Within the encryption protocol that governs bitcoin (Secp256k1 to be precise), the generated points publicKey_x and publicKey_y are a results of calculated coordinates within the finite field " G^K " (where G is a combination of GeneratorPoint_X and GeneratorPoint_Y and k is order value of n).

My question is, if we have only the Y coordinate belonging to a given publicKey, can we get the X coordinate?

or Is it only possible to derive Y from X and not the other way around?

If so how can this be achieved?