Ok, so all elements undergo radioactive decay. But why? I have been snooping around and what i find is that radioactive decay occurs because of instability of the atom nucleus in quantity, proton-neutron ratio and energy content; therefore we have alpha, beta and gamma decay consecutively. Therefore highly radioactive elements like Uranium undergo constant decay into less radioactive and more stable elements. Each half-life decay takes longer and longer in a exponential manner; therefore theoretically speaking, it takes forever for any element to completely decay into zero. Although it explains why radioactive decay occurs on unstable elements or isotopes, it doesn't explain why it occurs on stable elements. Unless, stable elements are not really "stable" but the rate of decay are rather slow and harmless to human beings so we label it "stable." Then if that is the case, then why elements are always decaying or always "unstable"? Of course, this just an assumption of mine. Anybody can provide me a more conclusive answer?