Report on a Century of Discoveries in Physics
and on this Year's Centennial Meeting
of the American Physical Society

Index of Topics

A Century of Discoveries in Physics

     Given that 1999 is the 100th anniversary of the APS and the last year of the second millennium, it is worth enumerating the seven great physics achievements of the 20th century, achievements that have transformed the way that humanity views the universe:

(1) The Unraveling of the Microscopic Constituents of Matter

"It is the nature of the World that small things make up larger things and that even smaller things make up the small."
-- From the Book of Subnuclear Physics
of The Bible According to Einstein.

     The concept of the atom had been hypothesized by Greeks two-and-half millennia ago. By the nineteenth century, the existence of atoms had been indirectly established. But the picture of the atom then was very different from that of today. In the nineteenth century, the atom was thought be a spherical blob of more-or-less uniform density. Nowadays, it is known that the atom possesses considerable structure: it consists of a tiny, heavy nucleus around which light-weight, negatively charged electrons swarm.
     The name atom, which means "indivisible," has become a misnomer -- the atom is not the most fundamental building block since it is constructed out of smaller units. Furthermore, the nucleus is composed of protons and neutrons, both of which weigh almost 2000 times the weight of an electron. As their names imply, the proton is positively charged while the neutron is neutral, having no electric charge. By the way, it was only in 1897 (two years before the founding of the American Physical Society) that the existence of the electron was established; previously, electricity was thought to be the flow of a liquid rather than of microscopic particles.
     Thirty-five years ago, scientists believed that the basic constituents of matter were protons, neutrons and electrons. Since then, high-energy accelerators have revealed that protons and neutrons are made up of three quarks. Quarks are microscopic, point-like entities with electric charges that are one-third and two-thirds of the charge of the electron.
     In summary, scientists have been able to divide matter into ever increasingly smaller units. After a century of experiment and discover, an impressive detailed picture of the basic consituents of all matter has been acheived. No one can say when this "reductionism" will end -- perhaps, 100 years from now in the year 2099, new microscopic building blocks will have been discovered.

(2) Quantum Mechanics

"To decide and then revise. To decide and then retreat.
Uncertainty will certainly confuse the wise."
--From the Book of Quantum Mechanics
of The Bible of According to Einstein.

     One of the greatest scientific achievements of physics in the 20th century is the discovery of quantum mechanics. It governs the dynamics of microscopic objects such as atoms and electrons. In this tiny world, things behave differently from the macroscopic world where classical mechanics rules. One feature of quantum mechanics is uncertainty. For example, the exact position of an electron in an atom is not knowable -- instead, the electron's position is probabilistically determined. The best metaphor for this is a cloud -- an electron in an atom is like a cloud with denser regions of the cloud representing places where the electron is most likely to be and less dense regions representing places where the electron is least likely to be. Another feature of quantum mechanics is discreteness. For example, an electron in an atom can only assume particular types of of motions, which are called states, and particular values for its energy, which are called energy levels.
     Quantum mechanics has important philosophical implications due to the uncertainty that it implies. Because the future is not determined, free will is possible. (At the end of the 19th century before the development of quantum mechanics, philosophers had thought that people's actions were predetermined since the dynamics of everything was predictable using Newton's classical laws.)
     The microscopic quantum world is so different from the macroscopic classical world that it is difficult for most people to comprehend. To quote from The Bible According to Einstein: "To venture into the atomic and the subatomic shall be like entering the stately pleasure-dome of Xanadu -- the scene shall be unimaginable." This book, which is written in biblical verse, presents an excellent intuitive description of quantum mechanics in terms of paths. Click here to go to that section of the book.

(3) The Discovery of the Vastness of the Universe

"And so it came to pass that thy visible Universe grew from a small patch of the full Universe. And, as for the rest of the Universe, know that it be vast and be beyond thy reach."
-- From the Book of Inflation of the Old Testament
of The Bible According to Einstein.

     Few people realize how much our picture of the universe has changed in 100 years. At the end of the 19th century, the universe was thought to contain only hundreds of thousands of stars arranged in no particularly interesting patterns. The most distance stars were though to be about 100,000 light years away (meaning that it would take light 100,000 years to travel from Earth to such distant stars; 1 light-year is about 10 trillion kilometers or 6 trillion miles). Today, astronomers have observed objects that are about 10,000,000,000 [= ten billion] light years away. Furthermore, they have discovered that the universe contains many interesting structures. Amazingly, it was not until the 1920's that it was realized that galaxies exist. Galaxies are vast collections of stars grouped together in a relatively localized region of the universe. A typical galaxy contains 100,000,000,000 [=one hundred billion] stars and is 100,000 light years in size. Most galaxies are pancake-shaped. Those with spiral arms are known as spiral galaxies. Others are ellipsoidal shaped, and still others are irregular in appearance. The galaxy in which the Sun and Earth reside is called the Milky Way, a name that arose because the other stars in this spiral galaxy create a band of whitish hue across the heavens, which can be observed with the naked eye on a particularly clear night sky. The two galaxies nearest to the Milky Way are the Small and Large Magellanic Clouds -- they are irregularly shaped and observable from Earth only from the Southern Hemisphere. The third nearest galaxy at a distance of about 1,000,000 light years is the famous Andromeda Galaxy. It was the first galaxy to be discovered and is spiral shaped.
     During the last three decades, astronomers have come to realize that 10 to 1000 galaxies often group together -- such a structure is called a galaxy cluster. There are also regions of the universe with relatively few if any galaxies -- these are known as giant voids. Thus, the large-scale structure of the universe consists of giant voids and galaxy clusters. Both are roughly 100,000,000 light years in size. It is estimated that the visible universe (that part of the universe for which light has had enough time to reach us and hence is, in principle, observable) contains 50,000,000,000 [=fifty billion] galaxies. Hence the number of stars in the visible universe is about 5,000,000,000,000,000,000 [=five million-trillion].
     In summary, the size of the visible universe is about 200,000,000,000,000,000,000,000 [=200 billion-trillion] kilometers or about 150,000,000,000,000,000,000,000 miles. This is about 200,000 times larger than the size that scientists thought it was in 1899. After a century of observation and discovery, we now have a reasonable picture of the universe and know our place in this immense world.

(4) Special Relativity

"And the fourth dimensional will baffle a man with a "Newtonian brain," for his visual world is three-dimensional, and his brain waves are three-dimensional, and his imagination is three-dimensional. But a man with an "Einsteinian brain" has a four-dimensional imagination and can picture a four-dimensional space."
-- From the Book of Special Relativity
of The Bible According to Einstein.

     Not only do Newton's laws of classical mechanics fail at small distances (where quantum mechanics provides the correct description), but they also fail at high speeds. Special relativity, as developed by Albert Einstein at the beginning of the 20th century, determines the dynamics of things travelling at high speeds. The effects of special relativity are only noticeable for objects moving at a reasonable fraction of the speed of light (300,000 kilometers per second or 186,000 miles per second). Fast-moving bodies behave in ways that are completely counter-intuitive to us, who have formed our expectations based on daily, human experiences. For a list of some of the amazing, counter-intuitive consequences of special relativity, click here. One effect that has become widely known is the equivalence of mass and energy as embodied in the famous equation E=mc2. The destruction of a small amount of mass produces an enormous amount of energy. This is the basis for atomic bombs. It is also the source of energy and light in a star including our star the Sun. One interesting consequence of special relativity is the unification of time and space into a four-dimensional world.

(5) General Relativity

"Gravity shall be the result of the curvature of space and time."
-- From the Book of General Relativity and Gravity
of The Bible According to Einstein.

     Another great 20th century contribution of Albert Einstein is the general theory of relativity. It provides deep insights into the nature of gravity. In this theory, heavy massive bodies such as the Earth and Sun cause spacetime to curve, much in the same way as a bowling ball -- when placed on a bed -- depresses the bed's surface. An object moving in such a curved spacetime no longer moves at a constant speed in a constant direction -- it accelerates, just like a marble, when thrown onto the bed with the bowling ball, moves toward the bowling ball. See animation. Since, by definition, forces are things that create accelerations, the curvature of spacetime is seen to be the source of the gravitational force. Two interesting consequences of general relativity are the black hole and the expansion of the universe (Click here to read a review of book The Inflationary Universe).

(6) Subatomic Forces

"Now the forces that control the subnuclear dominion shall be the strong force, electromagnetism and the weak force."
-- From the Book of Subnuclear Physics
of The Bible According to Einstein.

     In the 18th century, three fundamental forces were known: gravity, magnetism and the electric force. By the end of the 19th century, there were only two fundamental forces: In what is undoubtedly the greatest achievement in physics of the 19th century, the magnetic and electric forces were unified into one force, which is called electromagnetism. It turns all that all magnetic fields are created by the motion of charge, and charges, of courses, are the source of the electric force. In 1899, scientists thought that there were only two fundamental forces: gravity and electromagnetism. And since physicists had a complete understanding of these two forces, they thought that they knew all.
     But during the 20th century, two new fundamental interactions were discovered. They are subatomic, meaning that they act at scales much smaller than an atom and inside the nucleus. The strong nuclear force binds three quarks to form the proton and the neutron. It also holds together the protons and neutrons in a nucleus. The weak subnuclear force is responsible for certain radioactive decay of nuclei.
     Nowadays, it is often said that there are four fundamental forces, but, in fact, the pioneering work of Steven Weinberg, Sheldon Glashow and Abdus Salam has reduced the number back to three. In 1969, they succeeded in unifying the weak force with electromagnetism. Thus, the fundamental forces are gravity, the electroweak interactions and the strong nuclear force.

(7) The History of the Universe

"And in the future, man will better understand the Universe of ancient times. And the point at which man's understanding starts will sooner start. Thus as man in time moves forward, he shall look further back.
In walking forward, he shall walk back."
-- From the Book of Prophets
of The Bible According to Einstein.

     At the end of the 19th century, the age of the universe was thought to be several hundred million years. Today, it is estimated to be about 15 billion years. Scientists now know that the Earth is 4.6 billion years old and that the first life forms emerged as primitive microscopic organisms 3 billion years ago. In 1899, the ideas of Darwin had begun to be accepted by a majority of people, but little was known about the evolutionary tree of life. Today, the relations between the different life forms of the past have been mapped out with impressive detail.
     In 1899, hardly anything was known about the history of the universe. Nowadays, cosmologists have deduced a general picture of what transpired starting at 10-12 seconds (one trillionth of a second) after the Big Bang beginning. For a list of some of the main events, click here. The universe started as an extremely hot concentration of mass and energy. As time advanced, the universe expanded, meaning that the fabric of space stretched. Through this stretching, material was dispersed and the universe cooled. Eventually, gravity took hold of higher concentrations of matter, causing them to collapse into galaxy clusters at larger scales and into stars at smaller scales. The process of star formation through gravitational collapse continues today, although at a slower rate.
     The evolution of the universe, earth and life is a great history story, a story that astonishes and enlightens, a story that cannot be told in a few paragraphs, but is told as a wonderful narration of amazing events in The Old Testament of The Bible According to Einstein.

The American Physical Society and Its Centennial Celebration

     From March 20 to March 26, 1999, the American Physical Society (APS) celebrated the extraordinary celebration of its 100th anniversary in the largest gathering of physicists ever! Present at the meeting in Atlanta, Georgia were more than 50 Nobel laureates!

Meeting Summary

     Program highlights included symposia on unsolved problems in astrophysics, on the pattern formation in fluids, on the search for the ultimate structure of matter, on industrial research, on computers in physics, on the impact of science on technology, on environmental and medical physics, on lasers and semiconductors, on science policy for the new millennium, on improving physics education, on milestones in polymer physics, on the role of physics in national defense, and on the histories of nuclear physics, quantum mechanics, atomic physics, magnetism, relativity and particle physics. There were featured plenary talks entitled "Physics and the Information Revolution" and "Physics and the American Culture." In a seminar entitled "The Physics of The Very Large and The Very Small," Nobel Laureate Steven Weinberg felt that particle physicists, although lacking the appropriate experimental data, were on the right track in constructing an ultimate unified theory based on superstrings or M theory. An international panel discussed worldwide energy research, international cooperation in physics and the Large Hadronic Collider Project of CERN in Geneva, Switzerland. In addition, researchers from all parts of the United States presented their latest scientific results in more than 700 specialized, technical seminars. On the other end of the spectrum (so to speak), there were public lectures on the physics of sports, of star trek and of music. Before an audience of more than 5000 spectators, theoretical physicist Stephen Hawking, the author of the best-seller A Brief History of Time, argued that the universe is a self-contained system without boundaries in a talk entitled "The Universe in a Nutshell." Concerning the recent supernova evidence for an accelerating universe, Hawking commented that he now thinks it is very reasonable that a cosmological constant exists and that the universe may keep flying apart forever. When science magician Bob Friedhoffer seemed to make a deck of cards disappear only to reappear in his mouth, Hawking smiled saying, "That's why I'm not an experimental physicist. You can never believe the evidence."
     Popular physics demonstrations took place in the Olympic Park, the SciTrek Museum and in Atlanta's public schools. Halls of exhibitions underscored a century of scientific discoveries, some of the new experimental projects such as LIGO that will try to directly detect gravitational waves for the first time, and the history of the APS. Special displays on women and minorities emphasized their contributions to physics. More than 11,000 participants attended the centennial celebration.

The APS in the Past and as of Today

     The first meeting of the American Physical Society took place on May 20, 1899 in the Fayerweather Hall of Columbia University in New York. A constitution and bylaws were adopted on October 28, 1899. Henry Augustus Rowland was elected as the APS's first president. In his acceptance speech, Rowland made a statement that would set the philosophy of the American Physical Society: "Let us hold our heads high with a pure conscience while we seek the truth, and may the APS do its share now and in generations yet to come in trying to unravel the great problem of the constitution and laws of the universe."
     The first elected vice-president of the APS was Albert A. Michelson, who had become famous for the Michelson-Morley experiment of 1887, which attempted to measure the Earth's speed through ether.
     In 1899, the American Physical Society had only 61 members. Today, there are more than 40,000, and the APS is divided into 33 units according to fields: The 14 main divisions are astrophysics; atomic, molecular, and optical physics; biological physics; chemical physics; computational physics; condensed matter physics; fluid dynamics; high polymer physics; laser science; material physics; nuclear physics; particles and fields; physics of beams; and plasma physics.
     With such a large organization and so many physicists, one would think that all the research problems would have been solved. But this is not the case; there are some challenging issues and great mysteries still to be resolved (See JSP's report on the greatest unsolved problems in science).
      The APS provides an environment in which scientific progress can be achieved. Researchers publish their results in the journals of the APS: Physical Review Letters; Physical Review A, B, C, D and E; and Reviews of Modern Physics. Members also discuss physics ideas, present experimental data, and propose new theories at dozens of conferences organized by the APS each year.
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