Good day fellow members. I wanted to take this opportunity to discuss something that I have recently taken a great interest in. Like all interesting
topics, I happened upon this one by pure coincidence. Since then, however, I have devoted much time to researching this topic, and would like to spark
some discussion with you here on this. The topic I ran across was that of entropy; or as it’s also referred to here, heat death of the universe.
The “heat death” is one of many possible final states of the universe. In this scenario, the universe has run down to a state of no free energy.
This makes it impossible to sustain motion or life.
The idea of heat death stems from the second law of thermodynamics, which states that entropy tends to increase in an isolated system. Therefore, if
the universe lasts for a sufficient time, it will asymptotically approach a state where all energy is evenly distributed. (1)
In a heat death, the temperature of the entire universe would be extremely close to absolute zero. Heath death is, however, not the same as “cold
death” or the “Big Freeze”, in which the universe simply becomes too cold to sustain life due to continued expansion, though the result is
Inflationary cosmology suggests that in the early universe, before cosmic expansion, energy was uniformly distributed (2), and thus the universe was
in a state similar to heat death. However, the two states are in fact very different: in the early universe, gravity was a very important force, and
in a gravitational system, if energy is uniformly distributed, entropy is quite low, compared to a state in which most matter has collapsed into black
holes. Thus, such a state is not in thermal equilibrium, and in fact there is no thermal equilibrium for such a system, as it is thermodynamically
unstable. However, in the heat death scenario, the energy density is so low that the system can be thought of as non-gravitational, such that a state
in which energy is uniformly distributed is a thermal equilibrium state, i.e., the state of maximal entropy.
The final state of the universe depends on the assumptions made about its ultimate fate, and these assumptions have varied considerably over the late
20th century and early 21st century. In a "closed" universe that undergoes recollapse, a heat death is expected to occur, with the universe
approaching arbitrarily high temperature and maximal entropy as the end of the collapse approaches. In an "open" or "flat" universe that continues
expanding indefinitely, a heat death is also expected to occur, with the universe cooling to approach absolute zero temperature and approaching a
state of maximal entropy over a very long time period. There is dispute over whether or not an expanding universe can approach maximal entropy; it has
been proposed that in an expanding universe, the value of maximum entropy increases faster than the universe gains entropy, causing the universe to
move progressively farther away from heat death. Finally, some models of dark energy cause the universe to expand in ways that result in some amount
of usable energy always being available, preventing the universe from ever reaching a state of maximum entropy. The expectation of the scientific
community as of 2007 is that the universe will continue expanding indefinitely.
I’d like to get your thoughts on this and whether or not you think this is a realistic fate for our universe or not. Any comments welcome.
(2) An introduction to cosmological inflation (arxiv.org...