Discovery of Atntimatter, and the Ultimate Fate

After the discovery of it in the early 1930s, antimatter  was the popular topic for imagination amongst physicists. "Star Trek" fans know antimatter as the high-energy fuel of the Enterprise, the stuff that sends the starship faster than the speed of light. That kind of space travel isn't likely to materialize. But the theoretical possibilities of antimatter have long seduced science fiction stories and scientists with promises of amazing revelations about the nature of distant galaxies and the origins of the universe.

Perhaps the most amazing thing about antimatter is that it was conceived of at all. In 1928, British physicist Paul Dirac set out to solve a problem: how to reconcile the laws of quantum theory with Einstein's special theory of relativity. Through complex mathematical calculations, Dirac managed to integrate these disparate theories. He explained how things both very small and very fast. In this case, electrons near the speed of light.. behaved. This was a remarkable achievement in its own right, but Dirac didn't stop there. He realized that his calculations would work for an electron with negative charge, but also for an electron with positive charge, that's an unanticipated result.

Dirac argued that this anomaly was in fact the electron's "antiparticle," the subatomic equivalent of the "evil twin." In fact, he asserted, every particle has an "antiparticle" with nearly identical properties, except for an opposite electric charge. And just as protons, neutrons, and electrons combine to form atoms and matter, antiprotons, antineutrons, and antielectrons (called positrons) combine to form antiatoms and antimatter. His findings led him to speculate that there may even be a mirror universe made entirely of antimatter.

Many new particles are produced by the annihilation of an electron and a positron Dirac's equations marked the first time something never before seen in nature was "predicted", that is, assumed to exist based on theoretical rather than empirical evidence, solely on the basis of theory guided by the human imagination. His prediction would be confirmed in experiments by Carl Anderson in 1932. Both men won Nobel prizes for their efforts.

Physicists have learned a great deal about antimatter since Anderson's discovery. One of the more dramatic findings (custom-made for many a science fiction adventure) is that antimatter and matter explode on contact. Like lovers caught in a doomed relationship, matter and antimatter initially attract (thanks to their opposite charges) and then destroy each other. Because these annihilations produce radiation, scientists can use instruments to measure the "wreckage" of their fatal collisions. No experiments have yet been able to detect the antigalaxies or vast stretches of antimatter in space that Dirac imagined. Scientists still send observatories into space to look for them, though, just in case.

CERN's Antiproton Decelerator (AD) slows down high-energy antiprotons so that their properties can be studied. But the question that really confounds physicists today springs from the same fountain that captured the imagination of the public: that matter and antimatter annihilate when they meet. All the theories of physics say that when the universe burst into existence some fifteen billion years ago with the Big Bang, matter and antimatter existed in equal amounts. Erupting from a celestial cauldron of unfathomable temperatures, matter and antimatter materialized and then annihilated repeatedly, finally disappearing back into energy, known as the cosmic background radiation. The laws of nature require that matter and antimatter be created in pairs. But within a millifraction of a second of the Big Bang, matter somehow outnumbered its particulate opposite by a hair, so that for every billion antiparticles, there were a billion and one particles. Within a second of the creation of the universe, all the antimatter was destroyed, leaving behind only matter. So far, physicists have not been able to identify the exact mechanism that would produce this apparent "asymmetry," or difference, between matter and antimatter to explain why all the matter wasn't also destroyed.
Is there an anti-universe? What would it look like? Rolf Landua describes the goal of the ATHENA experiment. You will need RealPlayer in order to view this video. Today, antimatter appears to exist primarily in cosmic rays -- extraterrestrial high-energy particles that form new particles as they penetrate the earth's atmosphere. And it appears in accelerators like CERN's, where scientists create high-energy collisions to produce particles and their antiparticles. Physicists study the properties and behavior of manufactured antiparticles, and the antimatter they form when they combine, hoping to find clues to this asymmetry mechanism.

Most scientists believe that a subtle difference in the way matter and antimatter interact with the forces of nature may account for a universe that prefers matter, but they haven't been able to definitely confirm that difference in experiments. Theories suggest that even if equal amounts of matter and antimatter were created with the Big Bang, disparities in their physical properties, such as decay rate or life span, which might favor a matter-filled world. In 1967, Russian theoretical physicist Andrei Sakharov postulated several (yet a bit complex) conditions necessary for the prevalence of matter. One required something called "charge-parity" violation, which is an example of a kind of asymmetry between particles and their antiparticles that describes the way they decay. By comparing the way particles and antiparticles move, interact, and decay, physicists have been trying to find evidence of that asymmetry ever since.
Is the proton a mirror image of the antiproton? John Eades describes the goals of the ASACUSA experiment at CERN. You will need RealPlayer in order to view this video. To find that evidence, physicists conduct two types of extremely difficult experiments, in an effort to observe matter and antimatter directly. One produces antiparticles and antimatter from high-energy collisions in particle accelerators, and then makes precision measurements of them; these measurements are then compared with everything we know about their matter opposites to identify any detectable differences.

Whatever the outcome of such experiments, physicists will continue to push the limits of human imagination trying to fix this little hole (albeit not the only one) in their beautiful theory. While theoretical physics manages to explain with extreme precision a good part of what we know about the laws of nature as experiments confirm so far, asymmetry doesn't quite fit into the framework. But who knows? In their search for that elusive mechanism that would help explain the mystery of why we're here, physicists might uncover something totally unexpected, opening the door to an amazing new discovery no one has yet imagined.

Why there were so much antimatter?

In the first few moments of the Universe, enormous amounts of both matter and antimatter were created, and then moments later combined and annihilated generating the energy that drove the expansion of the Universe. But for some reason, there was an infinitesimal amount more matter than anti matter. Everything that we see today was that tiny fraction of matter that remained.

But why? Why was there more matter than antimatter right after the Big Bang? That's really a puzzling question is the fields of research areas in physics. Researchers from the University of Melbourne think they might have an insight.

Just to give an idea of the scale of the mystery facing researchers, here’s Associate Professor Martin Sevior of the University of Melborne’s School of Physics:

“Our universe is made up almost completely of matter. While we are having entirely used to this idea, this does not agree with our ideas of how mass and energy interact. According to these theories there should not be enough mass to enable the formation of stars and hence life.”

“In our standard model of particle physics, matter and antimatter are almost identical. Accordingly as they mix in the early universe they annihilate one another leaving very little to form stars and galaxies. The model does not come close to explaining the difference 0between matter and antimatter we see in the nature. The imbalance is a trillion times bigger than the model predicts.”

If the model predicts that matter and antimatter should have completely annihilated one another, why is there something, and not nothing?

The researchers have been using the KEK particle accelerator in Japan to create special particles called B-mesons. And it’s these particles which might provide the answer.

Mesons are particles which are made up of one quark, and one antiquark. They’re bound together by the strong nuclear force, and orbit one another, like the Earth and the moon. Because of quantum mechanics, the quark and antiquark can only orbit each other in very specific ways depending on the mass of the particles.

A B-meson is a particularly heavy particle, with more than 5 times the mass of a proton, due almost entirely to the mass of the B-quark. And it’s these B-mesons which require the most powerful particle accelerators to generate them.

In the KEK accelerator, the researchers were able to create both regular matter B-mesons and anti-B-mesons, and watch how they decayed.

“We looked at how the B-mesons decay as opposed to how the anti-B-mesons decay. What we find is that there are small differences in these processes. While most of our measurements confirm predictions of the Standard Model of Particle Physics, this new result appears to be in disagreement.

In the first few moments of the Universe, the anti-B-mesons might have decayed differently than their regular matter counterparts. By the time all the annihilations were complete, there was still enough matter left over to give us all the stars, planets and galaxies we see today.

Where did all the antimatter go?

This problem is actually a very famous problem in Physics known as the Baryon Asymmetry problem, which refers to the fact that there is an imbalance in Matter and Anti-Matter in the observable Universe. The Big Bang should have created equal amounts of Matter and Anti-Matter, which is certainly not the case. Neither Quantum Physics, nor the Relativity theory can provide a solution to this problem. As of yet, we do not have a definite answer to this problem, but we do have some possible explanation:

1. Annihilation: There are regions in the Universe where Anti-Matter dominates. In simple words, our Universe is divided into two regions: where matter dominates and the other where anti-matter dominates. We live in the Matter dominated region of the Universe. Antimatter atoms would appear from a distance indistinguishable from matter atoms, as both matter and antimatter atoms would produce light (photons) in the same way. Only in the border between a matter dominated region and an antimatter dominated region would the antimatter's presence be detectable, as only there would be matter/antimatter annihilation and production of gamma rays as a consequence. Presumably such a boundary would lie in deep intergalactic space.
2. Violation of CP-Symmetry: CP stands for Charge Parity. CP-symmetry states that the laws of physics should be the same if a particle is interchanged with its antiparticle (C symmetry), and when its spatial coordinates are inverted ("mirror" or P symmetry). The Big Bang should have produced equal amounts of matter and antimatter if CP-symmetry was preserved; as such, there should have been total cancellation of both—protons should have cancelled with antiprotons, electrons with positrons, neutrons with antineutrons, and so on. This would have resulted in a sea of radiation in the universe with no matter. Since this is not the case, after the Big Bang, physical laws must have acted differently for matter and antimatter, i.e. violating CP-symmetry. This must be so because of the extreme conditions during the Big Bang.
3. Electric Dipole Moment : The presence of Electric Dipole Moment violates Parity as well as Time symmetry. As such, an Electric Dipole Moment would cause Matter and Anti-Matter to decay at different rates, possibly leading to the matter-antimatter imbalance today. This may seem confusing, but because of the limited space, time and knowledge, you'll have to bear with who's explaining the stuff.