Many phenomena investigated by physicists are not static but evolve probabilistically with time (i.e. Stochastic process). The universe itself is perhaps one of the best examples. It has been expanding ever since the Big Bang. Similarly, growth of networks like the Internet are also ever growing systems. Another example is polymer degradation where degradation does not occur in a blink of an eye but rather over quite a long time. Spread of biological and computer viruses too does not happen over night.