Antimatter: A Place in the Universe
The most tantalizing subjects in physics are those which still refuse to yield clear answers to our questions. The geometry of the universe (and hence the end fate of the universe), why time runs forward, sources of dark energy, the coronal heating problem (why is the sun’s atmosphere much hotter than its surface?): this reads like a to-write list of fascinating physics articles. There’s also what may be the last unsolved riddle from classical physics: the full theoretical modelling of turbulent systems.
This lava parabola in Hawaii falls in accord with the known laws of physics, but when flowing turbulently, it behaves in ways we still don't understand.
This article is about another unsolved mystery, one that’s been in the news recently: antimatter.
In essence, antimatter is not very special. It is stuff made out of antiparticles. The ‘anti’ is another label for particles, like charge. A particle is either a ‘particle’ or an ‘antiparticle’. This would be completely unremarkable if matter and antimatter were to be found in equal amounts in the universe, as positively and negatively charged particles are. On large scales, the universe is charge neutral.
As far as science has been able to tell, this is not so for ‘anti-ness’. Antiparticles are incredibly rare, only seen in very high energy interactions. This happens high in our atmosphere as cosmic rays (very fast protons or alpha particles) smack atmosphere, or deep underground where we humans engineer the conditions for creation of antimatter – head on collisions between particles traveling at huge speeds with enormous energies. Antiparticles disappear as soon as they are formed in these high energy collisions, in a process known as ‘annihilation’ – where matter and antimatter meet, they consume each other in a flash of energy.
Image comparing hydrogen with its infinitely rarer cousin.
It is just such an situation – or the circumnavigation of such – that has produced the recent news of antihydrogen. Deep underground in Switzerland a team working on the famous particle collider, CERN, have succeeded not only in producing antihydrogen, but in preventing its instant annihilation with regular matter by confining it using a magnetic field – trapping it. It is notoriously difficult to trap antimatter – as a physicist must in order to study the antiparticles. That this confinement has hit the news shows just how difficult it is. It was managed just 38 times for 170 milliseconds.
The difficulty in trapping neutral particles lies in their unsusceptibility to electric fields, and their tendency to disappear the instant they come into existence. The only way to pin down the antimolecules is by using a magnetic field, which interacts with their weak magnetic moments – the product of complicated reactions between the quantum fields of the antiproton and positron (antielectron) which make up antihydrogen.
The news is important because it represents a step towards the ability to conduct full scale analyses of antimatter. These analyses will allow physicists to test their models for the distribution of matter and antimatter in the universe. For one, the implications will effect our current understanding of gravity: if antihydrogen doesn’t fall at the same speed as hydrogen, it will allow particle physicists to sweep away a whole swath of models for the unification of general relativity (model for the very large scale universe) and quantum mechanics (model for very small scale universe). This kind of analysis is now just around the corner.
This image sums up the challenges of particle physics. Working with the invisible to model the real. Here, a positron curves under a magnetic field, in the opposite direction to an electron.
It is hard to explain how difficult this project has been for the ALPHA collaboration. They are manipulating invisible particles which disappear in a flash of light on contact with normal matter (air molecules, chamber walls, stray electrons or protons, anything). The entire operation must be carried out at super low temperatures (think outer space, not freezer), so that the created antihydrogen has an energy low enough to be trapped by the magnetic field. This news is not just a breakthrough, it is a monument to the painstaking, monstrously complicated work being undertaken below Switzerland.
The imbalance of matter with antimatter is one of physics’ greatest mysteries. No antimatter is observable from Earth. Any amount of antimatter would emit huge amounts of energy from its edges, where matter and antimatter would be in constant annihilation. No such energy is detected. As far as we can currently tell, no static antimatter exists in our universe. We only find it in the dance of creation and destruction which so well represents many concepts in physics and life. Read Fritjof Capra’s Tao of Physics if you’re interested in the mysticism which often matches physics.
There exists a verified asymmetry called the CP (charge and parity) violation. This allows for the favored production of matter over antimatter, but it doesn’t explain matter-dominance on its own. We also need basic violations of balance in reactions – essentially with more matter being created out of less – to fully support this theory of matter’s dominant emergence. This violation of balance has never been observed, not once; nor is the underlying mechanism of the CP violation understood.
Our current understanding of antimatter ends with more work required.
*
My physics professors would have said that there is no place for imaginings in science. I disagree. I think imagination is the essential catalyst for scientific discovery and revelation. If one cannot imagine the model you are trying to fit to your data, you are left nowhere. So I arrogantly present my imaginings:
In the case of the matter/antimatter imbalance, I have a personal theory: In the same way that a baryon, such as a proton, can be normal or ‘anti’, I believe that a universe can be normal or ‘anti’ and that we just happen to live in a normal universe, which was created in a pair of universes, along with a corresponding ‘anti’ universe. If you lived on the surface of a quark within a proton, you would be unaware that your encasing particle was actually a proton, not an antiproton. The stuff around you would all be matter rather than antimatter, although antimatter would be continuously flashing into creation (antiquarks) then disappearing into a hadron haze.
So in the case of our universe, matter balances with the antimatter in our antiuniverse pair, rather than within our own matter universe. Antimatter visits us briefly, coaxed out of a mulch of energy by our particle physicists. If my idea is true, when we look at antimatter, we are looking at our sister universe.
The comparison is imperfect, but it’s something to think about.
All images are under the Creative Commons license, from Wikimedia Commons. You can email the author at halhodson [at] gmail [dot] com.
Thank you for this intriguing insight into the mysterious natur of dark/anit-matter as well as for the affirmation of the power of imagination. I am intrigued by your notion of anti-matter being peephole into a 'sister' or parallel universe. Is this notion consistent with string-theories, or current attitudes to multi-universe potentialities? If we think we know little about anti-matter, we know ven less about Dark energy. Apparently Dark energy accounts for approximately three-quarters of the mass-energy of our little universe. It may take the form of a cosmological constant (constant energy density), or a scalar field - or quintessence with a variable energy density in time and space. Whatever the case, it's a rather large amount of a thing to have absolutely no true conception of. And is only further proof of our relative immaturity. Although, with each cosmic baby step that we take, I get a little more optimistic!
[...] (generally protons with enormous energies) enter the atmosphere, they can interact and produce an electron/positron pair, both with huge energies. These (charged) particles rip through the atmosphere much faster than the [...]
[...] we are, we have learned a lot about our surroundings and reality in general, how things work, the physical forces underpinning the universe, the psychological factors affecting our behavior, the diversity of life on the whole. We have also [...]
[...] direct asteroid impact, as illustrated by a species of bacteria that thrives in the crater’s such collisions create. Add to this the fact we now have the technology to uncover potentially inhabitable [...]