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?
One person alone on a planet is quite busy with feeding himself and all personal needs.
Not enough time for doing science.
He didn’t specify what kind of immortality, so let’s assume it’s the kind where you don’t have to worry about food, water, sleep, or dying
that could make it even worse, bc such a person has no motive to explore and research anything.
Boredom is often enough of a motivator, and nothing stops them from doing those things even though they don’t need to.