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?
While my initial reaction was “Yes”, I think that it’s rather “No”.
There are massive amounts of things to build and stuff to discover. And almost all of it, especially the physics, chemistry etc. stuff needs experimentation. Plenty of people had died or chronically made it difficult to do anything because of scientific experiments (think of Marie Curie or imagine what happens when you try to rediscover nuclear energy).
In our scenario, we say, that the person is immortal, but it could always happen, that they get stuck with certain illnesses or co. which significantly reduces their possible auctions. at some point they may be so limited, that they cannot do certain experiments at all and get stuck there forever.
I forgot to say that the immortality I’m talking about also makes it impossible to get challenged by illness and such