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?