Unfortunately the article itself was pretty short – more a press announcement than detailed science report. While the write-ups center around nothing being able to exceed the speed of light, the time travel component came from causality – an oversimplification being that nothing can occur before the event that caused it. That ramification should bleed into the quantum world according to the scientist and that is where many of the alternative time travel theories still lie, especially with entanglement.

Not sure where I was last summer when this came up, but…

As I understand it, the speed-of-light limit comes about from nothing more than the assumption that the universe is symmetric with respect to translations and rotations in space-time.

If you start with just that, you can derive all of special relativity — though only to say that there’s some constant that represents a “universal speed limit”. I don’t understand why it turns out that photons appear to travel at that speed, but Einstein’s reasoning shows that they do.

In any case, my point is that symmetry arguments alone are enough to enforce the speed-of-light limit, so that really only leaves the possibility of there being something like a wormhole or some other phenomenon that breaks down the symmetry.