My understandings of bitcoin backup by following things:
1. electricty.
2. limited supply - rareness - /fiat cant have it/
3. blockchain network - /fiat cant have it/
4. math - unbreakable, no forgery, speed of light. you cant break the math unless god.
5. people and idea - people's money, not property of any corporations and government, that makes ultimate world currency
gold has no future in 100 years if people become able to mine golds on asteroids, moon.
even nuclear physicists made it in lab 70 years ago