On the possiblity of an actual infinite

[S]ome have argued that it may be impossible to count to infinity, but it is possible to count down from infinity. But this objection seems patently absurd. For one thing, the number of members in both series is the same. Why would one be easier to cross than the other? Second, assume that someone had been counting toward zero from negative infinity from eternity past. If a person goes back in time form the present moment, he will never reach a point when he is finishing his count or even engaging in the count itself. This is because at every point, he will have already had an infinity to conduct the count.

J.P. Moreland, Scaling the Secular City, p. 31