Reel Science

The Hover Cars in Your Favorite Sci-Fi Movie Might Actually Be Possible

It all comes down to magnets.

Back to the Future 2 flying car
Universal Pictures
The Future of Transportation

In 1989, we were told the transportation of the future would float — as long as you weren’t over a body of water.

That’s the year Back to the Future Part II was released, which, as anyone who was a child in the late ’80s or early ’90s will tell you, was the cool one. Not because of plot, necessarily, but because that’s when Marty McFly (impersonating his future son) first took off on a hoverboard. But in the streets around him, you also had floating and flying cars.

The year is 2024 now, and we could be facing down a second Biff Tannen presidency, so where are our floating cars and hoverboards? Could we even make those? The answer right now is a solid… kind of, but it would be difficult and come with unintended consequences. And that’s because of how we’ve accomplished it thus far.

Levitation, How Does It Work?

The fundamentals of levitation are relatively easy. A paper published in Physical Review Applied last fall demonstrated the ability to make a magnet hover in place with, of all things, a Dremel tool. It built off a discovery first made by Hamdi Ucar in a paper published in Symmetry in 2021. Ucar’s discovery initially made Rasmus Bjørk, who led last year’s paper, very skeptical of the research.

“I browsed through it, and then decided that looks really long and it was published in some obscure journal that I hadn’t heard of before, so I didn’t give it a lot of credibility, it didn’t look sort of entirely plausible,” Bjørk,a professor at the Technical University of Denmark (DTU), tells Inverse. Two weeks later, a colleague contacted him about the paper, and Bjørk told him he didn’t buy it. “Then he wrote back, ‘But have you seen his YouTube channel?’”

“You need a high-speed motor and some magnets.”

That channel has, to date, 219 videos of various objects levitating. Eggshells, test tubes, walnuts, and lots and lots of bearings, many looking like they’ve been taken on a cellphone. It also, according to Bjørk, relies only on classical physics, nothing elaborate needed. It could really have been discovered anytime since 1865, when James Clerk Maxwell first described his theories on electromagnetism that proved foundational in our understanding of magnetic fields. “It doesn’t even require a very elaborate experimental setup,” he says. “You need a high-speed motor and some magnets.”

This new levitation method was real, but how did it work?

If you’ve played with magnets before, you know that there are positive and negative poles; opposites attract, and two magnets oriented to the same pole repel. Joachim Hermansen, a Ph.D. student in medical technology at DTU who has worked with Bjørk on the project, tells Inverse that the dremel needs enough space from the magnet and to reach a steady state in its energy output.

“What happens is basically that the magnet on the dremel acts as both a repelling force to the magnet when it gets too close, and ... an attractive force when it gets (farther) away,” he says. And as the magnet tumbles over and over, it creates a sort of stable levitation. But the magnet has to continue to spin for this to really work. “It’s gyroscopically stabilized the same way a spinning top is stabilized, so it doesn’t fall over because of gravity,” Frederik Laust Durhuus, a DTU physics Ph.D. student also involved in the research, adds. According to Rasmus, the poles of the magnet and the dremel need to align in order to reach this hovering state.

Hovering At Scale

“Maybe sometime in the future we will be able to make something that could do that kind of thing.”

Universal Pictures

Now, an egg and a dremel is one thing. But how do you get a hoverboard or floating car out of the deal? In principle, a large object doesn’t need as fast a rotation from a proportionally equal dremel, according to the group. (“The magnetic fields don’t care about sizes as long as everything is relatively the same size,” Bjørk says.) But gravity does care, making stabilizing larger objects more difficult. Basically, the heavier the object, the more likely it is to fall out of levitation due to the effects of gravity.

Because of this, the most immediate application is using the technology to hover things around, what Durhuus calls “contactless object handling.” “As long as the object is magnetic, you can do that with quite a lot of dexterity, having it fixed in the air and then moving around the rotating device,” he says.

“The technology I have right now requires magnets on both ends, so you need magnetically paved roads.”

Bjørk says that a basic problem is trying to get an object to levitate above one of the magnets. “You can’t levitate anything above anything like the hoverboard, which would be super nice if you could,” he says. If you try, it throws off the delicate balance of this magnetism. And even if you magnetized the roads, which you’d have to do to hover objects above them in this, it could have unintended consequences on other electronics or just magnetized metals in general. This is especially true with the kind of very strong magnets you’d need to make this work on a human scale in the first place. “So that is not necessarily the way to go — instead more research to improve and understand the phenomenon is needed,” Rasmus says.

But by understanding the particulars of this technology, new understandings of magnetism could usher in breakthroughs that bring us closer and closer to the hoverboard.

“Maybe if we understand this, maybe sometime in the future we will be able to make something that could do that kind of thing,” Bjørk says. “If we study these things in depth, what else can we discover? So, I’m not ruling it out, but the technology I have right now requires magnets on both ends, so you need magnetically paved roads.”

In other words, the movie got one thing right — if you get caught trying to hover over water, the bullies are going to get you.

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