From: baez@galaxy.ucr.edu (John Baez) Subject: Re: particles in an accelerated frame Date: 5 May 2000 16:58:04 GMT Newsgroups: sci.physics.research Summary: [missing] In article <3907BDE1.6000105@novell.uidaho.edu>, Jay Olson wrote: >I heard a nasty rumor a while back that observers in accelerated frames >of reference can "see" particles that aren't observed in an inertial >frame of reference. I was told these particles have a thermal spectrum. >Is there any truth to this? This effect, called Unruh radiation, has not been observed. However, the calculations which predict it are rock-solid, and make use of only ordinary quantum field theory. The predicted effect is very small: an observer accelerating at one centimeter per second squared would see blackbody radiation with a temperature of 4 x 10^{-23} Kelvin. So we wouldn't yet have seen it yet even if it exists. >It sorta makes sense when I think about >Hawking radiation, since the frame of reference that is fixed with >respect to the event horizon is accelerated (when sufficiently close to >the horizon). You're right that Unruh radiation and Hawking radiation are closely related. In fact Unruh discovered this effect when trying to better understand Hawking radiation. >If true, how does this thing work? The decomposition of field operators into annihilation and creation operators is not preserved by arbitrary coordinate transformations, and the number operator is defined using annihilation and creation operators, so an accelerating observer will have a different notion of how many particles happen to be around - what the unaccelerated folks see as a the vacuum, the accelerated observer will see as blackbody radiation. There are other ways to think about this, too. >Do the field operators somehow couple to the curvature? There ain't no curvature in Minkowski spacetime. Yet this Unruh radiation is predicted to be seen by an accelerating observer in Minkowski spacetime. So curvature is not really the crux of the problem! It's the definition of annihilation and creation operators that's the problem.