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Is absloute zero possible?
If it is does that mean that there is a highest possible tempature?
Also what is the lowest tempature ever reached so far?
No, absolute zero temperature can be approached but never reached. The
reason is that the efficiency of refrigerators goes to zero as the
temperature goes to zero, so even the tiniest heat leak could not be
There is no known highest temperature. However at sufficiently high
T, it is very unlikely that the laws of physics would resemble the ones
that we are used to. In the hot period very shortly after the Big Bang,
the basic interactions looked a lot different than they do now. At
temperatures above around 10^33 K, it's likely that the whole familiar
structure of spacetime would not persist. Maybe you could take that as
an upper limit.
As for the lowest T reacched to date, see:
(republished on 07/27/06)
Follow-up on this answer.