LogFAQs > #974067378

Any currency not backed by something is worthless.

This something can include, but is not limited to, the following.
Gold.
Trust.
Oil.
Prestige, which is really just another form of trust.
Any material that has fairly constant value.
Anything that results in trusting that it works because of some mixture of a rare item being held by a bank-like entity and trust that they know what they are doing.
Same as before, but replace the word "bank" with "country."

You get the point.
You need either backing, or trust. Backing you can get by backing it with an actual asset. Trust you can get by, well, being trusted, or by taking the stock market approach and hyping your thing up to where it is trusted as, well, a stock-like thing.

Even if we go full Star Trek utopian for the common citizen, currency will exist for things beyond the body's needs and living conditions and the most basic entertainment needs. And whatever else ST does.

Likewise, any all-digital currency is pointless since it will either be insecure, or it will be crypto. Take your pick. I will buy your gold and silver off you so that I can hire my castle full of coil-bowsman and gunners and swordsman when you are left in the dirt with nothing.

Mostly joking of course.