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."
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.
"To decide and then revise. To decide and then retreat.
Uncertainty will certainly confuse the wise."
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."
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."
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."
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).
"Now the forces that control the subnuclear dominion shall
be the strong force, electromagnetism and the weak force."
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.
"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."
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!
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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