Bitcoin has nothing to do with "cracking SHA256 hashes", for what it's worth. The only thing remotely related is how it brute-forces inputs until it generates hashes that begin with a certain number of bits set to 0.
Cracking hashes would imply that they're taking pre-existing hashes and reversing them to find the input.
So why'd you bring it up?
Cracking sha256 hashes implies trying to reverse a specific hash. There are literally thousands (millions?) of potential inputs that hash to a valid bitcoin mining block output. It's basically a race to find the first one matching the rules of the current block difficulty. The goal isn't to produce any one specific input/hash pair.
Hash collision should always be about finding matching content for a hash.
Be a bitch to search. But damn would we know the topography of the function space.
...I'll see myself out.
This myth was always intriguing to me. Where does it come from?
It's not a number of 0s (which would imply difficulty could only be doubled or halved), it's just finding a hash that is less than the target.