Highway to future

The ability to travel through time, whether it is to fix a mistake in the past or gain insight into the future, has long been embraced by science fiction and debated by theoretical physicists. While the debate continues over whether travelling into the past is possible, physicists have determined that travelling to the future most certainly is. And you don’t need a wormhole or a DeLorean to do it.

Einstein’s Theory of Special Relativity is the only way to travel through time. Real-life time travel occurs through time dilation, a property of Einstein’s special relativity. Einstein was the first to realize that time is not constant, as previously believed, but instead slows down as you move faster through space.

The theory is based on an experiment called “the twin paradox." In this scenario, one twin remains on Earth while another travels in a spaceship at near light

In his General Theory of Relativity, Albert Einstein argued that gravity was not just a force between two objects but rather the result of curved spacetime.

He coined the phrase “spacetime,” fusing the three dimensions of space and one dimension of time into a single term. Instead of treating space as a flat and rigid place that holds all the objects in the universe, Einstein thought of it as curved and malleable, able to form gravitational dips around masses that pull other objects in, just as a bowling ball placed in the centre of a trampoline would cause any smaller object placed on the trampoline to slide towards the centre.

As an object gets closer to the centre of a gravitational dip, time slows down for that object. This can be seen by looking at Einstein's theory on relativity which states that time moves more slowly as you move faster through space. More extreme changes happen near the Earth's core because gravity increases there; and, this difference in relative velocity between clocks on different parts of the planet is more dramatic.

This effect can be seen in GPS satellites, which orbit 20,200 kilometres above the Earth’s surface. These satellites have highly precise clocks onboard that gain an average of 38 microseconds per day due to time dilation. While this time gain seems insignificant, GPS satellites rely on their onboard clocks to maintain precise global positioning. Running 38 microseconds fast would result in a positioning error of nearly 10 kilometres, an error that would increase daily if the time difference were not constantly corrected.

A more dramatic example of time dilation can be seen in the movie Interstellar when Matthew McConaughey and his crew land on a planet with an extreme gravitational field caused by a nearby black hole. Because of the black hole’s intense gravitational influence, time slows dramatically for the crew on the planet, making one hour on the surface equal to seven years on Earth. This is why, when the crew returns to Earth, Matthew McConaughey’s daughter is an old woman while he appears to be the same age as when he left. 

Humans have never been able to jump years into the future. The reason for this is velocity. In order for humanity to send a traveller years into the future, we would either have to take advantage of the intense gravitational acceleration caused by black holes or send the traveller rocketing into space at close to the speed of light (about 1 billion km/h). With our current technology, jumping a few microseconds into the future is all humans can manage

What if, one day, technology advanced to the point where it was possible for a human being to travel close to the speed of light? This would be an interesting question on its own merits, but what is more intriguing is that if time dilation were observed while travelling near this speed limit (as predicted by Einstein's theory of relativity), then theoretically there could be some way for the traveller to use this time difference between his perspective and those he left behind.

If we can’t use time dilation to return to the past, does this mean that the past is forever inaccessible? Perhaps not. Einstein proposed that time travel into the past could be achieved through an Einstein-Rosen bridge, a type of wormhole. Wormholes are theoretical areas of spacetime that are warped in a way that connects two distant points in space.

Einstein’s equations suggested that this bridge in space could hypothetically connect two points in time instead if it were stable enough. “At the moment, even an Einstein-Rosen bridge cannot [be used to] go back in the past because it doesn’t live long enough – it is not stable,” Matthews explains.

It is a common fantasy to be able to travel back in time and see historical events first hand. While it would be fascinating to travel back in time to see the dinosaurs or meet Albert Einstein and show him the reality of time travel, perhaps it is best if the past remains untouched. Travelling to the past invites the possibility of making an alteration that could destroy the future.

New research suggests that time travel into the past is possible. The study, conducted by Dr. Ronald Mallett at the University of Connecticut, found that it would be theoretically possible to bend space-time and reach a point in history before we were born.

However, there appears to be more evidence that time travel into the past is not possible, and never will be. As the late Stephen Hawking said in his book Black Holes and Baby Universes: “The best evidence we have that time travel [into the past] is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future.”