The value of bitcoin is on security and limitation on supply. Maximum supply of bitcoin already pegged on 21million coin and no one control the supply. Beside that, the value of bitcoin is unhackable transaction data and its make trust on bitcoin price.
Bitcoin is a digital currency, so it's not physical. The value of Bitcoin is created because there are offers and requests from bitcoin users. The more demand the price will go up, while the more offers the price will go down. Bitcoin has no comparison, so that bitcoin cannot be intervened by anyone.