Question
What exactly is the heat death of the universe and
where can I find out more?
Asked by: Richard Hobbs
Answer
The 'heat-death' of the universe is when the universe
has reached a state of maximum entropy. This happens
when all available energy (such as from a hot source)
has moved to places of less energy (such as a colder source).
Once this has happened, no more work can be extracted from
the universe. Since heat ceases to flow, no more work can
be acquired from heat transfer. This same kind of
equilibrium state will also happen with all other forms
of energy (mechanical, electrical, etc.). Since no more
work can be extracted from the universe at that point, it
is effectively dead, especially for the purposes of humankind.
This concept is quite different from what is commonly referred
to as 'cold death.' 'Cold death' is when the universe continues
to expand forever. Because of this expansion, the universe
continues to cool down. Eventually, the universe will be
too cold to support any life, it will end in a whimper. The
opposite of 'cold death,' as you can see, is NOT 'heat death,'
but actually the 'big crunch.' The 'big crunch' occurs when
the universe has enough matter density to contract back on
itself, eventually shrinking to a point. This shrinking will
cause the temperature to rise, resulting in a very hot end of
the universe.
Discussions of the concept of 'heat death' can be found in
some thermodynamics textbooks. The ideas of 'cold death' and
the 'big crunch' can be found in textbooks on cosmology, such as
The Early Universe by Kolb and Turner. Or, if you prefer and less
technical discussion, you might want to try Black Holes and Time
Warps by Kip Thorne.
Answered by: Andreas Birkedal-Hansen, M.A., Physics Grad Student,
UC Berkeley
The heat death of the universe will only occur if the universe
will last for an infinite amount of time (i.e there will be no
big crunch).
It will occur because according to the second law of
thermodynamics, the amount of entropy in a system must always
increase. The amount of entropy in a system is a measure of how
disordered the system is - the higher the entropy, the more
disordered it is..
It is sometimes easier to imagine if you think of an experiment
on earth. A chemical reaction will only occur if it results in
an increase of entropy. Let us imagine burning petrol. We start
of with a liquid that contains atoms arranged in long chains -
fairly ordered. When we burn it, we create a lot of heat, as
well as water vapor and carbon dioxide. Both of these are small
gaseous molecules, so the amount of disorder of the atoms in
their molecules has increased, and the temp. of the surroundings
has also increased.
Now lets think what this means for the universe. Any reaction
that takes place will either result in the products becoming
less ordered, or heat being given off. This means at some time
far in the future, when all the possible reactions have taken
place, all that will be left is heat (i.e electromagnetic
radiation) and fundamental particles. No reactions will be
possible, because the universe will have reached its maximum
entropy. The only reactions that can take place will result
in a decrease of entropy, which is not possible, so in effect
the universe will have died.
I found that a good book on the subject is called 'The Last
Three Minutes' by Paul Davies. He describes how the universe
might die a heat death, and also argues that it may be possible
that a big crunch will occur instead.
Answered by: Sarah Al-Assam, Student at Tiffin Girls'
School, Kingston UK