How Scientists Hold Things That Cannot Be Simply Contained

The video opens by noting that some substances are very hard to hold in a standard container. The host gives three examples: plasma, which is too hot; a single atom, which is too small; and antimatter, which is too destructive.

Scientists have nonetheless developed ways around these problems. The host says the solutions have led to cancer treatments, power generation, and new understandings of the universe, which is the reason the video gives for wanting to hold things we cannot touch.

Alkali metals are all around us. The host says sodium probably powers the streetlights on your block, and lithium is a critical element in several kinds of long-lasting batteries. Storing and transporting them is therefore important, but putting them in a box is more complicated than it sounds.

Pure alkali metals cannot be exposed to oxygen. The host says oxygen is corrosive, and over enough time it completely converts pure sodium into sodium peroxide, leaving a different substance in the box than the one that was put in.

Water is not a solution either. Alkali metals are extremely electropositive, meaning they easily give up an electron. When they do, the electron bonds with water and releases energy, sometimes a great deal of it.

Instead, alkali metals can be kept in mineral oil, whose carbon and hydrogen atoms have similar electronegativities and bond with each other rather than pulling in other elements. They can also be surrounded by argon, a noble gas that already has all the electrons it needs and hardly reacts with anything. Lithium metal batteries are sealed in airtight containers, but the host warns that if the container is punctured they can catch fire or explode, which is why they should not be thrown in the trash.

The host calls fluorine gas the savage beast among the elements, a phrase attributed to the president of the Royal Swedish Academy of Sciences. Fluorine and its derivatives are useful: they appear in the Teflon coating on pans and in toothpaste that strengthens tooth enamel.

Fluorine gas is viciously reactive. It consists of two fluorine atoms bonded in a pair, and this bond is extremely weak, so fluorine will combine with almost any other element in the periodic table when given the chance. The host says several scientists died trying to isolate it.

The video says fluorine has been tamed through a process called passivation. When fluorine meets certain metal containers, such as stainless steel, it attacks the container walls and forms a thin fluoride layer. That layer is one of the very few compounds fluorine gas does not react with, so after the initial reaction the gas stops reacting with the container. The host describes this as putting the savage beast into a cage of its own creation.

Everything is made of atoms, but atoms are tiny, as small as 30 picometers, or 30 trillionths of a meter. The host says this makes holding even one atom difficult, but the effort can be worthwhile. Experts are trapping individual charged atoms, called ions, to try to build more powerful quantum computers, since this should allow them to work with more basic units of quantum information.

A Paul trap has three dimensions of electric and magnetic fields that pull ions into the center of the trap. This leaves a group of trapped ions, but scientists want only one, so they weaken the fields in a controlled way to let the excess escape, like lowering the sides of a container so the contents at the top spill out. The host notes that this innovation earned Wolfgang Paul and Hans G. Dehmelt the 1989 Nobel Prize in Physics.

The Paul trap works on charged particles, but some atoms needed for devices such as atomic clocks are not charged. For these, the host says a different kind of trap is needed: a specialized laser.

The reasoning is that even a neutral atom has charged protons in its nucleus. If a laser can focus tightly enough, it can isolate that slight pull on the protons and lock the atom in place, which the host compares to the world's smallest tweezers.

Antimatter is extremely rare in the universe, but the host says experts have figured out how to make it, so scientists do not have to find rare antiparticles in nature. Antihydrogen is made by combining one antiproton with one anti-electron, also called a positron, using electric and magnetic fields much like a Paul trap, except that the charges are reversed.

Containing antimatter is the difficult part, because it annihilates any regular matter it touches and the two combine into light. The host notes this reaction is extremely energetic, enough that scientists want to power spaceships with it, since only a tiny amount might be needed.

Once antihydrogen is created it is electrically neutral, so the Paul trap no longer works, and the atom must be trapped again immediately to avoid annihilation. Scientists place the antihydrogen in a trap and put that trap inside a second trap. The second trap uses the charge difference between the antiproton and the positron to hold them in place, and the video says this is reversed compared with the trap for a neutral atom because antiproton charges are the reverse of a proton's.

Photons move at almost 300,000 kilometers per second in a vacuum, nearly the distance from Earth to the Moon in a second. Catching them is useful because it could allow ultra-stable lasers for very accurate atomic clocks. The host says one way to hold light without slowing it is to bounce it back and forth in a small space, using two highly reflective mirrors that form a Fabry-Pérot cavity.

The process is more complicated than a ball bouncing, because light acts as a wave as well as a particle. When it behaves like a wave, the light can interfere with itself, and the mirrors must be spaced exactly so that the wave and its reflection arrive together and add up rather than cancel. If the spacing is off by about a billionth of a meter, the light waves partly or completely cancel each other out.

Using such cavities, light has been contained briefly, with some experiments reaching about a tenth of a second. The host says that in that time the photon travelled the equivalent of 40,000 kilometers, which is enough to go all the way around Earth.

A Bose-Einstein condensate is just a fraction of a degree above absolute zero, colder than anything reached on Earth, colder than the liquid nitrogen used in cryogenics, and colder than the outer reaches of space. The host says it is worth holding because it lets us see quantum mechanics directly, such as the wave behavior of particles.

The idea traces back to Satyendra Nath Bose, who studied photons, and Albert Einstein, who built on Bose's work. Bose's work predicted that at extremely low temperatures all atoms would enter the exact same quantum state, so that effects too small to see become a much larger quantum behavior. This only happens in extreme cold, when atoms are slow enough to move into the same state.

The difficulty is that at such low temperatures atoms stick to the wall of any physical container. The host explains that the walls would be far warmer than the atoms, and their heat would stop the atoms from becoming cold enough to form a condensate. In the host's words, the instant you trap something, it stops being the thing you wanted to hold.

To keep the atoms away from the container sides, scientists surround them with magnets and then cool them into a condensate. The host notes that many magnetic traps have a weakness at their core: at the exact center of the trap the magnetic field is zero, and the atoms can escape.

The problem is worse for condensates because they are so cold. Their low energy means the atoms cluster near the trap center, making escape more likely. The video describes a team at MIT that used gravity to pull the atoms down so they never reached the zero point. A German team dropped the condensate into a 120-meter freefall to remove gravity effects, and switched the magnetic field on and off to cool the gas.

If matter is heated enough it turns from a solid to a liquid, then a gas, and then a plasma. Superheated hydrogen plasma combines to form helium and releases an enormous amount of energy: the host says just a few grams is enough to supply the average person's total energy use for more than 60 years. Plasma is also the core of the Sun, so getting that energy is hard, since any material touching it would melt.

Plasma has so much heat that it pulls the protons and electrons of its atoms apart. Because charge is involved, magnetic fields can contain it, as with the ion traps described earlier. The host adds that plasma can only be held in certain shapes, because the movements of its electrons and much heavier atomic nuclei must cancel each other out to keep it stable.

A torus, or donut shape, allows these movements to cancel, so the plasma circulates steadily without touching the container sides. This is the principle behind the Tokamak, a machine commonly used to create fusion reactions.

The host closes by saying the video shows that the weirder the thing you want to contain, the wilder the containment solution gets. Sometimes, he says, the jar is just as interesting as what is inside it.