A Summing Up Let us, in these closing paragraphs, consider where our rapidly accumulating store of knowledge about the universe is leading us. That it provides satisfaction to a host of curiosity-motivated physicists and astronomers is beyond dispute. However, some view it as a humbling experience in that each increase in knowledge seems to reveal more clearly our …
Dark Matter At the Kitt Peak National Observatory in ‘Arizona, Vera Rubin and her co-worker Kent Ford measured the rotational rates of a number of distant galaxies. They did so by measuring the Doppler shifts of bright clusters of stars located within each galaxy at various distances from the galactic center. As shows, their results were surprising: The orbital …
The Universe Is Expanding As we saw in Section 38-10, it is possible to measure the relative speeds at which galaxies are approaching us or receding from us by measuring the shifts in the wavelength of the light they emit. If we look only at distant galaxies, beyond our immediate galactic neighbors, we find an astonishing fact. They …
A Pause for Reflection Let us put what you have just learned in perspective. If all we are interested in is the structure of the world around us; we can get along nicely with the electron, the neutrino, the neutron, and the”rotten. As someone has said, we can operate “Spaceship Earth” quite well with just these particles. …
The Basic Forces and Messenger Particles We turn now from cataloging the particles to considering the forces between them. The Electromagnetlc Force At the atomic level, we say that two electrons exert electromagnetic forces on each other according to Coulomb’s law. At a deeper level, this interaction is described by a highly successful theory called quantum electrodynamics (QED). …
The Quark Model In 1964 Gell-Mann and George Zweig independently pointed out that the Either. Way patterns can be understood in a simple way if the mesons and the baryons are built up out of subunits that Gell-Mann called quarks. We deal first with three ef them, called the up quark (symbol u), the down quark (symbol d), …
The Eightfold Way ‘Fire are ·eIght baryons-the neutron and the -that have a spin quantum number of ]. Table 45-3 shows some of their other properties. ~4ashows the fascinating pattern that emerges if we plot the strangeness of these ba~.oris against their charge quantum number, using a sloping axis for the charge quantum numbers. Six of the eight …
Still Another Conservation Law Particles have intrinsic properties in addition to the ones we have listed so far: mass, “charge, spin, lepton number, and baryon number. The find of these additional properties was discovered when researchers observed that certain new particles, such as the bone (K) and the sigma (~), always seemed to be produced in pairs. It …
The Leptons In this and the next section. we discuss some of the particles of one of our classification schemes: lepton or hadron. We. begin with the leptons. those particles on which the strong force does not act. So far. we have encountered. as leptons. the familiar electron and the neutrino that accompanies it in beta decay. ‘The …
An Interlude Before pressing on with the tuft of classifying the particles, let us step aside for a moment and capture some of the spirit of particle research by analyzing a typical panicle event-namely, that shown in the bubble-chamber photograph of The tracks in this figure consist of bubbles formed along the paths of electrically unchanged particles …