What does "random" mean wrt nuclear decay? From what I understand, the process of nuclear decay proceeds at a very predictable rate. Given a lump of say, U-235, half of all the nuclei in the lump will have decayed after 700 my. There is no way, though, to determine which nuclei in the lump will decay at any specific time, so this is considered random. But what actually triggers the decay? Apparently, the only reason the process is deemed random is because we don't have a way of probing the nucleus to look for some signal that will tell us that the nucleus is about to decay. If we were able to isolate and monitor a single U-235 atom, and somehow magically probe the nucleus to see all the inner goings-on, then what chain of events do you think we would look for to be able to say that the nucleus was on the verge of decay? I guess what I'm asking is: "Is the decay of a nucleus called 'random' simply because we are incapable of determining when it will decay, or is it called 'random' because there is no actual cause to the effect?"