PIERRE DE FERMAT (1601- 65) ANDREW WILES (b.1953)

1637 – France; 1993 – USA

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PIERRE DE FERMAT

Fermat’s theorem proves that there are no whole-number solutions of the equation x n + y n = z n for n greater than 2

The problem is based on Pythagoras’ Theorem; in a right-angled triangle, the square of the hypotenuse is equal to the sum of the squares on the other two sides; that is x 2 + y 2 = z 2

If x and y are whole numbers then z can also be a whole number: for example 52+ 122 = 132
If the same equation is taken to a higher power than 2, such as x 3 + y 3 = z 3 then z cannot ever be a whole number.

In about 1637, Fermat wrote an equation in the margin of a book and added ‘I have discovered a truly marvelous proof, which this margin is too small to contain’. The problem now called Fermat’s Last Theorem baffled mathematicians for 356 years.

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ANDREW WILES

In 1993, Wiles, a professor of mathematics at Princeton University, finally proved the theorem.

Wiles, born in England, dreamed of proving the theorem ever since he read it at the age of ten in his local library. It took him years of dedicated work to prove it and the 130-page proof was published in the journal ‘Annals of Mathematics‘ in May 1995.

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BENJAMIN FRANKLIN (1706-1790)

1752 – The New World

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BENJAMIN FRANKLIN

‘If you would not be forgotten when you are dead and rotten, either write things worth reading, or do things worth writing about’

Curious about how just about everything works, from governments to lightning rods, Franklin’s legacy, in addition to the many inventions such as lightning conductors, bifocal lenses and street lamps, was one of learning. He established one of the first public libraries as well as one of the first universities in America, Pennsylvania. He established the Democratic Party. Franklin was one of the five signatories of the Declaration of Independence from Great Britain in 1776 and was a later participant in the drafting of the American Constitution.

‘Benjamin Franklin’s choice for the signs of electric charges leads to electric current being positive, even though the charge carriers themselves are negative — thereby cursing electrical engineers with confusing minus signs ever since.
The sign of the charge carriers could not be determined with the technology of Franklin’s time, so this isn’t his fault. It’s just bad luck’

Franklin was a pioneer in understanding the properties and potential of electricity. He undertook studies involving electric charge and introduced the terms ‘positive’ and ‘negative’ in explaining the way substances could be attracted to or repelled by each other according to the nature of their charge. He believed these charges ultimately cancelled each other out so that if something lost electrical charge, another substance would instantly gain the same amount.

 

His work on electricity climaxed with his kite flying experiment of 1752. In order to prove lightning to be a form of electricity, Franklin launched a kite into a thunderstorm on a long piece of conducting string. Tying the string to a capacitor, which became charged when struck by lightning, vindicated his theories.

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BENJAMIN THOMPSON (1753-1814) known as Count Rumford

1798 – England

‘Mechanical work can be converted into heat. Heat is the energy of motion of particles’

Heat is a form of energy associated with the random motion of atoms or molecules. Temperature is a measure of the hotness of an object.

In the eighteenth century, scientists imagined heat as a flow of a fluid substance called CALORIC. Each object contained a certain amount of caloric. If caloric flowed out, the object’s temperature decreased; if more caloric flowed into the object, its temperature increased.

Like PHLOGISTON, caloric was a weightless fluid, a quality that could be transmitted from one substance to another, so that the first warmed the second up. What is being transmitted is heat energy.

Working for the Elector of Bavaria, Rumford investigated the heat generated during the reaming out of the metal core when the bore of a cannon is formed. According to the caloric theory, the heat was released from the shards of metal during boring; Rumford noticed that if the tools were blunt and removed little or no metal, more heat was generated, rather than less.

Rumford postulated that the heat source had to be the work done in drilling the hole. Heat was not an indestructible caloric fluid, as LAVOISIER had argued, but something that could come and go. Mechanical energy could produce heat and heat could lead to mechanical energy.

One analogy he drew was to a bell; heat was like sound, with cold being similar to low notes and hot, to high ones. Temperature was therefore just the frequency of the bell. A hot object would emit ‘calorific rays’, whilst a cold one would emit ‘frigorific rays’ – an idea raised in Plutarch’s De Primo Frigido. Cold was an entity in itself, not simply the absence of heat.

Rumford thought there was no separate caloric fluid and that the heat content of an object was associated with motion or internal vibrations – motion which in the case of the cannon was bolstered by the friction of the tools. He had recognized the relationship between heat energy and the physicists’ concept of ‘work’ – the transfer of energy from a system into the surroundings, caused by the work done, results in a difference in temperature.
This transfer of energy measured as a temperature difference is called ‘heat’.

Half a century was to pass before in 1849, JAMES JOULE established the ‘mechanical equivalent of heat’ and JAMES CLERK MAXWELL launched the kinetic theory. According to Maxwell, the heat content of a body is equivalent to the sum of the individual energies of motion (kinetic energies) of its constituent atoms and molecules.

US born Rumford founded the Royal Institution in London and invented the calorimeter, a device measuring heat.

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THOMAS ALVA EDISON (1847-1931)

1875 – USA

‘We don’t know one millionth of one percent of anything’

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THOMAS ALVA EDISON

‘Genius is one percent inspiration and ninety-nine percent perspiration’
Scorning high-minded theoretical and mathematical methods was the basis of Edison’s trial and error approach to scientific enquiry and the root of his genius.

1877 – Patents the carbon button transmitter, still in use in telephones today.
1877 – Invents the phonograph.
1879 – Invents the first commercial incandescent light after more than 6000 attempts at finding the right filament and finally settling on carbonized bamboo fibre.

Edison held 1093 patents either jointly or singularly and was responsible for inventing the Kinetograph and the Kinetoscope (available from 1894) the Dictaphone, the mimeograph, the electronic vote-recording machine and the stock ticker.

His laboratory was established at Menlo Park in 1876, establishing dedicated research and development centres full of inventors, engineers and scientists. In 1882 he set up a commercial heat, light and power company in Lower Manhattan, which became the company General Electric.

Experimenting with light bulbs, in 1883 one of his technicians found that in a vacuüm, electrons flow from a heated element – such as an incandescent lamp filament – to a cooler metal plate.
The electrons can flow only from the hot element to the cool plate, but never the other way. When English physicist JOHN AMBROSE FLEMING heard of this ‘Edison effect’ he used the phenomenon to convert an alternating electric current into a direct current, calling his device a valve. Although the valve has been replaced by diodes, the principle is still used.

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ALEXANDER GRAHAM BELL (1847-1922)

1875 – USA

‘The inventor of the telephone, Bell devoted much of his life to working with the deaf’

After emigrating to Canada from Scotland in 1870, Bell met Thomas Watson, who would help Bell’s theoretical ideas become physical reality. Bell believed that if the right apparatus could be devised, sound waves from the mouth could be converted into electric current, which could then be sent down a wire relatively simply and converted into sound at the other end using a suitable device. Bell’s telephone was patented in 1876.

Bell used the money brought in from his invention to found his company AT & T and the Bell Laboratories.
Just as THOMAS EDISON improved the viability of Bell’s telephone, so Bell enhanced Edison’s phonograph.

Bell spent some time educating Helen Keller and was instrumental in founding the journal ‘Science‘.

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ALBERT EINSTEIN (1879-1955)

1905 – Switzerland

  1. ‘the relativity principle: All laws of science are the same in all frames of reference.
  2. constancy of the speed of light: The speed of light in a vacuüm is constant and is independent of the speed of the observer’
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EINSTEIN

The laws of physics are identical to different spectators, regardless of their position, as long as they are moving at a constant speed in relation to each other. Above all the speed of light is constant. Classical laws of mechanics seem to be obeyed in our normal lives because the speeds involved are insignificant.

Newton’s recipe for measuring the speed of a body moving through space involved simply timing it as it passed between two fixed points. This is based on the assumptions that time is flowing at the same rate for everyone – that there is such a thing as ‘absolute’ time, and that two observers would always agree on the distance between any two points in space.
The implications of this principle if the observers are moving at different speeds are bizarre and normal indicators of velocity such as distance and time become warped. Absolute space and time do not exist. The faster an object is moving the slower time moves. Objects appear to become shorter in the direction of travel. Mass increases as the speed of an object increases. Ultimately nothing may move faster than or equal to the speed of light because at that point it would have infinite mass, no length and time would stand still.

‘The energy (E) of a body equals its mass (m) times the speed of light (c) squared’

This equation shows that mass and energy are mutually convertible under certain conditions.

The mass-energy equation is a consequence of Einstein’s theory of special relativity and declares that only a small amount of atomic mass could unleash huge amounts of energy.

Two of his early papers described Brownian motion and the ‘photoelectric’ effect (employing PLANCK’s quantum theory and helping to confirm Planck’s ideas in the process).

1915 – Germany

‘Objects do not attract each other by exerting pull, but the presence of matter in space causes space to curve in such a manner that a gravitational field is set up. Gravity is the property of space itself’

From 1907 to 1915 Einstein developed his special theory into a general theory that included equating accelerating forces and gravitational forces. This implies light rays would be bent by gravitational attraction and electromagnetic radiation wavelengths would be increased under gravity. Moreover, mass and the resultant gravity, warps space and time, which would otherwise be ‘flat’, into curved paths that other masses (e.g. the moons of planets) caught within the field of the distortion follow. The predictions from special and general relativity were gradually proven by experimental evidence.

Einstein spent much of the rest of his life trying to devise a unified theory of electromagnetic, gravitational and nuclear fields.

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NIKOLA TESLA (1856-1943)

1888 – USA

‘The transmission of high voltage alternating current (AC) over long distances is more efficient than the transmission of direct current (DC)’

DC transmission is no longer used anywhere in the world.

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NIKOLA TESLA

In the 1880s THOMAS EDISON (1847-1931) developed DC generation and set up his Edison light company to build power plants. DC loses much of its energy when transmitted through wires at long distances and DC power plants had to be close to cities.

In 1888 Tesla came up with an idea involving a rotating magnetic field in an induction motor, which would generate an ‘alternating current’. He invented the AC induction motor and suggested that the transmission of AC power is more efficient.

On 16th November 1896 the AC power plant at Niagara Falls built by George Westinghouse (1864-1914) became the first power plant to transmit electric power between two cities (from Niagara Falls to Buffalo).

Tesla’s development of AC power led to the invention of induction motors, dynamos, transformers, condensers, bladeless turbines, mechanical rev. counters, automobile speedometers, gas discharge lamps (forerunners of fluorescent lights), radio broadcasting and hundreds of other things. His patents number over 700.

The tesla (T), the SI unit of magnetic flux density, for measuring magnetism, is named in his honour.

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ROBERT MILLIKAN (1868-1953)

1909 – USA

The charge on the electron’

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ROBERT ANDREWS MILLIKAN

Millikan measured the charge on the electron.

His experiment showed that the electron is the fundamental unit of electricity; that is, electricity is the flow of electrons.
From his experiment Millikan calculated the basic charge on an electron to be 1.6 × 10-19 coulomb.
This charge cannot be subdivided – by convention this charge is called unit negative, -1, charge.

Millikan also determined that the electron has only about 1/1837 the mass of a proton, or 9.1 × 10-31 kilogram.

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ROBERT GODDARD (1882-1945)

1915 – USA

‘Demonstrates that rocket engines can produce thrust in a vacuum’

‘Robert Goddard stands as the epitome of the early American desire to conquer space’

It was generally believed that it would be impossible for a rocket to move outside of the Earth’s atmosphere, as there was nothing for it to push against in order to gain propulsion. Goddard had already gone a long way to revoking this assumption by 1907 in completing calculations to show that a rocket could thrust in a vacuum, and had backed up this concept with physical experiment in 1915.

His booklet “A Method of Reaching Extreme Altitudes” described the multi-stage principle and presented advanced ideas on how to improve the performance of solid-fuel rockets.

‘I have read very attentively your remarkable book A Method for Reaching Extreme Altitudes edited in 1919 and I have found in it quite all the ideas which the German Professor H.Oberth published in 1924′ (in a letter from Soviet engineer & author Nikolai Alexsevitch Rynin)

In 1926 he launched the world’s first liquid-fuelled rocket using gasoline and liquid oxygen; the 2.5 second, 41 feet flight proved that liquid-fuel propellants could be used to power a rocket instead of exploding in a catastrophic detonation.
Over the next decade, Goddard filed patents for guidance, control and fuel pump mechanisms.

In spite of his success (by 1935 he had launched a rocket at Roswell, New Mexico which traveled faster than the speed of sound and another which achieved an altitude of 1.7 miles – a record at that time) the US Government largely ignored his efforts until the space race gathered momentum in the 1940s and 1950s.
The government was eventually forced to pay one million dollars to Goddard’s widow for patent infringement in acknowledgement of the use they had made of his designs as a basis from which to begin development.

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EDWIN HUBBLE (1889-1953)

1929 – USA

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EDWIN HUBBLE

‘Galaxies are moving away from each other and us at an ever-increasing rate. The more distant the galaxy, the faster it is moving away’

This means that the universe is expanding like a balloon. The principle of an expanding cosmos is at the heart of astronomical theory.

Before 1930, astronomers believed that the Milky Way was the only galaxy in the universe. The discovery of Cepheid variables, which brightened and dimmed in a regular rhythm gave a clue as to the true size of the universe.

In 1923, Hubble spotted a Cepheid variable in the Andromeda Nebula, previously supposed to be clouds of gas. This led to the conclusion that Andromeda was nearly a million light years away, far beyond the limits of the Milky Way and clearly a galaxy in its own right. Hubble went on to discover Cepheids in other nebula and proved that galaxies existed beyond our own.
He began to develop a classification system, sorting galaxies by size, content, distance, shape and brightness. He divided galaxies into elliptical, spiral, barred spiral and irregular. These are subdivided into categories, a, b and c according to the size of the central mass of stars within the galaxy and the tightness of any spiraling arms.

The Earth’s atmosphere alters light rays from outer space; the Hubble Space Telescope, being above the atmosphere, receives images with far greater clarity and detail.
Construction began on the HST in 1977 and it was launched by the space shuttle discovery on 25 April 1990. The instruments can detect not only visible light but also infra-red and ultra-violet. Its camera can achieve a resolution ten times greater than the largest Earth based telescope.

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Hubble noticed that the galaxies appeared to be moving away from the region of space in which the Earth is located. It appeared that the further away a galaxy was, the faster it was receding. The conclusion was that the universe, which had previously been considered static is in fact expanding.

In 1915, EINSTEIN’s theory of relativity had suggested that owing to the effects of gravity, the universe was either expanding or contracting. Einstein knew little about astronomy and had introduced an anti-gravity force into his equations, the cosmological constant. Hubble’s discoveries proved Einstein had been right after all and Einstein later described the introduction of the gravitational constant as ‘the biggest blunder of my life’.

This detailed picture of the Helix Nebula shows a fine web of filaments, like the spokes of a bicycle, embedded in the colorful red and blue gas ring around this dying star. The Helix Nebula is one of the nearest planetary nebulae to Earth, only 650 light years away.This "double cluster," NGC 1850, is located in the Large Magellanic Cloud. It consists of a large cluster of stars, located near a smaller cluster (below and to the right). The large cluster is 50 million years old; the other only 4 million years old. The cluster is surrounded by gas believed to be created by the explosion of massive stars.This youngest-known supernova remnant in our galaxy lies 10,000 light years away in the constellation Cassiopeia. The light from this exploding star first reached Earth in the 1600s.

Hubble’s discovery that the universe is expanding led to the development of the ‘big-bang’ model of the universe.


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LINUS PAULING (1901- 94)

1931 USA

‘A framework for understanding the electronic and geometric structure of molecules and crystals’

An important aspect of this framework is the concept of hybridisation: in order to create stronger bonds, atoms change the shape of their orbitals (the space around a nucleus in which an electron is most likely to be found) into petal shapes, which allow more effective overlapping of orbitals.

A chemical bond is a strong force of attraction linking atoms in a molecule or crystal. BOHR had already shown that electrons inhabit fixed orbits around the nucleus of the atom. Atoms strive to have a full outer shell (allowed orbit), which gives a stable structure. They may share, give away or receive extra electrons to achieve stability. The way atoms will form bonds with others, and the ease with which they will do it, is determined by the configuration of electrons.

Earlier in the century, Gilbert Lewis (1875-1946) had offered many of the basic explanations for the structural bonding between elements, including the sharing of a pair of electrons between atoms and the tendency of elements to combine with others to fill their electron shells according to rigidly defined orbits (with two electrons in the closest orbit to the nucleus, eight in the second orbit, eight in the third and so on).

Pauling was the first to enunciate an understanding of a physical interpretation of the bonds between molecules from a chemical perspective, and of the nature of crystals.

In a covalent bond, one or more electrons are shared between two atoms. The two atoms are bound together by the shared electrons. This was proposed by Lewis and Irving Langmuir in 1916. Two hydrogen atoms form the hydrogen molecule, H2, by each sharing their single electron.

In an ionic bond, one atom gives away one or more electrons to another atom. So in common salt, sodium chloride, sodium gives away its spare electron to chlorine. As the electron is not shared, the sodium and chlorine atoms are not bound together in a molecule. However, by losing an electron, sodium acquires a positive charge and chlorine, by gaining an electron, acquires a negative charge. The resulting sodium and chlorine ions are held in a crystalline structure.
Until Pauling’s explanation it was thought that they were held in place only by electrical charges, the negative and positive ions being drawn to each other.

Pauling’s work provided a value for the energy involved in the small, weak hydrogen bond.
When a hydrogen atom forms a bond with an atom which strongly attracts its single electron, little negative charge is left on the opposite side of the hydrogen atom. As there are no other electrons orbiting the hydrogen nucleus, the other side of the atom has a noticeable positive charge – from the proton in the nucleus. This attracts nearby atoms with a negative charge. The attraction – the hydrogen bond – is about a tenth of the strength of a covalent bond.
In water, attraction between the hydrogen atoms in one water molecule and the oxygen atoms in other water molecules makes water molecules ‘sticky’. It gives ice a regular crystalline structure it would not have otherwise. It makes water liquid at room temperature, when other compounds with similarly small molecules are gases at room temperature.Water_animation

He devised the electronegativity scale, which ranks elements in order of their electronegativity – a measure of the attraction an atom has for the electrons involved in bonding ( 0.7 for caesium and francium to 4.0 for fluorine ). The electronegativity scale lets us say how covalent or ionic a bond is.

One aspect of the revolution he brought to chemistry was to insist on considering structures in terms of their three-dimensional space. Pauling showed that the shape of a protein is a long chain twisted into a helix or spiral, now known as an alpha-helix. The structure is held in shape by hydrogen bonds.
He also explained the beta-sheet, a pleated sheet arrangement given strength by a line of hydrogen bonds.

1922 – while investigating why atoms in metals arrange themselves into regular patterns, Pauling used X-ray diffraction at CalTech to determine the structure of molybdenum.

When X-rays are directed at a crystal, some are knocked off course by striking atoms, while others pass straight through as if there are no atoms in their path. The result is a diffraction pattern – a pattern of dark and light lines that reveal the positions of the atoms in the crystal.
Pauling used X-ray and electron diffraction, magnetic effects and measurements of the heat of chemical reactions to calculate the distances and angles between atoms forming bonds. In 1928 he published his findings as a set of rules for working out probable crystalline structures from the X-ray diffraction patterns.

Pauling’s application of quantum theory to structural chemistry helped to establish the subject. He took from quantum mechanics the idea of an electron having both wave-like and particle-like properties and applied it to hydrogen bonds. Instead of there being just an electrical attraction between water molecules, Pauling suggested that wave properties of the particles involved in hydrogen bonding and those involved in covalent bonding overlap. This gives the hydrogen bonds some properties of covalent bonds.

1939 – ‘The Nature of the Chemical Bond and the Structure of Molecules’
Pauling suggests that in order to create stronger bonds, atoms change the shapes of their waves into petal shapes; this was the ‘hydridisation of orbitals’.

Pauling developed six key rules to explain and predict chemical structure. Three of them are mathematical rules relating to the way electrons behave within bonds, and three relate to the orientation of the orbitals in which the electrons move and the relative position of the atomic nuclei.

      

      

Describing hybridisation, he showed that the labels ‘ionic’ and ‘covalent’ are little more than a convenience to group bonds that really lie on a continuous spectrum from wholly ionic to wholly co-valent.

1951 – published his findings one year after WILLIAM LAWRENCE BRAGG’s team at the Cavendish Laboratory.

CARBON BONDING
As carbon has four filled and four unfilled electron shells it can form bonds in many different ways, making possible the myriad organic compounds found in plants and animals. The concept of hybridisation proved useful in explaining the way carbon bonds often fall between recognised states, which opened the door to the realm of organic chemistry.

X-ray diffraction alone is not very useful for determining the structure of complex organic molecules, but it can show the general shape of the molecule. Pauling’s work showed that physical chemistry at the molecular level could be used to solve problems in biology and medicine.

A problem that needed resolving was the distance between particular atoms when they joined together. Carbon has four bonds, for instance, while oxygen can form two. It would seem that in a molecule of carbon dioxide, which is made of one carbon and two oxygen atoms, two of carbon’s bonds will be devoted to each oxygen.

Well-established calculations gave the distance between the carbon and oxygen atoms as 1.22 × 10-10m. Analysis gave the size of the bond as 1.16 Angstroms. The bond is stronger, and hence shorter. Pauling’s quantum .3-2. explanation was that the bonds within carbon dioxide are constantly resonating between two alternatives. In one position, carbon makes three bonds with one of the oxygen molecules and has only one bond with the other, and then the situation is reversed.

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SUBRAHMANYAN CHANDRASEKHAR (1910- 95)

1931 – USA

‘The maximum possible mass of a white dwarf star is 1.4 times the Sun’s mass’

Photograph of SUBRAHMANYAN CHANDRASEKHAR (1910-95) Using Albert Einstein’s special theory of relativity and the principles of quantum physics, Chandrasekhar formulated the idea in 1930 that it is impossible for a white dwarf star, which is supported solely by a degenerate gas of electrons, to be stable if its mass is greater than 1.44 times the mass of the Sun.

SUBRAHMANYAN CHANDRASEKHAR

The Chandrasekhar limit is a physical constant. It is the greatest mass a white dwarf star can have before it goes supernova, approximately 1.44 solar masses.
Chandrasekhar showed that it is impossible for a white dwarf star, which is supported solely by electron degeneracy pressure, to be stable if its mass is greater than 1.44 times the mass of the Sun. If such a star does not completely exhaust its thermonuclear fuel, then the limiting mass may be slightly larger.
Above this limit a star has too much mass to become a white dwarf after gravitational collapse. A star of greater mass will become a neutron star or a black hole.

The radius of a black hole is the radius of the event horizon surrounding it. This is the Schwarzschild radius, after the German astronomer Karl Schwarzschild (1873-1916) who in 1916 predicted the existence of black holes.
The Schwarzschild radius is roughly equal to three times the weight of the black hole in solar masses. A black hole weighing as much as the Sun would have a radius of 3 kilometres, one with the mass of the Earth would have a radius of only 4.5 millimetres.
A black hole’s effects occur within ten Schwarzschild radii of its centre.

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THOMAS HUNT MORGAN (1866-1945)

1933 – USA

‘The Mechanism of Mendelian Heredity’ (1915), ‘The Theory of the Gene’ (1926)’

Morgan laid the foundation for understanding MENDEL’s observations and helped to provide the science required to reinforce CHARLES DARWIN’s conclusions.

Starting with Mendel’s laws of segregation and independent assortment, Morgan investigated why there are far fewer chromosomes – the long thread-like structures present in the nucleus of every living cell, which grow and divide during cell splitting, – than there are ‘units of heredity’. Morgan could not see how these few chromosomes could account for all the changes that occur from one generation to the next.

Mendel’s ‘factors of heredity’ had been renamed ‘genes’ in 1909 by the Dane Wilhelm Johannsen.

When the organism forms its reproductive cells (gametes), the genes segregate and pass to different gametes.
Since it had been separately established that chromosomes play an important part in inheritance, then groups of genes had to be present on a single chromosome.
If all the genes were arranged along chromosomes, and all chromosomes were transmitted intact from one generation to the next, then many characteristics would be inherited together. This implicitly invalidates Mendel’s law of independent assortment, which dictated that hereditary traits caused by genes would occur in all possible mathematical combinations in a series of descendants, independent of each other.

Experimental evidence often seemed to back-up the mathematical forecasts for characteristics present in descendants that Mendel had suggested; Morgan felt that the law of independent assortment could not accurately model the process of arriving at the end result.

He began his experiments with the fruit fly, which has just four pairs of chromosomes, in 1908.
He observed a mutant white-eyed male fly, which he extracted for breeding with ordinary red-eyed females. Over subsequent generations of interbred offspring, the white-eyed trait returned in some descendants, all of which turned out to be males. Clearly, certain genetic traits were not occurring independently of each other but were being passed on in groups.
Rather than invalidating Mendel’s law of independent assortment, a simple adjustment was required to unite it with Hunt’s belief in chromosomes to produce his thesis.
He suggested that the law of independent assortment did apply – but only to genes found on different chromosomes. For those on the same chromosome, linked traits would be passed on; usually a sex-related factor with other specific features (such as, the male sex and the white-eyed characteristic).

The results of his work convinced Morgan that genes were arranged on chromosomes in a linear manner and could be mapped. Further testing showed that, as chromosomes actually break apart and re-form during the production of sperm and egg cells, linked traits could occasionally be broken during the exchange of genes (recombination) that occurred between pairs of chromosomes during the process of cell division. He hypothesised that the nearer on the chromosome the genes were located to each other, the less likely the linkages were to be broken. Thus by measuring the occurrence of breakages he could work out the position of the genes along the chromosome.
In 1911 he produced the first chromosome map showing the position of five genes linked to gender characteristics.

In 1933 Hunt Morgan received the Nobel Prize for Physiology.

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CHARLES RICHTER (1900- 85)

1935 – USA

‘A scale ranging from 0 to 9 to measure the magnitude of earthquakes’

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CHARLES RICHTER

The Richter scale is a numerical scale that gives the magnitude of an earthquake by calculating the energy of shock waves at a standard distance. The scale is logarithmic, so each additional point represents a tenfold increase in severity. Thus a magnitude 7.0 earthquake is 10 times as powerful as one of magnitude 6.0 and 100 times as powerful as one of magnitude 5.0.
In terms of energy, one unit represents an increase in the energy of roughly 3 times. A magnitude 7.0 earthquake unleashes about 1000 times the energy released by a magnitude 5.0 earthquake.

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HANS BETHE (1906-2005)

1938 – USA

‘Energy in stars is produced by hydrogen fusion reactions’

In nuclear fusion the nuclei of light atoms combine at very high temperatures and release enormous amounts of energy that is radiated from the surface of the star as heat and light.

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HANS BETHE

An ordinary star is one of the simplest entities in nature; it is a sphere of gas that is by mass 73 percent hydrogen, 25 percent helium and 2 percent other elements. The temperature in the centre is high enough to fuse four nuclei of hydrogen together to form one helium nucleus.

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EDWIN McMILLAN (1907- 90) GLENN SEABORG (1912- 99)

1940 – USA

‘Elements heavier than uranium in the periodic table (transuranium elements) are made artificially. Uranium (U, atomic number 92) is the heaviest element known to exist naturally in detectable amounts on the Earth’

In 1933 ENRICO FERMI showed that the nucleus of most elements would absorb a neutron.
In 1940 McMillan, a nuclear physicist, produced and identified the first artificial element, neptunium (Np, 93). In 1943 Seaborg, a chemist, succeeded in creating plutonium (Pu, 94).

So far more than 20 synthetic elements have been created. All are unstable, decaying with half-lives ranging from a year to a few milliseconds.
At least thirteen transuranium elements have been named after scientists:-
curium (Cm, 96: Marie and Pierre Curie [1944]), einsteinium (Es, 99: Albert Einstein [1952]), fermium (Fm, 100: Enrico Fermi [1952]), mendelevium (Md, 101: Dmitri Mendeleev [1955]), nobelium (No, 102: Swedish chemist Alfred Nobel (1833-96), known for his bequest for the foundation of the Nobel Prizes [1956]), lawrencium (Lr, 103: Ernest O. Lawrence, a physicist best known for development of the cyclotron [1961]), rutherfordium (Rf, 104: Ernest Rutherford [1968]), seaborgium (Sg, 106: Glenn Seaborg [1974]), bohrium (Bh, 107: Niels Bohr [1981]), meitnerium (Mt, 109: Lise Meitner [1982]); roentgenium (Rg, 111: named after Wilhelm Conrad Röntgen was first created in 1994 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany [1994]), copernicium (Cn, 112: named after astronomer Nicolaus Copernicus [1996]), flerovium (Fl, 114: named after Soviet physicist Georgy Flyorov [2012]).

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ISAAC ASIMOV (1920- 92)

1940 – USA

photo portrait of science fiction writer Isaac Asimov

ISAAC ASIMOV

  • First Law: A robot may not injure a human being or, through inaction, allow a human being to come to harm

  • Second Law: A robot must obey orders given it by a human being, except where such orders would conflict with the First Law

  • Third Law: A robot must protect its own existence as long as such protection does not conflict with the First or Second Law

            

The word robot was introduced into the English language from a 1921 play RUR (Rossum’s Universal Robots) by Czech playwright Karel Capek.

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ENRICO FERMI (1901- 54)

1942 – USA

Fermi established his reputation with his concept of radioactive beta decay, the theory that a proton could be created from a neutron via the shedding of an electron (a beta particle) and an antineutrino.

The Joliot-Curies had announced their discovery that radioactive isotopes could be generated artificially by showering certain elements with alpha particles in 1934. Fermi realised that the newly discovered neutrons would be even better suited to this purpose as their lack of charge would allow them to slip into elements’ nuclei without resistance.

Fission chain reaction

Fission chain reaction

Fermi established the concept of ‘slow-neutrons’ by placing a piece of solid paraffin in front of the target element during bombardment. Working his way through the elements he created a number of new radioactive isotopes.

He was awarded the 1938 Nobel Prize for physics and later the significance of his work when applied to uranium was realised. Using his neutron-bombarding technique in a series of experiments with 235uranium, Fermi and NIELS BOHR confirmed that a nuclear chain reaction could almost certainly be created as the basis of an atomic bomb.

By Dec 2 1942 his team had created an ‘atomic pile’ of graphite blocks, drilled with uranium, which went on to produce a self-sustaining chain reaction for nearly half an hour.

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WILLARD LIBBY (1908- 80)

1946 – USA

‘Radiocarbon can be used to estimate the age of any organic material. The radioactive isotope of carbon,14C (carbon-14) is present in all living things. When life stops 14C begins to decay. From the rate of decay the age (or time of death) of an organism can be calculated’

The two most common forms of carbon 12C and 13C, make up virtually all types of carbon and are stable – 12C is the simplest form and is made up of 6 protons and 6 neutrons; 13C is slightly heavier because it has one more neutron. 14C, known as radiocarbon has the unstable combination of 6 protons (defining it as carbon) and 8 neutrons.

In the late 1940s Libby led the team at the University of Chicago, USA, that developed radiocarbon dating using the radioactive isotope 14C.

Living things go on absorbing 14C until the time of their death. The half-life of 14C is 5730 years – once an organism dies, 14C begins to decay. As a result the ratio of 12C to 14C changes with time. By measuring this ratio, it can be determined when the organism died.

Libby suggested that minute amounts of radiocarbon come from the upper part of the atmosphere. He put forward the idea that when high-energy particles formed in deep space – cosmic rays – reach the atmosphere, they interact with nitrogen gas to form radiocarbon. He argued that the newly formed radiocarbon is rapidly converted to carbon-dioxide, CO2, and is taken up by plants during photosynthesis; with the result that the radiocarbon enters the food chain. Everything alive should therefore have the same radiocarbon concentration as the atmosphere.

Once an individual dies, some of the 14C atoms begin to disintegrate and give off an electron to reform nitrogen. Libby argued that if the original radiocarbon content is known. it should be possible to measure the remaining 14C in a sample of tissue to back-calculate its age, in a similar way to estimating how much time has passed by measuring the amount of sand left in the top of an egg timer.
By the end of the 1940s, Libby and his team had shown that the radiocarbon content of the air was the same around the world and that 14C could be used to date anything organic.

The crucial principle is the half-life of the unstable atom, the rate at which it will break down. The longer the half-life of a material, the further back in time a dating method can go. With radiocarbon, the dating range is 40,000 to 60,000 years.

When Libby originally measured the half-life of radiocarbon, he calculated it to be just over 5720 years. During the 1950s a new estimate of 5568 years was made by other researchers, who assumed that Libby had got his figures wrong and the 5568-year half-life was adopted by the scientific community.
It is now known that the half-life of radiocarbon is 5730 years, virtually identical to Libby’s original estimate. As a result of the large number of samples that had already been dated, the incorrect value of 5568-years is used in estimates – confusingly this is now termed the ‘Libby half-life’. As all labs use the same half-life value, all ages are directly comparable.

With radiocarbon dating the assumptions made are:

  1. that the atmosphere has had the same 14C content in the past as today
  2. that all things alive have the same radiocarbon content as one-another and as the atmosphere
  3. that no more radiocarbon is added to a sample after death

To obtain a final radiocarbon age, we have to use a point in time to compare against. 1950 is used as year zero and all ages are described relative to this as ‘before present’ (BP). Radiocarbon dating does not give a precise date and estimates are given within a range of uncertainty.

Libby received numerous awards for this work,including the 1960 Nobel Prize for Chemistry. Libby also worked on the Manhattan Project during World War II, helping to enrich the uranium used in the atomic bombs.

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WILLIAM SHOCKLEY (1910- 89)

1947 – USA

‘The First Transistor’

Shockley was a member of the team at Bell Laboratories investigating the properties of electricity conducting crystals, focusing in particular on germanium.
This research led to the development of the junction transistor, virtually invalidating the vacuüm tube overnight.

The First Transistor The transistor was developed in 1947 as a replacement for bulky vacuum tubes and mechanical relays. The invention revolutionized the world of electronics and became the basic building block upon which all modern computer technology rests. In 1956, Bell Labs scientists William Shockley, John Bardeen and Walter Brattain shared the Nobel Prize in Physics for the transistor. Shockley also founded Shockley Semiconductor in Mountain View, California -- one of the first high-tech companies in what would later become known as Silicon Valley. Photo: Bell Labs (581 x 580)

The First Transistor
Photo: Bell Labs

The transistor was developed in 1947 as a replacement for bulky vacuum tubes and mechanical relays. The invention revolutionized the world of electronics and became the basic building block upon which all modern computer technology rests.
In 1956, Bell Labs scientists William Shockley, John Bardeen and Walter Brattain shared the Nobel Prize in Physics for the transistor.

Shockley also founded Shockley Semiconductor in Mountain View, California — one of the first high-tech companies in what would later become known as Silicon Valley.

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