In the wise words of M.

C. Hammer,  you just can’t touch some things.

Whether they’re too hot, like  plasma (or M. C. Hammer), too small, like a single atom, or just too  destructive, like antimatter, some stuff is just very hard to  hold in a standard container.

But humans are famous for our ingenuity. And scientists have come up with ways around all of those problems to  hold what cannot be touched. Those solutions have led to cancer  treatments, power generation, and new understandings of the universe.

So we really do want to hold  stuff that we can’t touch. And these are the incredible  innovations that allow us to do it. [♪INTRO] Whether or not you’ve heard of alkali  metals, they’re all around you. Sodium probably powers the  streetlights on your block, and lithium is a critical element in several  kinds of long-lasting batteries.

So to have power and the stuff that our modern society is based on, we need a way to store, transport, and generally  contain those alkali metals. But that’s more complicated  than just putting them in a box. For one thing, pure alkali metals  can’t really be around oxygen.

Oxygen is corrosive. So with enough time, it completely converts pure  sodium into sodium peroxide. Which means that you would end up with a totally different substance in your  box than what you put into it.

Now, you could try putting  alkali metals into water to avoid the oxygen problem. Except it’ll do this: That’s because alkali metals  are extremely electropositive, meaning that they will easily give up an electron. And when they do that, the electron bonds with water and releases energy.

Sometimes a lot of energy. So you cannot expose an alkali metal to oxygen in the air and you also cannot  store it in water either. What you can do is put it in a  non-water-based liquid like mineral oil.

Mineral oil has a much more stable structure that prevents it from reacting with alkali metals. Its carbons and hydrogens have similar electronegativities and  bond equally to each other. So they’re not pulling in other elements to react the way that water and alkali metals do.

You can also surround an alkali metal with a gas like argon, which does not react with it either. Argon already has all of the electrons it needs, so it hardly reacts with  anything at all. It’s noble gas.

Or you can seal it up in an airtight container, like we do with lithium metal batteries. But if you puncture that container,  they can catch on fire or explode. And that’s why you don’t throw them in the trash.

You could end up with a dumpster fire. Ultimately, containing something as simple as a piece of metal can be harder than it sounds. But alkali metals are nothing compared to what the president of the Royal Swedish Academy of Sciences once called “the savage beast among the elements”: Fluorine gas.

Flourine and its derivatives  make a lot of things possible. It’s in the Teflon that keeps  your scrambled eggs from sticking to the pan and the toothpaste that  strengthens your tooth enamel. Fluorine can do a lot for  you. …if you can tame it.

Fluorine gas is viciously reactive. It's made of two fluorine atoms  bonded together in a pair. This bond is extremely weak,  so given an opportunity, fluorine will combine with pretty much any other element in the periodic table.

And that kind of reactivity can  have some grave consequences. Several scientists died trying  to isolate the savage beast. But we have tamed it through a  process called passivization.

When fluorine reacts with certain  metal containers, like stainless steel, it attacks the container walls,  forming a thin fluoride layer. This reaction creates one of the very few compounds that fluorine gas doesn't react with. So after that initial reaction, fluorine will not react with the container any more.

This savage beast can be put into  a cage... of its own creation. In a way, that’s exactly like the  next uncontainable item in our list, because everything is made of atoms. And since everything is made of atoms, it might not sound like such  a challenge to hold one.

But atoms are tiny – as small as 30 picometers. That's 30 trillionths of a meter. . So it’s hard to hold a single atom. …But it can be worth it.

Experts are trapping individual  charged atoms, or ions, in an attempt to make more  powerful quantum computers. Essentially, it should let them scale up how many basic units of quantum  information they’re working with. All we’ve got to do is isolate  one of the smallest things on Earth to get there.

And that is  where the Paul trap comes in. A Paul trap has three dimensions  of electric and magnetic fields. Those fields pull ions into  the center of the trap.

Which leaves you with a bunch of  trapped ions. But we just want one. So scientists can systematically weaken the fields to let the excess  out, sort of like lowering the sides of a container so  what’s at the top spills out.

And this was such a big innovation  that it earned Wolfgang Paul and Hans G. Dehmelt the  1989 Nobel Prize in Physics. And a pretty cool namesake.

But sometimes the atoms you need for, say, an atomic clock, aren't charged. In that case, you’ll need a different  kind of trap: a specialized laser. See, even a neutral atom has  charged protons in its nucleus.

So if a laser can focus tightly enough,  it can isolate that slight proton pull and lock the atom in place.  Like the world’s smallest tweezers! This technique is pretty amazing, but it would be no match for the next item on our list. Antimatter is extremely rare in our universe.

But that’s not the thing that is the most challenging part of getting a hold of it. Experts have actually figured  out how to make antimatter. So we don’t really have to, like, go out and find the rare anti-particle out there.

To make antihydrogen, you have to combine one antiproton with one anti-electron,  also known as a positron. Easy as pie! Or, possibly, as hard as anti-pie?

And they do that with electric and  magnetic fields, just like a Paul trap. Except that the charges are  reversed, because it’s antimatter. Once you’ve made it though, you  have the problem of containing it, because antimatter annihilates  any regular matter it comes into contact with.

The matter  and antimatter combine to form… nothing but light. When fluorine reacts with its container, it forms a cute little layer on it. When antimatter reacts with its container, both the container and the  antimatter cease to exist!

This reaction is extremely energetic. So energetic that scientists  want to power spaceships with it, since it might only take a tiny  amount of antimatter to do the job. The thing is: the Paul trap is  good at containing charged stuff.

And you just made a neutral antihydrogen atom. The moment the antihydrogen atom is created, the Paul trap no longer works. Antihydrogen atoms need to  be immediately trapped again, otherwise they will be  annihilated with regular matter.

So they have the antihydrogen in a trap, and they put that trap inside another trap. The second trap exploits the  difference in charge between an antiproton and positron to pull  them in and hold them in place, just like a trap for a neutral  atom, except reversed because the antiproton's charges are  the reverse of a proton's. And after all of that, we  have contained antimatter.

Which is pretty impressive for a substance that destroys everything it touches. We are soon going to move onto our next container for the uncontainable, but  first, it’s time for a quick ad. Thanks for watching SciShow and thanks to Brilliant for supporting this SciShow video.

Just like we know anyone  can love learning science, Brilliant knows anyone can be a math kid. Brilliant is an online math  tutor designed to help students, from fifth grade through  college, truly understand math. With class sizes ballooning  to be bigger than ever, Brilliant offers individual  support for your student.

It makes practice problems just for them to ensure that every concept sticks. Brilliant even helps them set goals and keeps them motivated so parents don’t have to. Click the link below or scan the  QR code to try Brilliant for free.

You can upgrade to Premium to unlock all courses. And right now, SciShow viewers can save 20% off an annual subscription at brilliant.org/scishow. The speed of light is famously  fast.

In a vacuum, the photons that make up light travel at almost  300,000 kilometers per second. That is almost the distance from  the Earth to The Moon in a second. It’s gonna be hard to catch  a photon moving that fast.

But people want to do it because if we do, we can make ultra-stable lasers  for super-accurate atomic clocks. So one way to capture a photon without slowing it down is to bounce it back  and forth in a small space. That keeps it in roughly one  spot so you can look at it.

And scientists do that with mirrors.  Two very highly reflective mirrors. Photons bounce between the mirrors on either side of a thing  called a Fabry-Pérot cavity. But it’s more complicated than  what you’re probably imagining.

It doesn’t work like a ball  bouncing back and forth, because light sometimes acts  like a particle and sometimes acts as a wave, which is  called wave-particle duality. And, while particles can merrily  bounce back and forth like a ball, waves can interfere with each other. And when it acts like a  wave, the light bouncing back and forth in the trap can interfere with itself, and then you would get dimmer and dimmer light until you reach total darkness.

So, for the trap to work,  the mirrors have to be spaced perfectly apart from each  other, at the exact location where the wave bounces at the  same time as its reflection. That way, they add together rather than interfering with each other,  and the light gets brighter. If this is off by just a tiny  bit, like a billionth of a meter, the light waves will partially or completely cancel each other out when they meet.

Using Fabry-Perot cavities,  light can be contained briefly, with some experiments reaching  about a tenth of a second. Which might not seem like  much, but in that time the photon has travelled the  equivalent of 40,000 kilometres …which would get you all the way around Earth. Now so far, we have covered fast things and tiny things and anti-things.

But how do you contain something as cold as a Bose-Einstein Condensate? This phase of matter is just a fraction  of a degree above absolute zero. That’s colder than it's ever gotten on Earth; colder than the liquid  nitrogen used in cryogenics; even colder than the outer reaches of space.

But we want to hold it because it lets us see quantum mechanics literally. Like all of the stuff about particles acting like waves was predicted by quantum mechanics. So we want to hold the forbidden cold stuff that two guys discovered a long time ago.

Satyendra Nath Bose was a  physicist who studied photons. And his work became the  foundation that another guy you might have heard of, called  Albert Einstein, then built on. Usually, quantum effects are tiny.

But when Einstein was reading Bose’s papers, he noticed something that would make it possible to observe those effects that  are normally too small to see. Bose’s work predicted that when  the temperature got extremely low, all atoms would go into the  exact same quantum state. With all the atoms acting  together, what was once too small to see becomes a much  larger quantum behavior.

When atoms are orchestrated together like that, it’s called a Bose-Einstein Condensate. And it only forms in the  extreme cold, because that’s the only time the atoms are slow  enough to move into the same state. But that’s not ideal for holding  it because at extremely low temperatures, atoms stick to the  wall of any physical container.

And, considering how much warmer the walls would be than the way-below-freezing  atoms, the heat from the walls would prevent the  atoms from being cold enough to form a Bose-Einstein Condensate. Once again, the instant you trap something, it stops being the thing you  wanted to hold in the first place! So to get around that problem, scientists can surround the atoms with magnets to keep them away from the sides of the container, and then cool them down so that they turn into a Bose-Einstein Condensate.

But many magnetic traps have  a weakness at their core, and I mean their literal core.  At the exact center of the trap, the magnetic field is zero,  and the atoms can escape. And what do we call a trap that lets you escape? We don’t call it a trap.

But this is particularly a problem  for Bose-Einstein Condensates because they are so cold. The temperature means its atoms are low energy. And lower energy atoms  cluster near the trap center, making them more likely to escape.

So there’s a team at MIT that has worked to solve this problem using gravity. They basically pulled the atoms down, so that they never reached the zero-point. There’s also a German team  that dropped the Bose-Einstein Condensate into a 120 meter  freefall to remove gravity effects.

And at the same time, they turned the magnetic field on and off to cool the gas down. As the saying goes, there's more than one way to trap a Bose-Einstein Condensate! But if you thought keeping a trap cold is hard, try keeping it unbelievably hot.

If you heat pretty much anything enough, it’ll turn from a solid into a liquid, and then a liquid to a gas,  and then a gas to a plasma. And plasma can be some powerful stuff! Superheated hydrogen plasma  combines to form helium, releasing an enormous amount of energy.

Just a few grams is enough to generate the average person’s total energy usage  for more than 60 years! Unfortunately, it’s hard to  get that energy because plasma is so hot! It literally  makes up the core of the Sun.

Any material that comes in  contact with it is gonna melt. Plasma has so much heat in  its system that it pulls the protons and electrons of  its atoms apart from each other. And since charge is involved,  we can make a container using magnetic fields, just like the  ion traps that I described before.

But plasma has an extra twist …or curve? It can only be held in certain shapes. Because its tiny electrons  and much more massive atomic nuclei are not synchronized like they would be if they were not so hot and still bonded together.

So to keep it stable, we need to get the movements of the electrons and ions  to cancel each other out. One shape that can do this is a torus, or for those of us not studying plasma, a donut. In that shape, the movements  cancel out and the plasma can stay in a steady circulation without  hitting the sides of the container.

This is the principle behind the Tokamak, a machine that is commonly used  to create fusion reactions. And yes, it is a donut shape.  Unfortunately, you cannot eat it, and superheated electrons do  not make very good sprinkles. If we have learned anything today,  it’s that the weirder the thing you want to contain, the wilder  the containment solution gets.

Sometimes the jar is just as  interesting as what is inside. [♪OUTRO]