user113231: 51% attacks are commonly discussed where one entity could potentially mine blocks ahead of the network. The assumption is that the attacker manages to acquire 51% of computational power. However, assuming that some entity manages to acquire much more computational power, and starting now over next few years if it manages to exceed total amount of work, can they fork a complete new chain from the genesis block ? Hypothetical case, but purely according to the rule of longest chain by Total amount of work, isn't it possible that in future one could overcome the total amount of work done until now and invalidate current chain completely ?

user76567: It is possible only in theory. In practice that would require many times the world’s total energy output to pull that off not to mention the amount of hardware needed. And even if they could why would they and not just mine bitcoin?

113231: <p>51% attacks are commonly discussed where one entity could potentially mine blocks ahead of the network. The assumption is that the attacker manages to acquire 51% of computational power. However, assuming that some entity manages to acquire much more computational power, and starting now over next few years if it manages to exceed total amount of work, can they fork a complete new chain from the genesis block ? Hypothetical case, but purely according to the rule of longest chain by <strong>Total amount of work</strong>, isn't it possible that in future one could overcome the total amount of work done until now and invalidate current chain completely ?</p>
 76567: <p>It is possible only in theory. In practice that would require many times the world’s total energy output to pull that off not to mention the amount of hardware needed. And even if they could why would they and not just mine bitcoin?</p>
