| Supersymmetry - the end of the line | Jon Butterworth and Herbi Dreiner Just before this blog moved to the Guardian, I wrote about a supersymmetry meeting I attended. Now my theory pal who organised it chips inIn case you missed it, I wrote about a conference on supersymmetry I went to last week, just before this blog moved home. I also gave some reasons why supersymmetry might, or might not, be seen as an attractive extension of the Standard Model of particle physics, given that there is no experimental evidence for it yet.Now my theory friend Herbi Dreiner, who I used to work with when I was a student and who organised the Bonn meeting, has given his view. Since I know there are heaps of supersymmetry fans out there, I thought I should bring it to your attention:The conference on "Supersymmetry and the Unification of Fundamental Interactions", which my colleagues and I organised in Bonn, finished yesterday. The entire week I was thinking I would drop into bed and sleep for a full day. But oddly, I feel quite refreshed. It was great fun listening to the talks and discussing with so many friends and colleagues, despite all the organisational headaches. The conference dinner was on an elegant boat which in an earlier life was used for the signing ceremony of the Schengen agreement. (For us mainland Europeans this is a big deal.)Supersymmetry seems alive and well and ready to face the challenge from the LHC. But what is supersymmetry? And what is so super about it? Why are we so taken with it, even though there is as yet no experimental evidence it actually exists? There are two main arguments. First, it is a solution to the "hierarchy problem". I will save this for a potential second post, if Jon invites me back. The other is indeed an aesthetic argument related to the "Coleman-Mandula theorem".Now, I tell myself every morning in front of the bathroom mirror that aesthetics is for wimps, but it is all the same an interesting argument.Symmetries have become a central pillar of our understanding of nature. A sphere is symmetric in the sense that if you leave me in a room with the sphere and come back in, you cannot tell if and by possibly how much and about which axis I have rotated the sphere. The sphere is highly symmetric. This, however, also makes a sphere kind of boring, since because it has to be the same in every direction it has no structure. If the sphere has a pattern on it, like for example an old black and white football, only very specific rotations are still undetectable. This is the remaining, reduced symmetry.It turns out that in the world of elementary particles there are two types of symmetry. One kind is internal symmetries. These govern the forces of nature like the electromagnetic force. Here a hidden, internal property of particles is changed. The other kind we call external symmetries and they affect the way particles fly through space and time. The appropriate external symmetry is described by special relativity, invented by Einstein in 1905. The undetectable transformations are called Lorentz transformations. In this case the laws of nature are unchanged if we look at the particles for example on a stationary train or one moving with constant velocity (and on smooth tracks!).Now how about Coleman and Mandula? They showed that in fact the Lorentz symmetries are the maximal external symmetry allowed in nature. If you were to introduce a larger more extensive symmetry the world would become so boring that particles could no longer interact. They would just fly around freely in space not knowing about each other. However, in their argument Coleman and Mandula neglected one external property of particles, their spin. This is a peculiar quantum property: they behave as if they had a small internal magnet. In specific units all the matter particles we know, e.g. the electron and the quarks, have spin 1/2. The force carriers like the photon have spin 1. Spin is an external property, which is affected by rotations in space. Now if we extend Coleman and Mandula and allow for discrete changes of spin by half a unit, we find a new maximal external symmetry of nature. This is supersymmetry. It is super because it goes beyond the previous external symmetries. If nature is supersymmetric the electron must have a partner with spin 0 and the photon a partner with spin 1/2 and all with many interactions.However, if this symmetry were at all extended (now also taking spin into account, of course) the resulting world would be boring and trivial with no interactions. Since we have now used up all external particle properties we believe this is the end of the line. This is what makes supersymmetry so special ... and to some beautiful.Of course, the data from the LHC over the next months and years, but also from precision measurements of certain particle properties, will decide whether any of this is real.Jon Butterworthguardian.co.uk © Guardian News & Media Limited 2010 | Use of this content is subject to our Terms & Conditions | More Feeds guardian.co.uk |
Harrabin's Notes Roger Harrabin on the impact of "sit-stand" flights bbc.co.uk |
Today's mystery bird for you to identify This is a challenging bird to identify, and the photograph shows a part of it that most people are not aware of. Can you tell me what family this bird is placed in?Mystery Bird: This species is found in tropical and sub-tropical swamps, estuaries and watersides in South America, from Venezuela to northern Argentina. [I will identify this bird for you in 48 hours]Image: Steven Duncan [larger view].Nikon D200 w/ AFS 70-200m f/2.8 VR lens, hand-held @ 200mm 1/400 sec f4This next photograph might give you a little more information to base your identification on.Image: Steven Duncan [larger view].Nikon D200 w/ AFS 70-200m f/2.8 VR lens, hand-held @ 200mm 1/400 sec f4This common species, endemic to South America, is part of a small group of birds that lack a structural feature that is unique to birds and their early ancestors. This same feature is shared with several endangered reptilian species, which are sometimes referred to as "living fossils". Can you tell me what that structure might be? It also has another special structure (pictured above) that has a specific function. What might that function be?Daily Mystery Bird Rules: 1. Please name at least one field mark that supports your identification, keeping in mind that more than one field mark is often necessary to distinguish between species. IDs without any supporting information are not valid and may be deleted by the moderators. 2. Expert and intermediate level birders: do NOT try to be the first to blurt out the mystery bird's ID. Instead, please provide helpful hints, such as descriptions, literary references, puns, personal anecdotes, and other forms of discussion and assistance for beginning birders and for those following on their iPhones without naming the species. Expert and intermediate birders are free to name the bird species 24 or more hours after it was first published.3. Each mystery bird is usually accompanied by a question or two. These questions can be useful for identifying the pictured species, but may instead be used to illustrate an interesting aspect of avian biology, behaviour or evolution, or may be intended to generate conversation on other topics, such as conservation. 4. Each bird species will be demystified 48 hours after publication. If you have bird images, video or mp3 files that you'd like to share with a large and appreciate audience, feel free to email them to me for consideration.GrrlScientistguardian.co.uk © Guardian News & Media Limited 2010 | Use of this content is subject to our Terms & Conditions | More Feeds guardian.co.uk |
Private spaceship makes first solo glide flight By 2010-10-11T03:51:23ZMOJAVE, Calif. (AP) -- Virgin Galactic's space tourism rocket SpaceShipTwo achieved its first solo glide flight Sunday, marking another step in the company's eventual plans to fly paying passengers.... hosted.ap.org |
Vital Signs: Screening: Side Effects From Endoscopic Procedures A new study reports that 1 in 100 patients experience complications serious enough to send them to the emergency room — a much higher rate than expected. feeds.nytimes.com |