Everyone’s talking about this crazy new
hoverboard that looks too good to be true. And it sort of is. But trust me, the truth
is super cool! That was a pun. You’ll get it once I explain how- y’know what, just
roll the intro. Hey McFly guys and girls, Julian here for
DNews. It’s 2015, the year Marty went re-back to the future, and Lexus has teased us all
with a short video of a functioning hoverboard being ridden around a skatepark. Is it real?
Is it possible? Yes and qualified yes. I’ll explain: What’s not shown in the video is the hidden
magnetic track Lexus installed in the Barcelona skate park. That may seem like cheating, but
it’s more complicated than just using magnets. If you’ve ever played with magnets and tried
to levitate one above the other, you know it’s not easy. As soon as you let go, the
magnet will just flip around and get sucked to the other one and that’s really the opposite
of what you want. But that problem doesn’t exist with some superconductors. A superconductor is a material that, when
cooled past a critical temperature, lets electrons move freely within it with zero resistance.
Obviously this makes them great for high current wires, but the freely moving electrons do
something else too. They create currents on the surface that screen the superconductor
from magnetic fields. As you cool a superconductor past its critical temperature it expels magnetic
fields, and this is called the Meissner effect. If you put a superconductor by a magnet, it
will repel it. Put one above the other, and it’ll levitate. This is called Quantum Levitation. But not all superconductors are created equal.
Some, called Type-II superconductors, actually have little vortices of current and the center
of each vortex is like an eye of a storm. In the middle, the material behaves normally
and lets some magnetic field lines, or flux, pass through. When I say “some” I should
note it’s still quite a lot. A 3 inch disk can have as many as 100 billion flux lines
passing through it. The superconductor will actually pin the flux lines and will appear
to lock itself in place levitating above a normal magnet. So they don’t just exhibit
Quantum Levitation, but Quantum Locking too. No, not like the weeping angels, Whovians.
Anyway, you can move the magnet around, even put the superconductor underneath it, and
it will still stay locked where it was. Plus with all those flux lines pinned down, a 3
inch disk just half a micron thick can support 70 thousand times its own weight. So it locks in place above a normal magnet,
but if the superconductor is above a circular magnet, it can rotate around the axis of the
magnet. You can expand that circular magnet to a track any size and shape you want and,
say, hide it under a skate park. Put a Type-II superconductor above it, give it a little
push, and it can happily zoom around the track no problem. Mind you, there are limitations.
The superconductor has to be cold. Like, really really cold. Even so-called “High Temperature”
superconductors need to be at least -135 degrees celsius. To hit those temperatures you need
to use liquid nitrogen, which explains the thin wisps of smoke and frost coming from
Lexus’ hoverboard. The superconductor also has to be thin, because the thinner it is
the stronger the flux-pinning effect. And the magnetic field can’t be too dense. Too
much flux per meter squared and the vortexes overwhelm the material, turning it back into
a not-so-superconductor. By the way, the unit for magnetic flux density is the Tesla. that’s
right, Tesla has his own unit of measurement. I thought you’d like that, internet. Type-II superconductors were discovered in
1935, 20 years before the first Back to the Future took place. But Robert Zemeckis wasn’t
around then to show us the way, and now in 2015 his vision is finally realized. So long
as you keep your super thin superconductor supercooled, you too can have a hoverboard.
Provided you don’t mind going around in circles on a magnetic track. Which would still
be really cool, but wouldn’t help you if you’re trying to get away from Biff’s
larcenous grandson. Magnetic levitation can be scaled up too and
because the only friction is from air, that means you can get going pretty fast. Trace
talks about maglev trains here.