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.

We'll get started in just a moment, but go ahead and start getting your questions in the chat

window so our moderators can start relaying those to me as soon as we start.

Please try to keep the questions concise and watch your spelling and try to be polite to others

in the chat.

We usually go for about an hour, so you probably want to grab a drink and a snack, though

we'll take a break about halfway through too.

With all that said, welcome and let's get started.

Good afternoon everybody and welcome to our live stream Q&A for April 2022.

This occasion happens to commemorate the second year of my wife actually

being our wonderful co-host for this thing. Here she is. Hi. As non-concernidentally, this is also

a second anniversary. So while I normally say afterwards that I will be taking comments that you

put in the questions of being them next day, you're welcome to put questions in the comments if we don't get to them today, but they'll probably be a couple

days before it gets them because we'll pretty much leave the live stream and going straight

on vacation for a couple of days. So with all that said, let's go ahead and get to your questions.

All right. Well, our first question is from Igor Briskin, and he wants to know if besides nuclear steam rocket engines,

what other options exist to travel the solar system quickly, like the new expanse?

I think the big problem in terms of trying to do anything with fusion that we have right now

is, of course, we don't actually have fusion yet, so we can't really say what's going to work

...