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Underground Lab To Probe Ratio of Matter To Antimatter
Wired reports on the Enriched Xenon Observatory 200, a particle detector scientists hope will answer the question of why there is significantly more matter than antimatter in the universe. Quoting:
"The new detector will try to fill in the picture, determining basic features of [neutrinos], like their mass and whether or not they, unlike almost all other particles, are their own antiparticles. That quirk is why some scientists believe neutrinos could be the mechanism for the creation of our matter-filled universe. Almost all other particles have an antiparticle twin that, if it comes into contact with the particle, immediately annihilates it. But if neutrinos are their own antiparticles they could conceivably be knocked onto matter's 'team,' thereby causing the cascading win for matter over antimatter that we know occurred. As the Indian theoretical physicist G. Rajasekaran put it in a speech [PDF] earlier this year, neutrinos that are their own antiparticles would explain 'how, after [the] annihilation of most of the particles with antiparticles, a finite but small residue of particles was left to make up the present Universe.'"
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Who says there is more matter than antimatter in the universe? Has anyone ever gone to the Andromeda galaxy? So how do we now it consists of normal matter? Doesn't matter react the same as antimatter in every possible way?
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If these particle detector scientists watched TNG, they'd know that there's only one ratio of matter to antimatter.
Does antimatter attract matter or repulse it (could a double star, one of antimatter and one of matter, i.e. where the stars revolve around each other exist?).
Would it be a prerequisite that a big bang produces as much matter as antimatter?
Bert
Does antimatter attract matter or repulse it
IANA particle physicist or cosmologist, but I can answer this one: it depends on which particles. For example, a position (anti-electron) has opposite charge to an electron and will thus attract electrons and repulse protons.
That's the premise in one of Larry Niven's old Beowulf Shaeffer stories (collected in Crashlander ). Shaeffer and a Steve Fosset-like millionaire come upon an isolated planet, only to discover to their dismay that it is made out of antimatter. Unfortunately, the relatively believable science ends there, because Niven's way of having them colonize it relies on a species of unobtainium
See the graphic at http://en.wikipedia.org/wiki/Elementary_particle and the article at http://en.wikipedia.org/wiki/Antiparticle is also of interest.
Elementary particles with no charge cannot have an anti-particle, since the definition of anti-particle has to do with having the opposite charge, as I understand things.
Actually, in the standard model, both neutrinos and antineutrinos exist and are distinct. The key point is that it is the weak, not electromagnetic, force that is important.
The weak interaction 'connects' leptons and neutrinos. For example, an electron can turn into an electron neutrino by emitting a virtual W- boson. Conversely, a positron turns into an anti-electron neutrino by emitting a virtual W+.
Just like electrons have non-zero electromagnetic charge, neutrinos and leptons have non-zero weak charge, known as 'weak hypercharge'. This enables them to interact via the weak interaction. Neutrinos have opposite weak hypercharge to antineutrinos, so there is a definite distinguishing feature.
In contrast, bosons like photons and the Z0 do not have antiparticles because their charges (electromagnetic, weak hypercharge, etc) are all zero.
As a corollary, gluons have antiparticles because their colour charge is non-zero.
IIRC, standard model neutrinos are Dirac particles, which have well defined antiparticles. However, the hypothesis being tested is whether or not neutrinos are actually Majorana particles, which are invariant under charge conjugation (that is, they are precisely the same particle as their antiparticle.). It all comes down to representation theory and the Lorentz group (and friends). If we claim that charge conjugation is an interesting transformation to examine, then we must clearly describe exactly how each of our fields (particles) changes when we apply that transformation. Dirac and Majorana particles transform two different ways, and we don't know that our conjecture that all the fermions are Dirac particles is actually correct.
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Dear citizens and members of the galactic Economic Council
The rumors about a shortage of antimatter to fuel or spacefleets and habitats is unfounded.
Everyday our scientists everywhere in this universe are finding new ressources, new anti-black stars to drill for our energy.
We used antimatter for thousands of millenia now, will continue for a lot more. I am happy to announce you the we finally opened for production that galaxy on the outer left reach of the milky way. There most advanced civilisation is a monkey like tribe that have barely learned to cover themselves and there was so to speak no Spaceflight activities to be observed.
One or two derelicts spacecrafts have been observed, but they use a primitive explosion system, so we are sure those Terrans will not mind if we pump their galaxy dry of the stuff.
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The Standard Model assumes that all three neutrino species (electron, muon, and tau) are massless, and is essentially agnostic about whether neutrinos are their own antiparticles. If a neutrino is (is not) its own antiparticle, we call it a Majorana (Dirac) particle. Most any reaction which could tell the difference between Majorana and Dirac neutrinos can't occur in a Standard Model with massless neutrinos, so the difference is subtly and has no real experimental consequence.
We know the Standard Model is wrong, however. From neutrino oscillations, we know that neutrinos have tiny masses. This suddenly means that there ARE experimental consequences: neutrino-less double beta decay is possible for Majorana neutrinos but not Dirac neutrinos, for example. This is what EXO and many other experiments (GERDA, MAJORANA, CUORE, ...) are looking for. Existing results aren't quite sensitive enough to tell the difference, but new ones may be.
Just because something is not part of the Standard Model doesn't mean that it's unpopular - we need to change the Standard Model somehow, after all, since it's wrong about neutrino masses! My impression (as a particle physicist, but not in this sub-field) is that most particle theorists actually expect neutrinos to be Majorana particles. There are very interesting theories based upon a scheme called the "see-saw mechanism" which can simultaneously explain why neutrinos have such tiny masses and why the universe has so much more matter and antimatter. If neutrinos are just boring old Dirac particles, it will be back to the drawing board!
In a perfect vacuum, it isn't. However, even the intergalactic medium isn't a perfect vacuum, and somewhere there would have to be a border between a matter region and an antimatter region. Such a region would give off a very specific gamma ray spectrum, with a peak at 511 keV due to positron-antipositron annihilation and several peaks in the 70-400 MeV range due to proton-antiproton annihilation; the rate of interaction would be low, but the surface area of the frontier so large that we should be able to observe it from Earth. If it is a more localized phenomenon (like Niven's star system), then it would be travelling through the interstellar medium, inside a galaxy, which is far denser.