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Until the 1960's the general consensus was that the universe is infinite years old (steady-state).

The second law of thermodynamics says that entropy always increases, so we'd expect that within a finite amount of time after "the beginning" the universe would be ultimately "white noise".

In other words, how could there be stars, planets or "things" if infinitely amount of years ago there universe would be totally chaotic?

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    $\begingroup$ I have the feeling that the second law of thermodynamics wasn't part of the general consensus pre-1960. $\endgroup$
    – oink
    Commented Jan 26, 2015 at 6:00
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    $\begingroup$ The creation of new matter (as was required in the steady-state model) would have increased entropy. Note also that, counterintuitively, galaxy formation also increases entropy. So I see no contradiction. $\endgroup$
    – lemon
    Commented Jan 26, 2015 at 9:33

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I would like to answer with the words of L.D. Landau, from his book Statistical Physics (first edition $1958$):

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The second law of thermodynamics says that entropy always increases

That is a common misconception. Second law of thermodynamics applies to thermodynamic systems and talks about changes of their equilibrium states only.

Universe is a very different system from systems dealt with in thermodynamics and is hardly in thermodynamic equilibrium.

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  • $\begingroup$ Yet, we talk about entropy of the universe today. $\endgroup$
    – Earth is a Spoon
    Commented Jan 26, 2015 at 8:26
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    $\begingroup$ We should talk less and think more. $\endgroup$
    – Ján Lalinský
    Commented Jan 26, 2015 at 18:19
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Thermodynamics says that entropy increases in a closed system.

The Steady State Theory claimed that the universe was not closed.

In 1929 Hubble showed that the universe is expanding. To explain how an expanding universe can be Steady State, they claimed that new matter was created continuously to keep the density constant.

This new matter would have very low entropy, thereby letting entropy have a Steady State too.

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