Three Scientific Revolutions: How They Transformed Our Conceptions of Reality (28 page)

But as peculiar as these predictions were, there was another just as weird. When the Hamiltonian (energy) of a single electron was predicted from his equation it showed two possible values, one negative and one positive. The existence of positive energy was of course well-known, but no one had ever encountered negative energy. Also, when using his improved Wilson cloud chamber to detect cosmic waves Carl D. Anderson observed tracks of what appeared to be light particles. On further investigation to determine whether they were negatively or positively charged, he found they were positive. Thus he accidentally discovered a new particle with a mass comparable to an electron but with an opposite positive charge that he named ‘positron,' after the electron. Given their opposite charges, when they interact they annihilate thereby producing two photons. Consequently, he had discovered a new kind of matter called “antimatter.” According to Crease and Mann:

From an embarrassment the negative energy states were transformed into a triumph for quantum electrodynamics, the first time in history that the existence of a new state of matter had been predicted on purely theoretical grounds. Dirac won the Nobel Prize in 1933; Anderson went to Sweden three years later. (p. 90)

In the following decades Dirac's quantum electrodynamics (QED), consisting of six quarks, six leptons, and five bosons, was developed into what became known as “the standard model” independently identified by three physicists: the Japanese born Sinitiro Tomonaga and two Americans, Richard Feynman and Julian Schwinger, all three receiving the Nobel Prize for their achievement in 1965. (I believe it was on July 4 or the 5, 2012, that the scientists at the European Organization for Nuclear Research (CERN) in Geneva announced the discovery of the Higgs boson, or “God particle” as it is now called.) Applying quantum mechanics to electromagnetic fields and to electrons (with the wave function of the electron also considered a field), they treated the fields not as a continuum but composed of discrete quanta.

According to Chris Quigg at the Fermi National Accelerator Laboratory (Fermilab):

QED is the most successful of physical theories. Using calculations . . . developed in the 1940s by Richard P. Feynman and others, it has achieved predictions of enormous accuracy, such as the infinitesimal effect of the photons radiated and absorbed by the electron on the magnetic moment generated by the electron's innate spin. Moreover, QED's descriptions of the electromagnetic interaction have been verified over an extraordinary range of distances, varying from less than 10
^-18
meter to more than 10
⁸
meters.
¹¹³

Continuing research on the magnetic moment, in 1933, after enhancing the original Stern-Gerlach experiment, Stern found that the magnetic moment of the proton was three orders smaller than that of the electron and that of the neutron, and despite being neutral has a “negative magnetic electric charge” similar to the proton. As typical of scientific inquiry, these “facts hinted that the neutron (and also the proton) have an internal structure which includes positive and negative charges, because magnetism always involves the motion of charges.”
¹¹⁴

Additional contributions were made by Wolfgang Pauli that include the introduction of the “exclusion principle,” the hypothesis of the “neutrino,” and the importance of spin in determining which particles and in what number can occupy an atomic orbit. An Austrian physicist with an unusually critical and acerbic manner who occasionally signed his communications with “The Wrath of God,” Pauli nonetheless was a gifted scientist who gained the esteem of his colleagues. His major contribution, “the exclusion principle” introduced in February 1925, added to Bohr's earlier explanation of the limitation of the kinds and numbers of electrons that could occupy the successive stationary orbits in his solar model of the atom. For this he was awarded the Nobel Prize in physics in 1945.

In due course it was found and proven theoretically that the Pauli exclusion principle is valid for any particle whose spin is not integral, i.e., [whose spin is] [1/2, 3/2, 5/2, etc. The laws of behavior of these particles are embodied in “Fermi-Dirac statistics.” . . . These are the statistics characterizing distinguishable objects. The particles themselves are called
fermions
. . . . Protons and neutrons are also fermions (spin ½) and thus in a nucleus they populate different energy levels just as the electrons in the atom do. (p. 60; brackets added)

In contrast, particles with integral spin or whole numbers are called “bosons” (after the Indian physicist S. N. Bose who, along with Einstein, identified them) and are not affected by Pauli's exclusion principle. Not being distinguishable by the four quantum numbers, they are governed by another kind of statistics named the “Bose-Einstein statistics” and since they are capable of having the same quantum numbers an unlimited amount can be located in a particular region of space. “It can be shown that the difference between fermions and bosons is related to the connection between the spin and the symmetry of the wave function of the particles” (p. 60).

Along with the discovery of the spin vector and quantum numbers, physicists were attempting to determine the sizes of the various particles that the wave-particle duality with its contrasting properties, along with the uncertainty principle with its obscurity, made particularly difficult. In the thirties physicists tried to measure the diameter of the electron and “arrived at the formula
r
=
e
²
/
mc
²
where
e
and
m
are the charge and mass of the electron and
c
the speed of light. This gave a value of 3 × 10
^-13
centimeters for the radius” (p. 61). But calculations made within the system QED, where the electron is considered a mere point, showed a more miniscule value of 10
^-16
centimeters while experiments on protons and neutrons “show that their mass and charge concentrated in a region with a diameter of about 1.2 × 10
^-13
centimeters (p. 61).

I shall now endeavor to present as lucidly and comprehensively as possible the subsequent discoveries of the major subatomic particles and forces that culminates the third revolutionary scientific development that not only extended or replaced Newtonian classical science, but also led to the creation of the contemporary conception, called “Quantum Chromodynamics,” of the inner composition of the subatomic particles previously mentioned. This proved exceedingly difficult because of the illusiveness and vagueness of the experimental evidence and the much greater reliance on mathematics. As a result the two major contributors to the new “Standard Theory,” Richard Feynman and Murray Gell-Mann, were at times in agreement and at times quite opposed, though it was Gell-Mann's interpretation that usually prevailed. His contributions to particle physics were extraordinary: the property of strangeness,V-A, the Eightfold Way, quarks (although for a long time he wavered as to whether they were real or just artifacts to preserve the mathematical symmetry), quantum chromodynamics (QCD), along with many others discoveries too numerous to cite.

The succeeding decades of the twentieth century following the Second World War, owing to the creation of the atomic bomb and the increasingly powerful atomic accelerators, such as the Large Hadron Collider at CERN, near Geneva; the Fermi National Accelerator Laboratory (FNAL) in Batavia, Illinois; the Brookhaven National Laboratory; and the Stanford Linear Accelerator (SLAC) produced the detection of a deeper domain of subatomic particles and forces by accelerating and colliding a deeper level of particles. Created out of the mass-energy equivalence stated in Einstein's formula
E = m
c
²
, they were predicted and/or discovered by such outstanding scientists as Eugene Wigner, Richard Feynman, Murray Gell-Mann, Julian Schwinger, Steven Weinberg, Sheldon Glashow, Hideki Yukawa, Samuel Ting, Burton Richter, Harald Fritzsch, and many others.

Such a mélange of new particles have been discovered along with the previously mentioned basic particles, such as the proton and neutron, that they have been compared to a zoo and required the creation of a new periodic table composed of hadrons with the hadrons further divided into baryons and mesons. Two new forces were added to gravity and electromagnetism, a strong force binding the nucleons and a weak force explaining the radio­activity within the nucleus that only acts within short distances. Furthermore, previous forces acting at a distance were superseded by an exchange of “virtual particles,” photons in electromagnetism, gluons in strong interactions, and the vector bosons W
^-
, W
⁺
, and Z
^o
in weak interactions. While hadrons react to both strong and weak forces, leptons only respond to the weak force consisting of the exchange of three bosons and photons.
¹¹⁵

As usual, at first it was thought that the hadrons and leptons, along with the photons and hypothesized gravitons completed the list of basic particles, but in 1964 Murray Gell-Mann and George Zweig introduced further particles accounting for the structure of the hadrons that Gell-Mann whimsically named “quarks” (taken from a passage in James Joyce's
Finnegans Wake
, “Three quarks for Muster Mark!”), that caught on! They do not have integral charges but fractional charges of plus two-thirds or minus one-third. And like the ancient “minima” of Epicurus, they never exist separately but are conjoined as pairs or triplets to form hadrons, a quark and an anti-quark comprising mesons and three quarks forming a baryon. Although originally they were just conjectures to explain the interactions of the hadrons, their depicted combinations into hadrons have been verified.

Continuing the discoveries endowed with fanciful names, two new charges were postulated, one called “strangeness” by Gell-Mann and another referred to as “charm” by Glashow, enabling physicists to account for hadrons and their interactions based on combinations of quarks classified as “flavors”: up (u), down (d), charm (c), strange (s), bottom/beauty (b), and top/truth (t) (pp. 291–95). Thus matter was classified into two groups, one consisting of six leptons and another of six quarks. Then a new quantum theory analogous to quantum electrodynamics (QED), based on the Yang-Mills gauge theory and group theory, was conceived and named “quantum chromodynamics” (QCD for short) by Gell-Mann (p. 291). It was so named because it consisted of a strong force or charge called “color” that binds the quarks within the hadrons.

Further unifications occurred when Glashow combined the weak and electromagnetic forces into an “electroweak theory” and Stephen Weinberg introduced the concept of “symmetry breaking” by the (postulated) Higgs boson introduced to explain how Glashow's W and Z particles acquired mass, the existence of which has been recently confirmed to the great satisfaction of nuclear physicists. The unification continued when in 1969 the Dutch physicist Gerardus ‘t Hooft discovered that Cartan's group theory could be applied to gauge theories that allowed Weinberg in 1973, utilizing the color charge, to create “a gauge field theory of strong forces,” the basis of QCD (pp. 278–79).

But the weak forces were still unaccounted for. Thus Glashow and James Bjorken wrote a paper in which they suggested that a new quark called “charm” could link QCD with the electroweak theory, despite the difficulty of its confirmation because quarks do not exist independently, but only in self-enclosed couplets or triplets within the hadrons. Yet their existence was eventually confirmed. And so the discoveries continued with the detection by Samuel Ting at Brookhaven and Burton Richter at SLAC of a new particle called “J” by Ting and “psi” by Richter, now known as the “J/Y particle.” They were awarded the Nobel Prize in 1976 for their discovery, and Glashow, Weinberg, and Salem shared the prize in 1979 for contributing to the theory of electroweak and electromagnetic interactions between elementary particles. And as a kind of culmination, Carlo Rubbia and Simon Van der Meer were awarded the Nobel Prize in 1984 for their confirmation at CERN of the existence of the W
^-
, W
⁺
, and Z
⁰
particles. Feynman, Schwinger, and Tomonaga had been awarded the Nobel Prize in 1963 while six years later in 1969 Gell-Mann was the single recipient of the prize for his numerous outstanding contributions to physics.

Despite these significant advances, the attempt to unify the strong and weak forces had just begun. Glashow and Howard Georgi advanced the effort toward unification in a series of papers published in 1973–1974, one of which carried the impressive title “Unity of All Elementary-Particle Forces.” If successful, their Grand Unified Theory (GUT as it came to be called) would combine quarks and leptons into one family, owing to their decaying into one another, while a “superweak force” was introduced to unify strong and electroweak interactions. Later in the same year Georgi, Weinberg, and Helen Quinn wrote a paper declaring that at very high temperatures or energies, such as existed at the time of the Big Bang, all the forces were unified. While not yet confirmed, at least the initial framework of a Grand Unified Theory was constructed.

In an
Atlantic Monthly
article published in 1984 with the bold title “How the Universe Works,” Crease and Mann summarized these achievements as follows:

The result is a ladder of theories. Firmly on the bottom is SU(3) [a Family of eight baryons Gell-Mann again fancifully designated the “eightfold way” after Buddha] × SU(2) × SU (1) [the SU stands for special unity group based on Cartan's group theory], whose predictions have been confirmed (“to the point of boredom,” Georgi says). . . . The W and Z particles were discovered at CERN . . . but the theory was so well established by then the event was . . . anticlimactic.

The GUTS proposed by Georgi and Glashaw and other physicists, that fully unite the strong, weak, and electromagnetic forces, are the next rung on the ladder. Although as yet unconfirmed . . . these theories are considered compelling by most physicists. Finally, at the top of the ladder, in the theoretical stratosphere, are supersymmetry and its cousins, which are organized according to a principle somewhat different from SU(5), though, like that model, they put apparently different particles together in groups. Supersymmetry groups are large enough to include gravity, but are so speculative that many experimenters doubt they can ever be tested.
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(brackets added)