Adam Elga

So it's the one that says –

Well, before you learn it's Monday, be 50-50 on the coin.

And after you learn it's Monday, be 50-50 on the coin.

And the way to visualize that kind of view is it's like a version of Bayesian updating.

But if you imagine probability getting pushed around by the updating, it's like you're imposing a firewall between worlds.

And when probability gets pushed around, it can't cross world boundaries.

So like,

The third or so the contrary view in the sleep and beauty problem is you have these three possibilities.

Heads Monday, tails Monday, tails Tuesday, when you eliminate tails Tuesday, that probability from tails Tuesday gets split up to the heads Monday and tails Monday possibilities in proportion with what was originally there.

This other view says, well, that

stuff, that probability stuff was already in the two waking world.

And so it can't cross the boundary to the other possible worlds.

All of it has to go over to tails Monday.

And that's how you get 50, 50.

I love it.

Having thought about that view, can we talk about a case?

Now, here's an instance where –

The limitations of the audio medium, I'm feeling them because I really would be wanting to draw this.

But let's try to do this case because I think it's a nice case to display what that view says.

And I'm not sure how it goes.