Scientists working at CERN have made a landmark finding, taking them one step closer to answering the question of why matter exists and illuminating the mysteries of the Big Bang and the birth of the Universe. The Big Bang should have created equal amounts of matter and antimatter in the early universe. But today, everything we see from the smallest life forms on Earth to the largest stellar objects is made almost entirely of matter. Comparatively, there is not much antimatter to be found. Something must have happened to tip the balance. One of the greatest challenges in physics is to figure out what happened to the antimatter, or why we see an asymmetry between matter and antimatter.
In their paper published in Nature the physicists from the University's College of Science, working with an international collaborative team at CERN, describe the first precision study of antihydrogen, the antimatter equivalent of hydrogen.
"The existence of antimatter is well established in physics, and it is buried deep in the heart of some of the most successful theories ever developed, said Charlton. "But we have yet to answer a central question of why didn't matter and antimatter, which it is believed were created in equal amounts when the Big Bang started the Universe, mutually self-annihilate?
"We also have yet to address why there is any matter left in the Universe at all. This conundrum is one of the central open questions in fundamental science, and one way to search for the answer is to bring the power of precision atomic physics to bear upon antimatter."
Antimatter particles share the same mass as their matter counterparts, but qualities such as electric charge are opposite. The positively charged positron, for example, is the antiparticle to the negatively charged electron. Matter and antimatter particles are always produced as a pair and, if they come in contact, annihilate one another, leaving behind pure energy. During the first fractions of a second of the Big Bang, the hot and dense universe was buzzing with particle-antiparticle pairs popping in and out of existence. If matter and antimatter are created and destroyed together, it seems the universe should contain nothing but leftover energy.
Nevertheless, a tiny portion of matter – about one particle per billion – managed to survive. This is what we see today. In the past few decades, particle-physics experiments have shown that the laws of nature do not apply equally to matter and antimatter.
Physicists are keen to discover the reasons why. Researchers have observed spontaneous transformations between particles and their antiparticles, occurring millions of times per second before they decay. Some unknown entity intervening in this process in the early universe could have caused these "oscillating" particles to decay as matter more often than they decayed as antimatter.
Consider a coin spinning on a table. It can land on its heads or its tails, but it cannot be defined as "heads" or "tails" until it stops spinning and falls to one side. A coin has a 50-50 chance of landing on its head or its tail, so if enough coins are spun in exactly the same way, half should land on heads and the other half on tails. In the same way, half of the oscillating particles in the early universe should have decayed as matter and the other half as antimatter.
However, if a special kind of marble rolled across a table of spinning coins and caused every coin it hit to land on its head, it would disrupt the whole system. There would be more heads than tails. In the same way, some unknown mechanism could have interfered with the oscillating particles to cause a slight majority of them to decay as matter.
It has long been established that any excited atom will reach its lowest state by emitting photons, and the spectrum of light emitted from them represents a kind of atomic fingerprint and it is a unique identifier. The most familiar everyday example is the orange of the sodium streetlights.
Hydrogen has its own spectrum and, as the simplest and most abundant atom in the Universe, it holds a special place in physics. The properties of the hydrogen atom are known with high accuracy, and one in particular, the so-called 1S-2S transition has been determined with a precision close to one part in a hundred trillion - equivalent to knowing the distance between Swansea and London to about a billionth of a metre!
Now in these latest experiments, the team have replaced the proton nucleus of the ordinary atom by an antiproton, and the electron substitute is the positron. By shining laser light at a well-defined frequency onto antihydrogen atoms held in a trap, they have seen that some of them get excited to an upper level, and in so doing leave the trap. This very first experiment has already determined the frequency of the antihydrogen transition to a few parts in a tenth of a billion.
The Hubble image at the top of the page shows the iconic Crab Nebula.
The Daily Galaxy via Cern and Swansea University