The Dancing Wu Li Masters (4 page)

Unfortunately, most physicists are not like Rabi. The majority of them, in fact,
do
spend their lives doing what other people have told them is important. That was the point Rabi was making.

This brings us to a common misunderstanding. When most people say “scientist,” they mean “technician.” A technician is a highly trained person whose job is to apply known techniques and principles. He deals with the known. A scientist is a person who seeks to know the true nature of physical reality. He deals with the unknown.

In short, scientists discover and technicians apply. However, it is no longer evident whether scientists really discover new things or whether they
create
them. Many people believe that “discovery” is actually an act of creation. If this is so, then the distinction between scientists, poets, painters, and writers is not clear. In fact, it is possible that scientists, poets, painters, and writers are all members of the same family of people whose gift it is by nature to take those things which
we call commonplace and to
re-present
them to us in such ways that our self-imposed limitations are expanded. Those people in whom this gift is especially pronounced, we call geniuses.

The fact is that most “scientists” are technicians. They are not interested in the essentially new. Their field of vision is relatively narrow; their energies are directed toward applying what is already known. Because their noses often are buried in the bark of a particular tree, it is difficult to speak meaningfully to them of forests. The case of the mysterious hydrogen spectrum illustrates the difference between scientists and technicians.

When a white light, such as sunlight, enters a glass prism, one of the most beautiful of phenomena occurs. Out the other side of the prism comes not white light, but every color in the rainbow from dark red to light violet, with orange, yellow, green, and blue in between. This is because white light is made of all these different colors. It is a combination, whereas red light contains only red light, green light contains only green light, etc. Isaac Newton wrote his famous
Optiks
about this phenomenon three hundred years ago. This display of colors is called a white-light spectrum. The spectral analysis of white light shows a complete spectrum because white light contains all of the colors that our eyes can see (and some that they cannot see, like infrared and ultraviolet).

However, not every spectral analysis produces a complete spectrum. If we take one of the chemical elements, for example, like sodium, cause it to emit light, and shine that light through a glass prism, we get only
part
of a complete spectrum.

If an object is visible in a dark room, it is emitting light. If it appears red, for example, it is emitting red light. Light is emitted by “excited” objects. Exciting a piece of sodium does not mean offering it tickets to the Super Bowl. Exciting a piece of sodium means adding some energy to it. One way of doing this is to heat it. When we shine the light emitted by excited (incandescent) sodium through a prism, or spectroscope, we do not obtain the full array of colors characteristic
of white light,
but only parts of it
. In the case of sodium, we obtain two thin yellow lines.

We also can produce a negative image of the sodium spectrum by shining white light through sodium vapor to see what parts of the white light the sodium vapor absorbs. White light passing through sodium vapor and then through a spectroscope produces the whole rainbow of colors
minus
the two yellow lines emitted by incandescent sodium.

Either way, the sodium spectrum always produces the same distinct pattern. It may be composed of black lines on an otherwise complete spectrum of colors, or it may be composed of colored lines without the rest of the spectrum, but it always remains the same.
^*
This pattern is the fingerprint of the element sodium. Each element emits (or absorbs) only specific colors. Likewise, each element produces a specific spectroscopic pattern which never varies.

Hydrogen is the simplest element. It seems to have only two components; a proton, which has a positive charge, and an electron, which has a negative charge. We must say “it seems to have” because there is not one person alive who has ever seen a hydrogen atom. If hydrogen atoms exist, millions of them can exist on a pinhead, so small are they calculated to be. “Hydrogen atoms” is a speculation about what is inside of the watch. We can say only that the existence of such entities nicely explains certain observations that would be very difficult to explain otherwise, barring explanations such as “the devil did it,” which still may prove to be correct. (It is this kind of explanation that drove Galileo, Newton, and Descartes to create what is now modern science.)

At one time physicists thought that atoms were constructed in the following way: At the center of an atom is a nucleus, just as the sun is at the center of our solar system. In the nucleus is located almost all of the mass of the atom in the form of positively charged particles (protons) and particles about the same size as protons but without a
charge (neutrons). (Only hydrogen has no neutrons in its nucleus.) Orbiting about the nucleus, as the planets orbit the sun, are electrons, which have almost no mass compared with the nucleus. Each electron has one negative charge. The number of electrons is always the same as the number of protons, so that the positive and negative charges cancel each other and the atom, as a whole, has no charge.

The problem with comparing this model of the atom with our solar system is that the distances between an atomic nucleus and its electrons are enormously greater than we picture the distances between the sun and its planets. The space occupied by an atom is so huge, compared with the mass of its particles (almost all of which is in the nucleus), that the electrons orbiting the nucleus are “like a few flies in a cathedral” according to Ernest Rutherford, who created this model of the atom in 1911.

This is the familiar picture of the atom that most of us learned in school, usually under duress. Unfortunately, this picture is obsolete, so you can forget the whole thing. We will discuss later how physicists currently think of an atom. The point here is that the planetary model of the atom formed the background against which a most puzzling problem was solved.

The spectrum of hydrogen, the simplest of the atoms, contains over one hundred lines! The patterns of the other elements are even more complicated. When we shine the light from excited hydrogen gas through a spectroscope, we get over one hundred different lines of color in a distinct pattern.
^*
The question is, “How can such a simple thing like a hydrogen atom, which has only two components, a proton and an electron, account for such a complex spectrum?”

One way of thinking about light is to ascribe wave-like properties
to it, and then to say that different colors have different frequencies, just as different sounds, which also are waves, have different frequencies. Arnold Sommerfield, a German physicist who also was an accomplished pianist, observed, tongue-in-cheek, that hydrogen atoms, which emit over one hundred different frequencies, must be more complicated than grand pianos, which emit only eighty-eight different frequencies!

It was a Danish physicist named Niels Bohr who came up with an explanation (in 1913) that made so much sense that it won him a Nobel Prize. Like most ideas in physics, it is essentially simple. Bohr did not start with what was theoretically “known” abut the structure of atoms. He started with what he really
knew
about atoms, that is, he started with raw spectroscopic data. Bohr speculated that electrons revolve around the nucleus of an atom not at just any distance, but in orbits, or shells, which are specific distances from the nucleus. Each of these shells (theoretically there are an infinite number of them), contains up to a certain number of electrons, but no more.

If the atom has more electrons than the first shell can accommodate, the electrons begin to fill up the second shell. If the atom has more electrons than the first and second shells combined can hold, the third shell begins to fill, and so on, like this:

His calculations were based on the hydrogen atom, which has only one electron. According to Bohr’s theory, the electron in the hydrogen atom stays as close to the nucleus as it can get. In other words, it usually is in the first shell. This is the lowest energy state of a hydrogen atom. (Physicists call the lowest energy state of any atom its “ground state.”) If we excite an atom of hydrogen we cause its electron to jump to one of the outer shells. How far it jumps depends upon how much energy we give it. If we really heat the atom up (thermal energy), we cause its electron to make a very large jump all the way to one of the outer shells. Smaller amounts of energy make the electron jump less far. However, as soon as it can (when we stop heat
ing it), the electron returns to a shell closer in. Eventually it returns all the way back to shell number one. Whenever the electron jumps from an outer shell to an inner shell, it emits energy in the form of light. The energy that the electron emits is exactly the amount of energy that it absorbed when it jumped outward in the first place. Bohr discovered that all of the possible combinations of jumps that the hydrogen electron can make on its journeys back to the ground state (the first shell) equals the number of lines in the hydrogen spectrum!

This is Bohr’s famous solution to the grand-piano mystery. If the electron in a hydrogen atom travels from an outer shell all the way to the innermost shell in one jump, it gives off a certain amount of energy. That makes one line in the hydrogen spectrum. If the electron in a hydrogen atom makes a tiny jump from an outer shell to the next shell inward, it gives off a much smaller amount of energy. That makes another spectral line. If the electron in a hydrogen atom jumps from shell five to shell three, for example, that makes yet another line. A jump from shell six to shell four and then from shell four to shell one makes two more spectral lines, and so on. In this way we can account for the entire hydrogen spectrum.

If we excite a hydrogen atom with white light instead of heat, we can produce the absorption phenomenon that we mentioned earlier. Each electron jump from an inner shell to a shell farther out requires a certain amount of energy, no more and no less. An electron jump from shell one to shell two requires a certain amount of energy, and only that amount. The same is true for a jump from shell five to shell seven, etc. Each jump that the electron makes from an inner shell to an outer shell takes a specific amount of energy, no more and no less.

When we shine white light on a hydrogen atom, we are offering it a whole supermarket of different energy amounts. However, it cannot use all that we have to offer; only certain specific amounts. If its electron jumps from shell one to shell four, for example, it takes that particular energy package out of the array of energy packets that we are giving it. The package that it takes out becomes a black line in the otherwise complete spectrum of white light. A jump from shell three
to shell four becomes another black line. A jump from shell one to shell two, and then from shell two to shell six (there are all sorts of combinations) makes two more black lines.

In sum, if we shine white light through hydrogen gas and then through a prism, the result is the familiar white-light spectrum, but with over one hundred black lines in it. Each of these black lines corresponds to a specific energy amount that was required to make a hydrogen electron jump from one shell to another shell farther out.

These black lines in the white-light spectrum form exactly the same pattern that we get when we shine the light emitted from excited hydrogen gas directly through a prism—except, in that case, the lines are colored and the rest of the white-light spectrum is missing. Of course, the colored lines are caused by the electrons returning to lower-level shells and, in the process, emitting energy amounts equal to what they absorbed when we first made them jump. Bohr’s theory permitted physicists to calculate the frequencies of the light given off by simple hydrogen atoms. These calculations agreed with observations. The grand-piano mystery was solved!

Shortly after Bohr published his theory in 1913, an army of physicists began the work of applying it to the other elements. This process was quite complicated for atoms with large numbers of electrons, and not all of the questions that physicists had about the nature of atomic phenomena were answered. Nonetheless, a tremendous amount of knowledge was gained from this work. Most of the physicists who went to work on Bohr’s theory, applying it and further developing it, were
technicians
. Bohr himself, one of the founders of the new physics, was a
scientist
.

This is not to say that technicians are not important. The technician and the scientist form a partnership. Bohr could not have formulated his theory without the wealth of spectroscopic data at his disposal. That data was the result of countless laboratory hours. It was beyond Bohr’s capacity, as one person, to substantiate his theory. Technicians did this for him by applying it to the other elements. Technicians are important members of the scientific community. However, since this is a book about Wu Li Masters and not about
technicians, we will use the word “physicist” from now on to mean those physicists who are also scientists, that is, those physicists (people) who are not confined by the “known.” From the little that we know about Wu Li Masters, it is evident that they come from this group.