Antimatter (Encore)
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The following is an encore presentation of Everything Everywhere Daily. It is the most expensive substance in the world by a wide margin. When it was first proposed, it was actually proposed in jest. However, decades later, the joke turned out to have been true. It's a fundamental part of the universe, and by all accounts, it should be everywhere. Yet, it can't be found anywhere, and physicists aren't really sure why. Learn more about antimatter, how it was discovered, and what it is on this episode of Everything Everywhere Daily.

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Most of you have probably at least heard of antimatter. Antimatter isn't something out of science fiction, although it might be used in science fiction stories. Antimatter is a real thing, and it isn't just real, it's a fundamental part of the universe. Before I go into exactly what antimatter is, I should give the very interesting story of how antimatter was discovered.

Back in the 19th century, matter and the structure of the atom still weren't understood. Radiation had yet been discovered and nobody knew that atoms had a nucleus, let alone about subatomic particles like protons or electrons. There were several theories put forward about the nature of matter during this time, which included theories of negative matter and the ether, which were all debunked rather quickly.

The first use of the term antimatter occurred in 1898 when the German-British physicist Arthur Schuster wrote two letters to the science journal Nature where he was just kind of spitballing ideas. The letters were not intended to be a serious scientific theory. Schuster talked about anti-atoms, which could then create anti-molecules, which could then create full anti-solar systems.

He also wondered if such antimatter would create a type of antigravity, which would repel normal matter. And he also proposed that such antimatter would annihilate regular matter if it came into contact with it. His letter, which was written decades before physicists actually proposed and could prove actual antimatter, ended up being extremely insightful, even if his ideas about antigravity turned out to be wrong. In the first decades of the 20th century, there was an explosion in knowledge about the workings of the atom, radioactivity, and subatomic particles.

Quantum physics was developed and we gained a better understanding of what exactly made up matter. But it wasn't until 1928 that our current understanding of antimatter began to develop. Paul Dirac, one of the founders of quantum physics, realized that the Schrodinger wave equation could allow for the existence of anti-electrons, or electrons with a positive charge instead of a negative charge.

In 1932, American physicist Carl Anderson proved the existence of anti-electrons when he was studying cosmic rays, for which he received the 1936 Nobel Prize in Physics. He dubbed these new anti-electrons positrons. Eventually it was discovered that all elementary particles have a type of symmetry. In addition to positrons, there were antiprotons as well that had a negative charge. Not only did these anti-particles have the opposite electrical charge, but they also exhibited other opposite quantum properties as well.

Despite being the opposites of each other, they would have the same mass and otherwise behave in exactly the same way. There's a whole lot more to the physics behind antimatter beyond saying that they're opposites of each other, but for the purpose of this episode, I think that explanation will suffice. A discussion of quarks, antiquarks, and elementary particles I will leave for a future episode.

It turned out that antimatter is being created all the time around us, albeit in very small amounts. When Carl Anderson discovered antimatter, he was looking at cosmic rays, which it turns out create antiparticles when they collide at high speeds with particles in the atmosphere. Likewise, beta radioactive decay produces positrons as well as electrons. It's possible to recreate the high-speed collisions of cosmic rays in particle accelerators, which can also create antiparticles.

It turns out that particles and antiparticles exhibit a type of symmetry, so that when you create an electron you also create a positron. When you create a proton you also create an antiproton. Perhaps the best known attribute of antimatter is that if it comes into contact with regular matter, the two particles will annihilate each other. The interaction will result in the creation of high energy photons, usually in the form of gamma rays, as well as neutrinos and possibly some other particles and antiparticle pairs.

The conversion of matter and antimatter into energy behaves according to the equation from Albert Einstein that you're probably familiar with. E equals mc squared. The energy created would be equal to the mass of the particle and antiparticle times the speed of light squared. Suffice it to say, converting a little bit of mass can result in an enormous amount of energy. At this point, you might have noticed a problem with what I've just told you.

If matter and antimatter are produced in pairs, and if matter and antimatter annihilate each other upon contact, then why do we exist in a world made up of matter? There should have been just as much antimatter as matter which was produced during the Big Bang. As far as we can tell, the entire observable universe is made up of regular matter.

If there were antimatter galaxies out there, there would have to be some boundary between the matter and antimatter universe, and that would produce a lot of gamma rays. And that has never been observed. Moreover, given the energy levels that would be involved, it should be something that would be very easy to observe. So then, where's all the antimatter? This is actually one of the biggest outstanding questions in physics.

There's no definitive answer to this question at this point, but the current thinking is that in the moments after the Big Bang, there must have been some imbalance in the amount of matter and antimatter for some reason. What caused this imbalance is unknown, but when the particles and antiparticles annihilated each other, there must have been particles left over. Either this initial leftover matter became the basis for the entire universe,

or the asymmetry manifest itself after each annihilation, creating an ever larger surplus of regular matter each time until there was no antimatter anymore. To answer this question, and again, it's one of the biggest outstanding questions in all of physics, you're going to have to study antimatter. But there is an enormous problem. How can you study something when even the most basic interaction with the substance will destroy it?

This is indeed a huge problem, but it's an engineering problem, not necessarily a physics problem. It starts with the creation of antimatter. As I mentioned, it's possible to create antimatter in a particle accelerator. Certain high-energy collisions will create particle-antiparticle pairs. Creating an antiparticle in a particle accelerator is actually the easy part.

Once you create the antiparticle, you then have to separate it from the particle. And everything from here on out has to be done in an almost perfect vacuum, because if even a single atom of regular matter were to interact with the antimatter, it would disappear. The antiparticle is then whizzing around at speeds near the speed of light inside the particle accelerator, which poses two problems. The first is, how do you contain it so it doesn't touch anything?

This is done with powerful magnets. Because antimatter exhibits the same properties as regular matter, it can be contained by magnets in the same way that regular matter can. The magnetic containment has to be constant or else you'll get an interaction with matter when it touches the walls. Assuming the antiparticle is contained, you then have to decelerate the particle. Yes, it has to go into a particle decelerator. This too is done with magnets and it's basically the opposite of a particle accelerator.

Finally, once you've slowed it down enough, you can contain it in what's known as a magnetic bottle. In 2011, researchers at CERN in Switzerland managed to create the first anti-hydrogen atoms, consisting of an antiproton and a positron. They were able to store the anti-hydrogen atoms for a whopping 17 minutes. In 2014, CERN also managed to send anti-hydrogen atoms in a magnetic beam, and they counted a whopping 80 anti-hydrogen atoms.

The current record for storing antiprotons is 405 days using what's known as a penning trap. Penning traps are magnetic devices that only work on charged particles like antiprotons or positrons, not neutral objects such as an anti-hydrogen atom. The process is incredibly difficult and incredibly expensive, and the end result is just a very small number of antiparticles.

The process is so expensive and the results are so meager that on a per-weight basis, antimatter is the most expensive substance in the universe. It's so expensive that estimates place the value of one gram of antihydrogen at somewhere between $62.5 to $2,700 trillion dollars.

Regardless of what estimate you use, it would be many times more than the entire gross national product of the United States and potentially more than the entire economic activity of the world. At the current rate of production, however, it would take 10 billion years to make one gram of antihydrogen. Despite the incredibly small amount of antimatter which has been produced, there have been limited studies on it, and it's confirmed many of the beliefs about how antimatter behaves the same as regular matter.

There are plans to find more efficient ways to create or perhaps harvest antimatter. One is to send a craft with a magnetic bottle up to the Van Allen Belt around the Earth, which contains a lot of energetic particles caught in the Earth's magnetic field, some of which include antiparticles. And the same could be done in the magnetic field around Jupiter. Even if you didn't get a lot, it would still be far more than what could be made on Earth.

Everything I've talked about so far is mostly theoretical. Yes, antimatter does exist, but there's not very much of it, and what is created naturally disappears almost instantly. Could there possibly be a practical use for this stuff? The answer is yes. First, I'll start by addressing what many of you are probably thinking. If antimatter and matter annihilate each other, couldn't you make an incredibly terrifying bomb out of the stuff? In theory, yes, you could.

However, as I've just explained, creating antimatter is really, really difficult and expensive. Entire antihydrogen atoms can't be stored for very long and the number of atoms you can make is tiny. Even assuming that you could solve those problems, it would be incredibly dangerous. Even the slightest problem with the magnetic containment or the slightest break in the vacuum seal would literally make your antimatter weapon blow up in your face.

The amount of matter which was converted to energy in the Hiroshima bomb was only about three quarters of one gram of matter. So, given the cost estimates I gave above, it would require a large part of the entire world's economy to create enough antimatter to make what would today be considered a small atomic bomb. So, this is something that I wouldn't lose any sleep over. But what if you didn't have to store any antimatter? What if you could just somehow use it as it was being created?

Well, it turns out that you not only can use antimatter, but it's actually pretty common. It's used in what is known as a PET scan. PET stands for positron emission tomography, and they're a pretty common tool in medicine. In a PET scan, the patient will ingest a small amount of radioactive substance that undergoes beta decay that will emit a positron. The positron is immediately annihilated and then emits gamma rays.

Detectors surrounding the patient capture these gamma rays, allowing the construction of three-dimensional images that reveal the distribution of the tracer and provide insights into cellular and metabolic processes. PET scans are used in a host of medical treatments, including cancer, heart disease, and infectious disease.

there is still an enormous amount that we don't know about antimatter, and much of our ignorance is due to the difficulty in studying it. Nonetheless, antimatter is a real thing, and it's a fundamental part of our universe. Even if we don't know why, there isn't more of it than there should be. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Austin Oakton and Cameron Kiefer.

I want to thank everyone who supports the show over on Patreon. Your support helps make this podcast possible. I'd also like to thank all the members of the Everything Everywhere community who are active on the Facebook group and the Discord server. If you'd like to join in the discussion, there are links to both in the show notes. And as always, if you leave a review or send me a boostagram, you too can have it read on the show.