# Predicting the future of a deterministic universe

## Main Question or Discussion Point

I was discussing with some friends the other day. We were philosophizing about a hypothetical universe which is governed by the principles of causal determinism. (Go look at the Wikipedia page on determinism for more details about causal determinism.)

Our first concern was: Could a computer, knowing the exact state of the entire universe at one moment, in theory, calculate the future of this universe?

We quickly came to the conclusion that, if the computer is outside the universe and cannot interact in any way with it, it can, in theory, calculate the future of this universe. But if the computer can interact with the universe, things get weird.

So some questions and assumptions arose.

Let's say an intelligent being, called Robert, in that universe, build such a computer and gives it all the information about the entire universe at one precise moment in the past (let's say 1 year ago exactly).

A first assumption poses problem:

A universe in which exists an intelligent being who knows the future is an incoherent universe. What I mean by that is: there is no possible configuration allowing such a universe to exist.

If that assumption is true, then we know the computer won’t show his future to Robert.

So what happens between the beginning of its calculation and the moment Robert look at the results?

First of all, when you think about it, you find that the computer will experiment a loop. When its simulation reaches the beginning of that said simulation, it will create a sub-simulation, which will encounter that same problem. So the computer will not be able to make progress.

But let’s say this is a computer we can’t even imagine, that can surpass that kind of problem (the loop). So what would happen in that case? I think it would simulate until the point where an intelligent being look at the result, and then the computer won’t be able to calculate/simulate a coherent continuation, just because such a continuation cannot exist.

Also, in the simulation, the computer simulates the moment he shows his future to Robert, but for that to happen, it must have already calculated the future, but for that to happen, it must have calculated the moment where Robert look at the result.

Well, my questions to you guys are:

Do you think my assumptions are right?
Is there something I did not consider?

And finally, did I post this in the right place?

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.Scott
Homework Helper
Answering your last post first: No, this is mostly philosophy and, to a lesser extent computer programming, and I have requested it be moved.
Is there something you did not consider: Yes, a couple of things.
1) Your "intelligent being" doesn't have to be intelligent, only able to hold information.
2) Your intelligent being doesn't have to have a complete or completely accurate notion of the future.
3) You underestimate your computer. When the computer encounters recursion (parts of the universe that contain all of the universe - or at least parts that include itself), it can encode those cases without actually replicating the data.

berkeman
Mentor

Drakkith
Staff Emeritus