Quantam Theory and Nature of Forces
Gravity was the first force in nature to be understood in at least a mathematical sense. Newton's theory shows that, even though separated by enormous distances, pieces of matter can influence each other's state of motion. Although less familiar in many respects, the electric and magnetic forces have been known since ancient times. Like gravity they both weaken as the square of the distance away from their source. In 1873 James
Clerk Maxwell (1831-1879) showed that a relationship exists among electricity, magnetism, and light-an amazingly unifying step.
In 1924 the French physicist Louis de Broglie (1892- ) pointed out that, like light, subatomic particles also have a wave nature, as well as a discrete natu reo This has been verified experimentally many times. It is now an accepted fact that matter and radiant energy have dual natures in that they show both wave and discrete properties. Taking de Broglie's idea, Erwin Schrodinger (1887-1961), an Austrian physicist, and Werner Heisenberg (1901-1975), a German physicist, independently constructed mathematical theories for atomic structure at about the same time (1925). Their theories were consolidated by Paul Dirac, an English physicist, into the mathematical formulation called quantum mechanics, the most rational and logical approach so far for understanding a vast variety of atomic phenomena. In reality there are no discrete electron orbits like those of planets in the solar system. Within the hydrogen atom, for example, are spherical regions surrounding the proton. In these regions the electron is spread into a pattern of standing waves, whose distribution corresponds to a discrete energy state of the atom.
All atomic properties are known to be the consequence of the electrical interaction between the nucleus and the electrons surrounding it. This electromagnetic interaction is responsible for the characteristic structure of each atomic species. These characteristic structures are responsible for the basic forms of matter, from simple rocks and crystals to flowers and even human beings. The electromagnetic force between the electron and the nucleus is 1039 times stronger than the gravitational force between them; no one has detected, nor is there any prospect of detecting, the effects of gravity within atoms or molecules.
By 1932 it was known that the nucleus was composed of protons and neutrons. This raised the problem of what force holds the nucleus together against the mutual electrical repulsion of the protons for each other. The solution of this question was the discovery of the strong nuclear force of attraction. It is about a hundred times more powerful than the electromagnetic force, but of very short range, and is capable of holding together nuclei with as many as a hundred or so protons.
Finally, a fourth force was discovered around 1935, the weak nuclear force, which is about 10-; times as strong as the strong nuclear force, or about a thousandth as strong as the electromagnetic force. This force is responsible for some changes in the nature of the nucleus that occur in radioactive decay. It is also a very-shortrange force. There is recent evidence that suggests that the electromagnetic force, the weak nuclear force, and possibly the strong nuclear force are actually different manifestations of
the same force acting differently at different distances between particles. Linking all four forces into one universal expression, the so-called unified field theory, still eludes us.
The reason we are familiar with the gravitational and electromagnetic forces is that they operate on the scale of our experiences. The other two, the strong and weak nuclear forces, are confined to the nuclear scale of existence. The gravitational force increases its intensity with increasing mass, whereas the other forces are independent of mass. In the cosmos, as we shall see in later chapters, gravity dominates. Gravity is responsible for motion and form in the cosmic realm.
Gravity was the first force in nature to be understood in at least a mathematical sense. Newton's theory shows that, even though separated by enormous distances, pieces of matter can influence each other's state of motion. Although less familiar in many respects, the electric and magnetic forces have been known since ancient times. Like gravity they both weaken as the square of the distance away from their source. In 1873 James
Clerk Maxwell (1831-1879) showed that a relationship exists among electricity, magnetism, and light-an amazingly unifying step.
In 1924 the French physicist Louis de Broglie (1892- ) pointed out that, like light, subatomic particles also have a wave nature, as well as a discrete natu reo This has been verified experimentally many times. It is now an accepted fact that matter and radiant energy have dual natures in that they show both wave and discrete properties. Taking de Broglie's idea, Erwin Schrodinger (1887-1961), an Austrian physicist, and Werner Heisenberg (1901-1975), a German physicist, independently constructed mathematical theories for atomic structure at about the same time (1925). Their theories were consolidated by Paul Dirac, an English physicist, into the mathematical formulation called quantum mechanics, the most rational and logical approach so far for understanding a vast variety of atomic phenomena. In reality there are no discrete electron orbits like those of planets in the solar system. Within the hydrogen atom, for example, are spherical regions surrounding the proton. In these regions the electron is spread into a pattern of standing waves, whose distribution corresponds to a discrete energy state of the atom.
All atomic properties are known to be the consequence of the electrical interaction between the nucleus and the electrons surrounding it. This electromagnetic interaction is responsible for the characteristic structure of each atomic species. These characteristic structures are responsible for the basic forms of matter, from simple rocks and crystals to flowers and even human beings. The electromagnetic force between the electron and the nucleus is 1039 times stronger than the gravitational force between them; no one has detected, nor is there any prospect of detecting, the effects of gravity within atoms or molecules.
By 1932 it was known that the nucleus was composed of protons and neutrons. This raised the problem of what force holds the nucleus together against the mutual electrical repulsion of the protons for each other. The solution of this question was the discovery of the strong nuclear force of attraction. It is about a hundred times more powerful than the electromagnetic force, but of very short range, and is capable of holding together nuclei with as many as a hundred or so protons.
Finally, a fourth force was discovered around 1935, the weak nuclear force, which is about 10-; times as strong as the strong nuclear force, or about a thousandth as strong as the electromagnetic force. This force is responsible for some changes in the nature of the nucleus that occur in radioactive decay. It is also a very-shortrange force. There is recent evidence that suggests that the electromagnetic force, the weak nuclear force, and possibly the strong nuclear force are actually different manifestations of
the same force acting differently at different distances between particles. Linking all four forces into one universal expression, the so-called unified field theory, still eludes us.
The reason we are familiar with the gravitational and electromagnetic forces is that they operate on the scale of our experiences. The other two, the strong and weak nuclear forces, are confined to the nuclear scale of existence. The gravitational force increases its intensity with increasing mass, whereas the other forces are independent of mass. In the cosmos, as we shall see in later chapters, gravity dominates. Gravity is responsible for motion and form in the cosmic realm.
