Science stuff
Jun. 17th, 2010 10:13 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
mmcirvinI post infrequently enough these days that instead of using me as a guide to interesting things happening in space, you're probably better off just reading Emily Lakdawalla's Planetary Society blog. Still, there have been some amazing things going on lately, even aside from the Hayabusa return that got a fair amount of attention (we'll see soon if it actually got anything). A few of the aforementioned amazing things:
Great pictures of the Japanese solar sail IKAROS, now fully deployed and ready to do some sailing. (The spacecraft sent out a couple of little deployable cameras just to get those shots.)
The Kepler mission releases a paper listing 312 candidate extrasolar planets, with the strong implication that those are the uninteresting ones, with information on 400 more awesome stellar systems coming in February. It wasn't long ago that a single extrasolar planet candidate would have been big news. Kepler detects them by looking for brightness fluctuations as the planets transit their parent stars, so it would only be able to find planets whose orbits are nearly edge-on to us (unless they're really close in).
Finally, here's some really interesting news from the world of particle physics: The D0 detector at Fermilab finds evidence of CP violation beyond the standard model. They found it in certain interactions involving the decay of B mesons, which my doctoral thesis was actually tangentially involved with, though I doubt the work I did was at all significant here. Anyway, what they found was that these particular reactions were more likely to produce pairs of muons than pairs of antimuons. The signal is at three standard deviations, so, if I recall correctly, it's not at the point where they can claim a solid discovery, but it's interesting enough to report results.
In "CP violation", the "C" means "charge conjugation symmetry" (the replacement of particles with their antiparticles), and "P" means "parity" (essentially, mirror reflection). A CP-violating interaction is one that doesn't go the same way if you replace all particles with antiparticles and then look at the mirror reflection of that.
CP violation is interesting for a couple of reasons.
First, in relativistic quantum field theory, CPT (CP with time reversal) is always a symmetry, so CP violation implies time-reversal asymmetry. So CP-violating interactions are exceptions to the rule that microphysical laws are always time-symmetric. The probability of an interaction happening in reverse, if you were to carefully reverse the motion of all the particles in the end conditions, would actually be different from the probability of the original interaction. (On the other hand, if you run the interaction backwards, replace all the particles with antiparticles, and mirror-reverse the spatial setup, then the probabilities will still be the same.)
Second--and this is what the authors are more concerned with--as far as anyone knows, we need CP violation in order to exist. Most theories of the early universe have matter and antimatter being created in equal amounts. But in the world we see, there is very little antimatter about. There must have been some imbalance left over (at least, in the part of the universe visible from here) when all that early matter and antimatter annihilated. Decades ago, Andrei Sahkarov figured out what conditions were necessary to bring about a matter-antimatter imbalance, and part of what you need is not just C violation but also CP violation. The Standard Model of Particle Physics actually involves a little tiny bit of CP violation, but it isn't enough; this is a longstanding mystery. The D0 collaboration think they may have observed some of the additional CP violation necessary to get a universe of matter.
The paper is also remarkable just as an example of the extraordinary lengths experimental particle physicists will go to to get these kinds of results. It's amazing that it's possible to even tease this kind of asymmetry out of the data. The transparencies linked to from the announcement give an outline of the analytical process, which takes advantage of some fortuitous cancellations between the uncertainties in various quantities to reduce the uncertainty in the final result, and it's pretty baroque.
The popular articles and blog posts on this go on about how it could be the result of there being more than one variety of Higgs particle, the thing responsible for giving quarks and leptons their masses; since Leon Lederman gave the Higgs particle the ridiculous name of "the God particle" they can have clever headlines about polytheism. The fact is, the Higgs field/particle as described in the Standard Model is just the simplest type available for the purpose; I don't think anyone really believed it was the end of the story, and a lot of particle physicists will be awfully disappointed if, say, LHC just finds one plain old Higgs. This result could be an early indication of something more interesting going on.
Great pictures of the Japanese solar sail IKAROS, now fully deployed and ready to do some sailing. (The spacecraft sent out a couple of little deployable cameras just to get those shots.)
The Kepler mission releases a paper listing 312 candidate extrasolar planets, with the strong implication that those are the uninteresting ones, with information on 400 more awesome stellar systems coming in February. It wasn't long ago that a single extrasolar planet candidate would have been big news. Kepler detects them by looking for brightness fluctuations as the planets transit their parent stars, so it would only be able to find planets whose orbits are nearly edge-on to us (unless they're really close in).
Finally, here's some really interesting news from the world of particle physics: The D0 detector at Fermilab finds evidence of CP violation beyond the standard model. They found it in certain interactions involving the decay of B mesons, which my doctoral thesis was actually tangentially involved with, though I doubt the work I did was at all significant here. Anyway, what they found was that these particular reactions were more likely to produce pairs of muons than pairs of antimuons. The signal is at three standard deviations, so, if I recall correctly, it's not at the point where they can claim a solid discovery, but it's interesting enough to report results.
In "CP violation", the "C" means "charge conjugation symmetry" (the replacement of particles with their antiparticles), and "P" means "parity" (essentially, mirror reflection). A CP-violating interaction is one that doesn't go the same way if you replace all particles with antiparticles and then look at the mirror reflection of that.
CP violation is interesting for a couple of reasons.
First, in relativistic quantum field theory, CPT (CP with time reversal) is always a symmetry, so CP violation implies time-reversal asymmetry. So CP-violating interactions are exceptions to the rule that microphysical laws are always time-symmetric. The probability of an interaction happening in reverse, if you were to carefully reverse the motion of all the particles in the end conditions, would actually be different from the probability of the original interaction. (On the other hand, if you run the interaction backwards, replace all the particles with antiparticles, and mirror-reverse the spatial setup, then the probabilities will still be the same.)
Second--and this is what the authors are more concerned with--as far as anyone knows, we need CP violation in order to exist. Most theories of the early universe have matter and antimatter being created in equal amounts. But in the world we see, there is very little antimatter about. There must have been some imbalance left over (at least, in the part of the universe visible from here) when all that early matter and antimatter annihilated. Decades ago, Andrei Sahkarov figured out what conditions were necessary to bring about a matter-antimatter imbalance, and part of what you need is not just C violation but also CP violation. The Standard Model of Particle Physics actually involves a little tiny bit of CP violation, but it isn't enough; this is a longstanding mystery. The D0 collaboration think they may have observed some of the additional CP violation necessary to get a universe of matter.
The paper is also remarkable just as an example of the extraordinary lengths experimental particle physicists will go to to get these kinds of results. It's amazing that it's possible to even tease this kind of asymmetry out of the data. The transparencies linked to from the announcement give an outline of the analytical process, which takes advantage of some fortuitous cancellations between the uncertainties in various quantities to reduce the uncertainty in the final result, and it's pretty baroque.
The popular articles and blog posts on this go on about how it could be the result of there being more than one variety of Higgs particle, the thing responsible for giving quarks and leptons their masses; since Leon Lederman gave the Higgs particle the ridiculous name of "the God particle" they can have clever headlines about polytheism. The fact is, the Higgs field/particle as described in the Standard Model is just the simplest type available for the purpose; I don't think anyone really believed it was the end of the story, and a lot of particle physicists will be awfully disappointed if, say, LHC just finds one plain old Higgs. This result could be an early indication of something more interesting going on.