A well known paradox that suggested time travel to be impossible, called the grandfather paradox, where a traveller goes back in time to prevent him or herself from being born, Hawking overcame by proposing that time travel to the past is impossible.
Any kind of time travel to the past through wormholes or any other method is probably impossible, otherwise paradoxes would occur. So sadly, it looks like time travel to the past is never going to happen. A disappointment for dinosaur hunters and a relief for historians.Hawking suggests that a means of travelling to the future would be by super speeds in a vehicle where the time elapsed during travel is less compared to that on earth. This would mean that when the travellers returned to earth, it would be in further in the future. For example, travelling for a day and returning to earth one year later.
But the story's not over yet. This doesn't make all time travel impossible. I do believe in time travel. Time travel to the future. Time flows like a river and it seems as if each of us is carried relentlessly along by time's current. But time is like a river in another way. It flows at diff erent speeds in diff erent places and that is the key to travelling into the future. This idea was first proposed by Albert Einstein over 100 years ago. He realised that there should be places where time slows down, and others where time speeds up. He was absolutely right. And the proof is right above our heads. Up in space.
Given that going back in time is impossible and the cost involved would be enormous, there really would be no point.
We are all time travellers, moving forward towards the future, albeit at at one second per second. There is no advantage to travelling through time faster than this rate and leaving our lives behind to go to a future that is uncertain. We may as well be cryogenically frozen, to wake years later.
As for travelling to the far reaches of space for research and then returning to earth, the travellers would return to a different world with possibly no memory of the mission itself.