That's the problem with all currencies, even precious metals: they depend on the acceptance of people, on belief that they have some sort of value, when in fact they're just a fantasy. It's not real! If an epic catastrophe hit tomorrow, and one had Gold bars, they'd be utterly worthless: nobody would willingly trade their food and uncontaminated water reserves for currency (and if they did, they'd soon die of hunger or thirst); you can't eat or drink Gold, nor can you eat or drink money.