Is entropy decreased in this scenario?
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When water freezes its entropy decreases. This does not violate the second law of thermodynamics. ... Entropy can decreasesomewhere, provided it increases somewhere else by at least as much. The entropy of a systemdecreases only when it interacts with some other system whoseentropy increases in the process.
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The mainstream answer is NO. Entropy can be reduced Locally (as evidenced by stars, planets and extremely complex ‘islands of very low entropy’ such as an Earth with an extraordinary Living biosphere).
But this small island of extremely low entropy has been made possible because Earth has been radiating a lot of heat away increasing the total entropy of the universe by more than the local entropy reduction.
There is, however, one aspect which still generates debate among scientists. What if the universe expansion came to a halt and the universe started contracting again? (in principle towards an unavoidable big crunch).
Many scientists argue that even in a contracting universe entropy would continue increasing and that the evolution towards the big crunch would be nothing like ‘the big bang evolution’ run in backwards motion.
Other however argue that the contraction would indeed be akin to running the expansion history the universe in reverse, so that entropy would start reducing, disordered states would assemble into more ordered ones, planetary systems might contract and fuse into a more primeval could of hydrogen, with heavy elements spontaneously fusing into lighter ones due to the increasing energy density and temperatures, and broken eggs might start reassembling into unbroken eggs and Time would effectively run backwards, until all the amazingly diverse universe we now have would return to a ball of scorching plasma (equivalent to the CMB time) and eventually keep contracting until a collapse in a big crunch of minimal entropy.
But this small island of extremely low entropy has been made possible because Earth has been radiating a lot of heat away increasing the total entropy of the universe by more than the local entropy reduction.
There is, however, one aspect which still generates debate among scientists. What if the universe expansion came to a halt and the universe started contracting again? (in principle towards an unavoidable big crunch).
Many scientists argue that even in a contracting universe entropy would continue increasing and that the evolution towards the big crunch would be nothing like ‘the big bang evolution’ run in backwards motion.
Other however argue that the contraction would indeed be akin to running the expansion history the universe in reverse, so that entropy would start reducing, disordered states would assemble into more ordered ones, planetary systems might contract and fuse into a more primeval could of hydrogen, with heavy elements spontaneously fusing into lighter ones due to the increasing energy density and temperatures, and broken eggs might start reassembling into unbroken eggs and Time would effectively run backwards, until all the amazingly diverse universe we now have would return to a ball of scorching plasma (equivalent to the CMB time) and eventually keep contracting until a collapse in a big crunch of minimal entropy.
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