Time Travel

"How to build a time machine" by Paul Davies

Some tricky questions. Where exactly are the past and future? Surely the past has disappeared and cannot be retrieved, while the future hasn't yet come into being. How can a person go to a world that doesn't exist.
Sir Issac Newton took a more abstract and mechanistic view of time. "Absolute, true and mechanical time, flowing equably without relation to anything external".
Einstein's work demolished Newton's view of both space and time, rendered meaningless the universal division of time into past, present and future, and paved the way for time travel.

1.How to visit the future.

 "Time is not absolutely defined", Albert Einstein

Einstein gave the concept of relative time. Time is elastic. According to special theory of relativity, the exact duration of time between two specific events will depend on how the observer is moving.

Experiment: Joe Hafale and Richard Keating 1971. They put highly accurate atomic clocks into airplanes, flew them around the world, and compared their readings with identical clocks left on the ground. The results were unmistakable: time ran more slowly in the airplane than in the laboratory, so that when the experiment was over the airborne clocks were fifty-nine nanoseconds slow relative to the grounded clocks-exactly the amount predicted in Einstein's theory.

Physicists call the slowing of time by motion the time dilation effect.
Einstein's time dilation factor


At half the speed of light, time is about 13 % slowed, at 99%, it is 7 times slower-1 minute is reduced to 8.5 seconds. Technically, the timewraps becomes infinite when the speed of light is reached. This is a sign of trouble. It tells us that a normal material body can't reach the speed of light.