If you were able to travel at the speed of light, all of your motion would be wrapped up in getting you to travel at the maximum speed through space, and there would be none left to help you travel through time — and, for you, time would stop. At the speed of light, there is no passage of time.
The person traveling at the speed of light would experience a slowing of time. For that person, time would move slower than for someone who is not moving. Also, their field of vision would change drastically. The world would appear through a tunnel-shaped window in front of the aircraft in which they are traveling.
Time Travel
Special relativity states that nothing can go faster than the speed of light. If something were to exceed this limit, it would move backward in time, according to the theory.
Therefore, it is only light that can travel at the speed of light – because it has no mass. The takeaway: Travelling at speed can change your experience of time, but time travel by traveling faster than the speed of light is sadly not possible.
The theory of relativity shows that light always travels at the same speed of around 300 million meters per second no matter how fast the observer is, therefore the relative speed of light is always the same. To keep the light speed the same, time would slow down.
If you were able to travel at the speed of light, all of your motion would be wrapped up in getting you to travel at the maximum speed through space, and there would be none left to help you travel through time — and, for you, time would stop. At the speed of light, there is no passage of time.
Changes to time and distance. Perhaps one of the most famous effects of special relativity is that for a human moving near the speed of light, time slows down. In this scenario, a person moving at near light speed would age more slowly. This effect is called time dilation.
According to NASA, time travel is possible, just not in the way you might expect. Albert Einstein's theory of relativity says time and motion are relative to each other, and nothing can go faster than the speed of light, which is 186,000 miles per second. Time travel happens through what's called “time dilation.”
Constant Speed
So what does this sentence really mean? Surprisingly, the answer has nothing to do with the actual speed of light, which is 300,000 kilometers per second (186,000 miles per second) through the "vacuum" of empty space.
Time travel to the past is theoretically possible in certain general relativity spacetime geometries that permit traveling faster than the speed of light, such as cosmic strings, traversable wormholes, and Alcubierre drives.
Thanks to Einstein, we know that the faster you go, the slower time passes--so a very fast spaceship is a time machine to the future. Five years on a ship traveling at 99 percent the speed of light (2.5 years out and 2.5 years back) corresponds to roughly 36 years on Earth.
At 99.99 percent of the speed of light, a craft traveling for one year would come back to a world that had aged more than 70 years in their absence. At 99.99999 percent of the speed of light, for a year, more than 2000 years would pass on Earth.
The simple answer is, anything moving through space at c, equal to the speed of light in a vacuum, experiences zero time flow. If you were to travel at the speed of light, you would experience no time.
Is it true that one hour in space is 7 years on Earth? No. The time-dilation effect of Einstein's relativity has nothing to do with space.
Albert Einstein's special theory of relativity states that photons—or particles of light—travel at a constant speed of 670,616,629 miles per hour. As far as we know, nothing can travel faster than this. But across the universe, particles are often accelerated to 99.99 percent the speed of light.
At any rate, the beam of light emitted by your flashlight would appear to reach the far wall instantly, as the speed of light is independent of your speed and would always be constant at about 300,000 kilometres per second in a vacuum.
Darkness travels at the speed of light. More accurately, darkness does not exist by itself as a unique physical entity, but is simply the absence of light. Any time you block out most of the light – for instance, by cupping your hands together – you get darkness.
Physics > Train of Thought > Light Speed. Light is fast! It can reach the universal speed limit — 186,000 miles per second. (If you could travel as fast as light, the universe would look very different.)
Speed of Light (c):
That works out to 299,792,458 m/s, or about 670,616,629 mph (miles per hour). To put that in perspective, if you could travel at the speed of light, you would be able to circumnavigate the globe approximately seven and a half times in one second.
Because space isn't curved they will never meet or drift away from each other. A flat universe could be infinite: imagine a 2D piece of paper that stretches out forever. But it could also be finite: imagine taking a piece of paper, making a cylinder and joining the ends to make a torus (doughnut) shape.
Einstein's theory of general relativity mathematically predicts the existence of wormholes, but none have been discovered to date. A negative mass wormhole might be spotted by the way its gravity affects light that passes by.
The laws of physics prohibit traveling backwards in time for many reasons. If we did travel backwards in time and changed the course of events, we would be altering the course of history.
Near a black hole, the slowing of time is extreme. From the viewpoint of an observer outside the black hole, time stops. For example, an object falling into the hole would appear frozen in time at the edge of the hole.
In special relativity, the speed of light is the ultimate speed limit to the universe. Nothing can travel faster than it.
One hour on Earth is 0.0026 seconds in space.
Thus, upon calculation we find that one hour on Earth is equivalent to seven years in space. Einstein's theory of Special Relativity stands as a explanation to this calculation.