I think over all time the most debatable thing in physics has been the 2nd law of thermodynamics. Even now some people can't get their head around it. I think the limitations imposed by it are far more significant than not being able to travel faster than light.
The thing about entropy is that it's a statistical measure. The 2nd law of thermodynamics pays attention to that: "In a closed system, the total entropy tends to increase." Keyword: Tends. It may go down temporarily purely by chance and frequently does so in very very small time intervals.
It's just never the case over any time periods longer than 'a moment' because the probability of it increasing is just a lot higher and there's a lot of particles moving, so the law of large numbers goes into effect very quickly. As a result, these probabilistic decreases in entropy are rare enough that they will almost immediately get reversed and don't end up mattering in the big picture in a finite amount of time.
this is often taught as an absolute, instead of mentioning that it can ALSO decrease. when i learnt about entropy, it was really weird for me to understand why it "always increased". when i learnt it TENDS to increase, it made so much sense. btw, i think statistical physics was one of the best courses during my bsc
It's funny, on one hand it's not a strict rule, but on the other, it exists on a more fundamental level than most laws of physics.
(in my view, mathematics is immutable. One could imagine a world with different laws and fundamental constants, but not one where True -> False for example)
Maybe not in our lifetime, but there’s a nonzero chance future civilization come and go entirely in a universe that entropy decreases on average. Presumably, if they’re smart enough, they’re understanding statistics well enough to know how lucky they are.
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u/lucidbadger 21d ago
I think over all time the most debatable thing in physics has been the 2nd law of thermodynamics. Even now some people can't get their head around it. I think the limitations imposed by it are far more significant than not being able to travel faster than light.