Thread: Radioactive Decay

I am aware that radioactive decay is a form of exponential decay as the common ratio of the decay of a radioactive isotope is 0 < x > 1. So obviously, as with all exponential decay, the number being multiplied by the common ratio will never become zero- just asymptotically approach zero.

However, this is where I am slightly confused- as if you have a finite amount of radioactive substance which has a decay rate between 0 and 1, then surely (given enough time) there will be literally "none" of the substance left; it will all have decayed. Is there some law of physics which prevents the entirety of a substance decaying? As I understand exponential decay in mathematical terms, but not in terms of a finite amount of substance which will continue decaying.

Any single atom has a finite probability of decaying during a given time interval. If there is a large enough number of them, the radioactive isotope follows an exponential decay rule. When you get down to the last atom, it comes down to probability. It might last a second or another million years.

Unless it is constantly being observed, in which case it is constantly being forced into the non-decayed superposition and will never decay.

Every atom in the universe is (for a given definition of constant) being constantly observed.

And for a given definition of observed presumably?

No, that's fairly well defined already. (It has nothing to do with humans.)