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Bitcoin's price soared past $56,000 on Friday, pushing the combined value of all bitcoins past the $1 trillion mark—at least in theory. That's more than the market capitalization of Facebook, though Apple, Alphabet, Amazon, and Microsoft are worth more. Bitcoin's value has almost doubled from $29,000 since the start of the year.

I say "in theory" because not all bitcoins are actually available for use. Each bitcoin (or fraction of a bitcoin) is secured by one or more cryptographic signatures. To transfer a bitcoin, you need to know its corresponding private key. And some of those keys have been lost—and it's impossible to know how many.

For example, a British man says he threw away a hard drive in 2013 that contained the keys to 7,500 bitcoins—worth around $400 million at today's price. He sought permission to excavate the dump containing the hard drive, but the request was denied.

(credit: fdecomite )

The world's cryptocurrency is now worth more than $1 trillion, with bitcoin accounting for a large majority of the value. The price of the oldest virtual currency has risen to almost $40,000, pushing the value of all bitcoins in circulation up to more than $700 billion.

Ether, the cryptocurrency of the Ethereum network, is now worth more than $140 billion. Then there's a long list of less valuable cryptocurrencies, including Tether at $22 million, Litecoin at $11 million, and Bitcoin Cash at $8 billion.

Bitcoin creator Satoshi Nakamoto is believed to own around 1 million bitcoins. Most of these were mined in the first two years of Bitcoin's existence when there was little competition. If he still has copies of the private keys that control these coins, that would give him a net worth of nearly $40 billion—enough to make him among the 40 wealthiest people on the planet. Nakamoto has never publicly revealed his true identity and has not communicated publicly since 2014.