Humans have come a very long way on our journey to understand the universe. From classical astronomers charting the movements of the stars, to the recent discoveries of the Higgs boson and gravitational waves, mankind’s progress in exploring the relationships between matter, space and time has been astounding. Despite these achievements, some of the most fundamental questions in physics remain largely unanswered. Nearly everything to do with antimatter—the bizarro matter that theoretically makes up half of the universe—falls into this category, though scientists at the European Council for Nuclear Research (CERN) may soon change that.
In rudimentary terms, antimatter is the opposite of matter—or more accurately, a mirror image of the matter that we interact with on a daily basis. Antimatter is made up of ‘antiparticles’, which are identical to normal atomic particles but have opposite charges. While matter contains positively charged protons, antimatter contains negatively charged antiprotons. Similarly, instead of the familiar negatively charged electrons, antimatter atoms are orbited by positrons, which carry a positive charge. Theoretically, there should be equal amounts of matter and antimatter occupying the universe. In reality, though, antimatter is elusive stuff. Current research involving the creation of antimatter may hold the key to unravelling one of the universe’s great mysteries.
The foundation for our understanding of antimatter was laid during the first half of the 20th century, by several giants of modern physics. In 1905, then patent clerk Albert Einstein published a paper describing his theory of special relativity. His theory, which was remarkably produced with thought experiments (ie: just thinking), put forth an explanation for the relationship between space and time that revolutionised our understanding of the universe.
A second major leap forward came in the mid 1920s, when Erwin Schrödinger (of Schrödinger’s cat fame) and Werner Heisenberg produced the basis for quantum theory. Their ideas gave rise to quantum mechanics, the uncertainty principle and the multiverse concept—forever changing how scientists think about the behaviour of energy and matter on atomic and subatomic levels. Unfortunately, their vision of quantum theory wasn’t compatible with Einstein’s theory of special relativity, as it failed to accurately describe the behaviour of particles moving at or near the speed of light. This gap was closed in 1928, when British physicist Paul Dirac developed an equation that bridged special relativity and quantum theory.
A peculiarity of Dirac’s equation is that it can be solved using either positive or negative numbers—meaning that it has two possible solutions. Dirac understood this to mean that for every particle in the universe, there must exist an equal and opposite particle. He described these opposite particles as ‘antimatter’ and theorized that the universe must contain equal quantities of matter and antimatter, which would have been produced simultaneously during the Big Bang. Furthermore, Dirac imagined that while our sun and Earth are made up of matter, there could be entire galaxies, solar systems and planets composed entirely of antimatter.
A central issue with Dirac’s theory is the relative lack of observable primordial antimatter in the universe. When matter and antimatter come into contact, they annihilate each other in a flash of energy. If the universe contains equal amounts of matter and antimatter, each with the power to completely extinguish the other, it’s surprising that from our observations of the natural world, the universe appears to consist almost entirely of matter.
In a picturesque mountainous setting in rural Switzerland, scientists at the CERN laboratory are working to answer this and other fundamental questions by exploring the composition of the universe. Using incredibly advanced tools such as particle accelerators and detectors, particle physicists have been able to glimpse the behaviour of the fundamental particles that dictate the laws of nature. Much of this research involves the use of antimatter, which CERN scientists have been successfully creating since 1995 for use in their experiments.
The production of antimatter typically begins in a device known as the ‘Antiproton Decelerator’, and involves the bombardment of metal blocks with high-energy proton beams. As the protons collide with the metal, the resulting bursts of energy have the potential to create pairs of protons and antiprotons—which happens roughly once in every million collisions. Antiprotons are then separated and directed using a complex system of magnetic fields, and slowed by passing them through clouds of electrons. Once sufficiently slowed (newly created antiprotons travel at close to the speed of light), the antiprotons are ready to be studied. In some experiments, antiprotons are slowed by passing them through clouds of cold positrons, resulting in the formation of antihydrogen—the simplest atom of antimatter.
Using magnetic fields, CERN scientists have been able to trap antihydrogen atoms, and sustain them long enough to be studied. By comparing antihydrogen atoms with hydrogen atoms, scientists are searching for differences in the properties of the two substances. Since matter and antimatter should be exact mirrors of one another, any observed discrepancies could provide exciting directions for new research, and help to explain the lack of observable antimatter in the universe.
While antimatter research is still in its infancy, the topic has been a staple of science fiction for years. Star Trek’s legendary Starship Enterprise had engines powered by antimatter, using the energy produced by antimatter/matter annihilation to travel at ‘warp speed’. Dan Brown’s popular thriller Angels and Demons sent protagonist Robert Langdon scrambling to stop an antimatter bomb from exploding over the Vatican. As is often the case with science fiction, these imagined uses might hold kernels of real potential for the future of antimatter research. CERN scientists are already investigating the potential of antiprotons to be used in cancer treatments, opening the door for a new wave of medical advances based in particle physics.
Despite the rapid pace of progress in recent decades, the central question of antimatter research has yet to be answered—if primordial antimatter makes up half of the universe, why haven’t we found it yet?
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Cosmic Journeys: The Riddle of Antimatter
‘Particle physicists working to unlock the secret relationship between matter and antimatter may yet discover an incredible source of energy that could allow us to travel beyond our own galaxy.’ [/geoip-content]