Medieval alchemists dreamed of transmuting lead into gold. Today, we know that lead and gold are different elements, and no amount of chemistry can turn one into the other.

But our modern knowledge tells us the basic difference between an atom of lead and an atom of gold: the lead atom contains exactly three more protons. So can we create a gold atom by simply pulling three protons out of a lead atom?

As it turns out, we can. But it’s not easy.