Sean Carroll

Some worlds don't have laws of physics, different dimensionalities of spacetime.

Some worlds don't have spacetime.

Some worlds are just a point, you know, like literally every possible world.

So necessity in that context is defined as something that is true in every possible world.

And there's very, very little that you could even think of, very few properties that count as necessary under that definition.

People have tried to argue for the necessity of God, but I think that their arguments are pretty weak, pretty feeble.

Possibility is when at least some worlds have a certain feature, okay?

And a lot of things are possible, as we learn on Mindscape.

But

They might not be actual in a large number of worlds or very many worlds at all.

So when I say the constants could have been different, I'm saying that I see no obstacle to imagining possible worlds that are more or less like ours, but the constants have different values.

Now, I might be wrong about that because, of course, it might be that the phrase, a

implies some levels of physics that we don't know about okay so if you were having this conversation in the 1850s and you didn't know about quantum mechanics you might have thought that worlds like yours had certain properties and then you realize oh my my own world doesn't even have these properties that i thought it did because i didn't know about quantum mechanics and so

That might be true for our universe as well.

It might be true, in other words, that the deep down laws of physics that give rise to our universe are incompatible with other values of the constants of nature.

I just think that's very unlikely given what we actually do know right now.

I don't even think that most possible worlds have something you would call constants of nature, so things could be very, very different.

I also think it's kind of a misguided attitude.

As a scientist, I think that we're not about looking for necessity in what happens.

We're about looking for actuality.