Is time travel real? What Pixar’s Lightyear Movie Shows About Einstein’s Theory

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Spoiler alert: This article explains a key plot point, but we’re not leaking anything you won’t see in the trailers. Thanks to the reader Florence, 7 years old, for her questions.

At the start of the new Disney Pixar film, Lightyear, Buzz Lightyear finds himself stranded on a dangerous distant planet with his commander and crew.

Their only hope of leaving the planet is to test a special fuel. To do this, Buzz must fly through space and repeatedly try to go into hyper-speed. But every attempt he makes comes at a terrible cost.

Each time Buzz takes off for a four-minute test flight into space, he lands on the planet and finds that many years have passed. The people Buzz cares about the most fall in love, have children and even grandchildren. Time becomes his greatest enemy.

What’s going on? Is this just science fiction, or could what happened to Buzz actually happen?

Time is relative: Einstein’s big idea

Buzz is experiencing a real phenomenon known as time dilation. Time dilation is a prediction of one of the most famous scientific theories ever developed: Albert Einstein’s theory of relativity.

Before relativity, the best theory of motion we had was Isaac Newton’s mechanics.

Newton’s theory was incredibly powerful, providing amazing predictions of the motion of planets in our solar system.

In Newton’s theory, time is like a single giant clock that counts seconds the same for everyone. No matter where you are in the universe, the master clock will show the same time.

Einstein’s theory of relativity broke the master clock into multiple clocks – one for each person and moving object. In Einstein’s picture of the universe, everyone carries their own clock with them.

A consequence of this is that there is no guarantee that the clocks will run at the same rate. In fact, many clocks will run at different rates.

Worse, the faster you travel relative to someone else, the slower your clock will be relative to theirs.

This means that if you’re traveling very fast in a spaceship – like Buzz does – a few minutes may pass for you, but years may pass for someone on the planet you left behind.

Time goes forward – but not backward

In a sense, time dilation can be thought of as a kind of time travel. It provides a way to jump into someone else’s future.

That’s what Buzz does: he jumps into the future of his friends left behind on the planet below.

Unfortunately, there’s no way to use time dilation to go back in time, to the past (as an important character talks about later in the movie).

Nor is it possible to use time dilation to travel into your own future.

This means that there is no known way for you to travel to the future and meet your older self, just by going really fast.

Time travelers above Earth right now

Time dilation may sound like science fiction, but it’s actually a measurable phenomenon. Indeed, scientists have conducted a number of experiments to confirm that clocks run at different rates, depending on their movement.

For example, the astronauts on the international space station travel to very high speeds compared to their friends and family on Earth. (You can watch the space station pass overhead if you know when to watch.)

This means that these astronauts age at a a bit slower pace. Indeed, the American astronaut Buzz Aldrin, from whom Buzz in Lightyear takes his name, would have experienced a very small time dilation during his trip to the Moon in the 1960s.

Real-life astronaut Buzz Aldrin reportedly experienced a tiny bit of time dilation during his trip to the Moon in 1969. Source: Bizony Pier/NASA

But don’t worry, astronauts on the International Space Station won’t feel or notice expansion at any time. It has nothing to do with the extreme time jumps seen in Lightyear.

Aldrin was able to return safely to his family, and astronauts in space will now too.

To infinity and beyond

Obviously, time dilation could have a significant cost. But it’s not all bad news. Time dilation could one day help us travel to the stars.

The universe is a huge place. The nearest star is at 40,208,000,000,000 km. Getting there is like traveling around the world a billion times. Traveling at ordinary speed, no one would ever survive long enough to make the trip.

Time dilation, however, is also accompanied by another phenomenon: length contraction. When moving very quickly towards an object, the distance between your spaceship and that object will appear to be reduced.

Very roughly, at high speeds everything is closer. This means that for someone traveling at high speed, they could get to the nearest star in a matter of days.

But time dilation would still be in effect. Your clock would slow down compared to someone’s clock on Earth. So you could make a round trip to the nearest star in a few days, but by the time you get home, everyone you know would be gone.

This is both the promise and the tragedy of interstellar travel.

Sam BaronAssociate Professor, Australian Catholic University

This article is republished from The conversation under Creative Commons license. Read it original article.

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