wowt explains: what is antimatter?

Like warp drives, suspended animation, and teleportation, antimatter is a frequent staple of science fiction. But what exactly is it, and could we ever use it to do amazing things?
sci-fi antimatter bomb

By this point, practically all of us know that antimatter is the mirror opposite of matter and that it’s basically the most powerful and efficient explosive we could ever hope to create. Normally, this is where science fiction grabs the concept and uses it to create plans for vast spacecraft and apocalyptic weapons, which is usually a sure sign of a real discovery stretched well beyond its scientific plausibility. But when it comes to antimatter, some amazing things are actually quite plausible if we ever figure out a way to mass produce and control it. One day it could very well power our homes and send spaceships to other stars. Until then, however, we’re still trying to answer some basic questions about what it is and why it still exists.

what is antimatter?

Antimatter is matter like we know it with one important twist. Its electrical charges are polar opposites to matter thanks to the way the subatomic particles that create it are arranged. In ordinary matter, a negatively charged electrons orbit atomic nuclei. In antimatter, the mirror image of an electron is a positron which, as the name suggests, has a positive charge. They have the same mass and are made of the same basic building blocks, just arranged in a different way. Technically speaking, antimatter can combine the same way ordinary matter does and things like planets and stars made of antimatter are possible, but there’s simply too much matter for structures like that to accumulate undisturbed in the universe we occupy.

how and when was antimatter discovered?

Its existence was first hypothesized in the 1880s since solutions to equations governing the behavior of matter predicted that “negative matter,” or matter with an opposite charge, should be able to exist in some form. Work by Paul Dirac in 1928 confirmed the validity of these ideas and an experiment by Carl Anderson found evidence of their existence in 1931, when one such particle passed through a lead plate in a way that could only be possible if that particle had a charge opposite to that of normal matter. That particle was a positron from a shower of cosmic rays, proving that antimatter both existed and could be found in nature.

However, for the discovery to validate the full implications of Dirac’s work, researchers would need to find more massive and complex antimatter particles. Antiprotons were first detected in 1955 when Emilio Segrè and Owen Chamberlain used a particle collider designed for that exact purpose and saw 38 such particles created among some two million other subatomic events. This discovery showed that antimatter could theoretically form entire atoms and the building blocks of matter as we know it did have mirror opposites, which was further validated in 1974 when Soviet scientists detected antihelium atoms, and 1995, when researchers at CERN created antihydrogen atoms.

where can you find antimatter?

High speed particle collisions in space produce antimatter, as do some thunderstorms. You can also create antimatter in particle colliders, intentionally or not. As noted, it’s not really possible to find vast reservoirs of antimatter in space, especially as complex atoms of say, antioxygen or antisilicon, because it would collide with ordinary matter and explode, but there may be clouds of antihydrogen and antihelium floating around galactic cores, created in high speed collisions between cosmic rays and matter ejected from supermassive black holes in galactic centers. It’s also thought that ancient galaxies may have large haloes of simple antimatter as well.

One of the strangest places to find antimatter is during the implosion of a very massive star. While ordinarily, titanic suns collapse into a black hole, some are so massive, registering between 130 and 200 solar masses, they disintegrate in an event known as a pair-instability supernova when they run out of fuel. As their outer layers are blown off, gravity pulls the remaining plasma back to their cores so violently, the process creates antimatter which then annihilates almost everything left of the star. Closer to home, the Van Allen radiation belt around Earth is thought to contain a tiny, but steady supply of about 10 milligrams of positrons.

how much antimatter can we create here on earth?

Not very much. It takes millions of collisions to get just a few particles of antimatter, and so far, we’ve only produced nanograms of the stuff, mostly positrons. There are approaches which can create a lot more than that, but the total output would still be measured in milligrams. We also can’t create too much of it because any time antimatter comes in contact with even a molecule of matter, something very difficult to avoid here on Earth, it explodes. If we produced just 500 milligrams of antimatter, we’d be dealing with the equivalent of trying to keep a Hiroshima-like event from happening every nanosecond, so manufacturing any even remotely notable amount of the stuff would be very dangerous.

how much does antimatter cost?

From a practical standpoint, you can’t buy antimatter. It’s not for sale and there’s no device in which it could safely be transported to you. But if you were to try and put a price on it, one gram would cost about $60 trillion. Why is it so expensive? Because it requires very complex, extremely rare, high precision equipment, and quite literally millions of attempts to make just a few short-lived atoms, never mind quantities visible with the naked eye. We could lower those costs by creating dedicated infrastructure for manufacturing them, but even then, the lowest estimates come out to $25 million per milligram and an appropriate device to transport it will still need to be designed and tested.

can we even contain antimatter?

Yes, by using a device called a Penning trap. Inside, antimatter is sealed in a vacuum and kept away from any matter in the containment chamber by magnetic fields. But that’s actually the catch here. Since the device relies on magnetic repulsion to keep antimatter isolated, there’s no way to store uncharged antimatter particles. For those, we need to use “optical tweezers,” or tightly focused laser beams that keep them away from any matter with which they’d react. Of course, there’s a time limit based on the amount of energy available to keep the containment going. So far, the record for the longest preservation of antimatter is about 17 minutes.

why does antimatter explode on contact with matter?

In short, because of the opposite magnetic charges, matter and antimatter unwind each other down to a subatomic level. This process turns their building blocks into pure energy and emits a bright flash of gamma radiation. This is fundamentally different than fission, in which atomic nuclei are torn apart by high speed collisions, releasing the energy that kept them bound into a single element, and fusion, in which atoms reshuffle when combined, giving off the energy from their unstable states during the event. Here, the very building blocks of the atoms and even the elementary particles themselves come undone, leaving nothing but the energy that once glued them together racing outwards.

why is the universe made of matter and not antimatter?

Apparently, it’s due to a weird quirk of particle physics in which matter has a very slight edge over antimatter in high energy environments, much like the one right after the Big Bang. You see, if matter and antimatter are the same thing, just with a different charge, they should have just cancelled each other out at the dawn of the universe, leaving a very boring cosmos full of radiation and quantum fluctuations. But as it so turns out, some particles are just a tad more likely to decay into matter rather than antimatter after a collision, which meant that antimatter was doomed to be in the minority at the dawn of the universe.

what does antimatter look like?

Just like ordinary matter. If the quirk we discussed in the previous question went the other way and we ended up in the universe made of antimatter, which would be just ordinary matter to us in the scenario, of course, it would behave in much the same way. Since atoms of antimatter reflect light the same way regular atoms do, it’s not a stretch to imagine that a rock made of antimatter would look just like a normal rock. And this is a bit of a strange thing to wrap your mind around if you imagine a pebble made of antimatter floating through space, being hit with another pebble of ordinary rock, and exploding with a brilliant flash of gamma rays.

can antimatter fall upwards?

No. Antimatter is still matter and it obeys the same exact laws governing our universe. Since it has mass, physics dictates that it must follow the whims of gravity the same way that ordinary matter does. In fact, thanks to its opposite charge, some equations say that antimatter should actually fall a tiny little bit faster, an idea currently being tested by CERN to understand more about gravity and charges of subatomic particles. But regardless of whether those models are right or not, there is absolutely no scenario under which you can drop antimatter in a gravity well and expect it to fall upwards.

what would happen if you touched antimatter?

Depends on how much antimatter you touched. A few particles would be undetectable, but if you had all the antimatter that we’ve ever made land in the palm of your hand, you’d need a new arm, as well as new eardrums and extensive medical treatment. Grab enough antimatter to show up as a speck of dust freed from a Penning trap and you’d be turned into a red mist while the building around you becomes high speed debris. Basically, the more antimatter you come in contact with, the more of your matter and the matter around is converted to energy with very violent results, and the human body can only take so much explosive force, so of you touch more than just a nanogram of it, you would die instead of just being gravely injured.

could we use antimatter to make weapons?

Theoretically? Yes. Practically? With great difficulty. As already noted, an amount of antimatter equivalent to a large pill detonates with the force of the bomb dropped on Hiroshima, about 20 kilotons or so. A kilogram would nearly match the biggest nuclear warhead design ever tested, the 50 megaton Soviet Tsar Bomb. Using it as a weapon of mass destruction would also come with the added benefit of avoiding radioactive fallout, since unlike fission, no unstable, heavy elements were released in the blast, everything was turned into energy. However, unlike nukes, which have to be carefully goaded into exploding, an antimatter weapon would be extremely fragile and easily prone to detonation.

Imagine the vibration of a missile tipped with an antimatter warhead shaking something loose in a Penning trap or misaligning the optical tweezers for even a fraction of a second. The whole thing would detonate, possibly even in its silo. For such weapons to work, they would need the ability to create massive amounts of antimatter on the fly, something simply not possible with current technology. However, it’s hard to rule out advances in antimatter creation resulting in a device using high powered lasers to produce a directed spray of positrons into a containment chamber until it reaches enough mass for the desired yield just a fraction of a second before hitting its target, and releasing them into the device’s core with a powerful blast.

could we use antimatter to explore space?

Absolutely. There are numerous plans to leverage its explosive capabilities to make better, faster, more powerful spacecraft and improve energy generation. In fact, figuring out a way to safely produce and destroy it may be the only way humans can efficiently explore beyond our solar system, using antimatter drives as backups for, or in tandem with solar sails, or enabling small fusion reactors to generate energy to support those living on board. And, of course, as we just noted, having a device capable of doing that would come in handy for building weapons to defend ourselves from bad encounters with hostile alien life and defending ourselves against comets and asteroids zooming around in distant solar systems.

# science // antimatter / futurism / particle physics


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