How to Time Travel
Time isn’t a constant. Instead, thanks to Albert Einstein’s theory of relativity, we know that both time and space act as variables based on the perspective of the observer.
Space encompasses the three dimensions that we directly interact with in every day life: length, width, and height. Time, on the other hand, is a whole new dimension. According to Einstein, time will speed up or slow down according to how fast the observer moves or its gravity relative to something else. The 4D environment that simulates this is known as the space-time continuum.
It is considered a continuum because every coordinate in space correlates to another coordinate in time. In other words, there are no missing points in the space-time function. Every place and every moment in history can be described by these coordinates.
This also means that if you were to divide the space-time continuum into multiple slices, you would be able to compare different points and their spatial geometry across time. One application of this would be comparing spatial geometry at consecutive points in time to see if the universe is expanding.
Interestingly enough, traveling through time has actually already been achieved. We can see this by looking at astronauts on the International Space Station (ISS) that age more slowly than we do on Earth. This effect is called a “time dilation” and it occurs because of the ISS’s high orbital speed. However, the time dilation on the ISS is very small, so the astronauts would have to remain on the spacecraft for over 100 years just to influence their time by a mere second.
To make a bigger jump through time, we would need to increase speed. Specifically, we would want to move at the speed of light, or about 299,792,458 meters per second. To move at such a speed, this would require an object with infinite mass and zero length. But an object like this seems physically impossible. Using a manmade machines today would fall apart before ever reaching that speed.