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A tip re antimatter scarcity.

  1. Oct 5, 2008 #1

    marcus

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    One of us, Oldman, had a suggestion recently that relates to the puzzle about the scarcity of antimatter. He mentioned the book by Helen Quinn and Yossi Nir. I haven't read this book so I can't recommend it, but I will pass along the tip.

    It is a popular-written book. Witty title, cute cover---supposed to look like a murder mystery or detective-story---The Mystery of the Missing Antimatter. By particle physicists but for wide audience. Here is an interview with the two authors

    http://www.powells.com/tqa/yossi.html

    We have another thread going in Cosmology forum about somebody else's notion of why anti is scarce. What I hope is, someone who has read this book will tell us, in brief, what Quinn and Nir say. Or maybe not even what they say, maybe forget Quinn and Nir and just sketch in brief what the conventional story is. When you start discussing a nonstandard cosmology idea it is generally good to first establish what the standard view is---so we all have that as a starting point.

    IOW if you are deviating, first describe what you are deviating from---if you are proposing an alternative first describe the usual model that it is an alternative to.

    I hope I'm correct in assuming that what Quinn and Nir provide is the usual notion or notions, the prevailing ideas of why antimatter is scarce.

    this page gives you links so you can scan the TOC to scope what their approach is.
    http://press.princeton.edu/titles/8475.html

    Here's the TOC
    http://press.princeton.edu/TOCs/c8475.html

    I'm counting on Oldman to contribute some comment because he brought it up and recommended.
     
    Last edited: Oct 5, 2008
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  3. Oct 5, 2008 #2

    marcus

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    I take it that at this point there are no firm answers, but there are at least some conventional notions based on standard particle physics and standard cosmology. Here is a small sample of Quinn and Nir:

    ==quote==
    ... an active topic of current work. This much we do know: The fate of antimatter to disappear was sealed by the time the Universe was no older than a millionth of a second. At that time, matter particles and antiparticles were both still very abundant, but there must have been a tiny edge for particles over antiparticles, about one extra particle for every ten billion particle–antiparticle pairs. This tiny excess is all that matter needed for a total victory over antimatter in the present Universe. All the visible structures in the Universe that we observe today—planets, stars, galaxies, clusters of galaxies—are made from that surplus of particles over antiparticles. While we know for sure that the tiny excess of matter over antimatter existed when the Universe was a millionth of a second old, it is very likely that the crucial events that created this excess happened well before, sometime between 10−40 and 10−12 seconds, the period that is accessible to our theories but not to experiments. This makes the mystery of the missing antimatter a very exciting one: it gives us a window into extremely early times, and tests our particle physics theories under conditions that we cannot recreate in our experiments. Matter and antimatter obey very similar but not quite identical physical laws. We know that a tiny difference between the laws of nature for matter and antimatter exists because we have seen it in experiments. It is now incorporated into our theories of particle physics. We can use these theories to develop a picture of how and when an imbalance of matter and antimatter could develop. We can even calculate how big the imbalance should be. That calculation makes predictions for conditions we can observe today, for the amount of matter in stars and galaxies compared to the amount of radiation in the background microwave signal that we see from all directions in space.

    But the mystery of the missing antimatter is not solved! Our modeling tells us that the present theory of elementary particles and their interactions, the so-called Standard Model, which matches correctly the results of numerous laboratory experiments, must be flawed or incomplete. For, if it were the full story, the disappearing antimatter would have taken along with it too much of the matter; too few protons and neutrons would persist to make just a single galaxy, such as our own Milky Way. So this is the mystery of the missing antimatter in its modern variation: What laws of nature, not yet manifest in experiments and not part of our current Standard Model, were active in the early Universe, allowing the observed amount of matter to persist while all antimatter disappeared from the Universe?...
    ==endquote==
     
    Last edited: Oct 5, 2008
  4. Oct 12, 2008 #3
    The reason that I'm so late with a comment is that I've run aground on The Mystery of the Missing Antimatter, because as well as being no cosmologist, I'm also no particle physicist. The details of particle physics spelled out here take time to digest.

    Although it's title, cover and the illustrations seem intended to amuse, this book is actually a wolf in sheep's clothing. Helen Quinn is a very distinguished particle physicist (from SLAC) and Yossi Nir has a chair at the Weizmann Institute in Israel. They write authoritatively for laymen, clearly and very carefully, about difficult matters like the concordance model of cosmology, the importance of symmetry in physics and especially about violations of CP symmetry. They explain CP symmetry clearly and how it might still be responsible for our universe having no antimatter, even though the observed amount of CP violation (in full agreement with the robust Standard Model of particle physics) is insufficient to explain the gross asymmetry of our universe. The missing antimatter is indeed a great unresolved mystery, as central to cosmology as dark matter and dark energy.

    I find this a fascinating and intricate tale. It's written from the perspective of mainstream particle physicists and should be refreshing for folk with a cosmological outlook. Its 34 page timeline of developments in cosmology and particle physics is particularly helpful.

    If any contributers to this forum can still spare $29.95 in these turbulent financial times, invest it in this book. Trust me, as your financial advisor always tells you!
     
  5. Oct 14, 2008 #4
    In what way are the laws of physics different for matter and antimater?

    Also in that 'other' antimater thread I mentioned Fienman diagrams, That was probably off the wall and wrong but would like to hear an educated comment on it. The idea came from reading a popular book 'In Search of Shroedinger's Cat" that I read many years ago.
     
    Last edited: Oct 14, 2008
  6. Oct 14, 2008 #5
    I would like to contribute what I call the big belch & fart theory towards this discussion. A super super massive fast spinning 'singularity' might spew massively forth through its two poles (like blackholes appear to have jets) giving a clockwise spin universe out one pole and an anti-clockwise spin universe out the other end. Our visible matter universe might be a small part of the belch and an opposite mainly antimatter universe might be the fart.

    I know this is not a forum for speculative theories but I thought it might add some amusement. ;)
     
  7. Oct 14, 2008 #6

    turbo

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    If the inventory of particles and antiparticles includes not only real but virtual particles, the 120 OOM imbalance in virtual particle influence so frequently cited by Penrose makes the scarcity of antimatter a lot less problematic. It would only take at bit of extra attraction and concentration of one vs the other to result in the universe we see today. CERN's researchers may or may not measure a difference in the gravitational infall rate of neutral hydrogen vs neutral anti-hydrogen (once they have produced sufficient quantities of that) to give us another key to this puzzle.
     
  8. Oct 14, 2008 #7

    Nereid

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    Like oldman, I too have read the book; like oldman, I too recommend it ... it is about as good as this kind of book ever gets.

    To boot, its publisher is Princeton University Press, and publication date 2008.
     
  9. Oct 16, 2008 #8
  10. Oct 28, 2008 #9
    From a particle physics point of view, it is about cross sections and channels. As noted above, a specific symmetry, called CP symmetry is broken. If CP symmetry is preserved, the event rates for particles and antiparticles in the same interactions should be identical. Empirically, we know this isn't true (Measured event rates are not the same.), so we know CP symmetry is violated. We can make a model (It is well known.) that incorporates this measured symmetry breaking.

    Since event rates for matter are not the same as for antimatter, then it is possible to start with energy and end with a collection of particles that are not evenly balanced between matter and antimatter. Now let matched pairs annihilate. There will be some particles left over, so we will have gone from space containing only energy density to space that contains some energy density and some matter, without matching antimatter.

    This process is referred to as baryogenesis, and as indicated above, the details are not yet understood.

    John
     
  11. Oct 29, 2008 #10
    Very clearly and simply put, John, but your last sentence is perhaps a liitle misleading. Correct me if I'm wrong here, please. I'm no particle physicist:

    Isn't the problem that yes, it is known that CP symmetry is violated. But the known amount of such violation is grossly inadequate to account for the observed density of ordinary matter. This is a major mystery that remains to be resolved. It is the whole point of Quinn and Nir's book.

    So, the asymmetry of the universe is far from being able to be dismissed as a detail that is not understood --- it's a big puzzle for both the standard model of particle physics and the LCDM model of cosmology.

    Roll on, repairs to the LHC!
     
  12. Oct 29, 2008 #11
    There are questions about whether the CP violation rate is a constant (or close to it) or does it vary with the energy density quickly enough to explain baryogenesis. Some exotic theories allow for a rate that varies enough to fix baryogenesis, but I can't claim to be convinced.

    Yes, this "detail" is a big deal. Sorry for the off hand language for it, but it is the way I'm used to talking about such things. It is one of the indicators that the standard model of particle physics can't be the final answer. In fact, it is possible that the high energy behavior where the standard model is known to fail is also hiding this answer. An example that is actually too simple to be the real answer is - imagine that the Higgs boson exists and that it interacts with matter in a way that displays a strong CP violation. Then, at energies where the Higgs is an important reaction channel, it could produce a very large asymmetry in matter compared to antimatter. We would expect to see hints of this in LHC if it were true, but I think this specific example is actually already excluded for other reasons. (If a Higgs based seesaw mechanism is responsible for mass generation, this would imply different masses for particles and antiparticles, which we don't see.)

    Does this cause problems for LCDM? That depends on how you define the LCDM model. I would define it is a "post inflationary" model, in the sense that any mechanism for generating the initial conditions seen at CMB last scattering (or maybe at nucleosynthesis, if you want to include element abundances in the model) follows the LCDM path. This allows for extensive freedom in the happenings of the first minute or so, including all of the current non-inflationary models. All of the first few seconds models are just trying to produce the conditions that are consistent with BBN and the CMB. Since Baryogenesis happens in this first few seconds time slot, it really isn't part of LCDM (at least as I view it).

    John
     
  13. Oct 29, 2008 #12
    Thanks for this clarification. Nice to read about opinions from what I take to be the particle physics side of things. You're right about the LCDM bit. I should rather have rather said that the asymmetry is a general puzzle for cosmology, not specifically for the LCDM model. I look forward to it being resolved, hopefully by the LHC.
     
  14. Oct 29, 2008 #13
    A quick fix because I was typing at 2AM my time for my last post.

    The Higgs mechanism isn't a seesaw. Sorry for saying it that way.

    John
     
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