cl0ud: The probability that you are alive at any given time is the total time that you are alive, say 80 years, divided by the total amount of time. So if the total amount of time is ∞, then the probability that you are alive at any given time is 80/∞ = 0.
You really have to read the whole paper to get the argument though.
slowtyper237: you are right that 1/∞ and n/∞ are the same but Huemer suggests we live infinitely many times.