How to time travel?
1. Travel to Future using Time Dilation
Time dilation, according to the theory of relativity, is the slowing down of one clock as compared to another clock because of their relative velocities. Let’s now explain it using an example: Suppose there are two spacecraft and each one has a clock that has the same time. Time will move slowly during the first watch and quickly during the second watch since the first spacecraft is traveling at 1000 mph and the second is moving at 100 mph.
Keeping the above statement in mind, if one of the two twins is left on Earth and the other is sent to orbit the earth at a speed of 240000 km/s in a spacecraft, then after journey of 6 years, the child who was left on Earth will be 10 years old after the journey.
And the child living in the spacecraft would have been only 6 years old. In this way, child traveling in spacecraft will reach 4 years in the future.
2. Making Use of Infinite Cylinders
This theory is proposed by an astronomer Frank Tipler, it is also known as the Tipler Cylinder.
According to Frank Tipler, if we roll a matter that is more than ten times the weight of the Sun to make an infinitely long and dense cylinder. If a spacecraft moved around this cylinder in a very precise spiral after spinning it for a billion revolution per minute, the spacecraft might be able to travel through time.
However, Stephen demonstrated that it is not possible to create a cylinder that is infinitely long, therefore using this technique to time travel would require negative energy.
3. Through Wormholes
Now, how are you going to use these wormholes for time travel? The force of gravity works to close the wormhole’s mouth, making it difficult to keep it open.
In order to overcome gravity’s effect and create these wormholes, we will require substances having negative mass, also known as exotic matters. According to physicists, the Casimir effect in quantum physics makes it possible to create the required negative energy.
Calculations, however, showed that a large amount of negative energy would be needed. Which is far beyond to the technologies that we have today.
Hope this helps! Please comment what you think.