Stephen Hawking has claimed that time travel to the future may be possible... in the future.

Of course he's not the first one to float this theory. Einstien also said something along these lines.

Still, even this short article admits that cause must come before effect. So don't go running out to buy those lottery tickets just yet. Travel back through time will never be possible.

We know this because we percieve the march of time in the universe to be liniear and therefore that is how it must be. Right?

In the interest of fairness, I will point out that there is nothing in Einstien's theories that forbids travel back in time. Nor has Hawking found the proof that it is impossible aside from his steadfast beleif that it should be so. One would think that something so fundamental as not being able to travel to the past would be easy to prove.