Bitcoin is having its 7th birthday, and its promise to change the way the world thinks about money is looking less and less hyperbolic. For one, the block chain technology underlying Bitcoin - the public ledger that makes the exchange transparent and accountable - is now being used to clean up Wall Street. A block chain-inspired service announced recently could open up the practice of lending stocks, and help prevent the kind of out-of-control short selling that led to the crash of 2008. But there are a lot people still don't understand about Bitcoin and block chain. We spoke with incoming Berkman Fellow Patrick Murck of the Bitcoin Foundation to explain. Flickr photo courtesy of btckeychain