Quote Originally Posted by factotum View Post
The problem isn't really computational capability but the ability to know what the current state of the universe is. Going back to my weather example from earlier, if you could somehow create a computer with perfect ability to calculate future weather, and you fed into it the exact values for temperature, pressure, wind speed and so on for points spaced one metre apart in the atmosphere--we'll ignore for now the absolute physical impossibility of making those measurements--and you let it run the simulation, it would still be completely different from the *actual* weather within a month, simply because it didn't have the information of what was happening in between those data points. Plus it wouldn't be able to take into account atmospheric variations caused by landslides or even people walking from one place to another.
Well, the area where computational ability comes into play is that the computer here is trying to fully simulate the universe, e.g. by using much more precise data points* as well as account for all of those random variations, to make predictions and in order to do that (with our current limitations) you need a universe-sized computer. Not that I don't agree with your overall point--I definitely should have elaborated more on that "among other things" in my post--it's just that, regardless, none of these are artifacts of determinism specifically--you'd have the same issues in a non-deterministic world.

*And, yes, there is a limit to how precise even a theoretically perfect simulations could be, but that's still not a consequence of a deterministic universe