Let’s say we left one single very smart guy (not necessarily with the knowledge: they may be able to understand hard stuff when taught it, but not know it already) alone on a copy of the earth. That person is also immortal. Could that person, by themselves, gain back all knowledge, maybe also experimental, or even surpass that is already available to us right now, before the planet gets inevitably engulfed by a sun turning red giant?
Right. Think of Cueball laying stones as a CPU, and the rate at which he can finish laying a row and return to the beginning as his clock speed.
Very long lines, then.
Mind-bogglingly long!