Time travel IS possible - but only if you want to go to the future and not come back, says Professor Brian Cox

Travelling through time may not be the far-fetched science fiction theory it was once thought to be, according to Professor Brian Cox.
Speaking at the British Science Festival, Cox declared to the audience: 'Can you build a time machine? The answer is yes.'
However, the theory only works when travelling to the future, and Cox explained that once in the future it's not possible to come back.

Professor Brian Cox, pictured left, explained to an audience at the British Science Festival that time travel is possible, based on Einstein's Theory of Special Relativity. In theory, if technology was developed that could transport large objects close to the speed of light, humans could travel like Doctor Who in his tardis, right

Professor Cox is set to give a scientific talk on the theory of time travel to mark the 50th anniversary of Doctor Who in London next week.
The talk will form part of a set of anniversary shows that will be shown before the BBC's Day of Doctor episode on 23 November.

During his speech at the Birmingham-based science festival, Cox said time travel has already been done, on a very small scale.
He added that if the technology was developed to accelerate larger objects, it could be possible for humans to travel to the future, similar to Doctor Who's Tardis in the TV show.
Yet this technology doesn't exist yet, and will never exist that could take people to the past.

Cox told the audience that Einstein's Theory of Special Relatively states to travel forward in time, an object needs to reach speeds close to the speed of light. As it approaches these speeds, time slows down but only for that specific object. It's impossible to travel to the past, though, as seen in Back to the Future, pictured

'You can go into the future; you've got almost total freedom of movement in the future,' said Cox. 
This means that Marty McFly in Back to the Future science fiction film trilogy could have travelled to 2015.

EINSTEIN'S SPECIAL RELATIVITY

Einstein’s theory of relativity was based on two principles.
These include the principle of relativity,  which states that the laws of physics don’t change, even when objects move at constant speeds relative to each other.  
It also looked at the principle of the speed of light.
Einstein observed that the speed of light is the same for everyone, regardless of how their movement related to the light source.
Einstein's theory explains that if two objects are moving through space and want to compare what they can see, the only thing that matters and helps determine this comparison is how fast the two objects are moving relative to each other.
The special theory specifically includes movement in a straight or uniform line at a constant speed. 
If an object starts travelling faster, curves, or veers off course, the special relatively no longer applies. 

However, he wouldn't have been able to return to 1985, or travel back to 1955 like he does in the first film.
'If you go fast, your clock runs slow relative to people who are still.
'As you approach the speed of light, your clock runs so slow you could come back 10,000 years in the future.'
The theory is based on Einstein's Theory of Special Relatively that states to travel forward in time, an object would need to reach speeds close to the speed of light.
As an object approach these speeds, time slows down but only for that specific object travelling.
For example, people flying over the Atlantic will experience time passing marginally slower than people on the ground.  
'In General Relativity, you can do it in principle,' continued Cox.
'It's to do with building these things called wormholes; shortcuts through space and time. But most physicists doubt it.
'Hawking came up with the 'chronology protection conjecture' - physics we don't yet understand that means wormholes are not stable.'

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