Scientists say time travel is possible - and humans have already done it, the Daily Mail reports.
From H. Г. Wells to Christopher Nolan's "Interstellar," the possibility of time travel has excited people for centuries.
But although it sounds like pure science fiction, physicists now believe that time travel really is possible. In fact, scientists say humans have already done it.
But before you start planning your trip to ancient Rome, experts warn that real time travel is nothing like what we see in the movies.
It may seem obvious, but here on Earth, we're all moving through time at the rate of one second per second.
Thanks to Einstein's theory of general relativity, however, it is possible to travel through time faster than that speed.
The faster one moves, the faster one can travel forward in time - leaping centuries in mere minutes when approaching the speed of light.
Although this effect is imperceptible at slower speeds, it means that all the astronauts on the International Space Station (ISS) are "time travellers" skipping forward into the future.
In movies like Terminator, time travel usually involves getting into a machine and moving to a completely different time and place in the past or future.
True time travel, however, does not consist of jumping from one point on the timeline to another.
According to NASA, "time travel" is traveling at a speed greater than one second per second.
And while that may sound impossible, the space agency says it's actually possible.
In fact, everyone moves forward in time at different speeds depending on where we are and how fast we are moving.
That means time travelers are all around us every day, and you could be one too.
In 1915. Albert Einstein presented his theory of general relativity to the Prussian Academy of Sciences in Berlin and proved that time travel is possible.
As strange as this situation sounds, Einstein's theories show that this kind of time travel is not only possible, but extremely common.
Dr Alasdair Richmond, a philosopher and time travel expert from the University of Edinburgh, told MailOnline, "Einstein taught us that how fast time passes in your surroundings varies depending on your speed."
Essentially this means that the faster you travel, the slower you experience time.
So if you're on a plane or train, you'll sense time slower than anyone standing still, and experiments have shown this to be true.
In 1971, two scientists named Joseph Haefele and Richard Keating decided to prove Einstein's theory by inducing time dilation here on Earth.
The scientists took two ultra-precise atomic clocks and loaded them onto commercial airplanes capable of flying around the world in a single flight.
One clock was sent east and the other west, then they were compared to a third clock that was left stationary on the ground.
The clock moving east with the rotation of the earth moved faster than the one on the ground and thus elapsed less time.
At the same time, the clock that was flying westward against the earth's rotation was moving slower than the clock on the ground, and thus actually elapsed more time.
And just as predicted by general relativity, when the clocks landed, Haefele and Keating found that the clock flying east lost 59 nanoseconds, while the clock flying west gained 237 nanoseconds.
According to this theory, anyone who spends a lot of time moving at high speed is a time traveller.
The astronauts aboard the ISS orbit the Earth at nearly 17,500 miles per hour (28,100 km/h), high enough to experience a bit of time travel.
For example, NASA astronaut Scott Kelly has now spent 520 days on the station and, as a result, has aged slightly slower than his identical twin, Mark Kelly, who has remained on Earth.
Although these effects are imperceptible, they are common enough to cause technical problems for precision systems like GPS satellites.
Because satellites orbit at about 8,700 mph (14,000 km/h), they are constantly moving forward in time, and their on-board clocks must account for this difference.
If GPS satellites do not adapt to time, they will not be able to determine their own position in space and will be useless for accurate navigation.
While traveling forward in time is a natural consequence of physics, traveling into the past is another story.
"Travelling backwards in time is much, much more complicated," says Dr Richmond.
However, while in practice it is probably impossible, Dr Richmond points out that travelling back in time is "theoretically possible".
This is because going backwards requires bending time and space.
Professor Peter Watson, a theoretical physicist at Carleton University, says: "You can bend spacetime using mass: that's actually gravity in Einstein's formulation.
In principle, we could make spacetime so bent that there would be a hole in it.
The resulting structure would be known as a wormhole or tunnel through spacetime.
Unfortunately, maintaining a stable wormhole for long enough to pass through it requires "negative mass", which is only a theoretical possibility.
Furthermore, even if we were able to use a wormhole or other device to create a "closed time-like loop", we could never use it to travel further back than the day it was created.
Dr. Richmond points out, "If I built the world's first closed time-like curve generator tomorrow afternoon, I could not use it to travel to any time before tomorrow afternoon.
So while traveling back in time may be theoretically possible, traveling back to meet your parents as Marty McFly in Back to the Future is still impossible. | BGNES
