Stephen Wolfram

And so the fact that the claim that we believe that we are persistent in time, we have this single thread of experience, that's the statement that somehow we managed to aggregate together those separate threads of time that are separated in the fundamental operation of the universe.

So just as in space, we're averaging over some big region of space and we're looking at many, many of the aggregate effects of many atoms of space.

So similarly, in what we call branchial space, the space of these quantum branches, we are effectively averaging over many different branches of histories of the universe.

And so in thermodynamics, we're averaging over many configurations of many possible positions of molecules.

Yeah.

So what we see here is, so the question is, when you do that averaging for space, what are the aggregate laws of space?

When you do that averaging over branchial space, what are the aggregate laws of branchial space?

When you do that averaging over the molecules and so on, what are the aggregate laws you get?

And this is the thing that I think is just amazingly neat.

Well, yes, but the question is, what are those aggregate laws?

So the answer is, for space, the aggregate laws are Einstein's equations for gravity, for the structure of spacetime.

For branchial space, the aggregate laws are the laws of quantum mechanics.

And for the case of molecules and things, the aggregate laws are basically the second law of thermodynamics.

and the things that follow from the second law of thermodynamics.

And so what that means is that the three great theories of 20th century physics, which are basically general relativity, the theory of gravity, quantum mechanics, and statistical mechanics, which is what kind of grows out of the second law of thermodynamics,

All three of the great theories of 20th century physics are the result of this interplay between computational irreducibility and the computational boundedness of observers.

For me, this is really neat because it means that all three of these laws are derivable.

So we used to think that, for example, Einstein's equations were just sort of a wheel-in feature of our universe, that they could be, the universe might be that way, it might not be that way.

Quantum mechanics is just like, well, it just happens to be that way.

And the second law, people kind of thought, well, maybe it is derivable.