Elementary-Particle Physics Revealing the Secrets of Energy and Matter (1998) / Chapter Skim
Currently Skimming:
2 What is Elementary-Particle Physics?
2 What is Elementary-Particle Physics?
Pages 21-32
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 21... ...
Performing experiments to investigate the physics of elementary particles requires extremely sophisticated instruments and theoretical tools. This chapter relives the ancient quest to find the fundamental constituents of matter, shows how this quest is shaped by relativity and quantum mechanics, introduces the forces (interactions)
|
From page 22... ...
It was discovered that elements combine with other elements according to very simple rules: Two hydrogens plus one oxygen make one water "molecule." The essentially limitless number of chemical "compounds" that are found in nature are then the result of combinations of elements. At the beginning of the nineteenth century, John Dalton proposed an atomic theory of matter: The elements themselves are collections of tiny indestructible atoms characterized by their atomic weights (oxygen atoms weigh 16 times as much as hydrogen atoms)
|
From page 23... ...
Each atom has a tiny positively charged nucleus, about 10,000 times smaller yet. Negatively charged electrons occupy the space surrounding the nucleus.
|
From page 24... ...
These additional generations appear to have nothing to do with "ordinary tangible matter." Yet they were important in the first moments of the universe and have a profound role in our understanding of nature. The masses of the quarks and leptons range from zero, or near zero, for neutrinos to almost 200 times the proton mass for a t quark.
|
From page 25... ...
Chapter 7 discusses just how these technological marvels work; for now, Table 2.2 lists the major accelerators presently used in particle physics in the United States. With high-energy accelerators, particle physicists can effectively "trade" energy for mass, allowing them to directly produce particles that weigh many times more than the particles being accelerated.
|
From page 26... ...
Quantum mechanics provides a precise expression for the probability of a decay at a particular time; this probability is all we can know. It is still not known why the world obeys quantum mechanics, but that it does is both beautiful and incontrovertible.
|
From page 27... ...
, but the arrangement of its electrons determines its chemical activity. It may be an inert noble gas, it may combine in a regular way to form a crystalline metal or a complex molecule, and complex molecules may combine to form living cells.
|
From page 28... ...
This is supplied by radioactive decay of heavy nuclei in Earth's interior. One of the key processes in radioactive decay of heavy nuclei is called beta decay another manifestation of the weak force whereby a neutron in a nucleus transforms into a proton and the nucleus emits an electron and a neutrino.
|
From page 29... ...
The four fundamental forces encountered gravity, electromagnetism, the weak force, and the strong force underlie all observed phenomena. Over the years, other forces have been hypothesized, but experiments searching for them have so far produced null results.
|
From page 30... ...
It may even be that gravity is also subject to unification so there would be in a real sense just one force. LAWS OF NATURE Underlying the electrical, magnetic, gravitational, and other phenomena of particle physics are a number of general principles.
|
From page 31... ...
" The principle of directing beams of subatomic particles to collide with other particles, observing what emerges from these encounters, and interpreting the results via models of their interaction remains the major technique for exploring the physics of elementary particles. Accelerators provided more energetic beams that were then used to study phenomena at much smaller distances than could be done simply by using the particles from natural radioactivity.
|
From page 32... ...
Finally, because an electron lacks substructure and behaves in a point-like way, it is a useful probe for exploring the structure of the proton. An electronproton collider provides information about the structure of a proton that is not available from a proton collider and provides an opportunity to search for hypothesized objects that combine both quark and lepton characteristics.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.