Most people would agree there is not enough time in the day to do everything that needs to be done. On the other hand, time can seem to crawl at a snail’s pace doing a mundane task of which you have little interest. But no matter what time always seems to click by and appears to be constant and unchanging. The idea that there could be more or less time depending on where you are and how fast you are traveling would seem ludicrous. But over 100 years ago someone suggested this very idea. In 1905 physicist Albert Einstein proposed the theory of relativity when he joined both of his theories of special and general relativity into one. Special relativity focused on particles and their interactions but did not take into account gravity. General relativity describes gravity and it’s relation to other forces of nature. The new combined theory of relativity then linked three dimensional space with the fourth dimension of time. Einstein’s new theory of relativity replaced the more than 200 year old theory of mechanics that was first propose by Sir Isaac Newton in 1687. In this, Einstein was able to show that time is an illusion and is not constant. Time is relative to the viewer. For someone traveling at the speed of light time will appear to move much slower than someone who is stationary. For the stationary person looking at the person traveling at the speed of light, time would appear to move much quicker. So time is relative to the position of where you are viewing it from. Einstein called this idea time dilation. It is the difference in elapsed time measured by two observers due to a velocity difference. Essentially this is saying that one person moving at a faster velocity than the stationary person will experience slower time than the person who is stationary. The person who is stationary will age more than the person who is moving at the higher velocity. As crazy as it sounds, this principle has been proven many times already by very precise clocks on the space shuttle or satellites which move slower while in space relative to clocks on earth. One of the more fascinating ways this theory has been proven is by comparing the genetics of astronauts who have traveled in space verses people stationary on Earth. Scott and Mark Kelly are twins who both joined NASA as astronauts in 1996. Because they are twins they became perfect subjects for studying the effects of space on the human body. With one remaining as the control subject and one performing the mission in space, tests could be run to detect what changes or effects space was having on the human body. In 2015 Scott Kelly began a 1 year stay aboard the International Space Station (ISS) orbiting above Earth while his twin brother Mark remained on Earth. The time Scott spent on the ISS was at a faster speed than his brother Mark who was stationary on Earth. To put this into perspective, we first have to understand that the ISS is orbiting the Earth at over 17,000 mph. So as Scott moved through space at this faster speed he aged less than his brother who aged normally because he was stationary. While the amount of slower aging was small he nonetheless is now 13 milliseconds younger than when he left. The reason this is interesting is that as the faster a person travels the slower time moves and aging slows down as well. For example, if someone could travel at the speed of light, a trip that lasted 4 years for them would be 137,000 years here on Earth. Therefore, in essence time travel is possible for the person who travels at the faster speed with time moving slower so that aging is slowed relative to the place headed. When the person arrives at the destination they would have barely aged but the place arriving at would have experienced time much faster and would in essence be a future version from when the person started their journey.

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