Using experimental "traps" based on magnetic fields and laser beams like that shown in the above image, scientists have created clouds of atoms suspended in space with temperatures less than 0.1 nanokelvin (10-10 K), extremely close to absolute zero. These temperatures are far far colder than outer space, which is a relatively toasty 3 millikelvin (3×10-3 K) because of the cosmic microwave background radiation (another topic we will discuss during the semester), a remnant of the Big Bang that occurred 14 billion years ago. Scientists using these innovative traps have made remarkable discoveries of new states of matter at ultra-low temperatures, including Bose-Einstein condensates (which we will discuss in the course) and strongly interacting systems of fermions.
As to the question of
the hottest
possible temperature: you will learn in Physics 363
that temperatures for magnetic spin systems can be negative
which implies that such a spin system is hotter than any
system with a positive temperature (heat will always flow
from a negative temperature system to a positive temperature
system). If you feel magnetic spins are "cheating" (you
can't disintegrate some object by bringing it in touch with
a negative temperature system), then physicists believe that
the largest possible positive temperature is likely the
Planck temperature TP, which is obtained
by combining four of the fundamental constants of
nature: TP = ( h c5
/ (G k2) )1/2 ≅
1032 K where h is Planck's constant
fundamental to quantum mechanics, c is the speed of
light, G is the universal gravitational constant
associated with Newton's universal law of gravity,
and k is Boltzmann's constant, of central
importance to thermal physics. At such immense temperatures,
which presumably occurred at the earliest moment of the Big
Bang, massive particles move ultrarelativistically and
collisions between such particles lead to the creation of
matter, antimatter, and even tiny black holes that distort
local space-time in a complicated mess that currently lies
beyond what the known laws of physics can handle. Advances
in string
theory and in other efforts to unify gravity with
quantum mechanics may possibly resolve the question of
whether there is a largest temperature and what is its
value.