[ecesena]

Addresses are created offline for scalability reasons, meaning that not having to interact with the blockchain is a feature, not a bug.

There are 2 levels of collision that are theoretically possible. The tldr is that both are really hard, way harder than mining itself, so you'd better spend your time mining that trying to find collisions in the address space.

The first level is that you can generate the same private key, i.e. guessing exactly 256 bit. Prob is 1/2^256.

The second level is that you find a collision in hashing the public key onto the address. Hash is a combination of sha256+rimemd160, but in fact it's a hash onto 160 bits, so the probability of finding a collision is 1/2^80 because of the birthday paradox.

When you generate a new address, you can certainly add an extra step and verifiy if it's used already in the blockchain. If you find a collision, though, please send it to me before discarding it :)