First of all, I would like to show you similarities between Bitcoin and gold.
The value of both are driven by both scarcity and demand.
No, bitcoin is not scarce, its been driven by it demands and supply, while gold by the scarcity nature of how its been mined and refined.
The both are decentralized, and the both have limited supplies, the list goes on...
Gold is centralized because you cant get it without going through a centralized institution or known person that sells for it, while bitcoin is decentralized because of the use of the p2p network.
In Bitcoin transaction is transparent, but with Gold authenticity can be disputed etc.
Because bitcoin makes use of the blockchain technology which is an open distributed ledger, while gold work entirely on a platform different from this and you have to go through some process which requires kyc or physical appearance before you can acquire it.