What color is antimatter? (and what is it too)
- Advaith Vankamamidi
- Dec 21, 2022
- 4 min read
Updated: Dec 22, 2022
Imagine this. In the far, far future, an astronaut is doing maintenance on his antimatter-powered satellite. Because they’re extremely careless on this specific day, they float a little too close to the engine and are ejected into orbit, somehow being transformed into the antimatter version of themselves. As they begin to slowly disintegrate away, as antimatter does, they look back for the last time at the once familiar Earth, but this time, unfamiliar in certain ways. The planet is spinning in the opposite direction, and instead of the friendly blue and green, it’s colors are completely inverted, now purple and beige. I’ll admit, science-fiction isn’t my specialty. The vast majority of people will find something wrong with my hastily concocted story. But while most of these people may be critiquing the depressing nature or the lack of substance, physicists would have a very different, more scientific complaint about the colors involved in this particular story. In 2018, researchers at CERN (Conseil Européen pour la Recherche Nucléaire, or the European Center for Nuclear Research) settled the debate around the color of antimatter. But to understand what the research truly means, it is first necessary to understand what the substance in question really is, and why such a debate garnered the attention of some of the brightest minds in the world.
Written By: Advaith Vankamamidi
December 21, 2o22
Antimatter has been the center of lots of fantasy and hyperbole. Ideas for the harvesting of infinite energy and time travel are just some of the many creative interpretations of its uses. To understand antimatter, its easiest to start by understanding its more abundant and familiar cousin, matter. Matter is the term used to reference, for all standard intents and purposes, things that have mass and volume (It is worth noting that a lot of the myths surrounding antimatter are actually referring to anti-mass, which, unlike the former, has not been discovered yet). Particles, or the ‘stuff’ of the universe can be split into two categories, fermions, and bosons. The differences between the two categories has a very mathematical explanation involving quantum spin, but simply put, bosons are particles that carry forces and are intrinsically massless, such as photons, whereas fermions are the things that have mass, such as quarks. Anything that qualifies as matter can be broken down into a combination of various fermions. In other words, things that are made of atoms or make up atoms are considered matter.
Matter has various different types of properties, which allow them to interact with the rest of the universe in different ways. These properties can be classified as fundamental or emergent. Properties are considered fundamental if they cannot be explained by combining interactions between other properties. For example, mass is fundamental, since it is intrinsic to its substance. It is impossible to explain mass as a result of, for example, electronic charge, or temperature. If, however, they can be explained in this way, they are called emergent. On the atomic scale, there are four fundamental properties that correspond to the four fundamental forces: Electric Charge, Mass, Spin, and ‘Color,’ although the color referenced in this context is completely different compared to the color that people are used to interacting with (These properties are not always fundamental either, but the explanations as to why take many years of college to learn and are not necessary for the current question). Charge defines interaction with the electromagnetic force, mass interaction with the gravitational force, and spin and color with the weak and strong forces respectively. In summary, matter has different intrinsic values attached to it that defines how it interacts with the forces of the universe.
With these definitions in mind, the definition of antimatter becomes easier to explain. Antimatter is considered the charge-reversed parity-inverted counterpart of matter. ‘Charge inverted’ means that antimatter particles are matter particles that have the opposite charge, so antielectrons, called positrons, have positive charge, whereas antiprotons have negative charge. Parity refers to the spin, or ‘handedness’ of a particle. Particles that have counterclockwise angular momentum are considered ‘right-handed,’ and clockwise particles are ‘left-handed.’ The antimatter counterparts of particles have their handedness swapped, so right-handed electrons would be related to left-handed positrons. The idea of antimatter being related to matter counterparts is far from a simple coincidence. In fact, they result in very real phenomena when the two interact, as the hypothetical astronaut experienced when they phased out of existence. One of the most puzzling, counterintuitive, and weird parts about physics on the atomic scale, known as quantum mechanics, is wave-particle duality. In essence, every single thing we consider a particle is also simultaneously a wave propagating through space and time. Physicists are still arguing on a complete explanation as to why such a phenomenon exists, and this duality leads to the birth of ideas on multiverses and consciousness, which are far beyond the scope of a simple explanation on the color of antimatter. The waves that represent particles of matter are exactly the same as their antimatter counterparts, only reflected across the plane they were travelling on. For example, if a particle was represented by a sine function, the antimatter version of the particle would be that function times negative one, or flipped across the x-axis.
The question that was trying to be answered when CERN conducted their experiment on the color of antimatter was why there was so much more matter than antimatter. Given that antimatter is just inverted matter, it would make sense that there would be an even split between both in the universe. However, since that is not what we observe, there would need to be some fundamental difference that occurs when reflecting the waves of matter across the fabric of spacetime. Upon conducting their experiment, trying to see whether antihydrogen (one positron orbiting an antiproton) looked any different than regular hydrogen, they discovered that the two materials reflected the same amount of light and so were visibly the same color.
The experiment is one of a long line of experiments trying to answer why the universe is the way it is, why it ‘prefers’ the negative-charged-electron containing sometimes right-handed matter so much more than its counterpart. While it is unfortunate that this preference is not based on something as easily observable as light and color, it does help particle physicists better understand the nature of the rare substance and allows us to confidently say that any antimatter astronauts in the far, far future can view the Earth in its vibrant blues and greens.
Works Cited:
-https://www.popularmechanics.com/science/a25908/how-to-make-and-trap-antimatter/
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