They have logical problems such as the grandfather paradox.

What you're struggling with is what they used to call on Earth the grandfather paradox.

It's a bit like one view of the grandfather paradox, where some quirky event always prevents you from completing the murder.

Despite the name, the grandfather paradox does not exclusively regard the impossibility of one's own birth.

The grandfather paradox has been used to argue that backwards time travel must be impossible.

Stories of this type are complicated by logical problems such as the grandfather paradox.

To better understand what we're dealing with here, consider the famous grandfather paradox.

This leads to seemingly paradoxical resolutions to the grandfather paradox.

For instance, the grandfather paradox has no solution, and leads to an inconsistent state.

This, the "grandfather paradox," is so named because of the thought experiment used to illustrate it.