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We know that our universe was in low entropy state at the earlier time after the Big bang. But we also know that the temperature at that times was enormously high. But what the third law of thermodynamic says ? It says that if $T$ goes to zero, entropy of the system also goes to zero, which is not the case for the universe at the very beginning.

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    $\begingroup$ If I may ask a question... how did we measure the entropy of the universe after the big bang? Can you point me to an experimental paper that does that? $\endgroup$
    – CuriousOne
    Sep 6 '15 at 10:56
  • $\begingroup$ CuriousOne, we can not measure the entropy of universe after the big bang but we can deduce that as we know that the entropy is increasing in forward direction in time, hence it must had been in low entropy state in backward in time. $\endgroup$ Sep 7 '15 at 5:48
  • $\begingroup$ Also i have seen all the answers but i didn't get my answer. Everybody wrote how entropy is increasing but nobody wrote about third law of thermodynamics.. $\endgroup$ Sep 7 '15 at 5:51
  • $\begingroup$ Early universe consisted of particles whose energies were like energies of cannonballs. If we see a pile of cannonballs, we say "there is some solid state matter there". Do you get the idea? Universe changed from solid state to its current state. $\endgroup$
    – stuffu
    Sep 7 '15 at 11:45