The idea of time travel has fascinated humanity for centuries, with countless works of science-fiction exploring this concept of travel between different epochs in time. However, since the publication of the general relativity theory by Albert Einstein in 1915, time travel went from being a speculation to a reality.
One of the key insights of this theory, that allows making the previous statement, is that time isn’t constant, but rather varies depending on the speed of an object and the strength of gravity it experiences. So, contrary to what was thought in the past, time doesn’t flow uniformly for all the bodies in the universe. Time passes more slowly for objects moving at high speeds or subject to very intense gravitational fields.
The practical implication of this concept is that if we were to travel at very high speeds, we would experience time differently from the one that would experience, for example, the population that was found on Earth. This has been experimentally verified using atomic clocks (the most precise ones in existence) equipped on satellites and high-speed planes. The result was that the clocks that moved faster indicated a lower time than those that had remained on the Earth’s surface.
Travelling to the future
Even if, at least nowadays, there is no known way to come back in time, we know it is possible to travel to the future using the phenomenon previously described, known as time dilation. If we travelled in a spacecraft at a near-light speed, a short period of time for us could represent decades or centuries on Earth.
For example, travelling at 80% of the speed of light, when a year would have passed for us, on the Earth 1 year and 240 days would have gone by. An increase in the speed doesn’t make the time decrease in a proportional way, but the effect is exponential. Travelling at 90% of the speed of light, a year on the spacecraft would correspond to more than 2 years on Earth. If the speed were 99.9% of the speed of light, after a journey of one year, on the Earth more than 22 years would have passed.
It is important to mention that a person that travels in the spacecraft has the sensation that the time on the spacecraft passes as quickly as if she was on Earth, that to say, she doesn’t feel to be moving in slow motion. It is from the point of view of an observer on our planet that it is perceived that the time on the spacecraft is slower.
However, it is evident that there are lots of challenges to achieving these enormous speeds. One of them is that we would need to build a rocket capable of reaching near-light speeds, which would require a huge quantity of energy. Another problem is finding a way to safely transport humans at those incredibly fast speeds. This would require shielding to protect them from the intense radiation associated with travel at so high speeds, and be able to accelerate and slow down the spacecraft without risking their lives.
Nowadays, the only way for our time to pass a little bit more slowly is to get into a plane or a rocket, even if we would only save a negligible amount of time. For many years to come, travelling to the future in an appreciable way will still present an infinity of technological challenges.