Time travel is a concept that has fascinated many people for centuries. It is a recurring theme in many science fiction stories. The ability to perhaps revisit our past and change the outcome of our actions or to take a look at our future and escape the present is very tempting. But, can human beings challenge the laws of nature and make time travel possible? In a manner of speaking, time travel is part of our daily lives!
To better understand what time travel means one must first understand the concept of time in physics. As per defined by the Oxford dictionary, time is: “the indefinite continued progress of existence and events in the past, present, and future regarded as a whole”. However, the concept of time in physics is similar to the x, y and z dimensions in a coordinate system. These are our first three dimensions, that can be plotted and replotted to show a change in position. We can equivalently think of time, our fourth dimension, as a quantity which can be plotted to represent its passage, in a manner akin to a timeline. Our position in space is dependent on time, and can be changed as time progresses. However, time is independent of our position, and is perceived as linearly progressing regardless of where we are located. Time is the dimension in which events are ordered from past to present and then to future.
Sometimes we can think of ordinary occurrences as examples of “time travel”. In an elementary example, we all travel in time every single day. During the last month, we have moved a month forward in time. Another way to put this is that we travel in time at a rate of one hour per hour. Another basic example of daily time travel could be a very long flight across time zones. For example, a flight leaving Australia at the early hours of the morning, say 3:00 A.M. on December 31st would arrive to New York twenty four hours later, at approximately 11:00 A.M on December 31st. How is it possible, though, to arrive on the same date if the time of travel was a whole day? This is because of the difference in time zones. A person aboard that flight would technically travel in time to the past. Similarly, a person flying in reverse, from New York to Australia, would “travel into the future”, thanks to the difference in time zones. These daily events wouldn't ordinarily be thought of as examples of time travel, but it is indeed travel in the fourth dimension.
Astronauts in the International Space Station (ISS), in a way, experience “time travel” in the more traditional sense. Time actually passes slower on Earth in relation to time in space, in a phenomenon called “time dilation”. Time dilation is the difference of elapsed time as seen by a stationary observer vs. an observer moving relative to the other. In space, time appears to pass slower than here on Earth. This is what astronauts on the ISS could experience as “time travel”. On average, for every six months that pass for humans on Earth, astronauts on the ISS experience about 0.007 seconds less. Although it is a small difference, in a way it can be considered “time travel” because of the difference in perceived time.
Time travel is indeed a daily fact. Its hard to think about ordinary events as time travel, even though we are in fact traveling in the fourth dimension. Classic examples of time travel, such as massive time machines and complex paradoxes are unfortunately yet unobtainable with modern physics, although it is fun to think about it and theorize. Meanwhile, we can sit comfortably with the thought that every day we travel in time, and as such, we are all time travelers.
References
“Is Time Travel Possible?” Nasa.gov.
travel.html> 1 December 2013.
Bonsor, Kevin, and Robert Lamb. "How Time Travel Works" 20 October 2000. HowStuffWorks.com. 30 November 2013.
Toothman, Jessika. "How do humans age in space?" 28 September 2010. HowStuffWorks.com. 4 December 2013.
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