be static (equilibrium), but stuff is churning beneath the surface. That allows Boltzmann fluctuations.
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Vacuum Fluctuations are the differences b/w quantum and classical states. Classically-definite observables can have a quantum variance. #qf
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Zero-point energy, virtual particles, the Lamb shift -- all due to vacuum fluctuations. But notice something important...
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Nothing actually "fluctuates" in vacuum fluctuations! The system can be perfectly static. Just that quantum states are more spread out.
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Measurement Fluctuations are the bridge b/w Boltzmann and Vacuum fluctuations. They occur when you repeatedly observe a quantum system.
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By itself, a system can be static, but observational outcomes are probabilistic. Observe over and over again, get different results.
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That makes us confuse (static) vacuum fluctuations with (dynamical) Boltzmann fluctuations. We think what we see is what really is.
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But quantum mechanics says that what really exists is very different from what we see. In an atom, electrons aren't fluctuating at all.
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All of which is crucial for understanding Boltzmann Brains. A topic for another day. For more see: http://arxiv.org/abs/1505.02780
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Worth pointing out that my discussion of quantum fluctuations betrays my Everettian (many-worlds) sympathies. Your mileage may vary.
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