Sean Carroll on Twitter: "All of which is crucial for understanding Boltzmann Brains. A topic for another day. For more see: https://t.co/Ge1uVqd6wR #qf"

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Sean Carroll ‏@seanmcarroll Jan 16

Talk about quantum fluctuations can be vague. There are really 3 different types of fluctuations: Boltzmann, Vacuum, & Measurement. #qf
17 retweets 28 likes
Sean Carroll ‏@seanmcarroll Jan 16

Boltzmann Fluctuations are basically classical: random motions of things lead to unlikely events, even in equilibrium. #qf
12 retweets 18 likes
Sean Carroll ‏@seanmcarroll Jan 16

The *macro*state of a system can be static (equilibrium), but stuff is churning beneath the surface. That allows Boltzmann fluctuations. #qf
9 retweets 15 likes
Sean Carroll ‏@seanmcarroll Jan 16

Vacuum Fluctuations are the differences b/w quantum and classical states. Classically-definite observables can have a quantum variance. #qf
8 retweets 12 likes
Sean Carroll ‏@seanmcarroll Jan 16

Zero-point energy, virtual particles, the Lamb shift -- all due to vacuum fluctuations. But notice something important... #qf
5 retweets 12 likes
Sean Carroll ‏@seanmcarroll Jan 16

Nothing actually "fluctuates" in vacuum fluctuations! The system can be perfectly static. Just that quantum states are more spread out. #qf
8 retweets 21 likes
Sean Carroll ‏@seanmcarroll Jan 16

Measurement Fluctuations are the bridge b/w Boltzmann and Vacuum fluctuations. They occur when you repeatedly observe a quantum system. #qf
4 retweets 15 likes
Sean Carroll ‏@seanmcarroll Jan 16

By itself, a system can be static, but observational outcomes are probabilistic. Observe over and over again, get different results. #qf
6 retweets 19 likes
Sean Carroll ‏@seanmcarroll Jan 16

That makes us confuse (static) vacuum fluctuations with (dynamical) Boltzmann fluctuations. We think what we see is what really is. #qf
5 retweets 15 likes
Sean Carroll ‏@seanmcarroll Jan 16

But quantum mechanics says that what really exists is very different from what we see. In an atom, electrons aren't fluctuating at all. #qf
15 retweets 18 likes