Greatest Minds and Ideas of the Western World

Website Created By Phil Norfleet

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 Moslem theologians.

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 table:

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 Cthulhu (1926)

Discussion

The ideas cited in the above table are discussed in more detail in the following thirteen sections:

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 speeds.

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 planetary orbits.

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 earth-centered system.

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 naked-eye.

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 universe.

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 Way Galaxy.

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 universe.

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 20th centuries.

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 Milky Way.

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 below.

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 Constant.

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 megaparsec!

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 current landscape.

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 offspring.

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 Charles Lyell.

 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 years;

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 "specialization."

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 implications:

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 species.

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 following paragraphs:

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 lowly origin.
 

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 understood.

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 automatically determined.

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 century.

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 M₁M₂/d²

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 on gravitation:

" ... 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 indeterminate quanta.

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 Heisenberg.

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:

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 as follows:

1)  Max 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.

2)  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. 

3)  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.

6)  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 actually predicts.

7)  Max Born (1882-1970) - Probability Density

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 gives the 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 viewed.

8)  Wolfgang Pauli (1900-1958) - Exclusion Principle

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.

9)  Paul 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:

E² = m²c⁴

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 1927.

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, Max Planck, Marie Curie, H. A. Lorentz, Albert Einstein, 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, Paul Dirac, Arthur H. Compton, Louis de Broglie, Max Born, Niels Bohr. Standing, left to right: A. Piccard, E. Henriot, P. Ehrenfest, E. Herzen, T. De Donder, Erwin Schrödinger, E. Verschaffelt, Wolfgang Pauli, Werner Heisenberg, R. H. Fowler, L. Brillouin.
 

Section 13. Construction of machines that match or exceed human intelligence are possible.

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 table:

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:

 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:

 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: