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.

Asking the impossible.

The Big Bang is often described as the beginning of everything, of space, time, matter,

and energy, is the cosmic drumbeat that launched the universe we see today.

Yet even as we trace the galaxies racing apart, the background radiation still humming from those

early moments, and the abundance of hydrogen and helium forged in the fires of the first seconds,

a deeper question lingers. What came before? At first glance, it seems like a natural question,

as intuitive as asking what lies beyond the horizon or what

happened yesterday, but with the Big Bang, we quickly run into a problem. Time itself is thought to

have begun with that event. There was no yesterday, no earlier moment ticking away. There may

have been no ticking at all. Space and time are inseparable,

at least in this universe, package pair, and asking what's before this universe, much like asking

what's outside the universe, gets problematic and non-intuitive. In fact, the answer to both

might be nothing. To ask what came before the Big Bang might be like asking what's north of the North Pole,

a question that solves not because the answer is hidden from us, but because it has no

meaning within the framework we understand.

You can still go further up, or sideways, rising off the planet, but that's not further north,

just up. And similarly, you know if there's more beyond or before this universe, it might be that

time and space do not apply, same as left or right, don't mean anything in the context of planetary

...