Earlier quoted context omitted.
Here's an even crazier version: we develop a quantum computer the size of Jupiter with seemingly infinite computational capacity, and "scan" and simulate the earth. Similar to how a sufficiently advanced AI application today could probably take an overview picture of a pool table at any point in a game, and deduce the past shots that had to be taken in order for it to result in it's current state, you might be able t…
That sounds enticing, but I think you could never rewind the state of the Earth without considering the variables external to it. If you couldn't also simulate anything that could alter the course of events, such as exposure to the Sun, I think you'd end up accumulating enough lossy transitions that the simulation would be rendered (ha) worthless in a deterministic sense. If we consider that only simulating the atoms…
"So we expand the computer to simulate everything. Hell, if we were to correctly determine the state of the universe at the big bang and simulate every atom since then we could answer everything about the past, have a perfect image of the present (intelligence dream!), predict the future... We could simply write an algorithm to know where or if intelligent life exists outside of Earth..."
Then, after some consideration I realized that the smallest possible computer capable of simulating every particle in real time... was probably reality itself.