Radiometric dating decay curves
It is sufficient to observe you traveling at 20 meters in a single second, and then do the math.
Every single time he plays, he has a one-in-six chance of dying, and this is true no matter how long he's been playing. If we have an atom of Na, then no matter how old it is, it has a 50% chance of decaying in the next 2.6 years; and if it survives that period of time, then it has a 50% chance of decaying in the next 2.6 years; and so on.What is more, for each isotope, this half-life is constant: it is a property of the isotope, and virtually unaffected by external circumstances. In the first place, it should be true in principle: it can be deduced from the underlying laws of quantum mechanics.In the second place it is confirmed by actual observation: shortly after the discovery of radioactive decay, scientists began trying to change the decay rate by subjecting unstable isotopes to heat, pressure, magnetism, and so forth, with negative results.With the exception of gamma decay, which need not concern us here, this will involve changing the number of protons, or neutrons, or both, and so also changing the atomic number, the atomic weight, or both.There are a number of mechanisms by which decay may take place.