The biggest risk of time travel, George told his project managers, is that it may create causal singularities.
Explain, they said.
You travel into the past. Now, you can’t go back and shoot your grandfather, because then you would never be born to travel into the past. The classic paradox.
OK, they said.
But you might inadvertently change something - even something trivial - that could trigger big displacements in the worldline. And we would never know it!
No problem, they said.
George’s time probe materialized in the late Devonian, squashing a trilobite.
Nargh shoggoth, they said, engulfing their dinner.