Fiat money is money that is guaranteed to the State, of course I never hesitate. the use of the bitcoin I think only as an alternative, fiat money is still the largest and can not replace by any included bitcoin.
Yeah that's true fiat is really old and it has been around for more than 500 years while bitcoin is just a 8 year old digital currency which currently has many flaws which can affect the use of it in daily life while fiat is instant as we don't need any sort of confirmation and it is widely accepted anywhere in the world.
Fiat is guaranteed by the State, yes, but at any given time, the State can turn their back to their people and say that they aren't backing the fiat anymore. That's why it's still risky to put all of your money in fiat even though it's very unlikely to happen. Fiat has been around for a really long time, it came around 700 BC (Source:
History of Coins) which makes the concept of it very very old. Everything will eventually be replaced by something better and once everyone started using bitcoins, fiat will be replaced by bitcoins.