This question lies behind the plot of Probability World, a "science fiction whodunnit thriller" written by Warwick grandfather Dennis Crips.
The only way the book's young heroes Emily and Francis can solve the mystery is to find a way to travel to the future.
But Mr Crips has had to overcome the paradox central to all time travel stories – that it is impossible to travel to the future and then back to the past and alter it.

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Mr Crips said: "The view I've taken is that you cannot go to the future, find out what's going to happen and come back and alter it, but in principle everything we do has some influence on the future."
Taking his inspiration from Arthur C Clarke, Mr Crips aimed to keep his plot within the bounds of scientific possibility. The idea of a cloaked hero dashing through a star gate does not appeal to the retired engineer – he wants to know how the star gate would work.
Mr Crips said: "A time travel project would last for decades, it would cost a fortune, and why would somebody do it? I wanted to describe it as a real project with real engineering solutions."
Instead of the real future, his characters visit a 'probable' world, a kind of simulator for the future, via a parallel universe.
And when he uses a base at the south pole of the moon, it is because travel to another universe needs to take place in a vacuum.
Mr Crips revealed he "invented crises" to keep the plot interesting.
When his heroes need to return, they find the moon has shifted in its orbit, and their love life also suffers some turbulence.
Then disgruntled Third World nations also rise up and attempt to reclaim the planet by staging a peaceful invasion of America.
Mr Crips said: "My question is, who are the terrorists – and that gets revealed at around page 350."
With all its complexities and parallel plots, the 69-year-old said the story "just flowed" when he began writing it.
He has begun a sequel, and also hopes to publish a collection of short stories he has written for his grandchildren. Mr Crips is relaxed about whether the books will sell - he is more impressed by how advances in technology mean he can have a book in print so cheaply.
Probability World is published by Diggory Press and will be launched at Warwick Books in Market Square, Warwick on July 15. For more information about the book:
www.diggorypress.com