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Underground Lab To Probe Ratio of Matter To Antimatter

Posted by Soulskill on from the scotty-unavailable-for-consult dept.

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.'"

82 comments

  1. How can you tell? by Entropy98 · · Score: 1

    I thought it wasn't possible to tell antimatter from matter from afar?
    --
      IP Finding

    1. Re:How can you tell? by CRCulver · · Score: 4, Interesting

      I thought it wasn't possible to tell antimatter from matter from afar?

      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

    2. Re:How can you tell? by F�an�ro · · Score: 1

      -Spoiler-

      I remember the story differently:

      They cannot figure out why the planet and sun are such an anomaly
      (high velocity indicating origin outside of the milky way, no sign of interstellar debris, unusual high activity of the sun)

      They argue about landing on the planet, even thought their ships hull gets damaged by an unknown force

      In the end they decide not to risk it, and go back to civilisation, and only then are told that their hull must have been damaged by antimatter, that therefore the whole system was made of antimatter, and that they would have died attempting to land

      IIRC they never go back to this planet, is there a followup story?

    3. Re:How can you tell? by CRCulver · · Score: 1

      I think Niven's telling of a way to colonize it was in one of his later collections, N-Space or Playgrounds of the Mind. It's been a few years, though.

    4. Re:How can you tell? by Ernesto+Alvarez · · Score: 1

      "Crashlander" follows the story of Beowulf Shaeffer for a few years (it's actually a set of different short stories held together by a "glue" story). It is said in the glue story that matters got complicated, the UN got involved and eventually nobody went back due to bureaucratic reasons.

      --
      GPG 0x1B479C78
    5. Re:How can you tell? by davolfman · · Score: 1

      I thought they tossed a UN flag down to watch the fireworks though.

    6. Re:How can you tell? by hpa · · Score: 3, Informative

      I thought it wasn't possible to tell antimatter from matter from afar?

      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.

    7. Re:How can you tell? by Enigma2175 · · Score: 1

      due to positron-antipositron annihilation

      Am I missing something? Isn't a "antipositron" an electron? Generally the anti- prefix goes with the antimatter, not the matter.

      --

      Enigma

    8. Re:How can you tell? by sjames · · Score: 1

      In my recollection, the idea that it might be colonized using a stasis field was one reason Niven opened Known Space to other writers and took a bit of a hiatus himself (and then went back and covered the earlier history a bit). He felt that too many problems were too easily solvable at that point.

    9. Re:How can you tell? by hpa · · Score: 1

      I meant electron-positron annihilation, of course. My brain had "proton-antiproton" in its head when I wrote that, and so it came out weird.

    10. Re:How can you tell? by pugugly · · Score: 1

      Pardon my naivete, but given the theories of hyperexpansion in the early universe, isn't it just as likely that the preponderance of matter was strictly local, the same way the differences in the background radiation were exceedingly small, but sufficient differentiate spacial regions?

      Neat as any gamma ray spectra at X keV would be, I would presume that any ongoing border between a matter/antimatter region would create sufficient 'pressure' for the regions to not mix, the same way dropping sodium on water causes it to 'skitter' across the surface because the energy of the chemical reaction is sufficient to keep it out of the water itself.

      So, if there *was* a local preponderance of matter that was gradated into an area with a local preponderance of antimatter, the energy released at those border regions would tend to blow themselves away from each other during the same timeperiod that hyperexpansion would be causing that 'temporary' separation to become permanent?

      Pug

      --
      An Invisible Entity of Vast Power whose existence must be taken on faith alone: Liberal Media
    11. Re:How can you tell? by Agripa · · Score: 1

      In the last two Ringworld books, the design of the UN ships reveals that they are powered by antimatter and as I recall, The Hindmost tells his allies that the UN has possession of an antimatter system which presumably is the same one Shaeffer and Elephant visited. The Kzinti's source of antimatter remains a mystery. The most recent Man-Kzin Wars book might discuss it.

      Shaeffer must have been good about keeping secrets since his son Louis apparently does not know about any of his father's exploits. Oddly enough, he does not even figure them out at the very end of the fourth book when presumably he could.

    12. Re:How can you tell? by RockDoctor · · Score: 1

      Spoiler for yourself CRCulver (715279) and Ernesto Alvarez (750678) : there is significant new matter on this in the recent "Juggler of Worlds" by LarryN and ANOther.
      .
      .
      .
      Spoiler space
      .
      .
      .
      There isn't any plan to colonize the antimatter planet as such, but there is a plan to send people and/ or equipment to mine the antimatter planet. The military implications of this are not lost on the pacified species (Kzinti) of Known Space, nor on the several remaining dangerous, if not aggressive, species (not named - RTFn).
      The materials needed for this mining job are not "Unobtanium" in the universe - stasis fields are well-known if poorly understood phenomena in Known Space ; the other component in the plan was "fine control of magnetic fields", which for a universe that's had 500 years of experience with on-ship fusion power plants, should be a well-established technology. Stasis fields to prevent matter contacting antimatter (at the same time - stasis is a time-dilation technology), including any crew ; magnetic fields to manipulate the antimatter. Well established technology in the universe, but it's still a dangerous undertaking.
      I'm still debating if JoW is a piece of classic Niven. I haven't re-read it yet, which isn't a very good sign.

      --
      Birds are not dinosaur descendants;birds are dinosaurs, for all useful meanings of "birds", "are" and "dinosaurs"
    13. Re:How can you tell? by badkarmadayaccount · · Score: 1

      Actually the 'positron-antipositron' bit makes more sense from my POV. If anti- means antimatter, why not make it consistent?

      --
      I know tobacco is bad for you, so I smoke weed with crack.
    14. Re:How can you tell? by mindstrm · · Score: 1

      If anti means antimatter, you would express it as
      electron / antielectron.

      Antielectron == positron

  2. the neutrinos are everywhere by someone1234 · · Score: 4, Funny

    Even in your closet!
    So you don't have to look afar.

    --
    Patents Drive Free Software as Hurricanes Drive Construction Industry
    1. Re:the neutrinos are everywhere by BiggerIsBetter · · Score: 4, Funny

      Even in your closet!

      Neutrinos are gay?

      --
      Forget thrust, drag, lift and weight. Airplanes fly because of money.
    2. Re:the neutrinos are everywhere by TheLink · · Score: 2, Insightful

      Researchers are trying to figure out whether neutrinos are straight or bi, they think this might help explain why the rest of the universe is mostly straight (allegedly).

      Except most of them are not even sure what >90% of the universe is made of, so what makes them so sure that the rest of the universe is mostly straight?

      --
    3. Re:the neutrinos are everywhere by Anonymous Coward · · Score: 0

      Researchers are trying to figure out whether neutrinos are straight or bi, they think this might help explain why the rest of the universe is mostly straight (allegedly).

      No. Since "being straight" means that you tend to unite with the opposite gender in order to release loads of free energy ("ah-ah-ah", followed by offspring), while "being gay" describes same-sex mating[1], I'd say the question is whether neutrinos are gay or bi (an answer might help explain why the rest of the universe is mostly gay (allegedly)).

      Oh fuck ...

      [1] I have no real explanation for the release of free energy in this case, but there's definitely no offspring; I think you get the idea ...

    4. Re:the neutrinos are everywhere by zenyu · · Score: 1

      I have no real explanation for the release of free energy in this case, but there's definitely no offspring; I think you get the idea ..

      My understanding was that matter and anti-matter are more like straight women and straight men. When anti-matter and matter collide they emit gamma rays, and if the gamma rays are sufficiently dense they can condense back into either matter or anti-matter. So there are at least three good explanations for a mostly female universe: either there were more women to begin with, the laws of physics were different in this respect in the beginning, or when gamma rays condense more women are produced. My hope would be on the last one since it feels most efficient and we can test it in my lifetime, but we don't understand the mechanism for any of those scenarios. If we finish up the standard model and there is perfect symmetry everywhere then we'll have to accept that the universe was either born imbalanced or the laws of physics were somehow different at the beginning. Which would be unfortunate, because we probably won't have any means to simulate and observe a big bang anytime soon.

      And before someone say the laws of physics never change, General Relativity and the Standard Model may be nearly as incomplete as Newtonian physics. Remember, Newtonian physics explains almost all of the workings of our solar system and was good enough for a long time. General Relativity may similarly be limited to the workings of the sparse universe we can observe today.

      PS I've been out of school a long time and only took physics because it was a requirement for an engineering degree, but if I'm way off I'm sure some physics grad student will correct me. :)

    5. Re:the neutrinos are everywhere by Anonymous Coward · · Score: 0

      You're close. The actual reason for the excess matter was the passing of the "One Particle Law" 15 billion years ago. Antiparticles were mostly victims of the resulting infanticide.

    6. Re:the neutrinos are everywhere by rrohbeck · · Score: 1

      Gays are everywhere! Vote yes on 8! We have to stem the tide of gay neutrinos! Think of the children! They'll all be made gay if we let the neutrinos take over the school system!

      --
      thegodmovie.com - watch it
  3. How so? by KasperMeerts · · Score: 4, Interesting

    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?

    --
    As long as there are slaughterhouses, there will be battlefields.
    1. Re:How so? by Anonymous Coward · · Score: 5, Informative

      If there had been an exactly equal amount of matter and antimatter since the birth of the universe, it would have long ago annihilated into photons. Since this has manifestly not occurred, one is in excess of the other. Which one you label as "matter" and which one "antimatter" is purely down to personal preference.

      Some differences can be observed in the behaviour of matter and antimatter; for example, in a magnetic field, electrons will curve in one direction and positrons in another. Another example is the asymmetries observed in the oscillations of mesons (the classic example being the K0) which reveal a clear, fundamental difference between matter and antimatter.

    2. Re:How so? by daniel_newby · · Score: 5, Informative

      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?

      Gas is observed between the galaxies, but not the hard radiation that would be produced when it reached a galaxy and annihilated.

    3. Re:How so? by Anonymous Coward · · Score: 5, Informative

      Even an easier explanation. The annihilation of antimatter with matter gives off very distinct spectral patterns. We know what these are, and we have calculated them for any observable red/blue-shift range. We've yet to observe any great quantity, or even a 'halo' around any other galaxies. In an equally distributed universe, you would see such things, as high-velocity matter from one universe collided with another, and give off pretty lights. We don't see such, hence, the universe is mostly matter.

    4. Re:How so? by walter_f · · Score: 1

      Additionally, if some far away galaxy consisted completely of antimatter, to the inhabitants of this galaxy we would clearly be the "antimatter people".

      Like in telecommunications with another civilization somewhere else in the universe it would not be a trivial task to agree upon the meaning of "left" vs. "right" (no political pun intended here).

      --
      "My parents have been on vacation to a planet where the dominant species has no lateral symmetry - and all they brought me is this lousy F-shirt!"

    5. Re:How so? by Anonymous Coward · · Score: 0

      One key difference between antimatter and matter is the mass/charge balance for particles that experience the electromagnetic force. (For instance, an ionized antihydrogen atom will have a negative charge for the same mass; it will still produce the same contribution to gravitational lensing that an ionized hydrogen atom will, but the opposite charge leads to different interactions with other charged particles).

      Any particles that experience the electromagnetic force will -- in large quantities -- produce absorption lines and scatter patterns for background light sources, and when excited (by gravitation or astrophysical ASE) produce emission lines. We observe the Lyman-Alpha forest when observing the sky, and given a substantial amount of antimatter between us and any distant source of well-defined EM emission, as from a type IA supernova or a quasar, the L-A forest line patterns would be clearly different. Stellar fusion involving antimatter like antihydrogen would be visible spectrally, as well. We might not see one single antimatter star at a distance of Megaparsecs, but we would see a galaxy of them, or even galaxies containing a few percent of them even at Gigaparsec distances, even if they weren't annihilating with the normal matter.

      Finally decays of particles which experience the weak nuclear force are somewhat different -- we can distinguish the decay of antineutrons from that of neutrons, by astronomical observation of enough of either. Radioisotopes of anti-elements would be obvious in the sky, if they existed in large numbers.

      Moreover, interactions between matter and antimatter produce clear emissions patterns, including those in configurations which are metastable (electron-positron positronium, proton-antiproton protonium (although it's generally very short-lived metastability...), and so forth). Annihilation emissions would be obvious in spectral studies of the sky, and again would make for an obviously unusual Lyman-Alpha forest along any sight path.

      There is a question about whether there are small amounts of antimatter which we have simply not observed yet. Some of the work around TFA is in trying to determine if there is a process for producing small, localized amounts of antimatter from collisions with neutrinos. This sort of interaction summed across the whole observable universe would lead to a very large amount of antimatter but spread out so diffusely it may be hard to detect. There are other possible sources of diffuse/localized antimatter from pair production in free space (interactions with gravitation or dark energy might cause the pair to separate before mutually annihilating -- "realizing" a real pair from a virtual one. However, it seems unlikely that we will find a large concentration of antimatter along the lines of an antimatter galaxy, largely because we would expect to see annihilation lines (relatively) recently in the big bang/inflation/expansion timeline.

  4. Obviously these guys need to watch more Star Trek by MichaelBuckley · · Score: 5, Funny

    If these particle detector scientists watched TNG, they'd know that there's only one ratio of matter to antimatter.

  5. Questions for a physicist in this field by kanweg · · Score: 4, Interesting

    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

    1. Re:Questions for a physicist in this field by Anonymous Coward · · Score: 5, Informative

      Does antimatter attract matter or repulse it

      *Charged* antimatter will attract its matter counterpart electrostatically via the Coulomb force. For example, an electron will attract a positron. This does not occur for neutral particles.

      The gravitational attraction between bodies must also be considered: it is negligible between individual particles, but comes into effect for macroscopic objects. The gravitational interaction is determined by the amount of mass present, and is always attractive, regardless of whether it is between matter or antimatter.

      (could a double star, one of antimatter and one of matter, i.e. where the stars revolve around each other exist?).

      A star will be (on average) neutrally charged, otherwise Coulomb repulsion between like charges will break it apart. Therefore it is fair to say that both the matter and antimatter star will be electrically neutral or at least not significantly charged.

      Even if there were two charged objects, the Coulomb force, like the gravitational force, follows the inverse square law, so extra electrostatic attraction will be equivalent to more mass.

      In either case, a stable orbit could form.

      Would it be a prerequisite that a big bang produces as much matter as antimatter

      I'm moving out of my depth here, but the answer is probably no. Even if it did, future interactions between particles may cause an imbalance (as is thought to have occurred in our universe). A prerequisite for what, anyway?

    2. Re:Questions for a physicist in this field by shma · · Score: 4, Informative

      Would it be a prerequisite that a big bang produces as much matter as antimatter?

      I'm moving out of my depth here, but the answer is probably no. Even if it did, future interactions between particles may cause an imbalance (as is thought to have occurred in our universe). A prerequisite for what, anyway?

      I'm afraid the answer is actually yes, at least if you replace 'a prerequisite' by 'excepted from the laws of physics'. Since there is nothing in the laws of physics to make us believe that matter is 'preferred' over anti-matter, we naturally assume that the amounts of both in the early universe are the same. The problem with this most natural assumption is that, if there was the same amount of matter and anti-matter in the universe, and they stayed in thermal equilibrium as the universe cooled (which is true for most of its history), they would almost completely annihilate and there would be too little matter left over today to make up what we presently see. So we need an event that favours matter over anti-matter to produce the required leftover matter we see. This is called the baryogenesis problem. Of course, you CAN just demand that the required extra matter be put in as an initial condition, but most physicists shun that approach, especially since the matter excess is one part in 10 billion, an unnaturally small number which would have to be put in by hand. We prefer to find a way to generate that asymmetry dynamically.

      --
      I came here for a good argument
    3. Re:Questions for a physicist in this field by Anonymous Coward · · Score: 0

      especially since the matter excess is one part in 10 billion, an unnaturally small number which would have to be put in by hand.

      Why?

      We prefer to find a way to generate that asymmetry dynamically.

      Once again, why? Why isn't postulating that such an event must exist nothing more than forcing the universe into a preconceived box, and as such no different from something like creationism?

    4. Re:Questions for a physicist in this field by shma · · Score: 1

      Once again, why? Why isn't postulating that such an event must exist nothing more than forcing the universe into a preconceived box, and as such no different from something like creationism?

      Saying "there may be a way of generating this asymmetry dynamically, and if so we should look for it" is not forcing the universe into a pre-conceived box. It is the opposite view, that anything we measure should just be explained away as an initial condition of the universe ("that's just the way things started out"), that is closer to creationism ("it's just the way god created it").

      --
      I came here for a good argument
    5. Re:Questions for a physicist in this field by Anonymous Coward · · Score: 0

      "the matter excess is one part in 10 billion" sounds like rubbish. It's not mentioned in your link, and think about it: If 99.99999999% of the initial mass of the universe transformed into energy according to E=mc^2, then after thermal equilibrium every particle in the universe would be flying around much faster than LHC speeds.

    6. Re:Questions for a physicist in this field by byornski · · Score: 1

      microwave background radiation

    7. Re:Questions for a physicist in this field by Bananenrepublik · · Score: 1

      The gravitational attraction between bodies must also be considered: it is negligible between individual particles, but comes into effect for macroscopic objects. The gravitational interaction is determined by the amount of mass present, and is always attractive, regardless of whether it is between matter or antimatter.

      This is an unproven assertion. Noone ever built a large enough lump of antimatter to verify that its gravitational force is indeed attractive. It is true that within the current physical theories gravity is always attractive (leaving aside the cosmological terms), yet, unless this is verified by experiment it is but a very convincing assumption.

    8. Re:Questions for a physicist in this field by Anonymous Coward · · Score: 0

      It is not clear wether antimatter reacts to gravity in the same way as matter does.
      http://arxivblog.com/?p=450
      The force of gravity on antimatter has never been directly measured but a growing number of physicists believe that such an experiment is within their grasp. Today, a group attempting to design an experiment called AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) outline their plans to measure this force.
      In some ways itâ(TM)s an ambitious plan. The team wants to build AEGIS at CERN, the European particle physics laboratory near Geneva, where the building blocks of antihydrogen, low energy antiprotons and positrons, are in relatively good supply.
      more in the paper about AEGIS

    9. Re:Questions for a physicist in this field by Anonymous Coward · · Score: 0

      Not a troll, more like informative.

    10. Re:Questions for a physicist in this field by Anonymous Coward · · Score: 0

      The CMB is very weak, 410 very low energy photons per cm^3, while the mass density of the universe is often quoted to be 1 hydrogen atom per m^3, which is much more mass-energy per volume. Indeed, Wikipedia says that the CMB makes up a fraction of roughly 5e-5 of the total density of the universe. That's not the 0.9999999999 we're looking for.

    11. Re:Questions for a physicist in this field by hawkfish · · Score: 1

      Once again, why? Why isn't postulating that such an event must exist nothing more than forcing the universe into a preconceived box, and as such no different from something like creationism?

      Saying "there may be a way of generating this asymmetry dynamically, and if so we should look for it" is not forcing the universe into a pre-conceived box. It is the opposite view, that anything we measure should just be explained away as an initial condition of the universe ("that's just the way things started out"), that is closer to creationism ("it's just the way god created it").

      But the model that you use to "generate the asymmetry dynamically" can be described as "that's just the way things started out" too, so I'm not sure what the distinction is here...

      --
      You will not drink with us, but you would taste our steel? - Walter Matthau, The Pirates
    12. Re:Questions for a physicist in this field by shma · · Score: 1

      Initial conditions for the universe, by definition, can't be tested through observation. Any model worthy of examination that explain baryogenesis will produce other observables.

      --
      I came here for a good argument
  6. Basic answer by pjt33 · · Score: 3, Informative

    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.

  7. Re:Obviously these guys need to watch more Star Tr by Trip6 · · Score: 2, Funny

    If they're not careful they'll lose anti-matter containment and open up a rift in the space-time continuum.

    --
    I hate being bipolar; it's awesome!
  8. Re:Obviously these guys need to watch more Star Tr by Ihmhi · · Score: 1

    Has a breach in Matter/Anti-Matter containment ever opened up a time rift? Not AFAIK...

    --
    Random Thoughts From A Diseased Mind (Not For Dummies)
  9. To pick a nit by yttrstein · · Score: 2, Informative

    That may not need to be picked, but as I understood it, a neutrino isn't actually it's own anti-particle, strictly, it's that a neutrino doesn't actually have a known strictly defined antiparticle equivalent. I understand it *looks* like I'm saying the same thing, but I do see a difference, however subtle.

    It's been theorized, I think, that the former is true, that it really is it's own antiparticle, based on hypothesized neutrinoless double-beta decay--which, if true, insinuates the former. But this is clearly outside the standard model and is having difficulty gaining popularity, as far as I know, since it hasn't actually been seen yet.

    The other I suppose "just so" method of defining a neutrino as its own antiparticle is by working nomenclature--there are four different kinds of neutrinos in this sense; muon, electron, and their two counterparts--anti-neutrinos if you will, which are still technically neutrinos.

    I'm not a particle physicist, and I may very well be wrong in many places above. So if there is anyone about who can correct me I would very much appreciate it.

    1. Re:To pick a nit by j-beda · · Score: 3, Informative
      At the very least, you have forgotten the third family, the Tau and Tau-neutrino.

      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.

    2. Re:To pick a nit by Anonymous Coward · · Score: 3, Informative

      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.

    3. Re:To pick a nit by The_Wilschon · · Score: 4, Interesting

      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.

      --
      SIGSEGV caught, terminating

      wait... not that kind of sig.
    4. Re:To pick a nit by rasputin465 · · Score: 2, Interesting

      a neutrino isn't actually it's own anti-particle, strictly, it's that a neutrino doesn't actually have a known strictly defined antiparticle equivalent.

      IAAPP. Neutrinos have very well-defined antiparticles, and we observe them all the time in nature. We can verify that they and neutrinos have quantum numbers that are opposite to one another. Normally, for charged particles, the antiparticles have the opposite charge and so there is no question that these are distinct. But for neutral particles, really the only non-zero quantum number available is the handedness (this is related to helicity, which describes if their spin is left-handed or right-handed with respect to their motion). We have only observed left-handed neutrinos and only right-handed antineutrinos. But the question arises, is that the ONLY difference? Because with the observation of neutrino oscillations, we have evidence that neutrinos have mass (which is not allowed in the standard model), and so their helicity is not fixed. If this is true, then whether a particle is a neutrino or antineutrino is simply a matter of reference frame, and hence neutrinos are their own antiparticles (similar to the way that photons are their own antiparticles).

    5. Re:To pick a nit by yttrstein · · Score: 1

      Haha, this is working the nomenclature! Well, I'm glad it doesn't just happen in chemistry. Who was it who said "Science is the study of naming things incorrectly"

    6. Re:To pick a nit by Kagura · · Score: 1

      Why does the existence of neutrino oscillations mean that neutrinos must have mass? IANAPP, so I don't know how being a massive particle makes it able to oscillate between other kinds of neutrinos.

    7. Re:To pick a nit by Anonymous Coward · · Score: 1, Interesting

      Why does the existence of neutrino oscillations mean that neutrinos must have mass?

      Over simplifying (IANAPP): to oscillate, a thing much change. To change, a thing must experience time. Things traveling at the speed of light cannot experience time (a consequence of special relativity). A massless neutrino would travel at the speed of light.

      Since neutrinos oscillate, they experience time, which means they cannot travel at the speed of light, which means they cannot be massless, which means they must have mass.

    8. Re:To pick a nit by Kagura · · Score: 1

      I was about to call you a loony, but that seems like a realistic explanation. Thanks for the reply, can anybody confirm this?

    9. Re:To pick a nit by Anonymous Coward · · Score: 0

      (posted anonymous because I have moderated)

      Yes, this is a very good and simple explanation IMHO.

      -Ricin

    10. Re:To pick a nit by Ricin · · Score: 1

      Hmff, /. undid the moderations anyway. THEN WHY DO THEY ASK? :) Oh well.

    11. Re:To pick a nit by Anonymous Coward · · Score: 0

      I think the "to oscillate, a thing must change" answer is a bit loony.

      A better way of putting it is that neutrino oscillations involve a change in the intrinsic energy of a neutrino. Energy couples to the Einstein Stress-Energy-Momentum Tensor in Relativity, but one component of the energy is intrinsic (the rest mass) while the other depends on movement through a frame of reference. (The rest mass is the energy of a particle in a frame of reference in which it experiences no accelerations at all).

      The Standard Model predicted that the rest masses of the three types of neutrinos were all zero; all the energy of a neutrino was due to its relativistic motion, as with a photon, with a different non-rest-mass explanation for their different theoretical (and observed) interaction energies.

      The expectation from theoretical cosmology (looking through various telescopes) is that the average rest mass of all three types of neutrino must be less than 50 eV/c^2 or the universe would collapse gravitationally because of the sheer number of neutrinos in it. Observational cosmology has helped reduce this to less than 0.3 eV/c^2 or we could not see what we do in the cosmic microwave background, the Lyman-Alpha forest, or the various galaxy surveys (such as the Sloan).

      Otherwise, cosmology had little to say about neutrino rest mass other than that the Standard Model was useful in the area of quantum cosmology, for example, and WIBNI it were zero so as to preserve the Standard Model as a general tool.

      However, there is good evidence (from solar and terrestrial neutrino sources) for changes in the intrinsic energy (rest mass) of a neutrino, and that has consequences. Alternatively, you could look at the consequences and say that therefore neutrinos must have a rest mass (spot the relativist).

      The consequence of a nonzero rest mass, and three different masses, is that the propagation through flat, free space of the three types of neutrino will occur at different speeds. The more rest mass a particle has, the more it will lag behind at the ultrarelativistic limit (i.e., moving near the speed of light). This very small lag is observable because of interference effects (constructive interference causes flavour change). Very small here means that in a "race" among neutrinos travelling in parallel with a photon, the lag from one particle to the next would be less than a metre per billion years. However a metre is a LOT of neutrino-lengths, and more particularly a lot of neutrino-semi-lengths, so in a billion years there will be lots of shifting of the amplitudes of the flavour and mass wave functions of a neutrino. That is the oscillation; the flavour we observe is related to the square of the amplitude of the wave functions.

      Flipping this around, flavour change is observed and fits an interference pattern related to a difference in plane wave propagation speed of the neutrino types, which in turn fits the acceleration curve of particles with intrinsic mass in special relativity. The fit is very very good given the observations made to date, so therefore it is safe to conclude with high confidence that neutrino oscillations mean neutrinos have mass.

      The really simple way of putting it is that massive things are harder to accelerate to near the speed of light; neutrinos (if massless) would be so close to the speed of light as to be indistinguishable from photons (and each other) in a race. They are distinguishable from photons in a race -- they're slightly slower.

      Oscillation is an artefact of the slower movement; at ultrarelativistic speeds interference sets in causing a flavour change to be observed.

  10. Do a lookup on... by Anonymous Coward · · Score: 0

    Harold Aspden and see if this ties in with any of this. It's a bit over my head concerning the math.

  11. This makes me wonder by LaughingCoder · · Score: 1, Flamebait

    Why does it matter if there is more matter than anti-matter? What is the matter with these people?

    --
    The more you regulate a company, the worse its products become.
  12. 'But' tutorial by Schiphol · · Score: 0, Offtopic

    Finite but small? Finite but big, fine. Infinite but small, fine. Finite and small, fine. Finite but small, no sir.

  13. Reserves still going strong, no need to panic ! by da5idnetlimit.com · · Score: 4, Funny

    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.

    The message from SF DR SD 3, President of ExNegMat power industries.

    --
    It takes 40+ muscles to frown, but only four to extend your arm and bitchslap the motherfucker
  14. When I first read "probe" by unassimilatible · · Score: 1

    It sounded like there was going to be some government investigation into missing anti-matter, as if someone embezzled it.

    I guess I've got Quark on the brain from watching too much DSP DVDs.

    --
    Slashdot "libertarians": Small government for me, big government for those I disagree with. -1, I disagree with you
  15. "Underground lab" by oldhack · · Score: 1

    So it's an "underground lab" now, is it. I've better not catch you geeks smoking in the basement.

    --
    Fuck systemd. Fuck Redhat. Fuck Soylent, too. Wait, scratch the last one.
    1. Re:"Underground lab" by Anonymous Coward · · Score: 0

      No smoking is allowed in our underground area. Tobacco contains polonium-210 and lead-210, both of which are radioactive and can cause backgrounds in the detector. ;-)

  16. Extension to the Standard Model by jpflip · · Score: 4, Insightful

    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!

  17. Easy by Anonymous Coward · · Score: 0

    There is more matter in *this* part of the universe. In another part of the universe there are both equal amounts of matter and anti matter and hell breaks loose. Yet in other parts of the universe there is more antimatter. It's like when you have many red and black billiard balls and you throw them on the table: there is a possibility you'll have just four black balls in one corner. this is the antimatter corner.

    stupid scientists...

  18. Re:Obviously these guys need to watch more Star Tr by Requiem18th · · Score: 1

    I think Star trek has enough problems with space, time and continuity without the need for anti-matter.

    --
    But... the future refused to change.
  19. maybe its more simple by Anonymous Coward · · Score: 0

    maybe its more simple math
    in equal systems positive solutions are prefered.
    -1 * -1 = 1
    +1 * +1 = 1

    So if you start from nothing no dimensions etc no time etc.
    Equations like +1 * -1 happens less at the moment of creation a difrence in space time there doesnt have to be negative cration (force/antiforce) like +1 and -1 it would be unlickely even because it would imidietly cancel out such creation bigbang moment. The answe to this might thus be in the origin of simple math, and Oscars Razor.

  20. "galaxy on the outer left reach of the milky way" by Anonymous Coward · · Score: 0

    milky way IS the galaxy. Not funny I know.

  21. Antimatter -So What About Neutrons by JerryLs · · Score: 1

    Neutrons have no electrical charge, so what happens when one meets it's opposite? Opposite what?

    --
    Ad Astra Per Asper
  22. Underground lab? by rrohbeck · · Score: 1

    Aren't they supposed to make Meth or something? Why are they switching to Neutrinos? Do they give you an even better buzz? Has anybody tried Neutrinos? How was it?

    --
    thegodmovie.com - watch it
    1. Re:Underground lab? by ScreamingCactus · · Score: 1

      Neutrinos are lame - almost no effect at all! You can barely even tell they're interacting with you at all. I prefer to stick with proton-centric multicyclic dipolar magnetoresitant plasmoidonigistics. They don't get you high, but by the time you've finished pronouncing them, the whip-its kick in and you're too stoned to finish talking :)

      --
      The path to enlightenment is truly through homemade drugs!
  23. dark matter vs dark antimatter by Anonymous Coward · · Score: 0

    Seeing as most of a galaxy's weight (mass) is dark matter couldn't half of that be anti dark matter? I'm pretty sure scientists have no idea about the energy signature of a dark matter antimatter annihilation. I believe it's supposed to be electrical neutral too.

  24. Not enough energy to create anti-matter by lpq · · Score: 0, Troll

    If E=Mc^2, then wouldn't -M*c^2=-E?.

    So in any localized area where there was more anti-matter, the negative energy produced from anti-matter conversions would annihilate any positive energy around, but if there is no energy around, the anti-energy wouldn't be able to exist in our universe. Only as positive energy could it remain in existence -- but positive energy can only inter-exchange with matter -- not anti-matter. Thus after all the matter and antimatter combined, some of the anti-energy would have disappeared/exited from our universe leaving only positive energy and positive matter. ...or something like that...:-)

    1. Re:Not enough energy to create anti-matter by ScreamingCactus · · Score: 1

      If this is a joke, forgive me for letting it WHOOSH over my head but... you really need to re-read the memo on matter/antimatter... you did get that memo, didn't you?

      --
      The path to enlightenment is truly through homemade drugs!
  25. Why not just run a simulation? by Anonymous Coward · · Score: 0

    Why not just create a bunch of antihydrogen and inject it into a magnetically isolated vacuum with some hydrogen, and watch what happens? Or if they think that most M/AM was anilihilated before atoms formed, then use antiplasma. If I'm not mistaken, creating antimatter is pretty much routine these days. Just throw some in an arena with its sworn enemy and see who comes out on top. Then review the battle footage to see why. Is that a stupid idea? (PS I'm not talking about watching individual anihilations but gathering information from aggregate statistics)