Imagine that someone had access to an alien super computer such that they could mine any block in nanoseconds. At that point, could that person create a chain with the same BTC genesis block, generate any/all the blocks and transactions they want, to the point where this new chain had a greater cumulative difficulty than the current chain? And if that person did this, would the network accept this chain, thus erasing the past 10+ years of BTC?
I realize the computational power to do this is theoretical, like this question. However, I still wonder what, if any, safe guards are in place to prevent something like this?