One strange thing about matter is that there is so much of it. Poets to the contrary, the same can be said about time: the universe has been, and will be, around for a while.
Today I learned that there's a (somewhat) meaningful distinction between stable elements and ones with extremely long half-lives. Take for example Bismuth-209. This was long considered to be a stable element, but it was shown about ten years ago that its half-life is about 1.9e19 years. That's more than a billion times longer than the estimated age of the universe.
Mean lifetime differs from half-life by a mere factor of ln 2, which means that if you're looking at a particular atom and waiting for it to decay you're going to need a few very good books with you. How can it possibly be shown that Bismuth decays?
Well, like I said, there's a lot of matter. Researchers took less than 100 gr of the material, devised very sensitive equipment, and recorded 128 decay events in five days. That's very roughly half a mole of matter, or 3e23 atoms.