The History and Future of Antimatter
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While Newton’s Third Law famously states that for every action, there exists an equal and opposite reaction, the same is true for everything else in the universe. Every component of matter—protons, neutrons, electrons, and the subatomic particles that compose them—has an equal and opposite counterpart, like an evil twin. Antimatter atoms have antiprotons instead of protons, antineutrons instead of neutrons, and positrons instead of electrons, and the charges of each particle are reversed.
The idea of antimatter originated in 1928 when physicist Paul Dirac was investigating the electron’s properties and found two solutions to an equation he derived, one for the electron and another for a particle with a positive charge: the positron. Dirac’s findings were proven in 1932 when scientists observed the positron while observing cosmic rays. Just like positive and negative numbers, the opposite charges of a particle and antiparticle cancel out, but instead of returning a zero, it results in a powerful burst of energy. Scientists theorize that the universe was created with equal parts of matter and antimatter, but an event following the Big Bang caused all the antimatter to disappear. As a result, scientists are investigating why we are living in an asymmetric universe composed exclusively of matter. In 1955, the European Council for Nuclear Research (CERN) used the Bevatron particle accelerator to discover the antiproton, a subatomic particle that is identical to the proton but has a negative charge instead of a positive charge. This initial experiment sparked a series of investigations to solve the mystery behind the universe’s asymmetry.
Following a series of discoveries, including that of the antineutron, CERN announced in 1978 that it had successfully stored several hundred antiprotons for the first time for 85 hours, a monumental feat, considering how quickly antimatter destroys itself in an environment made exclusively of matter. Then, a team of researchers at CERN’s Low Energy Antiproton Ring in 1995 collided antiprotons with xenon atoms and observed a burst of energy just billionths of a second after the collision. With this volatile reaction, the team knew that they had created the world’s first antihydrogen atom, a positron orbiting an antiproton instead of an electron orbiting a proton. Because hydrogen is the most abundant element in the universe, this milestone became a major step toward solving the mystery of matter-antimatter asymmetry. The next challenge was to find a way to study these antihydrogen atoms before they destroyed themselves. CERN accomplished this feat in 2011 with the Antihydrogen Laser Physics Apparatus (ALPHA), which traps the newly created antimatter using a magnet that prevents them from coming in contact with regular matter. By trapping these antiatoms, CERN unlocked a way to study them closely without the particles disintegrating immediately after creation.
Though antimatter research was originally devised to answer a question about the nature of our universe, it has also proved increasingly useful to humanity. Positron emission tomography (PET) is one way that antiparticles serve a practical role in the field of nuclear medicine, which uses radioactive substances to diagnose and treat disease. After a substance known as a radiotracer is introduced into a patient’s body via injection, it releases radioactive tracer molecules which emit positrons. The interactions between positrons and electrons in the body generate gamma rays, which are then picked up by a machine. PET scans are essential to diagnosing and monitoring cancer and other conditions such as heart and brain disorders. In addition, new research on antimatter is constantly being applied to tweak the positron tracers to detect different metabolic processes. For example, PET scans are regularly used to locate areas of decreased blood flow in the heart, and can also monitor Alzheimer’s disease in the brain of a patient.
CERN’s Antiproton Cell Experiment (ACE) proved that antimatter can be used to eliminate cancer cells and may be a more effective alternative to radiation therapy, which kills healthy cells in addition to cancer cells in its target area. The team hypothesized that annihilating the matter in cancer cells using antiprotons creates enough energy to destroy the nuclei of the cancer cells and create a sort of cellular shrapnel that destroys other cancer cells as well. The team tested their hypothesis by shooting a particle beam in each of two test tubes containing cancer cells: one encountered a beam of protons and the other antiprotons. The results showed that the antiproton beam took four times fewer particles to achieve the same effect the proton beam did, meaning that the antimatter therapy may inflict significantly less damage to healthy tissue. Though still in its infancy, the medical applications of antimatter demonstrated by ACE are key examples of how valuable antimatter research is to us, even if these results are just a byproduct of nearly a century of theory crafting and experimentation.
While these discoveries are profound, we have barely scratched the surface of antimatter research. In March 2021, CERN announced that it had successfully cooled antihydrogen down to near absolute zero, an accomplishment that would open new frontiers of antimatter research. Namely, supercooled antimatter allows scientists to run precision tests to investigate how antimatter interacts with gravity and why there is an imbalance of matter and antimatter in our universe. While we are still figuring out ways to study antimatter in a stable state, new studies like this will undoubtedly pave the way for groundbreaking technologies, such as a new form of cancer therapy or antimatter-guided propulsion. It is clear that CERN’s research on this subject will prove fruitful in many ways beyond just answering questions about our universe. Perhaps we may not live to see all the mysteries of the universe solved, but that does not mean we should discredit nearly a century's worth of work. While the ongoing quest to answer these questions may give us answers about the origins—and perhaps the end—of our universe, the byproducts of solving the universe’s mysteries are what really matter.