Re: to cold?

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Subject: Re: to cold?
Name: Hugh
Date: 12/10/2004 1:08:11 PM (GMT-7)
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In Reply to: Re: to cold? posted by Bob

There all sorts of ways to get states of matter with zero electrical resistance. As you mentioned, at low temperatures, many materials become superconducting. Also, in special circumstances, even non-superconductors can have states with zero electrical resistance, such as the quantum hall effect: when a pancake of electrons is cooled to a few mK, for certain values of a really strong magnetic field there is no resistance for current flow along a special axis. However, you could never use these systems to build a perpetual motion machine because you have to expend a lot of energy to maintain the special circumstances that made them have dissipationless electrical transport (such as creating a strong magnetic field, or keeping the thing cold).

I'm not saying that it's impossible to have a perpetual motion machine (people did believe at one time that the earth was flat!), but just that current it's extremely unlikely. One of the fundamental theorems of thermodynamics states that (and you can rigourously prove this) the maximum efficiency of an engine is 100%, and that this could only be achieved by using two thermal reservoirs where one of them is at absolute zero. Also using thermodynamics, you can prove that it's impossible to actually reach 0K. Accordingly, it's impossible to have a perfectly efficient engine, which is the requirement for a perpertual motion machine.

Who knows though, maybe in a 1000 years someone will find a loophole...

As for the blackholes slowing the aging of the stars, even if some stars were older than they appeared, I don't this wouldn't have any effect on the age of the universe (which is composed of many things other than stars). Morever, this time dilation due to large gravitational fields at the center of the galaxies wouldn't be very important unless the stars were REALLY close to the black holes (as in within the event horizon), and we wouldn't be able to see these stars anyway...

BTW, doesn't the prefix giga refer to a billion (10^9) so that 13.2 billion years ~ 15 giga years?

Whoa, I gotta stop ranting. Sorry!

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