> My next question is are there downsides to proof-of-stake, and why has bitcoin not moved towards it? The main threat against any cryptocurrency is that a mal

> My next question is are there downsides to proof-of-stake, and why has bitcoin not moved towards it? The main threat against any cryptocurrency is that a malicious actor will gain control of 51% of the voting power of the system, and use it in nefarious ways that ultimately break the cryptocurrency. Different Proof-of-X systems handle that problem in different ways. It's generally considered that Proof-of-Work is easier to 51% attack, but also easier to recover from that Proof-of-Stake. The attack and recovery both use the same mechanism - add more hardware mining power to the system. There is no hard limit on this baked into the system, it's just a matter of how much mining power is available to purchase irl. And recovery can be accomplished without having to hard fork the network. Proof-of-Stake on the other hand may be more difficult to 51% attack since it requires an attacker to obtain 51% of all the currency value in the system. But if this is accomplished, then it's difficult or impossible for the honest participants to rectify, since there's no more currency available to purchase. The attacker isn't going to sell them any of his 51%. So there's an inherent hard limit baked into the system, and the attacker now has 51% of it (including 51% of all newly created currency as well, since new currency is created by staking existing currency). The only fix is for the honest participants to hard-fork the network and create a new version of it that excludes the attacker. (There are other mitigations like slashing for malicious behavior designed to prevent attackers from gaining 51% in the first place). There are other differences, but I believe those are the main ones, and one reason why Bitcoin hasn't moved to it.