To explain more, for e.g., we hear that the USD was backed by the convertibility of this currency to precious metals until 1971. Now, what are altcoins backed by such as Ethereum or Litecoin? Are mathematical calculations performed by ASIC miners any useful in the real world?
USD is a Fiat currency, which is a currency not backed up by anything. Aas said above , USD is not backed by gold since long time ago.
Nothing is backing altcoins or even bitcoin. Some stable coins such as tether are supposedly backed up by USD