Time travel re-visited

There’s a new paper up on arXiv by a international group of  physicists which has an abstract starting with this:

This paper discusses the quantum mechanics of closed timelike curves (CTC) and of other potential methods for time travel. We analyze a specific proposal for such quantum time travel, the quantum description of CTCs based on post-selected teleportation (P-CTCs).

A middle section that includes this:

If it turns out that the linearity of quantum mechanics is only approximate, and that projection onto particular states does in fact occur – for example, at the singularities of black holes – then it might be possible to implement time travel even in the absence of a general-relativistic closed timelike curve. The formalism of P-CTCs shows that such quantum time travel can be thought of as a kind of quantum tunneling backwards in time, which can take place even in the absence of a classical path from future to past.

And a conclusion that ends with this:

In Sec. IV we have argued that, as Wheeler’s picture of positrons as electrons moving backwards in time suggests, P-CTCs might also allow time travel in spacetimes without general-relativistic closed timelike curves. If nature somehow provides the nonlinear dynamics afforded by final-state projection, then it is possible for particles (and, in principle, people) to tunnel from the future to the past.

Unfortunately, as I seem to be finding with some arXiv papers lately, it has a very layperson friendly introduction, but for the rest of the paper, it would help to be a physicist.  I don’t know why they don’t make the conclusion a lay reader friendly version of  what their paper means. 

Still, any arXiv paper that even mentions people tunnelling from the present to the past is noteworthy!