This is from Planetary #27. Warren Ellis and John Cassaday.
The idea, is that you can’t travel back in time to a time before the creation of the time machine. Since human nature, for all of time, would be interested in the earliest point of human history, the moment you turned on the time machine, an infinite number of future time travelers would appear. Just to check it out.
Thus, all of the future, from that moment, would be entirely mapped out.
Everything would have already happened in the future because everyone came back to visit the past. Every choice you have not yet made would have already happened.
"An infinite number of dead cats all arriving on your doorstep at once."