According to Back To The Future Part II, today, October 21, 2015, is the day Doc and Marty arrive from the wonderful world of 1985. They’re greeted by a world of flying cars, hoverboards and self-lacing shoes.
As far as time travel is concerned, making the journey from 1985 to 2015 is easy. Many of us took the long road, traveling at the usual 1 second per second through time. But we know it’s possible to make the journey in less time. A central property of special relativity is time dilation, where an object moving at some speed relative to you will appear to experience time at a slower rate. We see this effect in particle accelerators, where unstable particles moving at high speed decay at a slower rate than ones at rest relative to us.
Using time dilation, you could in principle travel away from Earth at high speed and return 30 years later. If you traveled at speeds approaching light, then your journey might only take a month for you while decades pass on Earth. The power required for such a journey is far beyond the total energy production of Earth, but it’s possible within known laws of physics. Traveling forward in time is easy.
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