If someone has such a generator/reactor, they could probably earn more by selling the technology than mining BTC.
People often get too focused on the energy component of mining.
Capital management, energy, and operations. It takes all three to mine BTC effectively. Just having free energy does not necessarily give you a competitive edge.
You also need to have good operations (machines, internet, shelter, heat management, personnel to build, maintain and troubleshoot machines, etc.)
You also need good capital management. How many ASICs do you buy? When/what price do you buy them? Do you raise equity or debt to buy machines? Do you sell machines opportunely? What do you do with the sats you earn?
As far as attacks go, this is why we have the difficulty adjustment. If a powerful miner wants to cause havoc, they could take hash offline after a large upward difficulty adjustment and cause longer than usual blocktimes for the next 2016 blocks. Or they could bring lots of hash online and make blocks go really fast for 2016 blocks.
However, a powerful miner is unlikely to do this kind of attack because it would make them uncompetitive from a capital management and operations standpoint
All of that is interesting, but I think the difficulty adjustment is the key point. No matter how low the marginal cost of computing goes, and there will always be a marginal cost, the difficulty adjustment can match it (at least that's my understanding).
There could be very interesting distributional effects from a small group of miners having access to substantially cheaper energy, though.
reply