Entropy is the measure of how chaotic a system is analogous to a box containing many dices, the dices can be stacked properly together forming a cuboidal structure or scattered everywhere even outside of the box.

Still with me ok I am wondering what happen if I (Maxwell's demon) were to flip the arrow in the 2nd law of thermodynamics so that in layman wording heat always flow spontaneously from COLDER to a HOTTER body... I am wondering for such a universe assuming the conservation of energy still hold so how would the mechanical machine works?

P.S: there is no reason why entropy works the way it is so let's have some fun ;D

  • $\begingroup$ Kinetic Energy tends to zero, potential energy is maximised, the universe stops expanding instantly after the Big Bang, the entire mass of the universe at absolute zero at one point in space $\endgroup$
    – nzaman
    Jan 28, 2021 at 8:09

3 Answers 3


Literally Nothing

In a universe where entropy decreased over time, the "big bang" would never take place. The state of the universe at that instant is one of minimum entropy, with all matter and energy concentrated in a single location. If entropy could only decrease or remain constant from there, no change would be possible.


It would be as if time flows backwards

Many scientists think that entropy alone is the only reason why there is an Arrow of Time. In actual fact, this distinguishing feature is the only reason why everything acts the way it does in our seemingly pure time-symmetric universe.

So reversing it might just make everything look like it moves backwards.

Of course, reversing it also moves the arrow of time rearward, which would then go back to a time that was not reversed, and thus time would be re-reversed so it would go forward again. Therefore, one could argue you can't actually reverse entropy at all.


Chain of big bangs, over and over. Strobe light universe

If energy flows from cold to hot along a medium, itd also probably remain true that the flow rate increases the greater the difference in temperatures.

After the big bang, when the laws of physics kick in n milliseconds after the explosion, there will be a temperature gradient in the densely packed matter of the universe, probably hotter in the centre of a sphere, cooler on the outer.

Heat would start to flow towards the hot side, increasing the energy towards infinity. Eventually whatever happens is beyond our understanding of physics - which only started applying a few milliseconds before - but my best guess is everything explodes again in a second big bang.

And over and over.

  • $\begingroup$ Everything exploding is not going to reduce entropy $\endgroup$
    – Slarty
    Jan 28, 2021 at 13:12

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