Greatest Ideas of Western Science
This web site primarily focuses upon the identification of certain
people whom I believe to be among the greatest thinkers of the Western
World. However, another approach to the intellectual history of the West is
to focus upon certain specific ideas which have been proven to be of the
greatest significance. These ideas, in most cases, were developed as the
result of the work of several brilliant and dedicated scientists over a
period of many years. I have selected thirteen ideas which I believe to be
among the most important intellectual contributions of Western Civilization
since the Renaissance.
The Medieval World View
At the close of the Middle Ages, which some people refer
to as the "Age of Faith" and which I call the "Age of Darkness," a certain
system of ideas for viewing the world, a Weltanschauung, was
prevalent not only in Christian Europe but also in the Islamic Middle East.
This world view was based upon beliefs first developed by certain ancient
Greek philosophers and natural scientists - most notably by Aristotle and
his followers. However, the basic ideas of these noble Greeks had been
subjected to considerable, self-serving "spin-doctoring" by Christian and
This world view was very earth-centric with human beings
considered to be the culmination of a divine creative process. The eight
principal elements of this world view were the following:
1) The entire universe, including Man, had been
created by a single, omnipotent God in only seven days.
2) This creation had taken place only a few
thousand years ago.
3) The Earth was the center of this universe with
the Sun, Moon, the five naked-eye planets (Mercury, Venus, Mars, Jupiter and
Saturn) and the stars all in separate but circular orbits around the earth.
The Sun and the Moon were considered to be planets, making a total of seven
planets, one for each day of the week!
4) The Earth was essentially flat and was composed
of four basic substances, i.e., fire, water, air and earth.
5) The physical laws which governed the Earth did
not necessarily apply to the heavens (the realm of God).
6) All the various species of plant and animal
life on earth had been created by God and had remained essentially unchanged
since the time of their creation.
7) Man was the last life form to be created; he
was considered unique among the other life forms due to his powers of reason
(intelligence). Also, Man was believed to represent the culmination of the
divine creation process.
8) The earth and all of the non-human life forms
on it were subordinate to Man. Indeed, as stated in Genesis Chapter 1,
Verse 28, Man was commanded to " ... be fruitful, and multiply and replenish
the earth and subdue it: and have dominion over the fish of the sea, and
over the fowl of the air, and over every living thing that moveth upon the
earth. ... "
The above beliefs were not only accepted by most of the
educated people of the early 15th century, adherence to these beliefs was
strongly enforced by the ecclesiastical authorities of the time. The
validity of these beliefs was considered to be a matter of Faith; any
deviation from these views was interpreted as a denial of religious truth
and placed the soul of the unbeliever in danger of God's eternal damnation.
To "assist God," the religious authorities were also prepared to take
actions against the physical body of the unbeliever. These actions included
torture and even death by burning at the stake!
Fortunately, at least in Western Europe, the forces of the
Renaissance and Reformation utterly destroyed the temporal power of the
Christian Church to exercise such egregious thought control.
By the end of the 20th century, the first five of the
above stated eight beliefs had been disproved beyond a reasonable doubt. In
addition, at least among most intelligent and well educated people in the
Western World, the last three beliefs have also been discarded.
Unfortunately, there are still many people in Europe, North America and
elsewhere in the world, who still adhere to beliefs 6, 7 and 8. To many of
these people, the commandment contained in Genesis 1:28 still applies, and
much harm to the Earth's Biosphere continues to be incurred.
Thirteen Ideas Which Revolutionized the World
Over the last 450 years or so, there have been at least
thirteen fundamental ideas, generated by European and American thinkers,
which totally destroyed the Medieval belief system and put in its place a
new Weltanschauung of notably superior elegance and sophistication.
The first twelve of these ideas are now widely accepted by most scientists
and mathematicians, not only in Europe and North America, but in the rest of
the world as well.
These thirteen ideas are summarized in the following
1. The Earth moves in an elliptical orbit around the
||Copernicus, Bruno, Kepler,
2. The physical laws of Earth also apply to the rest of
3. The stars are like the Sun but are very far away.
||Bruno, Huygens, Bessel
4. Our Sun is just one of many stars in a group called
the Milky Way Galaxy.
||Kant, William Herschel
5. Our Milky Way Galaxy is just one of many galaxies in
||Huggins, Slipher, Curtiss,
6. Our universe is in a condition of continuous
7. Our Earth and the universe are very old - many
hundreds of millions of years.
8. Slow evolutionary processes explain diversification
and change in living species.
9. Man is only an animal who has evolved from more
10. All life forms on Earth possess molecular,
self-replicating entities called genes.
||Mendel, de Vries,
Tschermak, Correns, Crick, Watson
11. Gravity, under certain conditions, is able to alter
the structure of space and time.
12. Structure of matter and energy may be understood as
13. Construction of machines that match or exceed human
intelligence are possible.
||Turing, von Neumann,
Wiener, Shannon, Minsky, McCarthy, Kurzweil
Even though the new Western belief system is a substantial
improvement over its medieval predecessor, its impact upon the significance
and importance of Planet Earth and its living occupants is devastating! The
Earth is now viewed as just a small planet orbiting a minor yellow dwarf
star located on the outskirts of a huge galaxy composed of hundreds of
millions of stars; even our galaxy is only of average size in a universe
containing millions of other galaxies. Furthermore, the life forms on Earth
are now known to be little more than bio-chemical machines driven by
self-replicating molecular substances called genes.
Even the human species have been reduced to being just
another group of animals, albeit very intelligent ones, who have evolved
from much more primitive and simple life forms. Man differs from the beast
only in degree not in kind! The only remaining aspect of human uniqueness
is his intelligence and even this quality is no longer believed to be
unique. It is now evident that artificial machines can be constructed which
can approach, equal or even exceed human intelligence! The projected
timetable for machines achieving human level intelligence varies depending
upon which computer scientist you wish to believe. However, there seems to
be a general consensus that machines of equal or greater intelligence than
humans will be possible by the end of the 21st century!
In light of the above, I am forced to recall the warning
given to us by the late, great Howard Phillips Lovecraft as follows:
"The most merciful thing in the world, I think, is the
inability of the human mind to correlate all its contents. We live in a
placid island of ignorance in the midst of black seas of infinity, and it
was not meant that we should voyage far. The sciences, each straining in its
own direction, have hitherto harmed us little; but some day the piecing
together of dissociated knowledge will open up such terrifying vistas of
reality, and of our frightful position therein, that we shall either go mad
from the revelation or flee from the deadly light into the peace and safety
of a new dark age."
H. P. Lovecraft from The Call of
ideas cited in the above table are discussed in more detail in the following
Section 1. The Earth moves in an elliptical orbit around the Sun.
In ancient times, to most human observers, it appeared
that the Earth stood still and all the heavenly bodies moved around it.
Thus, when attempting to describe how the cosmos (universe) works, the
ancient Greek thinkers, particularly Aristotle, conceived of a large,
stationary Earth at the center of the universe, with the Sun, Moon, planets
and tiny stars orbiting about the Earth in perfect circles at constant
In the 2nd century A. D., the basic Aristotelian concept
was transformed into a powerful mechanical model by a Greek astronomer
working in Alexandria, Egypt, Claudius Ptolemy(85-165 A. D.). His model of
perfect circular motions, although very complex, accurately predicted the
positions of the sun, moon, and stars. The model even accounted for the
strange motions of the five wandering stars - the naked-eye planets. These
five heavenly bodies (Mercury, Venus, Mars, Jupiter and Saturn) appeared not
to circle perfectly around the earth but rather to change speed and
sometimes even traveled in strange retrograde paths. This behavior was
accounted for in Ptolemy's model by adding epicycles to each of the five
Over the next 14 centuries, astronomical data accumulated
and became more accurate. The Ptolemaic model was retained but was made
more refined and complicated by both Arab and European astronomers. Even
so, the Ptolemaic model did not involve any physical explanations as to why
the heavenly bodies should so move. The mechanical principles of motion in
the heavens were considered to be quite different from those describing the
motion of objects on earth.
About 50 years after the discovery of the Americas, in
1543, a Polish astronomer named Nicolaus Copernicus (1473-1543) proposed a
different model of the universe. He discarded the premise of a stationary
Earth and proposed that the Earth and planets all circled around the sun. In
his model, the apparent erratic motion of the planets could also be
accounted for and in a more intellectually pleasing way. However, the
Copernican model still used perfectly circular motions and was nearly as
complicated as the old earth-centered Ptolemaic model. Also, the Copernican
model violated the prevailing common-sense notions about the Earth, in that
it required the apparently immobile earth to turn completely around on its
axis once a day. An even greater objection to the Copernican model was that
the Earth would lose its position at the center of the universe.
Furthermore, an orbiting and revolving earth was thought to be inconsistent
with the Holy Bible! Most scholars perceived little advantage in a
sun-centered model and were very reluctant to give up the traditional
A famous but unfortunate early advocate of the Copernican
system was Giordano Bruno (1548-1600). Bruno was ordained as a Roman
Catholic Priest in 1572. However, he soon became strongly influenced by the
ideas contained in the heretical Christian doctrine of Arianism. Also, he
become a strong advocate of the Copernican heliocentric system and in 1583
conducted a series of lectures re the Copernican theories at Oxford
University. Subsequently, Bruno decided to write down his ideas; he did this
in three dialogues on cosmology and three dialogues on morality. His ideas
on cosmology are quite remarkable for he not only argued for a moving Earth,
but he also argued for an infinite universe containing other stars like the
Sun and other worlds like the Earth. Of course, Bruno was aware that this
contradicted the Biblical version of the universe, but he put forward the
argument that the Bible should be seen as providing moral teaching, not the
teaching of physics. The free thinking Bruno finally encountered the power
of the Inquisition. in 1592, he was arrested and was brought to trial in
1593. Incredibly, this trial lasted for seven years!
The Roman Catholic Inquisition declared that his views on
physics and cosmology were theological and heretical; he was commanded to
retract. However, Bruno, being made of sterner stuff than Galileo (who
recanted in 1633), refused to retract. Instead, he answered by trying to
convince the Inquisition that his views were in accord with Christianity.
Finally, in 1600, Pope Clement VIII demanded that Bruno be sentenced as a
heretic and the Inquisition passed the death sentence on him. On hearing the
sentence he defiantly responded:
"Perhaps your fear in passing judgment on me
is greater than mine in receiving it."
Bruno was gagged so that onlookers would not be seduced by
any of his heretical statements and he was burned alive at the Campo de'
Fiori in Rome on 17 February 1600.
As astronomical measurements continued to become more
precise, it became clear that neither the sun-centered nor the
earth-centered system worked properly as long as all heavenly bodies had to
display uniform circular motion. A German astronomer, Johannes Kepler
(1571-1630), developed a mathematical model of planetary motion that
discarded both of these venerable premises—a stationary earth and circular
motion. In 1619, Kepler published his monumental work entitled The
Harmony of the World. In this book, Kepler set forth his now famous
three laws of planetary motion. He proposed that the planets naturally move
in elliptical orbits at predictable but varying speeds. His laws of
planetary motion turned out to be correct, but the calculations for ellipses
were difficult with the mathematical techniques known at the time, and
Kepler could offer no explanation as to why the planets moved in that way.
A famous contemporary of Kepler, the Italian Galileo
Galilei (1564-1642), built one of the first telescopes and used it to study
the sun, moon, planets, and stars. He made many discoveries that supported
the basic Copernican ideas of planetary movement. He discovered the four
large moons that orbited around the planet Jupiter, demonstrating that the
earth was not the only center of heavenly motion. With his telescope, he
also discovered craters and mountains on the moon, spots on the sun,
moonlike phases of Venus, and a vast number of stars not visible to the
Probably Galileo's greatest contribution to the
cosmological revolution was in promulgating these new ideas to the public.
In 1632, he published a book about this new world view entitled Dialogue
Concerning the Two Greatest World Systems. The book was written in a
popularized format in the Italian language (not the customary Latin); this
made the book accessible to most of the educated Italians of his time. Also,
he rebutted many popular arguments against an orbiting and spinning earth
and showed inconsistencies in the Aristotelian account of motion.
Like Bruno before him, in 1633, Galileo was put on trial
by the Roman Inquisition for his allegedly heretical beliefs. At this
trial, Galileo was forced to recant his beliefs; his life was spared but he
was put under house arrest for the remainder of his life. Even so, his
trial increased the public awareness of these issues and accelerated the
process of acceptance of the heliocentric cosmological system.
Section 2. The physical laws of Earth also apply to the rest of the
In the year that Galileo died (1642) the great Isaac
Newton was born. Newton brought together the ideas of Copernicus, Kepler
and Galileo, and went far beyond them, to create an entirely new
Weltanschauung. In his monumental book entitled Mathematical
Principles of Natural Philosophy, published in 1687, Newton presented a
mathematically described world view that accounted for the motion of objects
on earth and the motions of the distant heavenly bodies.
The Newtonian model was surprisingly simple. Using a few
key concepts regarding mass, momentum, acceleration, and force, Newton was
able to develop universal laws of both motion and gravity. With a single
set of ideas, he was able to account for the observed orbits of planets and
moons, the motion of comets, the irregular motion of the moon, the motion of
falling objects at the earth's surface, weight, ocean tides, and even the
earth's slight equatorial bulge. Newton made the earth part of a universe
that was elegant in its simplicity and majestic in its architecture.
Newton's universe could function automatically by itself according to the
action of forces between its parts.
Validity of the Newtonian system was dramatically verified
by English astronomer Edmund Halley's prediction, made in 1705, that
Halley's Comet would reappear in December 1758. Halley (1656-1742) had
calculated the motion of the comet based on Newton's principles. Indeed,
Newton's system prevailed as the dominant scientific view of the world for
more than 200 years. Belief in Newton's system was continually reinforced by
its usefulness in science and in practical endeavors, right up to (and
including) the exploration of space in the twentieth century. Even Albert
Einstein's theories of relativity did not overthrow the Newtonian world
view, but did modify some of its most fundamental concepts. Only the advent
of Werner Heisenberg's Quantum Theory (see below), developed in the late
1920's, finally precipitated the demise of the Newtonian world view.
Section 3. The stars are like the Sun but are very far away.
Many people's work was needed to prove
that the Sun is a star. In about 450 B. C., the Greek philosopher
Anaxagoras suggested that the Sun was a star up close (or, conversely, that
stars are Suns far away). This idea was again put forward by Aristarchus
of Samos, around 220 BC, but the idea did not catch on.
In 1543 just before he died, Nicolaus
Copernicus published a book entitled On the Revolutions of the Heavenly
Spheres in which he proposed his heliocentric system with the Sun in the
center and the Earth merely being one of the planets in orbit around the
Sun. In this model Copernicus set the Sun apart from the planets, but he
did not say anything about the stars.
The Italian philosopher, Giordano Bruno
(1548-1600) concluded that, if the Earth is a planet just like the others,
then it does not make sense to divide the Universe into a sphere of fixed
stars and a solar system. He said that the Sun must also be a star, that
the Universe is infinitely large, and that there are many worlds like the
Earth As noted above, He was condemned by the Roman Catholic Inquisition
and was burnt alive in Rome in 1600 for heresy.
In 1610, Galileo Galilei (1564-1642)
using one of the newly invented telescopes, noticed that stars look like
little points even when seen through a telescope, and concluded that stars
must be very far away indeed.
Johannes Kepler (1571-1630) studied the
positions of planets very carefully and from that determined his three Laws
of planetary motion that firmly put the Sun in the center of the solar
system with the planets orbiting the Sun. It was now clear that the Sun was
not a planet, though why these laws of planetary motion should be the way
they are was still unclear.
Christian Huygens (1629-1695) of Holland
determined the distance to the star Sirius, assuming that that star was as
bright as the Sun and appeared faint only because of its great distance. He
found that the distance to Sirius must be very great. By this time the idea
that the Sun is a star was being seriously considered by scientists.
Finally, in 1838, German mathematician
Friedrich Bessel (1784-1846), for the first time, measured the distance to a
star without any assumptions about the nature of stars; he found the
distance to be enormous. Distances to other stars were calculated soon
afterwards. Then a means to calculate the true brightness of stars,
corrected for their distance from Earth was devised. It was discovered that
most stars were about as bright as the Sun. Other things about the Sun were
also found to be like those of stars, such as surface temperature and
chemical composition. Accordingly, based on an overwhelming amount of
empirical evidence, it was concluded that the Sun was indeed a star.
Our Sun is now classified as a G2V star:
a main-sequence, yellow-dwarf star of moderate temperature.
Section 4. Our Sun is just one of many stars in a group called the Milky
To an observer on Earth, our Milky Way
is a great band of light lying in a huge arc across the sky. In 1610,
Galileo used his telescope to show that this band was composed of thousands
of stars that could not be resolved individually by the naked eye.
In 1755, the noted German philosopher
Immanuel Kant (1724-1804) suggested that this band of light was not really a
ring of stars orbiting around the Sun; instead he proposed that the whole
Milky Way was a flattened rotating disk or island universe of stars
containing the Sun within the disk.
In 1785, Kant's idea was investigated
observationally by the English astronomer Sir William Herschel (1738-1822).
He assumed that all stars were of equal luminosity, that their spatial
density was uniform and that space was transparent and hence that Newton's
inverse square law was obeyed. Unfortunately, he incorrectly concluded that
our Sun is located at the center of a lens-shaped system of stars with a
definite but rather irregular boundary.
It was not until the 20th century that
astronomers with better telescopes finally determined the true shape of our
galaxy and the Sun's position within it. Most notably, the work of Harlow
Shapley in 1918 and Robert Trumpler in 1930 finally resulted in a reasonably
accurate picture of the Milky Way Galaxy. The current view is that our
galaxy is indeed lens shaped with spiral arms, having a diameter of about
100,000 light years; the galaxy is estimated to contain about 200 billion
stars. Our sun is in orbit around the center of mass of the galaxy; the
period of rotation is about 220 million years. Currently the Sun is located
about 28 thousand light years from the galactic center.
Section 5. Our Milky Way Galaxy is just one of many galaxies in the
During the 18th and 19th centuries European astronomers
had noted fuzzy patches of light in the night sky, which they called
nebulae. Some astronomers thought these could be distant galaxies. However,
galaxies were not recognized as a distinct kind of nebular object until
detailed spectroscopic studies were conducted in the late 19th and early
Speculation centered around the possibilities that either
these nebulae were independent systems of stars (a view dating back to
Immanuel Kant), or that they were planetary systems in formation (an idea of
French mathematician Pierre-Simon Laplace). Sir William Huggins (1824-1910)
analyzed the Andromeda spiral nebula and determined that it showed a
continuous spectrum, thus indicating that it probably was another system of
stars similar to our Milky Way.
During the period 1912-1922, Vestro M. Slipher (1875-1969)
of the Lowell Observatory obtained spectra of a few galaxies showing large
radial velocities (the greatest then known). Subsequently, American
astronomer Heber Doust Curtiss (1872-1942), argued convincingly that the
radial spirals were extragalactic "island universes" like the Milky Way. Two
of the Curtiss arguing points were:
1) The "white nebulae" occur far from the galactic plane,
in fact avoiding it, unlike other nebular constituents; and
2) Some nebulae, seen edge-on, look much like the visual
Finally, in the 1920's, Edwin P. Hubble (1889-1953)
discovered a Cepheid variable (one of a class of pulsating stars whose
regular light variations are useful in estimate astronomical distances) in
the Andromeda Galaxy (M31) by using the 100 inch telescope at Mt. Wilson,
California. He also found Cepheids in other nebulae such as Triangulum
Galaxy (M33) and NGC 6833 and proved conclusively that they are outside our
Milky Way Galaxy therefore proving Kant’s hypothesis of “island universes.”
Section 6. Our universe is in a condition of continuous expansion.
Albert Einstein (1879-1955) and Edwin Hubble (1889-1953)
are the people most responsible for the discovery that our universe is
expanding. A brief summary of their achievements in this area is presented
In about 1910, when Einstein was developing his theory of
gravity as part of his General Theory of Relativity, his equations indicated
that the universe should be either expanding or collapsing. However, he
assumed that the universe was really static. Accordingly, his original
solution contained a constant term, called the cosmological constant, which
cancelled the effects of gravity on very large scales, and led to a static
universe. After Hubble discovered that the universe was expanding, Einstein
called the use of this cosmological constant his "greatest blunder."
At around this same time, large telescopes were being
built that were able to accurately measure the spectra, or the intensity of
light as a function of wavelength, of faint objects. Using this new data,
astronomers tried to understand the plethora of faint, nebulous objects they
were observing. Between 1912 and 1922, astronomer Vesto Slipher at the
Lowell Observatory in Arizona discovered that the spectra of light from many
of these objects was systematically shifted to longer wavelengths, or
redshifted. A short time later, Hubble and other astronomers showed that
these nebulae were distant galaxies.
After Einstein published his General Theory of Relativity
in 1915, scientists working with Einstein's gravitational equations
discovered some solutions that described an expanding universe. In these
solutions, the light coming from distant objects would be redshifted as it
traveled through the expanding universe. The redshift would increase with
increasing distance to the object.
In 1929 Edwin Hubble, working at observatories in
Pasadena, California, measured the redshift of a number of distant galaxies.
He also measured their relative distances by measuring the apparent
brightness of a class of pulsating stars called Cepheid variables in each
galaxy. When he plotted redshift against relative distance, he found that
the redshift of distant galaxies increased as a constant linear function of
their distance. The only explanation for this observation is that the
universe was expanding.
Hubble found that the other galaxies appeared to be moving
away from our Earth in all directions. The farther away a galaxy, the
faster it was receding from Earth. The Hubble Constant can be stated as a
simple mathematical expression, Ho = v/d, where v is the galaxy's radial
outward velocity (in other words, motion along our line-of-sight), d is the
galaxy's distance from earth, and Ho is the current value of the Hubble
The units of the Hubble Constant are "kilometers (km) per
second (s) per megaparsec." In other words, for each megaparsec (mpc) of
distance, the velocity of a distant object appears to increase by some value
(one megaparsec = 3.26 million light years). For example, if the Hubble
Constant was determined to be 50 km/s/mpc, a galaxy at a distance of 10 mpc,
would have a redshift corresponding to a radial velocity of 500 km/s.
In the last 20 years or so, substantial scientific effort
has gone into a determination of the current value of the Hubble Constant.
One investigation conducted by Allan Sandage of the Carnegie Institutions
derived a value of around 50 km/s/mpc. Another effort associated with Gerard
DeVaucouleurs of the University of Texas obtained results that indicate a
Hubble Constant of around 100 km/s/mpc.
In June 2001, the team which
manages the Hubble Space Telescope (HST) completed a major study to measure
the Hubble constant. After surveying Cepheids in 18 galaxies at various
distances using the HST, and combining their data with other measurements
from other estimates of the constant, the team calculated the Hubble
Constant to be 72 kilometers per second per
Section 7. Our Earth and the universe are very old - many hundreds of
millions of years.
Until the 19th century, most people in the Western World
believed that the Earth and the universe around it were only a few thousand
years old. Indeed, in 1650, Archbishop James Usher (1580-1656) of Ireland,
using the Bible as his data source, calculated that the universe had been
created in 4004 B. C. Thus, by his reckoning, the Earth was only about six
thousand years old!
Archbishop Usher's calculations notwithstanding, in the
18th and early 19th centuries, some European academics speculated on the
possibility that the irregularities in the Earth's surface had been shaped
by the same kind of slow change processes that they could observe occurring
at the present time. If that were the case, the earth might be much older
than a few thousand years. If valleys were formed from erosion by rivers,
and if layered rock originated in layers of sediment from erosion, one could
estimate that millions of years would have been required to produce the
The above argument made very slow headway until the early
1830's, when the English geologist, Sir Charles Lyell (1797-1875), published
the first edition of his monumental work entitled Principles of Geology.
The success of Lyell's book stemmed from its wealth of observations of the
patterns of rock layers in mountains and the locations of various kinds of
fossils, and from the persuasive reasoning he used in drawing inferences
from such data. His concept of slow geological change came to be known as
the Principle of Uniformitarianism or Gradualism. Based on his principles,
the Earth was estimated to be many hundreds of millions of years old.
In the 20th century, calculations, based on the physics of
radioactive decay of certain elements in the Earth's crust, would establish
that the Earth was indeed very old - about 4.5 billion years! Also, work by
American Astronomer Edwin Hubble on the rate of expansion of the universe
(see Section 6. above) provided a means of estimating the age of the entire
cosmos. This age was largely a function of the value you assumed for the
Hubble Constant (see Section 6. above). Given the current (June 2001) value
for this constant of 72 kilometers per second per megaparsec, an approximate
age for the whole universe of about 14 billion years may be calculated!
Lyell's Principles of Geology went through many
editions and was studied by several generations of geology students; they
came to accept Lyell's philosophy and to adopt his methods of investigation
and reasoning. Moreover, Lyell's book also influenced Charles Darwin, who
read it while on his worldwide voyages studying the diversity of species. As
Darwin developed his concept of biological evolution, he adopted Lyell's
premises about the age of the earth and Lyell's style of buttressing his
argument with massive evidence.
As often happens in science, Lyell's revolutionary new
view that so opened up thought about the nature of our world also came to
restrict his own thinking. Lyell believed that his idea of
Uniformitarianism implied that the earth had never changed in any sudden
way. In fact, Lyell believed that the Earth had not really changed very
much in its general features at all.
However, in the 20th century, new but contradictory
evidence began to accumulate. By the end of the twentieth century, most
geologists and evolutionary biologists believed that such gradualist changes
were only part of a complex geological and evolutionary process that also
included abrupt or even cataclysmic changes to the Earth and its life forms.
Section 8. Slow evolutionary processes explain diversification and change
in living species.
By the mid-19th century, Western Europe had achieved
spectacular advances in the physical sciences. Unfortunately, progress in
the life sciences had not kept pace. Prevailing attitudes with respect to
the study of living species had hardly progressed beyond the thinking of
Aristotle and his Greek and Roman successors. This situation was soon to
change largely due to the efforts of two English naturalists: Charles
Darwin (1809-1882) and Alfred Russel Wallace (1823-1913).
The fundamental biological problem was how to explain the
great diversity of both living organisms and extinct life forms.
Observations by natural scientists over the centuries had demonstrated that
the earth was populated with many thousands of different kinds of
organisms. Also, geologists, such as Sir Charles Lyell (see Section 7.
above), had gathered abundant evidence from the fossil record showing that
many other different life forms had once existed but now were extinct. What
was the origin of all these life forms - those now living and those which
were now extinct?
The prevailing Aristotelian view was that species did not
change; since the beginning of time, all known species had been exactly as
they were in the present. Perhaps, on rare occasions, an entire species
might disappear owing to some catastrophe, such as the Great Flood, or by
losing out to other species in the competition for food. However, no new
species could appear.
The above notwithstanding, in the late 18th and early 19th
centuries, rudimentary concepts concerning the possible evolution of species
was starting to appear. Indeed, Charles Darwin's grandfather, the physician
and naturalist Erasmus Darwin (1731-1802), had held such views.
One concept of evolutionary change was that organisms
might be able to change slightly during their lifetimes in response to
environmental conditions, and that those changes could be passed on to their
offspring. For example, giraffes, by stretching to reach leaves high on
trees, over successive generations, had developed long necks.
Darwin and Wallace offered a very different mechanism of
evolution. They theorized that inherited variations among individuals
within a species made some of them more likely than others to survive and
have offspring, and that their offspring would inherit those advantages. In
the above giraffe example, those giraffes who had inherited longer necks,
would be more likely to survive and have offspring. Over successive
generations, giraffes with the advantageous characteristic of having a long
neck would crowd out other shorter necked giraffes, and thereby give rise to
a new species of long necked giraffes!
By the 1850's, Charles Darwin had become a well known and
respected naturalist. However, he had not yet published any of his views
concerning evolution. He probably knew that such views would generate
substantial controversy and he, being a man of a somewhat reclusive nature,
did not want to be the center of a media feeding frenzy. However, an event
occurred which forced him to take action.
In February 1858, while on an expedition to
Malaya, another younger English naturalist, Alfred Russel Wallace
(1823-1913) suddenly, and rather unexpectedly, connected the ideas of
English economist Thomas Malthus (1766-1834) on the limits to population
growth to a mechanism that might ensure long-term organic change. This was
the concept of the "survival of the fittest," in which those individual
organisms that are best adapted to their local surroundings have a better
chance of surviving, and thus of passing along such traits to their
Excited over his discovery, Wallace penned an
essay on the subject and sent it off to Charles Darwin in England. Wallace
had begun a correspondence with Darwin two years earlier and knew that
Darwin was generally interested in "the species question." Wallace asked
Darwin to bring Wallace's paper entitled On the Tendency of Varieties to
Depart Indefinitely From the Original Type, to the attention of Sir
Darwin was in fact willing to do so, but not
for any reasons Wallace had anticipated. Darwin, as the now well-known story
goes, had been entertaining very similar ideas for over twenty years, and
now a threat to his priority on the subject loomed. Darwin contacted Lyell
to plead for advice on how to deal with this rather awkward situation.
Lyell and Joseph Hooker (1817-1911), a prominent botanist and another of
Darwin's close friends, decided to present Wallace's paper, along with some
unpublished fragments from Darwin's writings on the same subject, at the
next meeting of the Linnean Society. This meeting took place on 1 July 1858
and Wallace's paper was presented without first obtaining the author's
permission - Wallace being contacted only after the fact.
As of July 1858, Darwin had been working for
several years on a very large tome on the subject of natural selection;
however, it was still a long way from reaching completion. Wallace's
bombshell had the immediate effect of forcing Darwin to quickly publish a
compact, readable, and, ultimately, very successful work entitled On the
Origin of Species. This work was published less than eighteen months
later, in November of 1859. Although Darwin would overshadow Wallace from
that point on, Wallace's role in the affair was well enough known, to
scientific insiders at least, to ensure his future entry into the highest
ranks of scientific dialogue. It should in all fairness to Darwin be noted
that Wallace took full advantage of this opportunity, an opportunity he
might not otherwise have received.
Darwin's book On the Origin of Species set forth
several related theories:
1) evolution did occur;
2) evolutionary change was gradual, requiring millions of
3) the primary mechanism for evolution was a process
called natural selection;
4) the millions of species alive today arose from a
single original life form through a branching process called
The dramatic effect on biology of Darwin's On the
Origin of Species can be traced to several factors: The arguments that
Darwin presented were sweeping, clear and understandable; his arguments were
supported at every point with a wealth of biological and fossil evidence;
his comparison of natural selection to the "artificial selection" used in
animal breeding was persuasive; and the argument provided a unifying
framework for guiding future research.
The intellectual revolution initiated by Darwin sparked
great debates. At the time, some scientists opposed the Darwinian model
because they disputed some of the mechanisms he proposed for natural
selection and because they believed that it was not predictive in the way
that Newtonian science was. However, by the early twentieth century, most
biologists had accepted the basic premise that species gradually change,
even though the mechanism for biological inheritance was still not
altogether understood. Today the debate is no longer about whether evolution
occurs but about the details of the mechanisms by which it takes place.
Unfortunately, even now in the 21st century, among some
not very well educated members of the general public, there are those who
altogether reject the concept of evolution! Their rejection is not based on
scientific grounds but on the basis of what they take to be its unacceptable
1) that human beings and other species have common
ancestors and are therefore related;
2) that humans and other organisms might have resulted
from a process that lacks direction and purpose;
3) that human beings, like the lower animals, are engaged
in a struggle for survival and reproduction; and
4) the concept of evolution violates the biblical account
of the special (and separate) creation of humans and all other species.
Section 9. Man is only an animal who has evolved from more primitive
As discussed in Section 8. above, the English biologist
Charles Darwin (1809-1882) was one of several 19th century scientists who
advocated an evolutionary theory. Darwin published On the Origin of
Species in 1859 and set forth his theory that animals evolved through
variation and natural selection of those most fit to survive in particular
environments. In 1871, Darwin published a book entitled The Descent of
Man. In this book Darwin applied his evolutionary theory directly to
the question of human beings.
In The Descent of Man, Darwin concluded that man is
descended from certain less highly organized life forms. Some of the reasons
given by Darwin in supporting this conclusion are briefly summarized in the
1) There is a close similarity between man and the lower
animals in embryonic development, as well as in innumerable points of
structure and constitution. In light of the principles of evolution, it is
no longer possible to believe that man is the work of a separate act of
creation. The close resemblance of the embryo of man to the embryos of
animals such as fish, reptiles and lower mammals; the construction of man's
skull, limbs and whole frame on the same plan with that of other mammals,
the occasional appearance of vestigial structures (such as tails!) which man
does not normally possess but which are common to four legged creatures, and
many other analogous facts - all point to the conclusion that man is the
co-descendant with other mammals of a common progenitor.
2) Man incessantly presents individual differences in all
parts of his body and in his mental faculties. These differences or
variations seem to be induced by the same causes, and to obey the same laws
as those operating on the lower animals. In both cases similar laws of
inheritance prevail. Man tends to propagate at a rate equal to or greater
than his means of subsistence (an idea advocated by Thomas Malthus);
consequently he is occasionally subjected to a severe struggle for
existence, and the principle of natural selection becomes operational, at
least to some degree. Only slight fluctuating differences in the individual
are necessary for the work of natural selection. Accordingly, over a long
period of time these small differences accumulate and substantial physical
and mental change in the species man becomes possible.
3) The origin of man's high intellectual powers and
moral disposition is the greatest difficulty which presents itself, after we
have been driven to this conclusion on the origins of man. However, those
who adhere to the principle of evolution, see that the mental powers of the
higher animals are the same in kind with those of man, though different in
degree. The moral nature of man has reached its present standard, partly
through the advancement of his reasoning powers and partly from having been
rendered more tender and widely diffused through the effects of habit,
example, instruction, and reflection.
4) Based on the above, Darwin concluded that It was
probable that man had descended from "a hairy, tailed quadruped, probably
arboreal in its habits, and an inhabitant of the Old World." This creature
was probably also the ancient progenitor of the Old and New World monkeys.
In the 21st century, we would use the term primate for this early common
ancestor of man, the apes and the monkeys. It is important to note that
Darwin does not say that we descend from either the apes or the monkeys;
rather he says that we all descend from a common, very primitive ancestor
who lived in the very distant past.
Darwin was well aware of the consternation that his views
would cause among the general public. In his preface to Descent of Man,
he made the following statement which I quote in its entirety:
Man may be excused for feeling some
pride at having risen, though not through his own exertions, to the very
summit of the organic scale; and the fact of his having thus risen, instead
of having been aboriginally placed there, may give him hope for a still
higher destiny in the distant future. But we are not here concerned with
hopes or fears, only with the truth as far as our reason permits us to
discover it; and I have given the evidence to the best of my ability. We
must, however, acknowledge, as it seems to me, that man with all his noble
qualities, with sympathy which he feels for the most debased, with
benevolence which extends not only to other men but to the humblest living
creature, with his god-like intellect which has penetrated into the
movements and constitution of the solar system - with all these exalted
powers - Man still bears in his bodily frame the indelible stamp of his
I conclude this section with an anecdote concerning Thomas
Henry Huxley (1825-1895). He was another great English naturalist and a
stanch defender of the Theory of Evolution. Darwin was not a skilled
debater and he only very rarely appeared in public to defend his theories
himself. However, Darwin was ably represented by Huxley, who was also known
as "Darwin's Bulldog." In 1860, during a debate with Bishop Samuel
Wilberforce (1805-1873) of Oxford concerning Darwinism, the Bishop, in a
sarcastic manner, called out:
"I would like to ask Professor Huxley
whether it was on his grandfather's or his grandmother's side that the ape
ancestry comes in."
Huxley, after whispering to his dinner companion, "The
lord hath delivered him into my hands," took the podium and said:
"A man has no reason to be ashamed of
having an ape for his grandfather. If there were an ancestor whom I should
feel shame in recalling, it would be a man of restless and versatile
intellect, who, not content with success in his own sphere of activity,
plunges into scientific questions with which he has no real acquaintance,
only to obscure them by an aimless rhetoric, and distract the attention of
his hearers from the point at issue by eloquent digressions and skilled
appeals to religious prejudice."
Section 10. All life forms on Earth possess molecular, self-replicating
entities called genes.
In the late 19th century, not only theologians but also
many scientists opposed Darwin's Theory of Evolution. The main reason for
this opposition was that the scientists disputed some of the mechanisms
Darwin proposed for natural selection. Even so, by the end of the century,
most biologists accepted the basic premise that species gradually change,
even though the mechanism for biological inheritance was still not well
Unknown to most scientists, the mechanism for inheritance
had already been discovered by an Austrian monk named Gregor Mendel
(1822-1884) in the 1860's. Mendel's work on the hereditary transmission of
traits among ordinary garden peas was published in 1866 under the title
Versuche über Pflanzen-Hybriden (Experiments in Plant Hybridization).
The paper passed entirely unnoticed in European and American scientific
circles although, according to many historians of science, it is one of the
three most significant and famous papers in the history of biology. The
other two papers are: 1) the Darwin-Wallace paper (see Section 8 above) on
evolution by means of natural selection delivered to the Linnaean Society in
1858, and 2) the Crick-Watson paper (see below) submitted to the scientific
journal Nature on the double helical structure of DNA in 1953.
Mendel's studies in plant hybridization, using over 28,000
pea plants, established the existence of paired elementary units of heredity
(now called genes) and established certain statistical laws governing them.
Subsequent scientists have refined Mendel's conclusions and discovered the
system of particulate heredity by these discrete units or genes. Thus, the
traits that an organism inherits are not derived from a blending of the
characteristics of the organism's parents, but from the transmission of
discrete particles, called genes, from each parent. If organisms have a
large number of such genes and some process of random sorting occurs during
reproduction, then the variation of individuals within a species, essential
for Darwinian evolution, would follow naturally.
Mendel's work was rediscovered in 1900 by three European
botanists, apparently all working independently of each other. The three
botanists were: 1) Hugo de Vries (1848-1938) of Holland, 2) Erich Tschermak
(1871-1962) of Austria and 3) Carl Correns (1864-1933) of Germany. In the
1920's, research conducted with newer and more powerful microscopes revealed
that the genes are organized in complex molecular strands that split and
recombine in ways that furnish each egg or sperm cell with a different
combination of genes. By the middle of the 20th century, the genes were
found to be a part of the deoxyribose nucleic acid (DNA) molecules, which
control the manufacture of the essential materials out of which virtually
all of Earth's organisms are made.
In 1953, Francis H. Crick (born 1916) and James D. Watson
(born 1928) discovered that the DNA molecules possess a structure involving
two helical chains each coiled round the same axis, i.e., a double helix.
The two chains are held together by purine and pyrimidine bases. The planes
of the bases are perpendicular to the axis. and are joined together in
pairs. One member of each pair was a purine base and the other a pyrimidine
base; this arrangement permits molecular bonding to occur. They found that
only specific pairs of bases could be formed; thus, if the sequence of bases
on one chain is given, then the sequence on the other chain was
Since the Crick and Watson discovery, the science of
genetics has moved forward with great rapidity. In 1988 a United States
Government funded project to map the entire genetic sequencing (genome) of
humans was undertaken. In 1998, a privately funded genome project was
launched by scientist Craig Venter and the Perkin Elmer Corporation. Two
years later, on 26 June 2000, the two genome teams jointly announced that
they had each completed a draft of the human genome. In February 2001, the
respective genome drafts were published and subsequently made available free
of charge over the Internet. The draft genome published by the Government
team involved a genetic sequence that was about 2.7 billion base pairs in
length. Conversely, the Venter team's sequence was 2.65 billion base pairs
long. Studies made by the two scientific journals Nature and
Science, that first published the genome maps, concluded that there was
really very little difference between the public and private genome
sequences. To me, the most surprising thing to have come out of these
sequencing exercises is how few genes there are in the human organism - only
about 32,000. By comparison, the biologically very simple nematode worm (it
only possesses 959 cells!) contains 18,000 genes - more than half as many
genes as humans. Apparently, the genetic coding of humans is not
significantly more complex than the coding of very simple life forms.
Study of the chemistry of DNA and the mapping of the
genomes of lower animals and humans has provided dramatic chemical support
for biological evolution. The genetic code found in DNA is the same for
almost all species of organisms, from bacteria to humans. Indeed, within
the last few years, scientists have shown that the genetic similarity
between humans and chimpanzees is greater than 98%!
Section 11. Gravity, under certain conditions, is able to alter the
structure of space and time.
Most of the thirteen ideas discussed on this web page have
resulted from the cumulative work of several people over an extended period
of time. However, the concept discussed in this Section, was essentially
the work of just one man - Albert Einstein (1879-1955). Like Isaac Newton
before him, Einstein produced an entirely new theory of gravity which is now
usually referred to as the General Theory of Relativity. The following
brief paragraphs focus upon his revolutionary ideas concerning gravity and
its apparent effect upon the structure of space and time.
Prior to Newton, the prevailing concept of gravity was
based primarily upon the ideas of the Greek Philosopher Aristotle (384-322
B. C.) He believed that force, including gravitational force, could only
be applied by contact; force operating at a distance was impossible, and a
constant force was required to maintain a body in uniform motion. This
Aristotelian viewpoint dominated European physics until the late 17th
In 1687, Isaac Newton set forth a new theory of gravity in
his monumental work entitled (in English) Mathematical Principles of
Natural Philosophy. The book came to be known just as the Principia.
Newton's law of gravitation is expressed by the formula:
F = G
where F is the force between two bodies of masses
M1, M2 and d is the distance
between them. G is the universal gravitational constant. Newton's
theory of gravitation was highly successful and there was little reason to
question it for almost 200 years. However, his theory had one weakness -
how do each of the two bodies know that the other one was there? Some
profound remarks about gravitation were made by the great English physicist,
James Clerk Maxwell (1831-1879), in the year 1864. His major work on
physics entitled A Dynamical Theory of the Electromagnetic Field
(published 1864) was written:
" ... to explain the electromagnetic
action between distant bodies without assuming the existence of forces
capable of acting directly at sensible distances. ... "
At the end of his book Maxwell made the following comments
" ... After tracing to the action of
the surrounding medium both the magnetic and the electric attractions and
repulsions, and finding them to depend on the inverse square of the
distance, we are naturally led to inquire whether the attraction of
gravitation, which follows the same law of the distance, is not also
traceable to the action of a surrounding medium. ... "
Maxwell also noted that there is a paradox caused by the
attraction of like bodies. The energy of the medium must be decreased by the
presence of the bodies; Maxwell said:
" ... As I am unable to understand
in what way a medium can possess such properties, I cannot go further in
this direction in searching for the cause of gravitation. ... "
In 1900, the Dutch physicist, Hendrik Antoon Lorentz
(1853-1928) conjectured that gravitation could be attributed
to actions which propagate with the velocity of light. The French
mathematician, Henri Poincaré (1854-1912), in a paper published in July 1905
(submitted days before Einstein's special relativity paper), suggested that
all forces should transform according the Lorentz transformations. In this
case he noted that Newton's law of gravitation would not be valid; instead
Poincaré proposed a concept of gravitational waves that propagated with the
velocity of light.
In 1907, two years after proposing his special theory of
relativity, Einstein began to consider how Newtonian gravitation would have
to be modified to fit in with special relativity. At this point, Einstein
received an intuitive insight that he later described as being the happiest
thought of his life!
Einstein had suddenly realized that an observer who is
falling from the roof of a house experiences no gravitational field. As a
result he formulated what he called the "Equivalence Principle:"
" ... we shall therefore assume the
complete physical equivalence of a gravitational field and the
corresponding acceleration of the reference frame. This assumption extends
the principle of relativity to the case of uniformly accelerated motion of
the reference frame. ... "
Subsequently, in 1911, Einstein conjectured that the
bending of light in a gravitational field, which he had predicted in 1907 as
a consequence of the equivalence principle, could be checked with
astronomical observations. In 1907, he had only thought in terms of
terrestrial observations where there seemed little chance of experimental
verification. Another topic Einstein also discussed in 1911 concerned the
gravitational redshift - light leaving a massive body would be shifted
towards the red by the energy loss of escaping the gravitational field.
Einstein published further papers on gravitation in 1912
and 1913. However, the more he worked on his new theory of gravitation, the
more he realized that his knowledge of current mathematical ideas left much
to be desired. He said:
" ... in all my life I have not
labored nearly so hard, and I have become imbued with great respect for
mathematics, the subtler part of which I had in my simple-mindedness
regarded as pure luxury until now. ... "
One of Einstein's friends advised him to read the works of
the famous German mathematician, Bernhard Riemann (1826-1866) on
non-Euclidian geometry. Accordingly, for the next year or so, Einstein made
a concerted effort to get up to speed in the areas of tensor calculus and
differential geometry. Finally, in the middle of the year 1915, Einstein
visited the University of Göttingen where he spent a week lecturing on his
current progress in relativity theory. The great German mathematicians
David Hilbert (1862-1943) and Felix Christian Klein (1849-1925) attended his
lectures and Einstein commented:
" ... To my great joy, I succeeded
in convincing Hilbert and Klein completely. ... "
The Theory of General Relativity was now nearing its final
form. In November 1915, Einstein and Hilbert began an intensive
correspondence concerning the general theory. How much they learnt from each
other is hard to measure but the fact that they both discovered the same
final form of the gravitational field equations, within days of each other,
indicates that their exchange of ideas was helpful.
On 18 November 1915, Einstein made an important discovery
concerning the Planet Mercury. Einstein later wrote:
" ... For a few days
I was beside myself with joyous excitement. ... "
The discovery involved the perihelion of the planet
Mercury. In 1859, it had been noted that the perihelion (the point where the
planet is closest to the sun) advanced by 38" per century more than could be
accounted for by Newtonian mechanics. It appeared that Newton's inverse
square law was incorrect.
Since 1911, Einstein had realized the importance of
astronomical observations to his theories. He had worked with the German
astronomer, Erwin Finlay Freundlich (1885-1964), to measure Mercury's orbit
to the extent required to confirm the General Theory of Relativity. On 25
November 1915, Einstein submitted his paper entitled The Field Equations
of Gravitation; this paper gave the correct field equations for general
relativity. The calculation of the bending of light and the predicted
advance of Mercury's perihelion exactly fit the observational data without
the need to postulate any special hypothesis.
Einstein had reached the final version of general
relativity only after many iterations and errors along the way. In December
1915 he said of himself
" ... That fellow Einstein suits his
convenience. Every year he retracts what he wrote the year before. ..."
In March 1916, Einstein completed an article explaining
general relativity in terms more easily understood. The article was well
received and he later wrote another article on relativity which was widely
read and went through over 20 printings.
It should be noted that, in December 1915, a paper by
David Hilbert was published entitled The Foundations of Physics which
also contained the correct field equations for gravitation. Hilbert's paper
contained some important contributions to relativity not found in Einstein's
work. Also, Hilbert's paper expressed the hope that this work would lead to
the unification of gravitation and electromagnetism.
As of the beginning of the 21st century, the General
Theory of Relativity has stood the test of time well and has been repeatedly
verified by new experiments with a high degree of accuracy.
Section 12. Structure of matter and energy may be understood in terms of
In my opinion, of all the thirteen ideas discussed in this
short essay, the description of matter and energy in terms of indeterminate
quanta, as expressed in modern Quantum Theory, is by far the most
significant and profound. Indeed, I think most modern physicists would
admit that Quantum Theory is probably the most important and revolutionary
idea in the entire history of mathematical physics!
Unlike Relativity Theory, which was largely the product of
one man (Einstein), modern Quantum Theory was the work of nine physicists -
a sort of mini-ennead! These nine men, working during the period from about
1900-1927, produced the most significant achievement of 20th century
science. Even so, in my opinion, the key member of this ennead was Werner
Nobel Prizes in Physics
The above cited mini-ennead of nine physicists all were
awarded Nobel Prizes in Physics for their work in Quantum Theory. The
following table summarizes the facts regarding these awards:
Year of Award
||Louis de Broglie
||Wave Nature of
(Shared Prize with Schrödinger )
Schrödinger (Shared Prize with Dirac)
Nobel prizes for work in Quantum Theory notwithstanding,
Newtonian physics did not die easily. Most physicists of the early 20th
century were very reluctant to completely abandon the Newtonian system. It
was hoped that only a revision to the Newtonian System would be required.
Initially, a theory, now called the Old Quantum Theory, was proposed that
only modified Newtonian Mechanics. This "Old Theory" was largely the work
of the three older physicists of the mini-ennead, i.e., Planck, Einstein and
Bohr. Unfortunately, the Old Theory failed to explain all the experimental
data. It was the younger men - mainly Heisenberg, Schrödinger and Dirac-
who formulated a new theory, the so-called Copenhagen interpretation of
Quantum Theory, that is still in use today.
The role of each of the nine physicists may be summarized
Planck (1858-1947) – "Old Quantum Theory"
On 19 October 1900, German physicist Max
Planck made a ground-breaking presentation to the German Physical Society.
In his presentation, he provided an explanation to the problem of "black
body radiation." Any object with a higher temperature than its surroundings
loses heat by radiation. The hotter the object, the more radiation it
produces. Since a black body absorbs all frequencies, it should radiate all
frequencies equally. Instead, black bodies emit larger quantities of some
wavelengths than others. Planck proposed that radiant heat energy is emitted
only in definite amounts called quanta.
E = hv where v =
frequency of light and h = 6.626x10-34 Joule-seconds
Planck maintained that only certain
energies could appear and were limited to whole-number multiples of hv.
Planck originally called h a “quantum of action” since the product of
energy and time is known as action (based on Hamilton's principle of least
action). Today h is known as Planck's constant and symbolizes the
revolutionary new physics.
In 1900, Planck was a proper Victorian
gentleman of 42 years, a bit elderly for a revolutionary. Even so, his
discovery was to start the process of overthrowing Newtonian classical
physics. What he described was an answer to an old question in physics --
why does the color of radiation from any glowing body change from red to
orange and ultimately to blue as its temperature increases? Planck found he
could get the right answer by assuming that radiation, like matter, comes in
discrete quantities. And he called his little packets of energy "quanta"
from the Latin for amount.
Plank thought that some deeper
explanation of these quanta would emerge. However, it rapidly became clear
that this "quantification" of energy -- dividing it up into individual very
small pieces -- was actually a fundamental rule of nature. The classically
trained Planck didn't like this conclusion one bit. He, like Einstein (see
below) resisted it to his dying day, prompting his famous lament that new
scientific theories supplant previous ones not because people change their
minds, but simply because old people die.
Albert Einstein (1879-1955) – Photoelectric Effect
Prior to 1905 physicists had noted that
an electric current could be generated by exposing certain kinds of metallic
surfaces to light; the current produced was proportional to the intensity of
the light striking the surface. However, according to prevailing physical
theories, the maximum kinetic energy of electrons should not depend on
intensity but rather on the frequency of the light.
In 1905, Einstein published a paper
where he concluded that Planck's idea of light appearing as quanta (bundles)
was the key to understanding this photoelectric mystery. If the wavelength
is short enough, the electron cannot escape. The important thing is the
energy of the bundle and not number of bundles (brightness). Einstein's
paper on the photoelectric effect is now recognized as the first scientific
work utilizing quantum mechanics.
Although he had a major role in
destroying the Newtonian System, Einstein, like Planck (see above), could
never accept many of the revolutionary ideas of quantum mechanics,
particularly Heisenberg's Indeterminacy Principle.
Niels Bohr (1885-1962) - Theory of Atomic Structure
In 1913, Danish physicist Niels Bohr was
the first to apply the "Old Quantum Theory" of Planck and Einstein to atomic
structure. Bohr's theory accounted for the series of lines observed in the
spectrum of light emitted by atomic hydrogen. He was able to determine the
frequencies of these spectral lines to considerable accuracy by expressing
them in terms of the charge and mass of the electron and Planck's constant.
To do this, Bohr also postulated that an atom would not emit radiation while
it was in one of its stable states but rather only when it made a transition
between states. The frequency of the emitted radiation would be equal to the
difference in energy between those states divided by Planck's constant. This
meant that the atom could neither absorb nor emit radiation continuously but
only in finite steps or quantum jumps. This meant that the various
frequencies of the radiation emitted by an atom were not equal to the
frequencies with which the electrons moved within the atom. This was a bold
idea that some of Bohr's contemporaries found difficult to accept.
In 1916 Bohr was appointed professor of
theoretical physics at the University of Copenhagen and five years later, in
1921, the Bohr Institute opened with Bohr as its director. The Bohr
Institute became a leading center for quantum physics and many of the best
young theoretical physicists (including Heisenberg, Pauli, and Dirac) came
to Copenhagen just to work with Bohr.
4) Louis de Broglie (1892-1987) -
Wave-Particle Duality of the Electron
In 1924, French physicist Louis de Broglie developed the
thesis that nature did not single out light as the only entity to exhibit
wave-particle duality. He proposed that ordinary particles such as electrons
could also exhibit wave characteristics in certain circumstances. De Broglie
assumed that an electron has associated with it a system of "matter waves."
These waves possess crests that disappear at one point and appear an instant
later at another point. The distance between successive crests (λ)
is the "de Broglie wavelength" and it is calculated from λ = h/mv,
where h is Planck's constant and mv is momentum.
5) Werner Heisenberg (1901-1976) -
Quantum Matrix Equations and the Uncertainty Principle
In 1925, German physicist Werner
Heisenberg, using matrix algebra, developed a system called matrix
mechanics. It consisted of an array of quantities which, when appropriately
manipulated, gave the observed frequencies and intensities of spectral
lines. By 1927, he had formulated one of the greatest ideas of 20th century
physics - the Uncertainty Principle.
∆q∆p > h
The uncertainty of position
(∆q) of an electron in an atom multiplied by the uncertainty of its
momentum (∆p) must be greater than Planck's constant (h). The
uncertainty principle tells us that all observable quantities are subject to
changes determined by Planck's constant and we cannot know position and
momentum simultaneously. While a photon will not disturb any large object,
it does alter position and momentum when bounced off an electron.
Heisenberg's work was
fundamental to the development of the modern Quantum Theory which is still
being used today.
Erwin Schrödinger (1887-1961) -
Quantum Wave Equation
As stated in 4) above, Louis de
Broglie's had developed the theory that particles of matter have a dual
nature and in some situations act like waves. In 1926, Austrian physicist
Erwin Schrödinger produced the basic wave equation of quantum mechanics.
The Schrödinger equation treats electrons as matter waves:
The only problem with Schrödinger's equation was his interpretation of the
matter wave was wrong. He described ψ as the density
distribution--some regions rich in electron matter while others scarce. It
was Max Born (see below) who figured out what Schrödinger's equation
Born (1882-1970) -
In 1926, after his student Werner
Heisenberg had formulated the first laws of modern quantum mechanics, German
physicist Max Born collaborated with him to develop the mathematical
formulation that would adequately describe it. When Schrödinger put forward
his quantum mechanical wave equation, Born showed that the solution of the
equation has a statistical meaning of physical significance. Born's
interpretation of the wave equation proved to be of fundamental importance
in the new theory of quantum mechanics.
Schrödinger believed that the electron
was spread out in space and its density given by the value of ∆2.
Born proposed what is now the accepted interpretation: ∆2
probability density of finding the electron. The distinction between the
two interpretations is important. If ∆2 is small at a
particular position, the original interpretation implies that a small
fraction of an electron will always be detected there. In Born's
interpretation, nothing will be detected there most of the time, but when
something is observed, it will be a whole electron.
Accordingly, the concept of the electron
as a point particle moving in a well-defined path around the nucleus is
replaced in wave mechanics by probability clouds that describe the probable
locations of electrons in different states. Born's concept of probability
density represented a dramatic change in the way the physical world was
Wolfgang Pauli (1900-1958) -
In 1925, Austrian physicist Wolfgang
Pauli proposed a new quantum property called "two-valuedness." The
exclusion principle may be stated as:
No two electrons in an
atom can have the same set of four quantum numbers.
The "four quantum numbers" are the
coordinates of the three spatial dimensions plus the "spin" of the electron.
The exclusion principle subsequently has
been modified to include a whole class of particles of which the electron is
only one member. Modern physics now places all subatomic particles into one
of two classes: 1) particles that obey the Pauli exclusion principle called
fermions and 2) all other particles which are called bosons.
Dirac (1902-1984) - Quantum Electrodynamics
In 1927, English physicist Paul Dirac laid the foundations
for quantum electrodynamics when he developed an equation incorporating both
the quantum theory and the theory of special relativity. Dirac showed that
the correct relationship between mass and energy was not Einstein's equation
(E = mc2) but was actually:
When solving Dirac's equation, the solution can be either
positive or negative, i.e., E = + mc2 or E = - mc2.
But how can energy of an electron be negative? Dirac
predicted the existence of electrons with positive charge (antielectrons or
positrons). Dirac’s prediction was verified by experiments conducted in
1932 by American physicist Carl Anderson where positrons were indeed
detected. Dirac also predicted that every particle possesses an
antiparticle (antiproton, antineutron, etc.).
1927 Solvay (Belgium) Conference
The above paragraphs indicate that the major discoveries
of Quantum Theory were all accomplished during the years 1900-1927. Indeed
six of the nine most important discoveries occurred during the very short
period 1924-1927! The climax to this story occurred at the international
Solvay Conference of physicists held in Brussels, Belgium on 24-29 October
This particular Solvay Conference was attended by most of
the world's best physicists. The purpose of the
meeting was to discuss the newly developed quantum mechanics. A major paper
on the subject was presented to the conference attendees by Max Born and
Werner Heisenberg. Their paper concluded with a very bold statement:
We regard quantum mechanics as a
complete theory for which the fundamental physical and mathematical
hypotheses are no longer susceptible of modification.
The most famous scientists at this conference
were Planck, Einstein and Bohr.
These three men represented the older generation of physicists who had been
instrumental in the development of the so-called Old Quantum Theory. All
three men had originally opposed the new quantum interpretation of the
"young Turks" such as Heisenberg, Pauli and Dirac.
However, Bohr, after extensive discussions with Born and Heisenberg, had
previously became convinced of the overall validity of the new
interpretation. Accordingly, at the 1927 conference, Bohr took the lead in
arguing for acceptance of this new interpretation which later came to be
known as the "Copenhagen Interpretation" (named after the location of the
Bohr Institute). Bohr's principal opponent at the conference was the
redoubtable Albert Einstein.
Einstein was particularly troubled by Heisenberg's
Uncertainty Principle. Heisenberg, Bohr, and other
supporters of the new theory insisted that there was no meaningful way to
discuss certain details of an atom's behavior. For example, one could never
predict the precise moment when an atom would emit a quantum of light.
Einstein could not accept this lack of certainty; at the 1927 Conference, he
raised one objection after another. Yet each of Einstein's objections, set
forth as thought experiments, was successfully countered by Bohr. The
debate between Bohr and Einstein went on day and night, neither man
conceding defeat. During the debate, an exasperated Einstein purportedly
made the remark,
"God does not play dice." Bohr replied, "Einstein, stop
telling God what to do."
This photograph of
well-known scientists was taken at the international Solvay Conference of
October 1927. Among those present were the nine now famous physicists who
developed Quantum Theory. Their names are noted in red type. Front row,
left to right: I. Langmuir,
Marie Curie, H. A. Lorentz,
P. Langevin, C. E. Guye, C. T. R. Wilson, O. W. Richardson. Second row, left
to right: P. Debye, M. Knudsen, W. L. Bragg, H. A. Kramers,
Arthur H. Compton,
Louis de Broglie,
Standing, left to right: A. Piccard, E. Henriot, P. Ehrenfest, E. Herzen, T.
H. Fowler, L. Brillouin.
Section 13. Construction of machines that match or exceed human intelligence
In my opinion, the development of computer science,
including its sub-disciplines of artificial life and artificial
intelligence, was the most important new technological creation of the 20th
century. Like Quantum Theory, discussed in Section 12 above, this new area
of scientific endeavor was the work of many people over an extended period
of time. Even so, there are certain individuals who I believe were key
players in the creation of this new science. These key players may be
divided into three groups of four people each, for a total of twelve
individuals. In the paragraphs which follow I shall try to identify these
people and briefly describe their contributions which have culminated in the
extraordinary concept that soon we may be able to construct machines that
equal or exceed the human level of intelligence.
Marvin Minsky, who until recently was the head of the
Artificial Intelligence (AI) Laboratory at M. I. T., has described AI as the
art and science of making computers do things that we would consider
intelligent if people did them. Accordingly, intelligent machines are only
possible if sufficiently powerful computers are available.
The basic technological infrastructure and the willingness
to provide the financial resources necessary for producing such computers
did not become available until World War II. The first generation of these
computers were designed by a scientific elite drawn from Great Britain and
the United States during and immediately following the Second World War.
This elite included four very prominent mathematicians: Alan Turing
(1913-1954) of Great Britain, John von Neumann (1903-1957), Norbert Wiener
(1894-1964) and Claude Shannon (1916-2001) of the United States. These four
men were unquestionably the founding fathers of computer science and
artificial intelligence. Both John von Neumann and Alan Turing are
discussed in more detail on other pages of this web site. The most
significant technical papers written by these four mathematicians, relating
to computers and machine intelligence, are summarized in the following
The early computing machines all required large, specially
air-conditioned rooms, and were a programmers nightmare; each program run on
the computer required the physical reconfiguration of thousands of wires.
However, by the late 1940's, stored program computers, such as EDSAC, were
developed which made the job of entering programs much easier. Other
technical advancements in computer speed and efficiency, permitting the
rapid electronic processing of data, made the application of computers to
relatively complex problems feasible. Thus, by the mid-1950's, computer
capability had reached the minimum level necessary to support the new
discipline of artificial intelligence. The IBM 704 is generally considered
to be the first "supercomputer" and it was for this machine that much of the
very early AI software was written. The most significant of these early,
first generation, computers are briefly described in the following table:
Location of First Machine
||1500 Vacuum Tubes - Used in Code Breaking
||Bletchley Park, England
||Counter Wheels and Electro-Mechanical
||Over 17,000 Vacuum Tubes
||University of Pennsylvania
||3,000 Vacuum Tubes -1st Stored Program
||Manchester University, England
||5,400 Vacuum Tubes
||Census Bureau, Washington DC
||4,000 Vacuum Tubes and 10,000 Diodes
||Aberdeen Proving Ground MD
||2,400 Vacuum Tubes and 500 Diodes
||Los Alamos Laboratory NM
||Floating Point Registers, 36 Bit Words,
||Probably Rand Corporation CA
The theoretical foundations of computer science and
artificial intelligence were primarily the work of four very brilliant
mathematicians. These men had established the theoretical basis for the
hardware necessary to begin work in the AI field. It was now the turn of
the software people.
The starting date for serious work in AI is probably
1956. In that year, a two-month summer conference on thinking machines was
held at Dartmouth University. The attendees included Claude Shannon,
already discussed above, and four people who subsequently became the
dominant thinkers in the AI field for the next 20 years. These four men
were John McCarthy (b. 1927), Marvin Minsky (b. 1927), Herbert Simon
(1916-2001), and Allen Newell (1927-1992). The following table summarizes
the more significant accomplishments of these four men:
|Allen Newell and Herbert Simon
Logic Theory Machine (LTM) - a program that could prove
mathematical theorems using prepositional calculus
|Allen Newell and Herbert Simon
Solver (GPS) - a program that solves problems through a feedback
technique called "means-ends analysis"
programming language - used for writing AI applications software
|Herbert Simon and Allen Newell
||Published an important paper entitled
"Heuristic Problem Solving" - in the paper they predicted that a
computer would defeat the world chess champion within a decade!
Unfortunately, this did not happen until 1997 almost 30 years later!
|Marvin Minsky and John McCarthy
||Founded the Artificial Intelligence
Laboratory at M. I. T. - the first such lab in the world
||Founded the Stanford University
Artificial Intelligence Laboratory
|Marvin Minsky and Seymour Papert
||Wrote book entitled "Perceptrons"
- book was very damaging to neural-net research
||Wrote book entitled "Society
of Mind" - book argues that the human mind is composed of a
large number of simple, overlapping processes operating in parallel
Since the 1970's, the growth in the size and complexity
of the AI community was astounding. Many thousands of people are now
involved in various aspects of AI research. However, in my opinion, there
are four people who, at the end of the 20th century, were the leading advocates of the notion that
machines that equal or exceed human intelligence were not only possible but
would probably be developed within the next 100 years. These four prophets
of super-intelligent machines were: Ray Kurtzweil, Hans Moravec, William Joy
and Rodney Brooks.
The following table summarizes some of the more recent
writings of these men that support the idea of constructing machines that
equal or exceed human intelligence: