![]() Very recently, the ALPHA collaboration have been able to report the fine structure of antihydrogen up to the state using laser-induced optical excitations from the ground state and a strong external magnetic field. Of course it is only very recently that atomic versions of antimatter have been able to be created and trapped, allowing researchers to uniquely study the foundations of QED (and hence modern physics itself) from the perspective of this mirror-reflected anti-world. This is of course known as the Nobel-Prize winning Lamb Shift in hydrogen, a feature of the interaction between the quantum fluctuations in the electromagnetic field and the orbiting electron. In fact, the most successful theory of the 20th century, quantum electrodynamics (QED), properly accomodating anti-electronic interactions, also predicts a foundational test for both matter and antimatter hydrogen – the splitting of the and energy levels (I’ll leave a reference to a refresher on this notation). And not just the mass and magnetic moment, but also the fine structure (atomic transition frequencies). In particular, one of the most intriguing predictions of the invariance of the laws of physics under charge, parity and time transformations is that antihydrogen should share many of the same properties as hydrogen. What I’ll focus on is what we can do with it and what it means for fundamental physics. I’ll leave this up to a reference at the end. There are plenty more details of how the ALPHA collaboration acquires antihydrogen for study. cold) that cannot overcome the weak effect of external magnetism. Therefore not surprisingly, these are the atoms of very low kinetic energy (i.e. The difficulty however is in the complexity of external magnetic field required to ‘trap’ the neutral antihydrogen in space. Just like hydrogen, the orbit of a positron around an antiproton behaves like a tiny magnet, a property known as an object’s magnetic moment. Well this is precisely what the international ALPHA collaboration at CERN has been concerned with, providing “slowed-down” antiprotons with positrons in a device known as a Penning trap. But what if we start simple – gather together an antiproton and a single positron and voila, we have antihydrogen – the antimatter sibling to the most abundant element in nature. Hence it goes without saying that we can’t just keep them sealed up in Tupperware containers and store them next to aunty’s lasagne. Antimatter-matter pairs readily interact, releasing vast amounts of energy proportional to the mass of the particles involved. The trick with antimatter is to keep it as far away from normal matter as possible. Matter, but anti.įigure 1: The Hydrogen atom and its nemesis – antihydrogen. With such an exceptional result, we would want to be absolutely sure that all our experiments say the same thing, so that brings us the our current topic of discussion – antihydrogen. the amazing thing is that under all these transformations, the laws of physics behave the exact same way. A ‘CPT-transformed’ universe would be like a mirror-image of our own, with all matter as antimatter and opposite momenta. This is the simultaneous transformation of charge conjugation (C), parity (P) and time reversal (T), or CPT for short. So far one of these important symmetries has stood up the test of time with no observable violation so far being reported. These days our understanding of symmetries and how they relate to the phenomena we observe have developed so comprehensively throughout the 20th century that physicists are now often concerned with the opposite approach – applying the fundamental mechanisms to determine where the gaps are between what they predict and what we observe. For example, how many years after you first calculated the speed of a billiard ball using conservation of momentum did you realise that what you were doing was only valid because of the fundamental symmetrical structure of the laws of nature? And hence goes our life through physics education – we first begin from what we ‘see’ to understanding what the real mechanisms are that operate below the hood. From the idea that “for every action there is an equal and opposite reaction” to the vacuum solutions of electric and magnetic fields from Maxwell’s equations, we often take such astounding universal principles for granted. Physics often doesn’t delay our introduction to one of the most important concepts in history – symmetries (as I am sure many fellow physicists will agree). Article title: Investigation of the fine structure of antihydrogen
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