Duke Professor Campbell Harvey explains why a 51% Bitcoin attack has become profitable and feasible today "Why would you spend billions investing in mining equipment, take over the network, but then the price of Bitcoin collapses to zero, so you spend all this money to get nothing? The only way to justify it was a nefarious geopolitical entity, a country or organization wanting to do havoc, thinking it might spill over into the main financial system. That's the only way it made sense until a couple of years ago" "The difference today is the derivatives markets, these markets are highly liquid. What you want to do is simultaneously during the attack take a short position in Bitcoin, and with a short the ideal outcome is if the asset goes to zero. You'd have to do this offshore because it's blatant market manipulation, but it's feasible to launch a profitable attack. I contrast this with gold, there's no risk I can think of that the price of gold goes to zero"