Gold is backed by the fact that no one can replicate supernovae which are required to manufacture it, so it must be found. Thus it is scarce. It has several industrial uses and is a source of vanity for many humans, which has inherent value, as humans naturally take pride in adorning themselves. Gold has proven itself over millenia, since before prehistory really, to have value on the open markets. In fact, all rocks do. Gold is hardly unique in this matter. Rocks all have value, but some rocks are rarer than others, thus have more value than others. For example, even sand has value despite its ubiquity. Many companies make their entire profit from collecting and selling sand.

So, in sum, gold can be used in the manufacture of durable, long-lasting goods. It's crucial for certain electronics. There's a constant demand for it for turning into goods. Other rocks can be used for other things, like ground covering, structural support, etc. Bitcoin can be used for?... ? ... ? ... ? nothing

gold is a physical asset used in a [lot of stuff](https://geology.com/minerals/gold/uses-of-gold.shtml).

Gold bugs.

But even without them its value would not go to zero; ignoring the purely aesthetic uses (jewelry, decorations, etc.,) elemental gold has a wide variety of uses including corrosion-resistant electrical contacts, dental fillings, etc.; the James Webb Space Telescope mirrors have a gold coating as it is a good reflector of infrared radiation.

Copper. If the world decided it didn't like gold for jewelry and storing wealth, it would displace copper in electrical applications where you can take a slight conductivity hit in exchange for it not corroding. It's a huge price difference, but it's something. Bitcoin has no floor.

Gold, in the end, is a physical, shiny metal that people find aesthetically appealing and there's a limited amount of it out there. For thousands of years people have desired gold things and valued it.

Sure, people could collectively decide that gold isn't valuable and that certainly happens to some extent as the commodity markets fluctuate, but in general when you get to the bottom of the turtle stack, gold has more fundamental value than most other forms of money.

Yep. It’s circular logic all the way down.