This. ^
Fiat currency - its value is what it is said to be.
This is not necessarily a disaster, and it certainly didn't come about by accident. The advantage of a fiat currency is that it allows a cash value to be attributed to non-tangible things such as labour. In a modern economy where most people neither farm the land nor manufacture goods from their own raw materials, it's the only effective means of allowing economic growth. A currency tied to any finite resource, such as gold, can't in the long term cope with non-tangible assets.