Why Is CERN Making Antimatter?

Antimatter, a substance that annihilates matter upon contact, is being produced and studied at CERN, the European Organization for Nuclear Research. This process, governed by E=MC², is the most violent known in physics. CERN's antimatter factory creates approximately 20 million antiprotons per minute by accelerating protons to 99.93% the speed of light and smashing them into an iridium target. This makes antimatter the most expensive substance, valued at trillions of dollars per gram. The primary goal of creating antimatter is to study it and understand why the universe is predominantly composed of matter, a fundamental mystery in physics. This quest traces back to Paul Dirac's equation, which united special relativity with quantum mechanics and predicted the existence of antiparticles with the same mass but opposite charge as their matter counterparts. The accidental observation of the positron (anti-electron) a year later confirmed Dirac's theory. Quantum field theory explains that fundamental particles are excitations of quantum fields. An electron, for instance, is an excitation of the electron field. Antiparticles are mirror excitations in the same field, possessing identical mass and spin but opposite charge. When a particle and antiparticle meet, their opposite charges cancel, causing the excitations to disappear and the field to return to its ground state. This mass is converted into energy, primarily photons, in a process known as annihilation. The "Big Bang radiation catastrophe" highlights the problem of matter-antimatter asymmetry. According to the Big Bang theory, the early universe should have created equal amounts of matter and antimatter. If this were true, all matter and antimatter would have annihilated, leaving only radiation. However, the observable universe is filled with matter, indicating a significant imbalance. Initial hypotheses suggesting regions of antimatter in the universe were disproven by the lack of observed annihilation hot spots. Calculations based on the cosmic microwave background (CMB) reveal the extent of this asymmetry. For every billion particle-antiparticle pairs created in the early universe, approximately one matter particle survived the annihilation. This means that for every billion antimatter particles and billion matter particles, one matter particle was left over. This tiny imbalance is responsible for all the matter we observe today, including stars, galaxies, and life. This necessitates a subtle difference in how matter and antimatter behave under the laws of physics, a difference that is not easily explained. Physicists have spent decades searching for this asymmetry. Early investigations focused on three symmetries: charge (C), parity (P), and time reversal (T). CPT symmetry, a combination of these, is deeply rooted in special relativity. If CPT symmetry were broken, it would undermine our fundamental theories of physics. Therefore, the search has been for an asymmetry that accounts for the one-in-a-billion discrepancy while preserving the larger CPT symmetry. A crucial discovery came in the mid-1950s when Tsung-Dao Lee and Chen Ning Yang proposed that parity might not be conserved in the weak nuclear force. Chien-Shiung Wu's experiment with cobalt-60 confirmed this, showing that electrons were preferentially emitted in one direction relative to the nuclear spin, indicating that the universe favors a "left-handedness" in weak interactions. This groundbreaking finding, for which Lee and Yang received the Nobel Prize, challenged the prevailing belief in fundamental symmetries. Subsequent experiments revealed that even combined charge-parity (CP) symmetry could be violated. In 1973, Makoto Kobayashi and Toshihide Maskawa developed a framework within the Standard Model that explained observed P and CP violations while maintaining CPT symmetry. However, their model only accounted for an asymmetry of 10^-18, far too small to explain the observed matter-antimatter imbalance. This discrepancy suggests the existence of new physics beyond the Standard Model. To uncover this new physics, scientists at CERN are meticulously studying antimatter. The antimatter factory employs an antiproton decelerator (AD) and a secondary ring called ELENA to slow down antiprotons for experiments. These antiprotons are then sent to various experiments designed to probe their properties. One of the key challenges is storing antimatter. The Penning trap, inspired by Frans Penning, uses strong magnetic and electric fields to confine charged antiparticles in a vacuum. This technology allowed the BASE experiment to measure the charge-to-mass ratio and magnetic moment of the antiproton, finding them to be consistent with predictions. The next frontier is studying how antimatter interacts with gravity. While some early theories speculated about "anti-gravity" where antimatter would fall upwards, direct experimental verification is difficult due to the overwhelming strength of the electric force on charged antiprotons. To mitigate this, neutral anti-atoms are required. The GBAR experiment aims to create and precisely measure the gravitational acceleration of anti-hydrogen. This involves merging antiprotons with positrons to form anti-hydrogen atoms. A more complex method involves creating anti-hydrogen ions (one antiproton and two positrons), which can be trapped and cooled to extremely low temperatures (less than 10 micro Kelvin) using laser-cooled beryllium ions. Once cold, a laser pulse dislodges a positron, creating a neutral anti-hydrogen atom that falls under gravity. By precisely timing its fall over 20 cm, GBAR hopes to achieve an accuracy of 1% in measuring gravitational acceleration, far surpassing the preliminary results from the Alpha G experiment, which found antimatter falls down, consistent with normal gravity, but with large error bars. A significant development at CERN is the creation of the world's first portable antimatter trap by the BASE experiment. This Penning trap can store antiprotons for extended periods, with a current record of 614 days. This breakthrough allows for the transportation of antiprotons to other research institutions globally, expanding the opportunities for antimatter studies. While the "Angels and Demons" scenario of terrorists stealing a significant amount of antimatter to blow up the Vatican is a fictional concept, the simulation of 1/8 of a gram of antimatter shows its devastating potential, equivalent to 36% of the Hiroshima blast. However, CERN's antimatter production is minuscule; the total amount of antiprotons produced in 25 years is a trillionth of a gram. To produce 1/8 of a gram would require the factory to run for longer than the age of the universe. The energy produced by all the antiprotons made in a year would only heat 1 ml of water by about 1°C. Antimatter is also naturally produced in trace amounts on Earth. Bananas, for example, contain potassium-40, which decays and releases positrons. The average human body produces around 180 positrons per hour, making us "little antimatter factories" ourselves. Therefore, despite its destructive potential in large quantities, the antimatter produced and studied at CERN is not dangerous and is crucial for unraveling fundamental mysteries of the universe.