[sillysaurus3]

Another explanation, possibly unrelated to the slides:

It's hubris to (a) know the universe is probably infinite and (b) assume that life evolved anywhere within our slice of it.

Infinite! The universe seems to be infinite. If that's true, it seems just as likely that all intelligent life in the universe is completely alone.

[smilliken]

Consensus in physics is that the universe is finite[1]. Even if it weren't finite, it's likely still a moot question because the speed of light will inhibit us from every seeing outside a finite radius.

[1] https://en.m.wikipedia.org/wiki/Observable_universe

[sillysaurus3]

That's likely our observable portion of the infinite universe. It doesn't mean the universe is finite.

[oceanswave]

If your definition of infinite is also includes that the portion of the universe that actually has energy in it is 1/∞ then sure