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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 vapour 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
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