system
Given the following post, respond as if you're commenting on Reddit:
human
Is it possible that all elements are radioactive at some point -- even if it took the age of the universe for just one atom to decay?

How do we know that all elements aren't radioactive?  It seems rather arbitrary that some elements are radioactive while others are not.  Wouldn't proton decay be a form of radioactivity?  What makes one element radioactive while another element or different isotope is not?
gpt
The possibility of proton decay is one of the biggest questions in science. They have been able to put lower limits of 10^34 years as the half life of the proton.  Is the proton stable or does it have a really long half life?  We don't know yet.  Of course that also makes us wonder if the proton in other elements will decay after a ridiculously long time, making them radioactive as well.

Just for comparison, the longest measured half life is for Tellurium-128 which has a half life of 7.7 x 10^24 years, and the age of the universe is 13.8 x 10^9 years.

As for why are certain isotopes radioactive while others are stable?  Are the sum of the decay products less massive than the original nucleus?  If yes, then it will decay. You can think of putting balls (nuclei) around a hilly area.  If they are at a high potential (top of the hill) they will decay (roll down) to a more stable position at lower potential energy (the valley).