eli5 What is entropy and what are its biggest implications?
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Geez, there’s LOTS of ways to approach this. But at a fundamental level, entropy is the tendency for everything to become “disordered” if no energy is put toward maintaining order. Take a living human body for example – it is a highly ordered and complex system, with lots of very specific detailed parts doing very specific detailed things constantly in order to keep the living human body intact and living. This takes a huge amount of energy, which is why we need to eat often. When that person dies, the human body becomes less and less complex and less and less ordered. Pretty quickly, all the specific parts that used to do specific things stop doing much of anything and start to degrade. Formerly highly ordered complex molecules break down and with no repair system in place, they just degrade and degrade and degrade until the body is more or less a goopy mush with not much happening. Over longer time scales, the formerly highly ordered complex molecules break down into smaller and smaller constituents, and there is no order to what is left or how it’s “used.” It’s just a pile of elements and less complex molecules.
Another example is a skyscraper with lots of people inside, functioning utilities and waste removal, a cleaning and repair crew, etc. Lots of energy expended keeping the building functioning. Once it’s emptied and abandoned, utilities shut off, no longer maintained or repaired, it inexorably falls into a state of disrepair and disorder. Given enough time, what was once a hundred stories of glass, stone and steel arranged just so, becomes a steel skeleton jutting out from a pile of rubble. Given even more time, the steel rusts away and eventually, there’s hardly any structure or order left.
Essentially, everything tends toward disorder, and the only way to stop any particular thing from breaking down into a disordered heap is to expend energy maintaining its order. The kicker is that the energy has to come from somewhere, and the process of obtaining and using that energy unavoidably creates more disorder than the order preserved in the thing you’re working to keep ordered.
The implications are that the universe itself will tend to disorder more and more and more, and unless there’s a way to obtain energy from outside the universe or more energy simply comes into existence in ways we don’t understand (and don’t think possible), the inevitable result will be a completely disordered universe with no structure or complexity of any kind. Just endless nothingness where nothing ever happens, forever and ever and ever.
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