3. How many and what basic forces of nature have been identified until recently?
4. Which of these forces have a limited/an unlimited range?
5. Which of the basic forces are familiar/unfamiliar to everyone and why is it so?
6. What are the strong/weak forces responsible for?
7. What progress has been made recently in developing a theory of the basic forces of nature?
8. By means of what theories are the basic forces of nature described now?
• Study the block-scheme below and try to discuss or summarize the problem as a whole.
Forces
 |
weak
strong
intertwined
radioactive beta decay
pull/push
proton/neutron binding
CLASS WORK
READING (18B)
• Study the table given below. Read the passage and be prepared to discuss the problem using this table.
| THE FORCES IN NATURE | |||
| TYPE | INTENSITY OF FORCES (Decreasing order) | BINDING PARTICLE (Field quantum) | OCCURS IN |
| STRONG NUCLEAR FORCE | ~ 1 | GLUONS (no mass) | ATOMIC NUCLEUS |
| ELECTROMAGNETIC FORCE | - io-3 | PHOTON (no mass) | ATOMIC SHELL APPL1C. OF ELECTRICITY |
| WEAK NUCLEAR FORCE | ~io-5 | BOSONS Z°, W\ W(hcavy) | RADIOACTIVE BETA DECAY |
| GRAVITATION | ~io-38 | GRAVITON? | H EAVEN LY BODIES |
THE EXCHANGE OF PARTICLES IS RESPONSIBLE FORTHE FORCES
THE FOUR FORCES OF NATURE
One of the major achievements of modern physics has been the development over the past 20 years or so of a new class of grand unified theories to describe the forces acting between elementary particles.
There arc four different ways in which the various particles that make up the Universe can interact with one another. Each of these is a particular variety of interaction, or to use a more old-fashioned but more common term, a force (the forces are nuclear, electromagnetic, weak, gravitational). Of the four forces, two — the nuclear force and the weak force — make themselves felt only at incredibly tiny distances of 1013 centimeters or less. This is just about the width of the tiny nucleus that exists at the very center of the atom. It is only within the nucleus, in the immediate neighbourhood of isolated particles, that these forces exist. For this reason the term nuclear force is sometimes given to both, and they are differentiated by their relative strength into the strong nuclear force and the weak nuclear force. The weak force is responsible for such processes as the beta decay of a radioactive atomic nucleus; the strong nuclear force holds the nucleus together. The electromagnetic force governs the interaction of electrically charged particles; and gravity holds the Universe together.
Until the theories were introduced the four observable forces of nature seemed to be independent of one another. Two of these forces, the electromagnetic force and the weak nuclear force, arc already linked by the highly successful electrowcak theory, which treats them as different manifestations of a single underlying force. According to the prevailing view ofthe interactions of elementary particles, the force is transmitted between two particles by the exchange of a third, intermediary particle.
Such a description is the essence of a quantum field theory. In electromagnetic and weak interactions the exchanged particle is a member ofthe family called the vector bosons, named after the Indian physicist S.N. Bose. This term refers to a classification of particles according to one of their most basic properties: spin angular momentum. A boson is a particle whose spin, when measured in fundamental units, is an integer such asO, 1 or 2. "Vector" designates a boson whose spin value is equal to 1.
In the case ofelectromagnetism the exchanged vector boson is the photon, the massless and chargeless "wave packet" of electromagnetic energy that functions as the quantum ofthe electromagnetic field. The other two forces — gravity and st rong nuclear force — are thought to be transmitted by intermediary particles, namely the graviton and the eight particles called gluons.
The unified eleotroweak theory is the theory that predicts the existence of the three massive particles called intermediate vector bosons (also known as weakens; "intermediate" simply because of their mediating role between particles). The electroweak theory, which can now be considered the "standard" account of electromagnetic and weak interactions, for the first time made specific and testable predictions about the properties of intermediate vector bosons, including their mass. The goal of attempts to create a grand unified theory is to arrive at a more comprehensive mathematical structure that would incorporate both the electroweak force and the strong nuclear force (omitting only gravity, the fourth known force).
Scientific American, August, 1982
• Find equivalents for the following phrases.
лают о себе знать; различные проявления одной, лежащей в их основе силы; в соответствии с общепринятым мнением; целое число; обычное объяснение электромагнитных...; слабое взаимодействие; сильное взаимодействие; теория великого объединения; ...в непосредственной бл изости...
• Re-read the passage and answer the questions.