Travel back in time with me to the early 2000s.

Y2K had just failed to end the world,  emo music was coming onto the scene, and this weird new thing called  YouTube had just been invented. All the while, physicists were hard  at work making an invisibility cloak.

Well, kinda. They made a prototype  of a device that can shield objects from electromagnetic radiation  and cloak them from detection. Which is how we would make an invisibility cloak.

This particular one was just really specific, as it only worked for microwaves  coming from one direction. Even though that prototype was  pretty far from a perfect disguise, the principles behind the device  have had a lot of applications. Including, believe it or not, helping  make our cities invisible to earthquakes. [♪ INTRO] Okay but… how can a device make a city  invisible, to light or to earthquakes?

What does a cloaking device even do? Well, at the most basic level, it diverts waves. Everything we see is a reflection  of light bouncing off objects and back into our eyes.

So the idea with cloaking is to prevent  visible light from bouncing off an object. No bounce, no vision. How do you avoid the bounce, you may ask?

One way is to absorb the light. But if you absorb all the light,  you don’t get invisibility. You get black… at least until an object  heats up enough to start glowing.

So scratch that, we need another option. Luckily, we have one: divert the  light around an object entirely. Which sounds great!

Boom, solved! But the thing is, after you’ve  sent the waves around an object, you have to bring those waves back together. And if you aren’t careful, you’ll get a shadow.

Shadows happen when light doesn’t reach  its target for one of two reasons. It’s either blocked by an object directly,  or there’s destructive interference, which is what happens when two waves that don’t match up perfectly run into  each other and cancel each other out. In principle, if you could make the  light just go perfectly around an object, and meet back up on the  other side perfectly aligned and without losing any power, then  the object would be totally invisible.

If a wave is the same at point A and point C, it looks like nothing was in its path, even if something happened  along the way at point B. But to be truly invisible, you’d  need to pull off this optical trick from all angles and for all wavelengths of light. Which would be incredibly difficult.

It’s possible, though. And scientists have created some  proofs of concept over the years. The biggest, most exciting breakthroughs  are coming in the form of metamaterials: specially engineered materials  not found anywhere in nature.

They have special properties that are possible due to the structure of the  material, usually at the nanoscale. That team from 20 years ago were  the first folks to really start using these materials as cloaking devices, and they did it by squishing  electromagnetic waves into submission. Their prototype looked kind of like  a very high-tech roll of duct tape.

The core concept was to  use materials with specific electromagnetic properties that  are bent into specific shapes. With perfect design, the metamaterial  would divert electromagnetic waves around the donut and precisely combine  them back together on the other side, cloaking whatever object is hidden  inside the duct tape roll object. The materials they chose to meta-fy  were copper filaments bent into very specific shapes and printed onto fiberglass  cylinders at very specific intervals.

The key is that a conductive  material, like copper, can be bent such that it reshapes  electromagnetic waves in predictable ways. Every shape bends the waves a bit  differently, and when they work together, they squish incoming waves apart, guide  them around the outside of the roll, and push them back together on the other side. Boom.

Invisible. Mostly. Okay, so the prototype wasn’t perfect.

Being smushed around like that can  rob a wave of some of its energy, meaning when it comes back together, it doesn’t look exactly like it did  before, and casts a bit of a shadow. But this was 2006! Again,  YouTube had just been invented!

This was practically the dark ages! So it’s very impressive that in  2006 a team of researchers got a physical prototype invisibility cloak to perform quite similarly to the simulations  they were running on their computers. The other caveat of this experiment,  and it is a pretty big one, is that it was done with microwaves.

So… yeah, you could still totally see the  object that was meant to be invisible. But, to be fair, many promising  cloaks start their testing with longer-than-visible wavelengths, like microwaves. That’s because if you wanna mess  with an electromagnetic wave using metamaterials, the metamaterial structures have to be smaller than the  wavelength they’re manipulating.

Visible wavelengths are incredibly small. Like 1/100th of the width of a human hair small. So engineering materials smaller  than that is a huge challenge.

Microwaves, on the other hand,  are more like the size of a pea. Still small, but MUCH bigger than visible  wavelengths and much more practical! Now, obviously, it’s been 20 years, and scientists did not just stop trying to make cloaking devices.

There have been a ton of attempts  to turn things invisible. Some teams have tried fancy metamaterial coatings that scatter light so that the  reflected beams cancel each other out. But those only work at certain wavelengths so far, and the materials they’re made of can make the cloaks look darker  than everything around them.

Others have made tiny cloaks printed  on chips using even tinier waveguides to maneuver light around an object. But those don’t work in 3D just yet. Sheets of dielectrics with  tiny metamaterial shapes printed on them seemed promising.

But actually putting the thing together  results in flaws that cast shadows, and it only works with  microwaves at certain angles. Maybe we could make cloaks that adapt  in real time using sensors and AI. They could detect incoming light and  reflect it back such that the reflection mimics the background behind the cloaking device.

But these also only work for  limited light frequencies, and the principle feels a bit more  like blending in than disappearing. One team got creative with  positioning traditional lenses to bend light around objects. These make for some amazing looking pictures, but they’re not technically  what we’re talking about here.

The physics behind them is closer to a  telescope than a true cloaking device. They’re just basically optical illusions. That’s generally true across the  spectrum of these prototypes.

A quote-unquote real cloaking device  is so specific that pretty much nothing currently in development has reached the  threshold of a true cloaking device yet. Plus, if scientists are  being honest with themselves, they’re still mostly stuck working  outside of the visible light spectrum. And to be really honest, they’re  still pretty far off from truly cloaking anything in 3D,  let alone in the optical band.

Again, small wavelengths are hard. But big wavelengths are easier. And some of the most promising applications  for this tech are on a seismic scale.

Literally. Scientists want to use  them for anti-earthquake technology. But before we get to those city-sized  cloaking devices, we have a quick ad for you.

You’re still watching this video. So you’re probably getting something out of it. Maybe you’re even enjoying it.

For a lot of people, it’s hard to  imagine enjoying science and learning. You could have been one of those people. But after a little SciShow, who knows?

Maybe science can be pretty cool after all. If SciShow impacted you in  that way, or in any good way, you can help us make more SciShow videos. You have a chance to join Binorthedrunkdwarf,  Charlie Stanley, Harry Plumley, Parabola Queen and Raz Tirosh  as a President of Science and support SciShow production on Patreon.

However you’d describe SciShow videos,  they’re probably more approachable, digestible, dare I say fun, than reading a  textbook, falling asleep in a lecture hall, or trying to parse dense academic publications. So if you agree that these videos are valuable, please responsibly visit patreon.com/SciShow. When you think about it, cloaking  technology for earthquakes totally makes sense—earthquakes  are just what happens when seismic waves rattle  through the Earth’s crust.

These waves are huge, and  they carry a ton of energy! They can topple buildings, shake the  earth apart, and trigger tsunamis. But at the end of the day, a wave is a wave.

So if metamaterials can change the  path of an electromagnetic wave, there’s no reason the same can’t  theoretically be done for seismic waves, too. With a strategic arrangement  of meter-scale structures, there’s hope that we could design  buildings—or maybe even entire cities— that would be invisible to earthquakes. Historically, pretty much all  of our earthquake prevention can boil down to one of three methods.

First, you could stabilize a  structure by making everything as rigid as possible so it  doesn’t get shaken apart. Like, the Great Pyramids, for  instance, made of sturdy stone blocks. Second, you could build something  that can go with the flow.

They can bend and deform so  that nothing crumbles away. Like suspension bridges built to sway  with wind to keep themselves intact. And a third version of earthquake  management is energy dissipation.

Such as a counterbalance that sways opposite to the earthquake waves to  dampen intense oscillations. It’s basically the same as  pushing a kid on a swing set, but out of sync to slow them down. A great example of this is the massive  metal dampener at the heart of Taipei 101, one of the tallest buildings in the world.

The dampener moves and dissipates energy  so that the building doesn’t have to. And all of those methods are great. But some physicists and civil engineers think we can also add metamaterials to this list.

If you’re clever, you can arrange  disordered structures that break up a wave by shifting against each other out of sync, rather than seamlessly  conveying the seismic energy. Break up the wave, lose the energy, no more quake. The leading idea has been to drill  holes under or near buildings.

Sometimes they’re filled with cement, but their general purpose is just  to interrupt the seismic wave. Very much like how the copper  metamaterials interrupted and redirected the microwaves in that  cloaking experiment from 20 years ago. When a team initially tested  the drilling-out-holes method, they strategically bored a bunch  of 5-meter-deep holes in the ground to mimic the effect of the  metamaterials, but on a giant scale.

Then, they simulated an earthquake,  and found that the “quake”s power was reduced by 80% on the  other side of the boreholes! Those are pretty promising results  for this meter-scale metamaterial! Turns out drilling a bunch of holes could take a lot of stress off buildings  in seismically active zones.

Some researchers actually think it’s  possible that ancient megastructures, like the Coliseum, may have  accidentally benefitted from this seismic cloaking method, too. Even though the idea is promising, the team did run into some trouble during early tests. Initially the boreholes reflected the waves  instead of diverting or dissipating them.

And the last thing you wanna do is  shove earthquakes off of one building and right onto the building next door. So they need to work on  diverting the waves around, or dissipating the energy even more. So other experts have proposed drilling holes in the sides of the main boreholes to  hopefully mitigate this reflection.

That idea hasn’t been completely worked out yet, so there’s still lots of  work to do before boreholes become a popular form of earthquake proofing. In the meantime, there are still  other metamaterial-inspired cloaking strategies worth trying! For one, engineers could play around  with above-ground oscillators.

Strategically placed above-ground  pillars can oscillate in ways that disrupt the force of a seismic wave, to  functionally turn a sideways-moving wave into a downward-moving wave, sending an earthquake towards the center of the planet  instead of, you know, at us. Even cooler, it turns out that  forests could be natural versions of this kind of earthquake–cloaking device. Forests with a naturally disordered  arrangement of trees are capable of breaking up energy waves in the same way  as those disordered man-made pillars.

So far, we’re still a ways off from  actually deploying any of this kind of tech. Every version of these large-scale  metamaterials are pretty big, so engineers have to consider a  lot of factors when designing them. Then they’re very labor intensive to construct, and there’s the whole “some  stuff is still reflecting off the target and onto what’s nearby” thing.

But just like with the  metamaterial cloaking devices that inspired these  earthquake-proofing techniques, experts are excited about all  the applications still to come. And the best part is, these  techniques don’t have to stop at invisibility cloaks and earthquakes! Wave-manipulating metamaterials could  have a lot of other applications.

They could potentially be used to create extreme soundproofing materials or  noise cancellation devices. Or we could go the other direction,  and use nanostructures to focus waves, instead of only disrupting or dispersing them. Metalenses are already being deployed  in particle physics experiments, and could some day replace traditional  lenses in cameras or telescopes.

Looks like we’re truly on our way  to becoming wave-bending masters, and that’s cooler than  anything that happened in 2006. Take that High School Musical! [♪ OUTRO]