Time travel is possible, but only to the past says physicist

Time travel back in time may be possible as the laws of theoretical physics do not forbid it, according to astrophysicist Ethan Siegel of Lewis & Clark College in the Forbes blog 'Starts With A Bang.'

However, scientists have yet to discover the conditions needed to travel back in time, and construction a system large enough for humans certainly would not be easy.

Backward time travel would be enabled by the elusive counterpart to the known positive energy / positive or zero mass particles found all over in the universe – the negative mass/energy particles, which have long been theorised but never yet found.

'If this negative mass/energy matter exists, then creating both a supermassive black hole and the negative mass/energy counterpart to it, while then connecting them, should allow for a traversable wormhole,' Siegel writes.

'No matter how far apart you took these to connected objects from one another, if they had enough mass/energy – of both the positive and the negative kind – this instantaneous connection would remain.'

Under specific conditions, the rules of theoretical physics could create a series of elaborate wormholes that allow for transfer matter through time.

A wormhole to enable time travel can be created when the fabric of space-time is warped to provide a shortcut through time. But this will allow travel only backwards.

"If this negative mass/energy matter exists, then creating both a supermassive black hole and the negative mass/energy counterpart to it, while then connecting them, should allow for a traversable wormhole," Siegel added.

A wormhole of the kind will allow a person to be transported through it, "instantly disappearing from one location" before reappearing in another.

The wormhole could be constructed in such a way as to allow one end to remain nearly motionless, while the other moves at almost the speed of light.

Siegel constructs a scenario in which the destination is 40 light years away.

After the passage of one year, the fast-moving end of the wormhole would have aged 40 years, while on the other side only a year would have passed.