Gold is backed by Bitcoin because i will always buy 1 once of gold for 1 satoshi.
The question is not what back up bitcoin but what is backed by bitcoin.
Bitcoin is fundamental and backed by FAITH.
Taking total gold estimate from
here, which is just an estimate, and using the total ever bitcoin amount of 21 million, there is about 0.004 bitcoins per.
If gold and bitcoin were backing each other (trading at that price, 4 mBTC per ounce gold) the price of bitcoins would be about 430 000 USD.
To say you will buy gold at 1 satoshi per ounce, you would need about 52 btc to back up the entire world supply of gold.
