Hello, SFIA audio listeners. In this month's Nebula exclusive, Big Alien Theory,

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

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

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

Could we see a second Big Bang?

In the beginning, and we really do mean the very beginning, probably, there was the Big Bang.

But was it a one-time event, or could the universe be setting the stage for an encore?

At the end of July, we'll be taking a look

at the epochs of the universe and spending a fair amount of time dwelling on those first moments

after the Big Bang. I tend to feel like they often get skipped over. We also have our civilizations

at the end of time series that looks at all the ways life might try to persist in a dying universe

or escape,

depending on the in-time scenario, heat death, big rip, big crunch, conformal secret cosmology,

and so on. Yet as fascinating as the end of everything is, it is only half the story. Every

ending implies a beginning, and before we speculate about what might lie at the

last tick of the cosmic clock, it's also worth asking how the clock got wound up in the first

place, and whether it could be round again. We haven't spent much time talking about theories of how

the universe came to be, and there's a lot of them, enough that

today will be sticking strictly to Big Bang scenarios and saving alternatives for another

day.

They are four critical questions that always come up when discussing the Big Bang.

First is why it happened.

...