system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do atoms decay?

Say I have 2 atoms of gold, i cannot tell one apart from another, yet one is going to decay while another one will continue to be, so what makes 2 seemingly identical atoms behave differently? what is that something that makes them different? Is there some sort of fatigue at atom level?
gpt
It's hard to ELI5 for quantum physics. Atoms and the bits that make them up (protons, neutrons, electrons) and the bits that protons and neutrons are made of (quarks) all have behaviour that is different to what we consider 'normal' stuff.  It is natural for them to randomly change, with a chance of this change happening in a given time. It's just what they do, because they are all trying to get to what is known as their lowest energy state. Other things get in the way, like gravity, other Atoms and bits of radiation hitting them. But over time, everything at a quantum level is trying to change in order to reach lowest energy. So one atom might change now, one might change later, but eventually, everything in the universe will reach the low energy state.