Time travel is always an interesting topic to discuss. Being able to switch between the past, the present and the future is not a just fiction that was created by the mere imagination of writers and movie makers but is a theory that was developed by great scientists like Albert Einstein and Stephen Hawking. Till date, there is no such device called a time machine. But there are theories that actually state that time travel is possible. Let us take a closer look.
To understand time travel it is essential to know about two things called space-time and black holes.
Spacetime: Time is always considered to be an independent variable that keeps flowing continuously irrespective of the change in anything around it. But according to the theory of relativity, the flow of time varies at different points of space. The flow of time in earth need not be same as the flow of time in various points on space. Time varies along space like the variation of temperature at different points on earth. So time is considered as a dependent variable in this theory and it is said to depend on its location in space. Space is considered as a variable with three dimensions called length, width and height. But space-time is a variable that has four dimensions which have time as the fourth dimension. In the theory of relativity, space-time is used to calculate the variation of time at different points in space.
Black Holes: The black holes are not actually holes. They are heavenly bodies like planets that have incredibly high gravity. Gravity on earth pulls the earthly objects towards earth and prevents them from escaping to space. In the same way, the high gravity of the black holes pulls everything that passes across it in such a way that even the photons in the light waves are not allowed to escape. An object is visible to you only when your eyes see the photos bouncing off it. As the photons are pulled towards the black holes and are not allowed to bounce off, they become invisible in space. This is the reason why they appear dark and look like a black hole in space, hence the name.
Bottom line: The time flow on earth is different from the time flow near a black hole. If you can travel to a black hole, you can actually travel time. The next section of this article will explain this with better clarity.
Time travel theories
According to toStephen Hawking, “if you can spend a few years near a black hole, it is actually more years on earth”. According to Einstein, “if you can travel faster than the speed of light you can actually travel time”. Now by merging the two theories, we get a reasonable solution.
According to Stephen hawking, you can travel time by living near a black hole. Light is found to be the fastest thing in the universe but if a black hole can pull light into it then living near a black hole is possible only if something can travel fast enough to resist that gravity i.e. much faster than light. So both the theories of Einstein and Stephen Hawking merge at this point. To travel time one has to survive near a black hole (Hawking). To survive near a black hole, one has to resist the gravity of black hole. To resist the gravity of the black hole, one has to travel much faster than light (Einstein). So, the conclusion is, “if you can travel in a device that can travel fast enough to survive near a black hole, you can travel time”.
The relationship between velocity and time:
We know that velocity (V)=distance (L) / time (T)
So change in velocity = change in distance/change in time
or dT = dL/dV
This means the change in time depends on up on the change in velocity and change in distance. If you can change the velocity up to a certain level, you can actually control time. But this velocity has to be really really fast (much faster than the speed of light).
Fact: Light travels around the equator of earth seven times in a second. It takes about 8 minutes for light to travel from the sun to earth. Light is observed to be the fastest thing in universe ever.