What if the universe had turned out differently? Fred Adams pioneered the concept of what if universes, calculating what would happen if you changed gravity, electromagnetism, or the strength of the nuclear force. Would stars still form? Could planets exist? Would atoms even exist? And ultimately the most important question of all. Would we be here even to ask such questions? His work matters to you because it explains why our universe seems so perfectly suited for life. And whether or not that's a lucky accident or maybe points to something deeper. It gives scientific weight to the idea of the multiverse as well. Not just science fiction, but as a serious cosmological possibility. It shows that the laws of nature aren't just arbitrary. They might be constrained in surprising, elegant ways.

Franz doesn't just study the universe. He studies all the universes that could have been, and that helps us understand why we're here at all.

The other kind of fine tuning would be if you take a parameter and you just vary its value by a little bit, then you get a universe or something that's very different. Both of those fundamentally rely on the idea that if you change the constants a little bit, the universe doesn't work. So I think again, back to what we said earlier. The first step in the chain is to ask the more fundamental question, the starting question. What range of parameters work?

Fred Adams, welcome. All the way from Michigan, by way of Pasadena. Welcome to back to San Diego. You've been here a few times, and it's the first time sitting on the.

Podcast, actually, the second time sitting on the podcast.

Oh, that's right. Yeah, that's true, too.

But that was like seven years ago.

That's right. Everything before COVID is a mystery to me now.

Exactly, exactly.

Now we'll get to the multiverse. I think that's one of the most fascinating topics in all science. You know, maybe concurrent with the, you know, origin of life on other planets and our planet, etcetera, which you're involved with as well, or you've written about. And not only that, you've gone into forays with past guests and very popular guests. Constantine Petitjian, working on Jupiter's, you know, size the Deep Past. That was a fascinating paper that we got to hear about, but today you're here to talk about fine tuning and all sorts of really cool things that are related to the multiverse. But before we get there, we're speaking in early April, it's after April Fools, so everything's okay. It's after Liberation Day, so we're.

We're sorry.

We're liberated. You know, And I like the li. The living.

And we're no longer fools.

So we're liberated, not fools. That's right. Well, some. You know, I can't necessarily say I'm not a fool. But recently in the last few weeks there's been a lot of interesting data coming out that seem to be in conflict with each other if not with the standard model of cosmology. One from the Atacama Cosmology Telescope led by my friends Mark Devlin and Suzanne Staggs, who are also on Simons Observatory co directors. And that seemed to be very consistent with lam so called Lambda cdm. But prior to that, just a week or two before that were the DESI results.

Those seem to be kind of throwing a wrench into many of the different types of works, including the work about the end of all time and maybe suggesting there won't be eternity to wait or we won't have a big rip or we will have a, you know, heat death. Talk about what is the impact of has these new results that possibly the equation of state parameters changing. And begin by explaining what is the equation of state. Why is it so important and what would it mean if it were changing with time via dark energy not being a constant?

Well, there's a lot of questions in there.

That's right. That's my signature move is to.

So the basic idea is that the universe contains some weird component we'll say called dark energy, cosmological constant, vacuum energy. Lots of names and they can mean slightly different things in different contexts. But the basic idea is that empty space is not empty. It has an energy level associated with it. And that energy is in such a weird form and it has the weird effect that it makes the universe accelerate. And in order to understand the current cosmological data circa the year 2000, so the turn of the century, it seems that our universe is accelerating. And the simplest model that works is a cosmological model that has about 2/3 dark energy, vacuum energy, cosmological constant. Now to zeroth order it's a constant.