Caffeine has a half-life of approximately six hours. I understand this to mean that every six hours, the amount of caffeine in the body is half of what it was six hours prior. Does that mean that caffeine never completely leaves the body? It just keeps reducing to half after a fixed time ad infintum.
I guess a broader statement of my question is: When calculating the half life of a thing, is it true that it will never reach zero? And how is this used/reconciled in a more practical setting like when calculating the amount of caffeine in the body?