Of Particular Significance

First, a couple of things you might like to read:

• There was a long-overdue article from the New York Times as to how, after eight years of cuts from the Bush administration during good economic times, followed by additional inevitable cuts during the Great Recession, formerly world-leading scientific research efforts in the United States are on the verge of collapse, risking far more than the scientific research itself.  The situation is far more dire, in my opinion, than the tone of the article implies; the brain drain of talent leaving the US is frightening and well underway, and the problems are by no means limited to particle physics and astrophysics.
• The article that I described last month by Moni Bidin et al. that claimed (loudly, in the press) that there was little evidence for dark matter in the Sun’s interstellar neighborhood (but far from the center of the Milky Way galaxy) has been discredited by one of the world’s leading astrophysicists, working with a younger collaborator. The claim (made without a big press release) of Jo Bovy and Scott Tremaine, from the Institute for Advanced Study in Princeton, is that one of the assumptions on which the Moni Bidin et al. argument was based is inconsistent with data and therefore wrong, ruining the argument. Bovy and Tremaine have replaced this assumption with a different one that is consistent with data, and they conclude, in contradiction to Moni Bidin et al., that the corrected argument leads to the conclusion that there is indeed dark matter in the vicinity — roughly the amount one would expect from other considerations. In short, the Moni Bidin argument, once corrected, actually leads to more evidence in favor of the existence of dark matter! A short description of the situation is given on the Resonaances blog.

Second: I’m starting to think about a new section for this website.

Particle physics, quantum mechanics, and all the strange-sounding stuff that many physicists study are often thought of as esoteric, abstract, and irrelevant to ordinary life. But in fact our world is directly impacted, in many different ways, by quarks and photons and quantum uncertainty and the like; these things are not abstract at all. To make this point more accessible, a website like this one needs a good introductory section to help beginners make their way into the world of particle physics. So I’m going to be constructing this section over the coming months. Feedback from readers as to whether the material is readable and sufficiently introductory will be very valuable, so please feel free to offer your comments.

One of my first tasks is to talk about the architecture of the universe — how its parts are formed from smaller parts, on down to the smallest objects we know about so far. Of course there are many other introductions to this subject already on the web (and a few of them are even correct!) What I hope will make my presentation a little different is the inclusion of some insights into not only what we know about the structure of the universe but also how we know it, and additionally some comments on how our lives are impacted by each level of detail in the architectural hierarchy.

The first phase of this process will be to look at how ordinary matter that we are made from and surrounded by is constructed from the basic ingredients of electrons, quarks (and anti-quarks and gluons), and the strong nuclear, electromagnetic and gravitational forces. The figure below gives a preview of what’s coming (and you can click the figure for a larger version.)

The hierarchical architecture of ordinary matter. At the lowest known level are found electrons (e), quarks (u,d,s) and anti-quarks, along with force particles such as gluons. Up and down quarks, gluons and pairs of quarks and antiquarks make up the proton and neutron (the “nucleons”), and are held together by the strong nuclear force; a residual effect of that force holds the protons and neutrons together in atomic nuclei, of which there are a few hundred. The electromagnetic force allows electrons to attach themselves to nuclei, forming a hundred or so chemically distinct types of atoms. A residual effect of the electromagnetic force then binds the atoms together into a gigantic zoo of molecules, out of which the vast complexity of ordinary materials — the air, the sea, the rocks underfoot, and the immense diversity of life — are formed. Meanwhile gravity crushes the earth’s rock into a rough sphere and keeps the air, water, and living things from floating off into outer space.  The rough sizes of the objects appearing at each level of structure are indicated at right.