Adam Brown — Bubble universes, space elevators, & AdS/CFT

You could imagine our descendants deciding that they're not gonna just suffer the heat death, that they're gonna try and trigger a vacuum decay event to another vacuum with a lower cosmological constant. If it is possible for people just to wipe out their entire future light cone, libertarian fantasies can't really happen. Is it possible that 50% of all of the nuclear weapons ever dropped in combat were in fact dropped against direct orders? Take an exam I gave years ago in my graduate general activity class at Stanford, and give it to these models. Three years ago, zero. A year ago, a weak student. And now they essentially ace the test. These are the two most beautiful theories of 20th century physics. These two theories seem to be inconsistent with each other. There is, however, one fact about that merger that we are most confident about, and the answer to that involves black holes.

Today, I'm chatting with Adam Brown, who is a founder and lead of the Blue Chip team, which is cracking mass and reasoning at Google DeepMind, and a theoretical physicist at Stanford. Adam, welcome.

Delighted to be here. Let's do this.

Okay. We'll talk about AI in a second, but first, let's talk about physics.

Okay.

Um, first question, what is gonna be the ultimate fate of the universe and, h- how, you know, how much confidence should we have?

The ultimate fate is a really long time in the future, so you sh- probably shouldn't be that confident about the answer to that question.

Uh-huh.

Uh, in fact, our idea of the answer to what the ultimate fate is has changed a lot, uh, in the last 100 years. Ab- about 100 years ago, we thought that the universe was just static, wasn't growing or shrinking, was just sitting there statically. And then in the late '20s, Hubble and friends looked up at massive telescopes in the sky and noticed that distant galaxies were moving away from us and the universe is expanding. So, that's like big discovery number one. There was then, you know, a learned debate for many years about, you know, the universe is expanding, but is it expanding sufficiently slowly that it'll then recollapse in a big crunch, like a time reverse of the Big Bang, and that'll, that'll be super bad for us? Or is it gonna keep expanding forever, but just sort of ever more slowly, uh, as, as, you know, gravity pulls it back, but it, it keeps... it's fast enough that it keeps expanding? And there was a big debate around this question, and it turns out the answer to that question is, is neither. Neither of them is correct. In possibly the worst day in human history, sometime in the 1990s, we discovered that, in fact, not only is the universe expanding, it's expanding faster and faster and faster. It's what we call dark energy, or the cosmological constant is this, uh, you know, just a word for uncertainty, is making the universe expand, uh, at an ever faster rate, accelerated expansion, uh, as the universe grows. So, that's, that's a radical change in our understanding of the, the fate of the universe, and if true, is super-duper bad news.