If the Universe came to an end every time there was some uncertainty about what had happened in it, it would never have got beyond the first picosecond. And many of course don't. It's like a human body, you see. A few cuts and bruises here and there don't hurt it. Not even major surgery if it's done properly. Paradoxes are just the scar tissue. Time and space heal themselves up around them and people simply remember a version of events which makes as much sense as they require it to make.

the only thing that really gets hurt when you try and change time is yourself.

The best conversation I had was over forty million years ago,' continued Marvin.

Time travel? I believe there are people regularly travelling back from the future and interfering with our lives on a daily basis. The evidence is all around us. I’m talking about how every time we make an insurance claim we discover that somehow mysteriously the exact thing we’re claiming for is now precisely excluded from our policy.

Time travel, by its very nature, was invented in all periods of history simultaneously.