Scientists claim to have reversed time

Timey wimey: In theory, wormholes could allow us to jump through vast chasms of time and space. © Fred Mantel

Is time travel really possible? For centuries, humans have dreamed of leaping into the deep past or distant future. Will we ever do it? The answer lies in one of Einstein’s strangest theories.

When scientists said they had reversed the flow of time in a quantum computer last week, the news made headlines around the world. The team said that their experiment could, for the first time, open up ways of “investigating time reversal and the backward time flow”.

According to the Massachusetts Institute of Technology Review, it’s not quite as historic as it sounds. What the scientists did was closer to pressing rewind on a video. However, it’s a step in the right direction towards a goal that has captivated the human imagination for generations.

Will Tardis-style time travel ever be possible?

“We can jump forward into the future as much as we want. It’s only a matter of going really, really fast,” says Paul Sutter, an astrophysicist at Ohio State University.

It comes down to Albert Einstein’s theory of special relativity, which states that space and time are woven together in a fabric called space-time. Everything in space-time has a speed limit of 300,000 kilometres per second (the speed of light).

But the closer you get to the speed of light, the slower you travel through time. Scientists have already observed the effect using ultra-precise atomic clocks travelling on jet planes.

Imagine you left Earth aged 15 in a rocket travelling at 99.5% the speed of light (much faster than we can travel now), and only celebrated five birthdays on the craft.

When, aged 20, you returned to Earth, your classmates would be 65 years old and ready to retire. To them, you would have travelled into the future.

But going backwards in time is much, much harder.

According to Einstein’s theory of general relativity, time passes more slowly the closer you are to fields of gravity. This means that strange distortions of space and time can occur near black holes, which have mind-bogglingly intense gravitational pulls.

“When it comes to the past,” Sutter said, “the mathematics of general relativity does allow a few strange scenarios where you can end up in your own past. But all of these scenarios end up violating other known physics, like requiring negative mass or infinitely long rotating cylinders.”

So, the basic laws of physics seem to stand in our way — for now. But one day, in the far-flung future, could humanity have mastery over time?

Back to the future

Backward time travel is physically impossible, says physicist Richard Muller. And as for the future, space-time is expanding constantly. “Every moment, the universe gets a little bigger, and there is a little more time, and it is this leading edge of time that we refer to as now.” We will never be able to travel to the future because it “does not yet exist”. It is being created in the now.

But others are more hopeful. According to Stephen Hawking, while time travel would seem to be impossible according to 20th-century classical physics, it might be possible with our burgeoning understanding of quantum mechanics. Playing with quantum particles could create the negative energy we need to build a traversable wormhole, and hop through time. It’s far-fetched, but it might just work.

You Decide

  1. Could a time machine do more harm than good?
  2. Would you rather travel back to the past or into the future?

Activities

  1. Choose the moment in time that you would most like to visit. Write a few sentences explaining why.
  2. Draw a one-page comic book strip about a futuristic adventure involving time travel.

Some People Say...

“People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion.”

Albert Einstein (1879-1955), German-born physicist

What do you think?

Q & A

What do we know?
That Newsweek and other media outlets might have got a bit overexcited when they ran the headline: “Scientists Have Reversed Time in a Quantum Computer”. According to Technology Review, the scientist’s “technique might be useful for testing quantum programs. This is correct. But it’s a lot less interesting than a time machine”.
What do we not know?
If we did build a time machine, whether you could travel back in time and kill your own grandfather. This is known as the Grandfather Paradox. It’s ultimately a strange question about how changing the past might impact the present, which forms the basis of the 1985 classic film, Back to the Future.

Word Watch

Quantum computer
A relatively new field of computing that uses the principles of quantum mechanics to do strange things with data.
Massachusetts Institute of Technology
One of the USA’s top research universities.
Tardis
A fictional time machine in Doctor Who. The name is an acronym for Time And Relative Dimension In Space.
Speed of light
When we talk about light years, we are saying how long it would take to get somewhere if you were travelling at the speed of light. Our next-nearest star, Alpha Centauri, is over four light years away.
Atomic clocks
Clocks that use measurements of time far, far smaller than seconds, so they are incredibly accurate and precise.
Negative mass
Physicists believe that matter can have negative mass in the same way a particle can have a positive or negative charge. If you pushed an object with negative mass, it would accelerate towards rather than away from you.
Rotating cylinders
In 1974, Frank Tipler theorised that you could use a rotating cylinder to warp space time. However, scientists now think the machine would have to be infinitely long to work.
Stephen Hawking
In the physicist’s last book before his death, Brief Answers to the Big Questions, he seemed more open to the possibility of time travel than ever.
Traversable
Able to be travelled through.

Subjects

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