system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How is it possible that Bitcoin, created out of thin air, has market cap of over $4 billion?
gpt
Ultimately, all value is tied to how much people want a thing.  No different for bitcoins than for dollars or for cheeseburgers or for gold bricks. 

Bitcoin---as a relatively popular, relatively secure, relatively easy to understand cryptocurrency has attracted a large number of people who either find it useful, or expect that other people will one day want to buy it.  Given that, it's value is no more or less surprising than that of a successful song that was written out of thin air.