I've watched a series of you tube videos that show how money evolved from a convenient way of dealing with gold to a system of accounting which relies on faith in the US government. (The videos are from a US perspective, but it's not too different elsewhere). The US government is "reliable" in this sense becuse it represents the land, labour, food, mineral resources, etc, of the USA itself.
It's odd, because one of the key Venus Project ideas is the big database showing what tangible resources we actually have. The money that exists ultimately is supposed to represent these things, but apart from the fact that we can't measure the true worth (utility) of (say) a tree, compared to (say) a bus we don't actually know in total in one place what we have. If we did know this we would have better information on how much money there should be to represent it, instead of letting it grow arbitrarily.
The idea of coupling money to gold is unhelpful as the price of gold does not relate to the utility value of the actual resources we have and neither does the amount of gold that exists.
If we did know in total in one place what useful things we actually have, we could perhaps try to denominate it all in one unit, but would there be any point? If we direct ourselves to producing sustainable abundance, rather than getting money, we reduce and/or eliminate the vary scarcity that the free market is supposed to allocate out to everyone.