TIME TRAVEL- FICTION OR POSSIBILITY?
We all travel through time. We travel a year in time between birthdays. We are hurtling into the future at a rate of one second per second. But what about traveling years in the past or future? Is that possible? If no, then why not?
To go into detail, let’s talk about relativity. Einstein developed his theory of special relativity and theory of general relativity in 1905 and 1915. To put it simply, special relativity describes the relationship between space and time for objects moving at constant speeds. First, there is no absolute reference point, that is we measure everything in relation to something else. Second, the speed of light is constant (186,000 miles per second). And third, our universe has a speed limit, that is nothing can travel faster than the speed of light. So in accordance to this theory, the faster we travel, the slower we experience time. Considering this, the answer might seem simple, just travel faster and we can go to the future, but we can’t exactly accelerate humans to near light speed. However, Astronauts Scott Kelly and his twin brother, Mark Kelly have in fact experienced something similar. Scott Kelly spent 520 days in orbit, while Mark logged 54 days in space. Because of the difference in the speed at which they experienced time over the course of their lifetimes, there was a widened age gap between them! "So, whereas I used to be just 6 minutes older, now I am 6 minutes and 5 milliseconds older," Mark Kelly said in a panel discussion on July 12, 2020, "Now I've got that over his head." Another example to prove this theory, has been demonstrated by an experiment that used two clocks set to the same time. One stayed on earth and another flew in an airplane. After one rotation, on comparison there was time difference between the clocks. The one that traveled at high velocities in an airplane was slower than the one on earth!
We may not have been able to travel back into time or forward into the future, but we have applied the math of time travel in our everyday lives. One great example being The Global Positioning System or GPS. GPS satellites orbit around Earth very quickly. Which means for GPS satellites with atomic clocks, the effect of special relativity cuts 7 microseconds, or 7 millionths of a second, off each day. But at the same time, the theory of general relativity says that gravity curves space and time, causing the passage of time to slow down. This means that GPS satellites would experience lesser gravity and hence would tick faster. Now, that adds another 45 microseconds onto the GPS satellite clocks each day. Doing the math, the net result is an added 38 microseconds. This calculation is super important in accurately pinpointing a location. If scientists had not accounted for the additional time, we would be lost all the time. This kind of time travel may seem as negligible as the Kelly brothers' age gap, but given the hyper-accuracy of modern GPS technology, it actually does matter.
Although time travel like in the movies has not been done yet, and seems improbable, we do still apply the math of time travel more often than not. And speaking theoretically, let’s say we want to travel to the next millennium, we could build a fast starship, travel fast enough back and forth, and in a few days (for us) we can definitely be back here on Earth a millennium in the future. The science of this is completely uncontroversial and clear. Carlo Rovelli (Physicist and writer) said so himself. The only problem is finding the money for such a starship, and of course the deeper physics problems. Traveling to the past however, is much more complicated. The reason is that we would have to beat the entropic arrow of time (one way direction or asymmetry of time), which is not impossible. Looks like we got another reason to enjoy the present.
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