Spoiler alert: this article discusses a key plot point, but we wont disclose anything you wont see in trailers. Many thanks to reader Florence, 7 for her comments.
Buzz Lightyear gets stranded on a dangerous faraway planet with his commanding officer and crew at the start of the new Disney Pixar film, Lightyear.
Buzz has to travel into space and repeatedly attempt to flee to hyper-speed to get off the planet. However, each attempt comes with a significant price.
Buzz returns to Earth after a four-minute test flight to discover that many years have passed. The people he loves the most are women, who have children, and grandchildren. Time is his greatest foe.
What's going on? Is this just science fiction, or is it possible that what happened to Buzz actually happen?
The amount of time is relative, according to Einstein's major theory.
Buzz is experiencing a real phenomenon known as time dilation, which is a result of one of the most famous scientific theories ever discovered, Albert Einsteins theory of relativity.
Isaac Newtons mechanics was the best theory of motion before relativity.
Newton's theory was extremely powerful, providing astonishing data on the earth's rotation.
Time is like a single gigantic clock that ticks away the seconds in the same way for everyone in Newtons theory. No matter where you are in the universe, the master clock will display the same time.
Einsteins theory of relativity shattered the master clock into many clocks one for each individual and object in motion. In Einsteins view of the universe, everyone has their own clock.
There is no way to guarantee that the clocks will tick at the same rate. In fact, many clocks will tick at different rates.
The worse your clock will tick slower than yours if you travel faster than someone else.
This means that if you fly very fast in a spaceship as Buzz does, a few minutes might pass for you, but years might pass for someone on the planet you left behind.
Time is moving forward, but not backward.
Time dilation may be thought of in a way as a form of time travel. It is a means to enter the future of someone else.
Buzz does exactly what he does: he invests in the future of his friends left on the planet below.
Unfortunately, there is no way to use time dilation to travel backward in time, into the past (as one important character mentions later in the film).
It is also unlawful to use time dilation to travel into your own future.
That means there is no known method for you to go into the future and meet your older self, by going really fast.
Right now, time travelers are above Earth.
Time dilation may seem like science fiction, but it is in fact a real-life phenomenon. Scientists have conducted a number of experiments to verify that clocks are ticking at different rates depending on how they are moving.
When it comes to Earth, astronauts on the International Space Station are travelling at a very high speed compared to their friends and family on Earth. (You may observe the space station pass overhead if you know when to look up.)
This indicates that these astronauts are ageing at a slightly slower rate. Indeed, US astronaut Buzz Aldrin, from whom Buzz in Lightyear is named, would have experienced a little time dilation during his journey to the Moon in the 1960s.
Don't worry, the astronauts on the International Space Station will not experience or notice any time dilation. It's nothing like the extreme time jumps seen in Lightyear.
Aldrin was able to return to his family in good time, and the astronauts onboard now will too.
To infinity and beyond
Time dilation may come at a significant cost. However, it isn't all bad news. Time dilation might one day allow us to travel to the stars.
The universe is a vast place. The nearest star is 40,208,000,000,000 km away. Traveling around the world one billion times would be impossible. Traveling at an ordinary speed, no one would ever recover enough to make the journey.
Time dilation is accompanied by a second phenomenon: length contraction. When one travels very slowly toward an object, the distance between your spaceship and that object will appear to be contracted.
Everything is closer together at a very high speed, making traveling quite a breeze in a matter of days.
The effects of time dilation would still be in place. Your clock would be slower relative to the clock of someone on Earth. So, you may make a round trip to the nearest star in a few days, but by the time you return home, everyone you know would be gone.
Interstellar travel is both a promise and a tragedy.
Sam Baron, an Associate Professor at Australian Catholic University, is a research fellow.
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