Brian Keating opened by asking Rovelli to explain the frost on a window — how things left alone can become more ordered. Rovelli's answer is that entropy is not the same thing as disorder, and he ran through oil separating from water, a shaken box of balls settling to the bottom, and a beach sorting its grains from its stones. He thinks this is a case where popular science is bad, and where physicists are often confused themselves.
It's not true that things get disordered. In fact, very often in nature, things left alone get ordered. To imagine that to be free, you have to violate the laws of nature is stupid. You, Brian, can be in a superposition. You can be in LA and also in San Francisco. Your head is older than your feet.
That was Carlo Rovelli, one of the men who built loop quantum gravity, telling me that the second law doesn't say what I think it does. But he didn't stop there. Over the next hour, he's going to take apart the three things you were told that just ain't so. Ranging from the frost on the window where you may be sitting right now to the clock on your wall. And the clock is the one that really got me. He blew my mind by telling me that my head is older than my feet. And then he told me, why that's the least strange thing he was going to say. So Carlo, let's start with the frost. You're telling me that things left alone can get more ordered? That's not what I was taught. Walk us through that.
First of all, I do think that the thermodynamic arrow, it's very basic. A lot of phenomena which we connect to the direction of time. For instance, I remember our last conversation. We don't remember our next conversation, right? We have a picture of Brian young, we don't have a picture of Brian old. We can decide where to go to dinner tomorrow, but we cannot decide where to go to either yes. So there are all this profound difference between future and past. And I got convinced in the last, I would say, 10 years, working a lot about that. I've read a lot of people, that all these differences can all be traced to the thermodynamics era of time, to the entropic era of time. It's not obvious, but the reason we have memories of the past and not the future has to do with entropy growing. If it wasn't for entropy, there wouldn't be this dissimeter between. Now, have we fully understood the story? No, I think there are various aspects that we still get confused. And there are also, as you say, aspects that we oversimplify badly. Let me give you an example which is dear to me. We always make this story, okay? Take like latte, calf, coffee, and mix, and look, they mix. In fact, take water and vinegar, put some vinegar in water, mix, and you know, they mix. Now, take water and oil, mix, they separate. Oh, yeah? So is this contradicting our entire understanding of the universe? No, it's just things a little bit more complicated than the way they usually said. It's not true that under any definition of order or disorder, things get disordered. In fact, very often in nature, things left alone get ordered. And oil and water separating is one of the many examples of that. If you have a box with balls you shake and then you put it there on the table, all the balls go very nicely in order on the bottom. Okay? They order themselves. If you look at a beach, the ocean, all the little grains are together and the big stones are another side of the beach. They order by the same. Who ordered them? Okay? If you look at frost, the beautiful ordered structure then, who ordered them? I mean, a lot of things in nature get ordered by themselves. So the idea that entropy is disorder, careful. Under a proper definition of order, under proper definition of everything. But most of the things we call order and disorder are not connected to entropy in the way it's usually said. That's one example in which popular science is bad. In fact, maybe scientists are very confused about that themselves. And that's important, right? Because people are surprised because biology came in. The very complexity of biology. Biology is a lot of order. So on the crust of our planet, the Earth, there's all this structure that formed. Okay? People say, oh, this seems to be against entropy. No, why? Entropy grows and create orders just happen all over.
Let's talk about the early universe. You already mentioned the block
universe and Our mutual distaste of that hypothesis. I don't like that. I want to ask the why question. I really, I do want to ask the why question, but I know why questions are not usually answerable. But the universe was somewhat lower entropy, right? It was in a very special configuration. Does that, in your mind, point to some reason why the arrow of time points in one direction?
Yeah. Yeah, the two are very, very connected. It's not that one explains the other one, because we need an explanation for either. I think the past law entropy and the arrow time, psychological thermodynamics, are different manners of explaining, of pointing out to the same phenomenon about which I think there is more to learn.