Sean Carroll

Well, this comes down to the question of whether or not the ultimate laws of physics are in fact deterministic or not. You know, Laplace's demon is a thought experiment meant to illustrate the implications of determinism in classical physics. That's the whole point.

The point of Laplace's demon is that the information needed to predict what comes in the future is implicitly present in the moment right now. If you had the complete 100% comprehensive state of the universe. You never do, so that's just a thought experiment just to try to teach you what determinism really means. In quantum mechanics, for all intents and purposes, in the observable universe,

The point of Laplace's demon is that the information needed to predict what comes in the future is implicitly present in the moment right now. If you had the complete 100% comprehensive state of the universe. You never do, so that's just a thought experiment just to try to teach you what determinism really means. In quantum mechanics, for all intents and purposes, in the observable universe,

the laws of physics are not deterministic, okay? And I need to like put all those words in there with emphases about the observable universe for all intents and purposes, etc., because maybe there is a deterministic theory underlying what's going on. Both Bohmian mechanics or pilot wave theories and also many worlds in two very different ways are ultimately deterministic theories.

the laws of physics are not deterministic, okay? And I need to like put all those words in there with emphases about the observable universe for all intents and purposes, etc., because maybe there is a deterministic theory underlying what's going on. Both Bohmian mechanics or pilot wave theories and also many worlds in two very different ways are ultimately deterministic theories.

But in both of them, it is impossible for an actual observer in the actual universe to predict what is going to happen next. So it might depend on exactly what kind of Boltzmann—sorry, what kind of Laplace's demon you have in mind. Laplace's demon in Everett could predict the wave function of the entire universe, but there will be different observers observing different things.

But in both of them, it is impossible for an actual observer in the actual universe to predict what is going to happen next. So it might depend on exactly what kind of Boltzmann—sorry, what kind of Laplace's demon you have in mind. Laplace's demon in Everett could predict the wave function of the entire universe, but there will be different observers observing different things.

That's going to be inevitable, and those observers themselves will never be able to predict what will happen. In a hidden variable model, if that were plausible and fit the data, then presumably Laplace's demon would know what exactly was going to happen. So it depends on what you mean by quantum fluctuations and what you mean by Laplace's demon. Steve Bonner says, priority question.

That's going to be inevitable, and those observers themselves will never be able to predict what will happen. In a hidden variable model, if that were plausible and fit the data, then presumably Laplace's demon would know what exactly was going to happen. So it depends on what you mean by quantum fluctuations and what you mean by Laplace's demon. Steve Bonner says, priority question.

I've always wondered why cosmologists say we need to explain why the baryons in the current universe are almost all matter. If there were nearly equal parts matter and antimatter in the early universe, but randomly just a tad more matter, then after annihilation, that small amount is what you would see today.

I've always wondered why cosmologists say we need to explain why the baryons in the current universe are almost all matter. If there were nearly equal parts matter and antimatter in the early universe, but randomly just a tad more matter, then after annihilation, that small amount is what you would see today.

It looks to us like a lot, but we have no idea how much total matter and antimatter there was to start with. Given any amount of observed residual matter or antimatter, couldn't we come up with an initial combined mass sufficiently large to explain it all as just a small, statistically insignificant imbalance?

It looks to us like a lot, but we have no idea how much total matter and antimatter there was to start with. Given any amount of observed residual matter or antimatter, couldn't we come up with an initial combined mass sufficiently large to explain it all as just a small, statistically insignificant imbalance?

Well, hopefully you'll not be surprised to learn that cosmologists have thought about this quite a bit. And you have to be careful. Of course, generally, well, let's say one thing. In fact, what cosmologists believe is that there was almost exactly an equal amount of matter and antimatter, but not exactly.

Well, hopefully you'll not be surprised to learn that cosmologists have thought about this quite a bit. And you have to be careful. Of course, generally, well, let's say one thing. In fact, what cosmologists believe is that there was almost exactly an equal amount of matter and antimatter, but not exactly.

And you can work out from the equations and from what you observe how much more matter you needed than antimatter in the early universe. And the answer is about one extra proton per billion protons. So for every 10 to the 9 protons and antiprotons, there was 10 to the 9 plus 1 protons for every 10 to the 9 antiprotons. But that's not equal, right?

And you can work out from the equations and from what you observe how much more matter you needed than antimatter in the early universe. And the answer is about one extra proton per billion protons. So for every 10 to the 9 protons and antiprotons, there was 10 to the 9 plus 1 protons for every 10 to the 9 antiprotons. But that's not equal, right?

So could you explain it just as an initial condition? Sure. I don't think you can explain it just as a fluctuation, because you have to say a fluctuation of what? You would need some theory of the early universe. Sometimes you have a theory of the early universe, like you have theories like inflation, right?

So could you explain it just as an initial condition? Sure. I don't think you can explain it just as a fluctuation, because you have to say a fluctuation of what? You would need some theory of the early universe. Sometimes you have a theory of the early universe, like you have theories like inflation, right?

So in inflation, there is a predictive theory for where the baryons and the antibaryons come from, and you can calculate that. what the fluctuations should be, they're much, much smaller than one part in a billion, okay?