### About ten years ago scientist Dave Bacon, now at Google, presented that a time-travelling quantum computer could rapidly solve a bunch of problems, known as NP-complete, which mathematicians have lumped together as being hard. The problem was, Bacon's quantum computer was travelling around 'closed timelike curves'. These are paths through the fabric of spacetime that loop back on themselves. General relativity lets such paths to exist through contortions in spacetime identified as...