It that it takes more than a lifetime to figure out how to do it.
And that would be about the only problem left now that the Grandfather Paradox has been solved
A new kind of time travel based on quantum teleportation gets around the paradoxes that have plagued other time machines, say physicists.
Of all the weird consequences of quantum mechanics, one of the strangest is the notion of postselection: the ability to trigger a computation that automatically disregards certain results.
Here’s an example: suppose you have a long, tortuous expression in which there are a frighteningly large number of variables. The question you want answering is which combination of variables makes the expression logically true. And the conventional way to solve it is by brute force: try every combination of variable until you find one that works. That’s hard.
Postselection, however, makes the solution easy to find. Simply allow the variables to take any value at random and then postselect on the condition that the answer must be true. This automatically disregards any wrong’uns that come up.
And from there it dissolves into terminology that only the Mad Rocket Scientist and Joe understand.
And of course, all of that is garbage if Quantum Mechanics prohibits non-linearity.
I think the real question should be; How can teleportation work at the quantum level without being non-linear?