Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and add free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

This episode is sponsored by Brilliant.

Joffrey Chaucer said that all good things must come to an end, but this channel is not

the place for that kind of pessimism.

So today we'll be discussing ways we might postpone the heat death of the universe, and possibly even delay it entirely.

To do that we must first discuss what the heat death is and why we think it's going to happen.

The best place to begin is to note that there's a bit of a difference between what we

normally think of as heat and what the term means in physics.

Heat to us, in a casual and day-to-day sense, is how warm it is, but in a physics and

thermodynamics sense, it refers more to how entropic a system is, essentially what portion

of its total energy is heat energy.

Heat is a random motion of particles and we can only get work done using such a system

if it's got other energy still stored in it in other ways or if we connect it to something

colder.

As an example, the sun is very hot so we can easily get work done off it by connecting to something colder. As an example, the sun is very hot, so we can easily

get work done off it by connecting to something cooler, which we obviously have plenty of

choices for. It is making that heat by converting hydrogen into helium, photons, and neutrinos,

converting mass energy into heat energy in the process. A system is at maximum entropy when all those

options have been used up and everything is converted to heat that can be, hence heat death.

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