Most of us are fantasized by science fiction movies like Back to the Future, Doctor Who, Star Trek, and the latest installment of Christopher Nolan’s Interstellar where people hop in time to their past and future by traveling at the speed of light in some kind of vehicle or machine.
The concept was first popularized by H.G Wells in 1895. However, the concept has also been demonstrated in ancient mythologies such as “The Mahabharata”, “Pali Canon” and “Urashima Taro”. Although, considered vague by most of the viewers these concepts correlate to the Einstein’s theory of General Relativity.
According to his famous equation E=mc2, time travel is physically possible in the future but the other way around remains a greater challenge. The realm of Time Travel is a phenomenon which in simpler terms is dependent on speed or mass. Time slows down when the speed is high or when mass is increased to a near collapsible level.
Walking from Kathmandu to Pokhara would take more time than traveling in a vehicle moving at 60 kph. This is simply because the time is slower for the person inside the vehicle and faster for the person walking due to variation in their speeds. Now, consider the speed of the same car moving at the speed of light which is 299,792 kms. Time will be extremely slow for the person inside the car compared to the person walking, which also means that the person inside the car will age slower compared to the person walking as the time has slowed down for the person sitting inside the car, but due to the distance being extremely less the aging effect will be negligible.
To understand how mass can effect time we need to first understand the space-time fabric. A space-time fabric is an invisible fabric which expands throughout the universe. All the elements in our universe such as the galaxies, solar systems, and planets are contained on this fabric. We are yet to achieve 50% of the speed of light and reaching this speed will unfold many mysteries. But until then, everything is just a hypothesis which looks very haunting and appealing on paper.
There are theories where scientists have proposed the idea of faster-than light approach to travel back in time. If time becomes excessively slow at approaching the speed of light then exceeding the speed could cause the time flow backward, but off-course, moving an object at the speed of light makes its mass infinite.