dk-the-science-book_compress

["A PARADIGM SHIFT 249 LIFE ITSELF IS A PROCESS OF OBTAINING KNOWLEDGE KONRAD LORENZ (1903\u20131989) IN CONTEXT A mong the \ufb01rst to conduct These cranes and geese, hatched and scienti\ufb01c experiments on raised by Christian Moullec, imprinted BRANCH the behavior of animals on him and follow him everywhere. Biology was 19th-century English biologist Taking to the air in his microlight, he Douglas Spalding, who studied teaches them their migratory routes. BEFORE birds. The prevailing view was that 1872 Charles Darwin complex behavior in birds was mother\u2014within a critical period describes inherited behavior learned, but Spalding thought that after hatching. The mother\u2019s in The Expression of the some behavior was innate: it example triggers an instinctive Emotions in Man and Animals. was inherited and essentially behavior known as a \u201c\ufb01xed action \u201chardwired\u201d\u2014such as the tendency pattern\u201d in her offspring. 1873 Douglas Spalding of a hen to incubate her eggs. makes a distinction between Lorenz demonstrated this with innate (genetic) and learned Modern ethology\u2014the study goslings, which adopted him as behavior in birds. of animal behavior\u2014accepts that their mother and followed him behavior includes both learned and everywhere. They would even 1890s Russian physiologist innate components: innate imprint on inanimate objects, and Ivan Pavlov demonstrates behavior is stereotypical and, followed a model train in circles that dogs can be conditioned because it is inherited, it can on its track. Together with Dutch to salivate in a simple form evolve by natural selection, whereas biologist Nikolaas Tinbergen, of learning. learned behavior can be modi\ufb01ed Lorenz was awarded the Nobel by experience. Prize in Physiology in 1973. \u25a0 AFTER 1976 British zoologist Imprinting geese Richard Dawkins publishes In the 1930s, Austrian biologist The Sel\ufb01sh Gene, in which he Konrad Lorenz focused on a form of emphasizes the role of genes learned behavior in birds that he in driving behavior. called \u201cimprinting.\u201d He studied the way that greylag geese imprint on, 2000s New research reveals or follow, the \ufb01rst eligible moving growing evidence of the stimulus they see\u2014usually their importance of teaching among many species of animal, from See also: Charles Darwin 142\u201349 \u25a0 Gregor Mendel 166\u201371 \u25a0 insects to killer whales. Thomas Hunt Morgan 224\u201325","250 95 PERCENT OF THE UNIVERSE IS MISSING FRITZ ZWICKY (1898\u20131974) IN CONTEXT T he idea that the universe A decade later, Zwicky set out to might be dominated by measure the overall mass of the BRANCH something other than Coma cluster of galaxies. He used Physics and cosmology detectable luminous matter was a mathematical model called the \ufb01rst proposed by Swiss astronomer Virial theorem, which allowed him BEFORE Fritz Zwicky. In 1922\u201323, Edwin to calculate the overall mass from 1923 Edwin Hubble con\ufb01rms Hubble had realized that \u201cnebulae\u201d the relative velocities of individual the true nature of galaxies were in fact distant galaxies. cluster galaxies. To Zwicky\u2019s as independent star systems millions of light years beyond The universe The outer regions of galaxies rotate the Milky Way. is expanding more quickly than their visible mass 1929 Hubble establishes that at an ever suggests they should. the universe is expanding, and increasing rate. that galaxies move away from us more rapidly the farther Expansion is So they must have additional, hidden, away they are (the so-called caused by dark mass that would explain their rotation. Hubble Flow). energy, which This additional mass is known as AFTER accounts for dark matter, and accounts for 1950s American astronomer 68.3 percent George Abell compiles the \ufb01rst of all energy. 26.8 percent of all energy. detailed catalogue of galaxy clusters. Subsequent studies Just 4.9 percent of the universe\u2019s energy is accounted for of galaxy clusters have by visible matter. repeatedly con\ufb01rmed the existence of dark matter. 1950s\u2013present Various models of the Big Bang predict that it should have generated much more matter than that which is currently visible.","A PARADIGM SHIFT 251 See also: Edwin Hubble 236\u201341 \u25a0 Georges Lema\u00eetre 242\u201345 Rotational velocity Measured [km\/s] Calculated 200 100 50,000 100,000 Distance from center of galaxy (light years) If our galaxy\u2019s mass distribution matched that of its visible matter, Fritz Zwicky then stars in the galaxy\u2019s outer disk would move more slowly at greater distances from the massive center. Vera Rubin\u2019s research found that beyond Born in Varna, Bulgaria, in a certain distance the stars tend to move at a uniform speed regardless of 1898, Fritz Zwicky was raised their distance from the hub, revealing dark matter in the galaxy\u2019s outer halo. by his Swiss grandparents and showed an early talent for surprise, his results suggested Today it is widely accepted that physics. In 1925, he left for the that the cluster contained about dark matter constitutes around US to work at the California 400 times more mass than that 84.5 percent of the mass in the Institute of Technology suggested by the combined light universe. Any hopes that it might (Caltech), where he spent of its stars. Zwicky called this actually be normal matter in hard- the rest of his career. staggering amount of unseen to-detect forms, such as black holes matter \u201cdark matter.\u201d or rogue planets, have not been Aside from his work on borne out by research. It is now dark matter, Zwicky is also Zwicky\u2019s conclusion was largely thought that dark matter comprises known for his research into overlooked at the time, but by the so-called Weakly Interacting massive exploding stars. He 1950s, new technology had opened Massive Particles (WIMPs). The and Walter Baade were the up new means of detecting properties of these hypothetical \ufb01rst to show the existence of nonluminous material. It was clear subatomic particles are still neutron stars intermediate in that large amounts of matter are unknown\u2014they are not only dark size between white dwarfs too cool to glow in visible light but and transparent, but they do not and black holes, and coined still radiate in infrared and radio interact with normal matter or the term \u201csupernovae\u201d for the wavelengths. As scientists began radiation except through gravity. enormous stellar explosions to understand the visible and in which these massive invisible structure of our galaxy Since the late 1990s, it has stellar remnants are born. and others, the amount of \u201cmissing become clear that even dark By showing that one class mass\u201d fell substantially. matter is dwarfed by \u201cdark energy.\u201d of supernovae always reach This phenomenon is the force the same peak brightness The invisible is real accelerating the expansion of the during their explosions, they The reality of dark matter was universe (pp.236\u201341), and its nature also provided a means of \ufb01nally recognized in the 1970s, is still unknown\u2014it may be an measuring the distance to after US astronomer Vera Rubin integral feature of space-time itself, far-off galaxies independently mapped the velocity of stars orbiting or a \ufb01fth fundamental force known of Hubble\u2019s Law, paving the in the Milky Way and measured as \u201cquintessence.\u201d Dark energy is way for the later discovery the distribution of its mass. She thought to account for 68.3 percent of dark energy. showed that large amounts of of all the energy in the universe, mass are distributed beyond the with the energy of dark matter Key works galaxy\u2019s visible con\ufb01nes, in a amounting to 26.8 percent, and region known as the galactic halo. normal matter a mere 4.9 percent. \u25a0 1934 On Supernovae (with Walter Baade) 1957 Morphological Astronomy","252 A UNIVERSAL COMPUTING MACHINE ALAN TURING (1912\u20131954) IN CONTEXT Computing the A Turing machine answers to many number can, with the right BRANCH problems can be reduced instructions, compute Computer science to a series of mathematical the solution to any solvable algorithm. BEFORE steps, or algorithm. 1906 US electrical engineer Lee De Forest invents the This is a universal Varied tasks triode valve, the mainstay of computing machine. can be solved using early electronic computers. different sets of instructions in a programmable 1928 German mathematician David Hilbert formulates the device. \u201cdecision problem,\u201d asking if algorithms can deal with all I magine sorting 1,000 random This set of instructions is a kinds of input. numbers, for example 520, 74, sequence known as an algorithm. 2395, 4, 999\u2026, into ascending It begins with a starting condition AFTER order. Some kind of automatic or state; receives data or input; 1943 Valve-based Colossus procedure could help. For instance: executes itself a \ufb01nite number of computers, using some of A Compare the \ufb01rst pair of numbers. times; and yields a \ufb01nished result, Turing\u2019s code-breaking ideas, B If the second number is lower, or output. The idea is familiar to begin work at Bletchley Park. swap the numbers, go back to A. any computer programmer today. If it is the same or higher, go to C. It was \ufb01rst formalized in 1936, 1945 US-based mathematician C Make the second number of the when British mathematician and John von Neumann describes last pair the \ufb01rst of a new pair. If logician Alan Turing conceived the basic logical structure, or there is a next number, make it the of machines now known as architecture, of the modern second number of the pair, go to B. Turing machines to perform such stored-program computer. If there is no next number, \ufb01nish. procedures. His work was initially 1946 The \ufb01rst general-purpose electronic programmable computer, ENIAC, based partly on Turing\u2019s concepts, is unveiled.","A PARADIGM SHIFT 253 See also: Donald Michie 286\u201391 \u25a0 Yuri Manin 317 theoretical\u2014an exercise in logic. capable of being taken out and Alan Turing He was interested in reducing a exchanged for others and we have numbers task to its simplest, most something very akin to a universal Born in London in 1912, Turing basic, automatic form. computing machine.\u201d showed a prodigious talent for mathematics at school. He The a-machine Now known as the Universal earned a \ufb01rst class degree in To help envisage the situation, Turing Machine (UTM), this device mathematics from Kings Turing conceived a hypothetical had an in\ufb01nite store (memory) College, Cambridge, in 1934, machine. The \u201ca-machine\u201d (\u201ca\u201d for containing both instructions and and worked on probability automatic) was a long paper tape data. The UTM could therefore theory. From 1936 to 1938, he divided into squares, with one simulate any Turing machine. What studied at Princeton University number, letter, or symbol in each Turing called changing the rules in the US, where he proposed square, and a read\/print tape head. would now be called programming. his theories about a generalized With instructions in the form of a In this way, Turing \ufb01rst introduced computing machine. table of rules, the tape head reads the concept of the programmable the symbol of the square it sees, computer, adaptable for many During World War II, Turing and alters it by erasing and printing tasks, with input, processing of designed and helped build a another, or leaves it alone, as per information, and output. \u25a0 fully functioning computer the rules. It then moves to one known as the \u201cBombe\u201d to square either to the left or right, A computer would deserve crack German codes made by and repeats the procedure. Each to be called intelligent if it the so-called Enigma machine. time there is a different overall could deceive a human into Turing was also interested in con\ufb01guration of the machine, believing that it was human. quantum theory, and shapes with a new sequence of symbols. and patterns in biology. In Alan Turing 1945, he moved to the National The whole process can be Physics Laboratory in London, compared to the number-sorting then to Manchester University algorithm above. This algorithm is to work on computer projects. constructed for one particular task. In 1952, he was tried for Similarly, Turing envisaged a range homosexual acts (then illegal), of machines, each with a set of and two years later died from instructions or rules for a particular cyanide poisoning\u2014it seems undertaking. He added, \u201cWe have likely this was by suicide only to regard the rules as being rather than by accident. In 2013, Turing was granted 10 - 11100110 - 100 a posthumous pardon. Read\/print tape head Key work State register Action table 1939 Report on the Applications A Turing machine is a mathematical model of a computer. of Probability to Cryptopgraphy The head reads a number on the in\ufb01nitely long tape, writes a new number on it, and moves left or right according to rules contained in the action table. The state register keeps track of the changes and feeds this input back into the action table.","THE NATURE BONDOF THE CHEMICAL LINUS PAULING (1901\u20131994)","","256 LINUS PAULING IN CONTEXT I n the late 1920s and early Electron orbits 1930s, in a series of landmark BRANCH papers, American chemist y Chemistry Linus Pauling \ufb01gured out a z quantum-mechanical explanation BEFORE of the nature of chemical bonds. x x 1800 Alessandro Volta lists Pauling had studied quantum px orbital metals in decreasing order mechanics in Europe with the s orbital of electropositivity. German physicist Arnold y z Sommerfeld in Munich, with Niels 1852 British chemist Edward Bohr in Copenhagen, and with py orbital pz orbital Frankland states that atoms Erwin Schr\u00f6dinger in Zurich. have de\ufb01nite combining He had already decided that he Electrons orbit an atomic nucleus in power, which determines the wanted to research the bonding various ways\u2014in shells around the formulae of compounds. within molecules, and realized that center (s) or lobes along one axis (p). quantum mechanics gave him the 1858 August Kekul\u00e9 shows right tools to do so. A carbon atom has six electrons that carbon has a valency in total. The European pioneers of of four\u2014it forms four bonds Hybridization of orbitals quantum mechanics designated with other atoms. When he returned to the US, the \ufb01rst two as \u201c1s-electrons\u201d: Pauling published about 50 papers, these have a spherical orbital or 1916 American physical and, in 1929, he laid down a set shell around the carbon nucleus\u2014 chemist Gilbert Lewis shows of \ufb01ve rules for interpreting the like a balloon in\ufb02ated around a that a covalent bond is a pair X-ray diffraction patterns of golf ball in the center. Outside the of electrons shared by two complicated crystals, now known 1s shell is another shell containing atoms in a molecule. as Pauling\u2019s rules. At the same two \u201c2s-electrons.\u201d The 2s shell time, he was turning his attention is like another, bigger balloon AFTER to the bonding between atoms in outside the \ufb01rst. Lastly, there are 1938 British mathematician covalent molecules (molecules in \u201cp-orbitals,\u201d which have big lobes Charles Coulson calculates which atoms are bonded by sharing sticking out either side of the an accurate molecular orbital two electrons with each other), nucleus. The px orbital lies on the wave function for hydrogen. especially of organic compounds\u2014 x-axis, the py on the y axis, and those based on carbon. the pz orbital on the z-axis. The last two electrons of the carbon atom Quantum mechanics It can be modi\ufb01ed occupy two of these orbitals\u2014 provides a new way to to explain the structure perhaps one in px and one in py. describe the behavior of molecules. The new quantum-mechanical of electrons. picture of electrons treated their orbits as \u201cclouds\u201d of probability The nature of the densities. It was no longer quite chemical bond re\ufb02ects the right to think of the electrons as points moving around their orbits; quantum-mechanical rather, their existence was smeared behavior of electrons. across the orbits. This new nonlocal picture of reality allowed for some radical new ideas for chemical","A PARADIGM SHIFT 257 See also: August Kekul\u00e9 160\u201365 \u25a0 Max Planck 202\u201305 \u25a0 Erwin Schr\u00f6dinger 226\u201333 \u25a0 Harry Kroto 320\u201321 bonding. Bonds could either be By 1935, I felt I had an Diamond is pure carbon, and in strong \u201csigma\u201d bonds, in which essentially complete the crystal each carbon atom orbitals overlap head-on, or weaker, understanding of the nature is bonded to four others by more diffuse \u201cpi\u201d bonds, in which of the chemical bond. sigma bonds at the corners of orbitals are parallel to each other. a tetrahedron. This structure Linus Pauling explains diamond\u2019s hardness. Pauling came up with the idea that in a molecule, as opposed to a compounds were studied, the four Another possible way for carbon bare atom, carbon\u2019s atomic orbitals closest neighboring atoms were atoms to bond to other atoms is could combine, or \u201chybridize,\u201d often found in a tetrahedral for an s-orbital to mix with two to give stronger bonds to other arrangement. The crystal structure p-orbitals to form three sp2 hybrids. atoms. He showed that the s and p of diamond was among the \ufb01rst These stick out from the nucleus orbitals could hybridize to form structures to be resolved by in one plane, with angles of 120\u00b0 four sp3 hybrids, which would all be X-ray crystallography, in 1914. between them. This is consistent equivalent, and would project from with the geometry of molecules the nucleus toward the corners of a such as ethylene, which has the tetrahedron, with inter-bond angles double-bond structure H2C=CH2. of 109.5\u00b0. Each sp3 orbital can form Here, a sigma bond is formed a sigma bond with another atom. between the carbon atoms by one This is consistent with the fact of the sp2 hybrids, and a pi bond by that all the hydrogen atoms in the fourth, unhybridized orbital. methane (CH4), and all the chlorine atoms in carbon tetrachloride Lastly, an s-orbital can mix with (CCl4), behave the same way. one p-orbital to form two sp hybrids, As the structures of various carbon whose lobes stick out in a straight line, 180\u00b0 apart. This is consistent \u276f\u276f Methane Ethylene Diamond H H H CH pi bond H C sigma bond C H Four electrons in the HH carbon atom hybridize to form four sp3 orbitals. Three electrons in the carbon atoms hybridize to form three sp2 orbitals. The remaining pi bond unhybridized orbitals form a second pi bond O sigma bond C between the carbon atoms. Carbon dioxide Two electrons in Each carbon atom in a diamond O the carbon atom form is bonded by sp3 hybrids to four two sp orbitals, each other atoms to form the corner of which bonds with of a tetrahedron. The result is an an oxygen atom. in\ufb01nite lattice held together by The remaining two covalent carbon\u2013carbon bonds, orbitals bond to the which are immensely strong. oxygen in a pi bond.","258 LINUS PAULING with the structure of carbon Ionic bonding dioxide (CO2), where the sp hybrids each form a sigma bond with the oxygen, and a second pi bond is formed by the remaining two unhybridized orbitals. A new structure of benzene Sodium ion Chloride ion The structure of benzene, C6H6, had Na+ Cl- worried August Kekul\u00e9 when he \ufb01rst proposed that it was a ring, In sodium chloride, an electron in the sodium Lattice more than 60 years earlier. He atom moves into a chlorine atom to form two eventually suggested that the charged, stable ions. The ions are held together carbon atoms must be connected by electrostatic attraction to form a stable lattice. with alternate single and double bonds, and that the molecule Benzene ring oscillated between the two equivalent structures (p.164). H H H H H H H H Pauling\u2019s alternative solution was elegant. He said that the H H H H carbon atoms were all sp2 hybridized, so that the bonds H H H H between them and the hydrogen H H atoms all lie in the same xy plane and form an angle of 120\u00b0 with each sp2 hybridized orbitals 6 pz orbitals Pi bond other. Each carbon atom has one remaining electron in a pz orbital. In a benzene ring, the carbon atoms are bonded These electrons combine to form to each other and a hydrogen atom by sp2 hybridized a bond connecting all six carbon orbitals. The rings are bonded to each other by atoms. This is a pi bond, and, in it, the electrons remain above and a nonlocalized pi-bond formed from the six pz orbitals. below the ring, and away from the carbon nuclei (see right). their weight, but by their structure. electron outside that. The chlorine Benzene is held together in single atom is one electron short of a Ionic bonding molecules by covalent bonds stable complete shell. When they Methane and ethylene are gases between the atoms; that is, react, an electron is transferred at room temperature. Benzene and each bond comprises one pair from the sodium atom to the many other organic compounds of electrons shared between chlorine atom, and both acquire based on carbon are liquids. They two speci\ufb01c atoms. stable complete shells of electrons, have small, lightweight molecules but now the sodium has become a that can easily move around in the Sodium chloride has quite sodium ion Na+, and chlorine has gas or liquid state. Salts such as different properties. The silvery become the chloride ion Cl- (see calcium carbonate and potassium metal sodium burns energetically above). They have no spare nitrate, by contrast, are almost in the greenish gas chlorine to electrons to form covalent bonds, invariably solids, and melt only produce the white solid sodium but the ions are now charged: the at high temperatures. And yet a chloride. The sodium atom has a sodium atom has lost a negatively unit of sodium chloride (NaCl) has stable complete shell of electrons charged electron so now has a a molecular weight of 62, while around the nucleus, plus one spare benzene has a molecular weight of 78. The difference in their behavior is explained not by","There is no area of the world to some extent echoed the list of A PARADIGM SHIFT 259 that should not be investigated metals in decreasing order of electropositivity \ufb01rst introduced by Linus Pauling by scientists. There will Alessandro Volta in 1800. Pauling always remain some questions discovered that the covalent bond Linus Carl Pauling was born that have not been answered. formed between atoms of two in Portland, Oregon, US. He different elements (e.g. C\u2013O) is \ufb01rst heard about quantum In general, these are the stronger than might be expected mechanics while still in questions that have not yet from the average of the strengths Oregon, and won a scholarship of C\u2013C bonds and O\u2013O bonds. He to study the subject under been posed. thought that there must be some some of the world experts in Linus Pauling electrical factor that strengthened Europe in 1926. He returned the bond, and set out to calculate to become assistant professor positive overall charge; the chlorine values for this factor. The scale is at California Institute of atom has gained an electron and has now known as the Pauling scale. Technology, where he a negative charge. The ions are held remained for most of his life. together by electrostatic attraction, The electronegativity of an plus to minus\u2014a strong bond. element (strictly speaking in Pauling took great interest a particular compound) is a in biological molecules, Sodium chloride was the \ufb01rst measure of how strongly an and he discovered that compound to be analyzed by X-ray atom of the element attracts sickle-cell anemia is a crystallography. It was found that electrons toward itself. The molecular disease. He was in reality there is no such thing most electronegative element is also a peace campaigner, and as a molecule of NaCl. The \ufb02uorine; the least electronegative was awarded the Nobel Peace structure comprises an in\ufb01nite (or the most electropositive) Prize in 1963 for attempting array of alternating sodium and of the well-known elements is to mediate between the chloride ions. Each sodium ion is cesium. In the compound cesium US and Vietnam. surrounded by six chloride ions, \ufb02uoride, each \ufb02uorine atom pulls and each chloride is surrounded an electron entirely away from In later life, his reputation by six sodiums. Many other salts a cesium atom, resulting in an was damaged as a result of have similar structures: in\ufb01nite ionic compound Cs+F-. his enthusiasm for alternative lattices of one type of ion with medicine. He championed the different ions \ufb01lling all the gaps. In a covalent compound such use of high-dose vitamin C as as water (H2O), there are no a defense against the common Electronegativity ions, but oxygen is much more cold, a treatment that has Pauling explained ionic bonding electronegative than hydrogen, subsequently been shown in compounds such as sodium and the result is that the water to be ineffective. chloride, which is purely ionic, molecule is polar, with a small and also compounds in which negative charge on the oxygen Key work the bonding is neither purely atom and a small positive charge ionic nor purely covalent but on the hydrogen atoms. The 1939 The Nature of somewhere in between. This charges make the water molecules the Chemical Bond and the work led him to develop the stick together strongly. This Structure of Molecules concept of electronegativity, which explains why water has so much and Crystals surface tension and such a high boiling point. Pauling \ufb01rst proposed a scale of electronegativity in 1932, and he and others developed it further in subsequent years. For his work elucidating the nature of the chemical bond, he won the Nobel Prize in Chemistry in 1954. \u25a0","AN AWESOME POWER IS LOCKED INSIDE THE NUCLEUS OF AN ATOM J. ROBERT OPPENHEIMER (1904\u20131967)","","262 J. ROBERT OPPENHEIMER IN CONTEXT Splitting the nucleus of an atom of uranium releases three neutrons.\u00a0 BRANCH Physics The three released neutrons can cause the nuclei of up to three more atoms to split, but if at least one splits, a BEFORE chain reaction can be initiated. 1905 Albert Einstein\u2019s famous mass-energy equivalence Each time a nucleus is split, a fraction of its mass is equation E = mc2 describes turned into energy.\u00a0 how tiny masses \u201cstore\u201d large amounts of energy. The chain reaction The chain reaction can can be controlled by be uncontrolled, releasing 1932 John Cockcroft and enough energy to cause an Ernest Walton\u2019s experiments absorbing neutrons explosion (nuclear bomb). splitting lithium nuclei (nuclear \ufb01ssion reactor). with protons hint at the enormous energy locked An awesome power is locked inside the inside the nucleus. nucleus of an atom. 1939 Le\u00f3 Szil\u00e1rd spots that a single \ufb01ssion event of uranium-235 releases three neutrons and suggests that a chain reaction is possible. AFTER 1954 The USSR\u2019s Obninsk Nuclear Power Plant goes into operation. It is the \ufb01rst nuclear power station to generate electricity for a country\u2019s national grid. I n 1938, the world stood at the and this compulsion took the newly to be computed. Oppenheimer\u2019s threshold of the atomic age. graduated Harvard man to Europe, work in Germany has proved One man would step forward the center of a blossoming of crucial to calculating energy in to lead the scienti\ufb01c drive that theoretical physics. At G\u00f6ttingen modern chemistry, but the \ufb01nal would usher in this new era. For J. University, Germany, in 1926, he breakthrough that would lead to Robert Oppenheimer, this decision produced the Born\u2013Oppenheimer the atomic bomb came after he would ultimately destroy him. He approximation with Max Born, had returned to the US. was the administrator of the largest used to explain, as Oppenheimer scienti\ufb01c project the world had put it, \u201cwhy molecules are Fission and black holes seen\u2014the Manhattan Project\u2014but molecules.\u201d This method extended The chain reaction that led to the came to deeply regret his part in it. quantum mechanics beyond single building of the atomic bomb began atoms to describe the energy of in mid-December 1938, when Drive to the center chemical compounds. It was an German chemists Otto Hahn and Oppenheimer\u2019s varied professional ambitious mathematical exercise Fritz Strassmann \u201csplit the atom\u201d life had been characterized by a as a dizzying range of possibilities in their Berlin laboratory. They had ruthless drive to \u201cbe where it\u2019s at\u201d for each electron in a molelcule had been \ufb01ring neutrons at uranium,","A PARADIGM SHIFT 263 See also: Marie Curie 190\u201395 \u25a0 Ernest Rutherford 206\u201313 \u25a0 Albert Einstein 214\u201321 We knew the world would not John Archibald Wheeler at 92 protons and 146 neutrons. The be the same. A few people Princeton after the annual remaining 0.7 percent is made up laughed. A few people cried. Theoretical Physics Conference, of uranium-235 (U-235), whose Most people were silent. I led to the Bohr\u2013Wheeler theory nuclei contain 92 protons and remembered the line from of nuclear \ufb01ssion. 143 neutrons. The Bohr\u2013Wheeler the Hindu scripture: \u201cNow theory incorporated the \ufb01nding that I am become Death, the All the atoms of the same low-energy neutrons could cause destroyer of worlds.\u201d element have nuclei with the same \ufb01ssion in U-235, causing the atom J. Robert Oppenheimer number of protons in them, but to split and releasing energy in the number of neutrons can vary, the process. making different isotopes of the same element. In the case of When the news reached the uranium, there are two naturally West Coast, Oppenheimer, now at occurring isotopes. Uranium-238 Berkeley, was captivated. He gave (U-238) makes up 99.3 percent of a series of lectures and seminars on natural uranium. Its nuclei contain the brand new theory and quickly \u276f\u276f Uranium-235 but instead of creating heavier Barium elements by neutron absorption, or lighter elements by emission Krypton of one or more nucleons (protons or neutrons), the pair found that Neutron the lighter element barium was released, which had 100 fewer This one nucleons than the uranium nucleus. neutron starts No nuclear process understood at the time could account for the loss the chain of 100 nucleons. reaction Perplexed, Hahn sent a letter to The nuclear \ufb01ssion of uranium-235 colleagues Lise Meitner and Otto (U-235) is started when a neutron Frisch in Copenhagen. Within the hits a U-235 nucleus. The uranium month, Meitner and Frisch had atom splits to form an atom of barium \ufb01gured out the basic mechanism (Ba), an atom of krypton (Kr), and three of nuclear \ufb01ssion, recognizing how more neutrons. The three neutrons can uranium was split into barium and then go on to cause \ufb01ssion in more krypton, the missing nucleons were atoms, causing a chain reaction. Each converted into energy, and a chain time an atom splits, energy is released. reaction could follow. In 1939, Danish physicist Niels Bohr took the news to the US. His account, along with the publication of the Meitner\u2013Frisch paper in the journal Nature, set the East Coast scienti\ufb01c community ablaze with excitement. Conversations between Bohr and","264 J. ROBERT OPPENHEIMER saw the potential for making a realize the horri\ufb01c consequences We have made a thing, a most weapon of awesome power\u2014to his for a world heading toward war. terrible weapon, that has mind \u201ca good, honest, practical Pondering Rutherford\u2019s lecture, way\u201d to use the new science. But Szil\u00e1rd saw that the \u201csecondary altered abruptly and profoundly while laboratories in East Coast neutrons\u201d emerging from the \ufb01rst the nature of the world. And universities raced to replicate the \ufb01ssion event could themselves by so doing we have raised results of early \ufb01ssion experiments, create further \ufb01ssion events, again the question of whether Oppenheimer concentrated on his resulting in an escalating chain science is good for man. research into stars contracting and reaction of nuclear \ufb01ssion. Szil\u00e1rd J. Robert Oppenheimer collapsing under their own gravity later recalled, \u201cThere was little to form black holes. doubt in my mind that the world smaller facilities, it employed was headed for grief.\u201d 130,000 people and by its close had Birth of the idea swallowed in excess of US$2 billion The idea of a nuclear weapon was Experiments in Germany and (more than US$26 bn, or \u00a316 bn, in already in the air. As early as 1913, the US showed that the chain 2014 money)\u2014all in top secrecy. H. G. Wells wrote of \u201ctapping the reaction was indeed possible, internal energy of atoms\u201d to make prompting Szil\u00e1rd and another Early in 1941, the decision \u201catomic bombs.\u201d In his novel The Hungarian emigr\u00e9, Edward Teller, was taken to pursue \ufb01ve World Set Free, the innovation to approach Albert Einstein with separate methods of producing was set to happen in the year 1933. a letter. Einstein passed the letter \ufb01ssionable material for a bomb: In 1933 itself, Ernest Rutherford on to US President Roosevelt on electromagnetic separation, touched on the large amount of October 11, 1939 and just ten days gaseous diffusion, and thermal energy released during nuclear later the Advisory Committee on diffusion to separate isotopes of \ufb01ssion in a speech printed in Uranium was set up to investigate uranium-235 from uranium-238; The Times of London. However, the possibility of developing the and two lines of research into Rutherford dismissed the idea bomb in the United States \ufb01rst. of harnessing this energy as \u201cmoonshine,\u201d since the process Birth of Big Science was so inef\ufb01cient it required much The Manhattan Project that arose more energy than it released. from this resolution was science on the grandest scale imaginable. It took a Hungarian living in A multiarmed organization that Britain named Le\u00f3 Szil\u00e1rd to see spread over several large sites in how it could be done, and also to the US and Canada and countless J. Robert Oppenheimer Educated at the Ethical Culture had a notoriously sharp tongue school of New York City, Julius and a desire to be regarded as Robert Oppenheimer was a a superior intellect. Although thin, highly-strung boy with a he is best known for his work on quick grasp of concepts. After the Manhattan Project, his most graduating from Harvard lasting contribution to science University, he spent two years was his prewar research at at Cambridge University under the University of California, Ernest Rutherford, followed by a Berkeley, on neutron stars and move to G\u00f6ttingen in Germany, black holes. where he was taken under the wing of Max Born. Key works Oppenheimer was a complex 1927 On the Quantum character whose great talent Theory of Molecules was to be at the center of things, 1939 On Continued and he made in\ufb02uential friends Gravitational Contraction wherever he went. However, he","A PARADIGM SHIFT 265 On August 9, 1945, the plutonium bomb \u201cFat Man\u201d was dropped over Nagasaki in southern Japan. About 40,000 people were killed instantly, and many more died in the following weeks. nuclear reactor technology. On December 2, 1942, the very \ufb01rst controlled chain reaction involving nuclear \ufb01ssion was carried out on a squash court at the University of Chicago. Enrico Fermi\u2019s Chicago Pile-1 was the prototype for the reactors that would enrich uranium and create the newly discovered plutonium\u2014an unstable element that is even heavier than uranium, can also cause a rapid chain reaction, and can be used to create an even deadlier bomb. The Magic Mountain Alamos director. Germany had In October 1945, Oppenheimer met Selected to head up the Manhattan already surrendered by the time President Harry S. Truman and told Project\u2019s research into secret the bomb was dropped, and many him, \u201cI feel I have blood on my weapons, Oppenheimer approved Los Alamos scientists felt a public hands.\u201d Truman was furious. a disused boarding school at Los demonstration of the bomb was all Congressional hearings stripped Alamos Ranch in New Mexico that was necessary\u2014after seeing the scientist of his security as the site for research facilities its awesome power, Japan would clearance in 1954, ending his for the project\u2019s \ufb01nal stages\u2014the be sure to surrender. However, ability to in\ufb02uence public policy. construction of an atomic bomb. while Hiroshima was believed by \u201cSite Y\u201d would see the highest some to be a necessary evil, the By then, Oppenheimer had concentration of Nobel laureates detonation of a plutonium device\u2014 overseen the advent of the ever gathered in one place. called \u201cFat Man\u201d\u2014over Nagasaki military\u2013industrial complex and on August 9 was hard to justify. ushered in a new era of Big Since much of the important A year later, Oppenheimer publicly Science. In presiding over the science had already been done, stated his opinion that the atom creation of a new scienti\ufb01c terror, many of the Los Alamos scientists bombs had been dropped on a he became a symbol for the moral dismissed their work in the New defeated enemy. consequences of their actions that Mexico desert as merely a \u201cproblem scientists must now consider. \u25a0 of engineering.\u201d However, it was Oppenheimer\u2019s coordination of 3,000 scientists that made the construction of the bomb possible. Change of heart The successful Trinity test on July 16, 1945 and subsequent detonation of a bomb called \u201cLittle Boy\u201d above Hiroshima in Japan on August 6, 1945 left Oppenheimer jubilant. However, the event was to cast a long shadow over the Los","FUNDAME BUILDIN BLOCKS 1945\u2013PRESENT","NTAL G","268 INTRODUCTION Fred Hoyle describes Barbara McClintock James Watson and Sheldon Glashow how new elements demonstrates genetic Francis Crick discover presents a new are made in stars. symmetry model for recombination, the chemical electroweak showing how genes structure interactions. can move around on of DNA. a chromosome. 1946 1951 1953 1961 1948 1953 1957 1961 Richard Feynman works Harold Urey and Stanley Hugh Everett III is Charles Keeling on the new discipline Miller demonstrate a the \ufb01rst to propose shows that the of quantum possible chemical the many-worlds concentration of electrodynamics. mechanism for the carbon dioxide in the origin of life. interpretation air is increasing. (MWI) of quantum physics. T he second half of the The code of life proposed the apparently absurd 20th century saw rapidly At the University of Chicago theory that some organisms can improving technology in 1953, American chemists be absorbed by others, while both being employed in almost every Harold Urey and Stanley Miller continue to \ufb02ourish, and that this \ufb01eld of science, from telescopes to set up an ingenious experiment process had produced the complex chemical analysis. New technology to \ufb01nd out whether life could have cells of all multicellular life forms. has widened the possibilities started on Earth when lightning After years of scepticism, she for calculation and experiment. sparked chemical reactions in was vindicated by discoveries in The \ufb01rst computers were built the atmosphere. In the same genetics made 20 years after her in the 1940s, and a new science, year, two molecular biologists\u2014 proposal. American microbiologist Arti\ufb01cial Intelligence, has emerged. American James Watson and Briton Michael Syvanen showed how CERN\u2019s Large Hadron Collider\u2014a Francis Crick\u2014in a race against genes can jump from one species particle accelerator\u2014is the biggest rival teams in the US and Soviet to another, while in the 1990s, the piece of scienti\ufb01c equipment ever Union, \ufb01gured out the molecular old Lamarckian idea that acquired made. Powerful microscopes have structure of deoxyribonucleic acid, characteristics can be passed allowed the \ufb01rst direct glimpses or DNA, providing the key to the on gained new traction with of atoms, while new telescopes genetic code of life, which would the discovery of epigenetics. have revealed planets beyond our lead less than half a century later Knowledge of the mechanisms solar system. By the 21st century, to the complete mapping of the by which evolution can take place science has become largely a human genome. was becoming far richer. team activity, involving ever more expensive apparatus and Armed with new knowledge By the end of the century, interdisciplinary cooperation. about the genetic mechanism, American Craig Venter, fresh from American biologist Lynn Margulis running his own human genome","FUNDAMENTAL BUILDING BLOCKS 269 Peter Higgs suggests Lynn Margulis Yuri Manin suggests Craig Venter claims that there is a shocks her colleagues the idea of quantum to be able to design fundamental particle with the idea of computing. synthetic responsible for mass. endosymbiosis, in life forms. which whole organisms are absorbed by others. 1964 1967 1980 2010 2012 1964 1974 1985 Murray Gell-Mann puts Stephen Hawking Michael Syvanen says The Higgs boson is forward the idea of shows that black holes that genes can move detected by CERN. quarks, leading to the emit low-level from one species standard model of radiation. to another. particle physics. project, had created arti\ufb01cial life by fundamental particles of nature the three of space and one of planning its DNA on his computer. according to their properties. time. American physicist Hugh In Scotland, after many setbacks, Not all physicists were convinced, Everett III suggested that there Ian Wilmut and colleagues had but the power of the standard may be a mathematical basis for succeeded in cloning a sheep. model received a huge boost in the existence of more than one 2012 when the Higgs boson it universe. Everett\u2019s theory of a New particles had predicted was detected by constantly splitting multiverse In physics, the strangeness of CERN\u2019s Large Hadron Collider. was at \ufb01rst ignored, but has gained quantum mechanics was further supporters over the last few years. explored by American Richard Meanwhile, the search for Feynman and others, who a \u201ctheory of everything\u201d\u2014a Future directions explained quantum interactions theory that would unite all four Deep puzzles remain to be solved, in terms of exchange of \u201cvirtual\u201d fundamental forces of nature including an elusive theory that particles. Paul Dirac had correctly (gravity, electromagnetism, and would unite quantum mechanics predicted the existence of the strong and weak nuclear with general relativity. But antimatter in the 1930s, and forces)\u2014took many new directions. tantalizing possibilities are also in subsequent decades, more American Sheldon Glashow opening up, including a potential new subatomic particles emerged united electromagnetism with revolution in computing courtesy from the collisions of ever more the weak nuclear force into one of the quantum mechanical qubit. powerful particle colliders. From \u201celectroweak\u201d theory, while It is probable that new problems we this menagerie of exotic particles, string theory attempted to unite cannot even imagine will emerge. the standard model of particle every theory of physics into one If the history of science is a guide, physics emerged, arranging the by proposing the existence of six we should expect the unexpected. \u25a0 hidden dimensions in addition to","270 WE ARE MADE OF STARDUST FRED HOYLE (1915\u20132001) IN CONTEXT T he idea that stars generate Between 1946 and 1957, British energy through the process astronomer Fred Hoyle and others BRANCH of nuclear fusion was \ufb01rst developed Bethe\u2019s ideas to show Astrophysics proposed by British astronomer how further fusion reactions Arthur Eddington in 1920. Stars, involving helium could generate BEFORE he argued, were factories for fusing carbon and heavier elements up 1854 German physicist nuclei of hydrogen into helium. to and including the mass of iron. Hermann von Helmholtz A helium nucleus contains slightly This explained the origin of many suggests that the Sun less mass than the four hydrogen of the universe\u2019s heavier elements. generates heat through slow nuclei required to create it. This We now know that elements gravitational contraction. mass is converted into energy in heavier than iron form in supernova accordance with the equation explosions\u2014the death throes 1863 English astronomer E = mc2. Eddington developed a of massive stars. The elements William Huggins\u2019 spectrum model of star structure in terms of needed for life are made in stars. \u25a0 analysis of stars shows they the balance between the inward share elements found on Earth. pull of gravity and the outward pressure of escaping radiation, but 1905\u201310 Astronomers in the he did not \ufb01gure out the physics of US and Sweden analyze stars\u2019 the nuclear reactions involved. luminosity and group them into dwarfs and giants. Making heavier elements Space isn\u2019t remote at all. In 1939, German-born US physicist It\u2019s only an hour\u2019s drive 1920 Arthur Eddington argues Hans Bethe published a detailed away if your car could go that stars turn hydrogen into analysis of the different pathways helium through nuclear fusion. that hydrogen fusion might take. straight upwards. He identi\ufb01ed two routes\u2014a slow, Fred Hoyle 1934 Fritz Zwicky coins the low-temperature chain that term \u201csupernova\u201d for a massive dominates in stars like our Sun, and star\u2019s explosive end. a rapid, high-temperature cycle that dominates in more massive stars. AFTER 2013 Deep-sea fossils reveal See also: Marie Curie 190\u201395 \u25a0 Albert Einstein 214\u201321 \u25a0 what may be biological traces Ernest Rutherford 206\u201313 \u25a0 Georges Lema\u00eetre 242\u201345 \u25a0 Fritz Zwicky 250\u201351 of iron from a supernova.","FUNDAMENTAL BUILDING BLOCKS 271 JUMPING GENES BARBARA MCCLINTOCK (1902\u20131992) IN CONTEXT I n the early 20th century, the Variable colors in corn prompted laws of inheritance that had McClintock to trace the genetic BRANCH been described by Gregor recombinations responsible for this Biology Mendel in 1866 were re\ufb01ned as new variety, which she reported in 1951. discoveries were made about the BEFORE particles of inheritance, identi\ufb01ed chromosomes paired up when sex 1866 Gregor Mendel describes as genes, and the microscopic cells were formed, creating an X inheritance as a phenomenon threads that carry them, called shape. She realized that these determined by \u201cparticles\u201d\u2014 chromosomes. In the 1930s, X-shaped structures marked later called genes. American geneticist Barbara locations where chromosome pairs McClintock \ufb01rst realized that were exchanging segments. Genes 1902 Theodor Boveri and chromosomes were not the stable that were once linked together on Walter Sutton independently structures previously imagined, the same chromosome were shuf\ufb02ed conclude that chromosomes and that the position of genes in around, which resulted in new are involved in inheritance. chromosomes could alter. traits, including variable colors. 1915 Thomas Hunt Morgan\u2019s Exchanging genes This shuf\ufb02ing of genes\u2014called fruit \ufb02y experiments con\ufb01rm McClintock was studying genetic recombination\u2014produces earlier theories and show that inheritance in corn plants. A a far greater genetic variety in the genes can be linked together corncob has hundreds of kernels, offspring. As a result, the chances on the same chromosome. each colored yellow, brown, or of survival in different environments streaked, according to the cob\u2019s are enhanced. \u25a0 AFTER genes. A kernel is a seed\u2014a single 1953 James Watson and offspring\u2014so studying many cobs Francis Crick\u2019s double-helix gives a range of data on the model of the DNA that makes inheritance of kernel color. up chromosomes shows how McClintock combined breeding genetic material is replicated. experiments with microscope work on chromosomes. In 1930, she found 2000 The \ufb01rst human genome that, during sexual reproduction, is published, cataloguing the location of 20,000\u201325,000 See also: Gregor Mendel 166\u201371 \u25a0 Thomas Hunt Morgan 224\u201325 \u25a0 genes on humans\u2019 23 pairs James Watson and Francis Crick 276\u201383 \u25a0 Michael Syvanen 318\u201319 of chromosomes.","272 THE STRANGE THEORY OF LIGHT AND MATTER RICHARD FEYNMAN (1918\u20131988) IN CONTEXT O ne of the questions to particles interacted through the arise from the quantum exchange of quanta, or \u201cphotons,\u201d BRANCH mechanics of the 1920s of electromagnetic energy\u2014the Physics was how particles of matter same electromagnetic quanta that interacted by means of forces. comprise light. Photons can be BEFORE Electromagnetism also needed a created out of nothing for very brief 1925 Louis de Broglie theory that worked on the quantum periods of time in accordance with suggests that any particle with scale. The theory that emerged, Heisenberg\u2019s uncertainty principle, mass can behave like a wave. quantum electrodynamics (QED), and this allows \ufb02uctuations in explained the interaction of the amount of energy available 1927 Werner Heisenberg particles through the exchange of in \u201cempty\u201d space. Such photons shows there is an inherent electromagnetism. It has proved are sometimes called \u201cvirtual\u201d uncertainty in certain pairs very successful, although one of its particles, and physicists have of values at the quantum level, pioneers, Richard Feynman, called subsequently con\ufb01rmed their such as the position and it a \u201cstrange\u201d theory because involvement in electromagnetism. momentum of a particle. the picture of the universe that More generally, the messenger it describes is hard to visualize. particles in quantum \ufb01eld theories 1927 Paul Dirac applies are known as \u201cgauge bosons.\u201d quantum mechanics to \ufb01elds Messenger particles rather than single particles. Paul Dirac made the \ufb01rst step However, there were problems toward a theory of QED based on with QED. Most signi\ufb01cantly, AFTER the idea that electrically charged its equations often generated Late 1950s Julian Schwinger nonsensical in\ufb01nite values. and Sheldon Glashow develop the electroweak theory, which Time e1 Feynman diagrams unites the weak nuclear force Virtual photon show the ways in with electromagnetism. e2 which particles can e1 Path of \ufb01rst electron interact. Here, two 1965 Moo-Young Han, Yoichiro electrons repel each Nambu, and Oscar Greenberg other by exchanging explain the interaction of a virtual photon. particles under the strong force e2 in terms of a property now known as \u201ccolor charge.\u201d Path of second electron Space","FUNDAMENTAL BUILDING BLOCKS 273 See also: Erwin Schr\u00f6dinger 226\u201333 \u25a0 Werner Heisenberg 234\u201335 \u25a0 Paul Dirac 246\u201347 \u25a0 Sheldon Glashow 292\u201393 Particles interact by This exchange can exchanging photons. happen in many different ways, each with its own probability. The \u201cstrange theory Summing the Richard Feynman of light and matter\u201d probabilities of all possible events gives Born in New York in 1918, produces correct an accurate description Richard Feynman showed a results. of experimental results. talent for mathematics at an early age, and earned a Summing probabilities each other out: for example, the degree at Massachusetts In 1947, German physicist Hans probability of a particle traveling Institute of Technology (MIT) Bethe suggested a way of \ufb01xing in a particular direction may be before attaining a perfect the equations so that they mirrored the same as the probability of it score in mathematics and real laboratory results. In the late traveling in the opposite direction, physics for his graduate 1940s, Japanese physicist Sin-Itiro so adding these probabilities gives entrance exam to Princeton. Tomonaga, Americans Julian a sum of zero. Summing every After receiving his PhD in Schwinger and Richard Feynman, possibility, including the \u201cstrange\u201d 1942, Feynman worked under and others took Bethe\u2019s ideas and ones involving backward time Hans Bethe in the Manhattan developed them to produce a travel, produces familiar results Project to develop the atomic mathematically sound version such as light appearing to travel bomb. Following the end of of QED. It produced meaningful in straight lines. However, under World War II, he continued results by considering all the certain conditions, the summed his work with Bethe at possible ways that interactions probabilities do produce strange Cornell University, where could take place according to results, and experiments have he did his most important quantum mechanics. shown that light does not always work on QED. necessarily travel in straight lines. Feynman made this complex As such, QED provides an accurate Feynman showed a \ufb02air for subject approachable through his description of reality even if it feels communicating his ideas. He invention of \u201cFeynman diagrams\u201d\u2014 alien to the world we perceive. promoted the potential of simple pictorial representations nanotechnology, and late in of possible electromagnetic QED proved so successful that his life wrote bestselling interactions between particles, it has become a model for similar accounts of QED and other which provide an intuitive theories of other fundamental aspects of modern physics. description of the processes at forces\u2014the strong nuclear force work. The key breakthrough was has been successfully described Key works to \ufb01nd a mathematical way of by quantum chromodynamics modeling an interaction as a (QCD), while the electromagnetic 1950 Mathematical sum of the probabilities of each and weak nuclear forces have Formulation of the Quantum individual pathway, which include been uni\ufb01ed in a combined Theory of Electromagnetic pathways in which particles move electroweak gauge theory. Only Interaction backward in time. When summed, gravitation so far refuses to 1985 QED: The Strange many of the probabilities cancel conform to this kind of model. \u25a0 Theory of Light and Matter 1985 Surely You\u2019re Joking, Mr. Feynman?","274 LIFE IS NOT A MIRACLE HAROLD UREY (1893\u20131981) STANLEY MILLER (1930\u20132007) IN CONTEXT Earth\u2019s early atmosphere S cientists have long pondered contained a mixture the origin of life. In 1871, BRANCH of gases. Charles Darwin wrote in a Chemistry letter to his friend Joseph Hooker, Given enough energy, \u201cBut if\u2026we could conceive in BEFORE those gases might have some warm little pond, with all 1871 Charles Darwin suggests sorts of ammonia and phosphoric that life might have begun in reacted together. salts, lights, heat, electricity etc \u201csome warm little pond.\u201d present, that a protein compound More complex molecules was chemically formed ready to 1922 Russian biochemist might have been formed, undergo still more complex Alexander Oparin proposes providing the building changes\u2026\u201d In 1953, American that complex compounds blocks of the earliest chemist Harold Urey and his might have formed in a student Stanley Miller found a primitive atmosphere. life forms. way to replicate Earth\u2019s early atmosphere in the laboratory, and 1952 In the US, Kenneth A. Life is not a miracle. generated from inorganic matter Wilde passes 600-volt sparks organic (carbon-based) compounds through a mixture of carbon that are essential to life. dioxide and water vapor, and obtains carbon monoxide. Before the Urey\u2013Miller experiment, advances in chemistry AFTER and astronomy had analyzed the 1961 Spanish biochemist atmospheres on the other, lifeless Joan Or\u00f3 adds further likely planets in the solar system. In the chemicals to the Urey\u2013Miller 1920s, Soviet biochemist Alexander mix and obtains molecules Oparin and British geneticist J. B. S. vital for DNA, among others. Haldane independently suggested that if conditions on prebiotic 2008 Miller\u2019s former student (prelife) Earth resembled those Jeffrey Bada and others use planets, then simple chemicals newer, more sensitve could have reacted together in techniques to obtain many a primordial soup to form more more organic molecules. complex molecules, from which living things might have evolved.","See also: J\u00f6ns Jakob Berzelius 119 \u25a0 Friedrich W\u00f6hler 124\u201325 \u25a0 FUNDAMENTAL BUILDING BLOCKS 275 Charles Darwin 142\u201349 \u25a0 Fred Hoyle 270 Harold Urey and Stanley Miller Laboratory apparatus replicated Gases (Earth\u2019s atmosphere) Harold Clayton Urey was born the effect of lightning on early Earth\u2019s in Walkerton, IN. His work on primitive atmosphere, in a continual Spark the separation of isotopes led loop of chemical reactions. (lightning) to the discovery of deuterium, which won him the Nobel Prize Vapor (cloud in Chemistry in 1934. He went formation) on to develop enrichment of uranium-235 by gaseous Boiling water Condensing diffusion which was crucial for (Earth\u2019s oceans) column the Manhattan Project\u2019s development of the \ufb01rst atomic Heat source Cooled water (containing Power bomb. After his prebiotic organic molecules) supply experiments with Stanley Miller in Chicago he moved to Recreating Earth\u2019s building blocks of the proteins in all San Diego and studied the early atmosphere living things. Urey encouraged Moon rocks brought back by In 1953, Urey and Miller carried out Miller to send a paper about the Apollo 11. the \ufb01rst prolonged experiment to experiment to the journal Science, test the Oparin\u2013Haldane theory. In which published it as \u201cProduction Stanley Lloyd Miller was a closed series of connected glass of amino acids under possible born in Oakland, CA. After \ufb02asks, sealed from the atmosphere, primitive earth conditions.\u201d The studying chemistry at the they put water and a mixture of world could now imagine how University of California at gases thought to have been present Darwin\u2019s \u201cwarm little pond\u201d may Berkeley, he was a teaching in Earth\u2019s primitive atmosphere\u2014 have generated the \ufb01rst life forms. assistant at the University of hydrogen, methane, and ammonia. Chicago, and worked with The water was heated so that water In an interview, Miller said that Urey. Later, he became a vapor formed and wafted its way \u201cjust turning on the spark in a basic professor in San Diego. around all the \ufb02asks in the closed prebiotic experiment will yield loop. In one of the \ufb02asks was a pair amino acids.\u201d Scientists later found, Key work of electrodes, between which sparks using better equipment than was were passed continuously to available in 1953, that the original 1953 Production of Amino represent lightning\u2014one of the experiment had produced at least Acids under Possible Primitive hypothetical triggers for primordial 25 amino acids\u2014more than are Earth Conditions reactions. The sparks provided found in nature. Since Earth\u2019s early enough energy to break up some of atmosphere almost certainly My study [of the universe] the molecules, and generate highly contained carbon dioxide, nitrogen, leaves little doubt that life has reactive forms that would go on to hydrogen sulphide, and sulfur react with other molecules. dioxide released from volcanoes, occurred on other planets. I a much richer mixture of organic doubt if the human race is the Within a day, the mixture had compounds might well have been turned pink, and after two weeks created then\u2014and was indeed most intelligent form of life. Urey and Miller found that at least formed in subsequent experiments. Harold C. Urey 10 percent of the carbon (from the Meteorites containing dozens of methane) was now in the form of amino acids, some found on Earth other organic compounds. Two and others not, have also spurred percent of the carbon had formed on the search for signs of life on amino acids, which are the vital planets beyond the solar system. \u25a0","WE WISH TO SUGGEST A STRUCTURE FOR THE SALT OF DEOXYRIBOSE NUCLEIC ACID (DNA) JAMES WATSON (1928\u2013) FRANCIS CRICK (1916\u20132004)","","278 JAMES WATSON AND FRANCIS CRICK IN CONTEXT I n April 1953, the answer to on the challenge of DNA\u2019s structure a fundamental mystery about at the Cavendish Laboratory, BRANCH living organisms appeared in University of Cambridge, under Biology a short article published without its director, Sir Lawrence Bragg. fanfare in the scienti\ufb01c journal, BEFORE Nature. The article explained both DNA was the hot topic of the 1869 Friedrich Miescher \ufb01rst how genetic instructions are held day, and an understanding of its identi\ufb01es DNA, in blood cells. inside organisms and how they are structure seemed so tantalizingly passed on to the next generation. within reach that by the early 1920s Phoebus Levene and Crucially, it described, for the 1950s, teams in Europe, the US, others analyze the components \ufb01rst time, the double-helix and the Soviet Union were vying of DNA as sugars, phosphates, structure of deoxyribose nucleic to be the \ufb01rst to \u201ccrack\u201d DNA\u2019s and four types of base. acid (DNA), the molecule that three-dimensional shape\u2014the contains the genetic information. elusive model that allowed DNA 1944 Experiments show DNA simultaneously to carry genetic to be a carrier of genetic data. The article was written by data in some kind of chemically James Watson, a 29-year-old coded form, and to replicate 1951 Linus Pauling proposes American biologist, and his itself completely and accurately, the alpha-helix structure for older British research colleague, so that the same genetic data certain biological molecules. biophysicist Francis Crick. Since was passed to offspring, or 1951, they had jointly been working daughter cells, including those AFTER of the next generation. 1963 Frederick Sanger develops sequencing methods So beautiful it has to be true. The past in DNA to identify bases along DNA. James Watson The DNA molecule was not discovered in 1953, as is often 1960s DNA\u2019s code is cracked: popularly thought, nor were Crick three DNA bases of code for and Watson the \ufb01rst to \ufb01nd out what each amino acid in a protein. it was made from. DNA has a much longer history of research. In the 2010 Craig Venter and his 1880s, the German biologist Walther team implant arti\ufb01cially made Flemming had reported that \u201cX\u201d-like DNA into a living bacterium. bodies (later named chromosomes) appeared inside cells as the cells James Watson and James Watson (on the right) was during World War II. In 1947, Francis Crick born in 1928 in Chicago, IL. he went to Cambridge to study At the precocious age of 15 he biology and here began work entered the University of Chicago. with James Watson. Later, Crick After postgraduate study in became known for the \u201ccentral genetics, Watson moved to dogma\u201d: that genetic data \ufb02ow Cambridge, England, to team in cells in essentially one way. In up with Francis Crick. He later later life, Crick turned to brain returned to the US to work at the research and developed a theory Cold Spring Harbor Laboratory in of consciousness. New York. From 1988, he worked on the Human Genome Project, Key works but left after a disagreement over patenting genetic data. 1953 Molecular Structure of Nucleic Acids: A Structure for Francis Crick was born in 1916 Deoxyribose Nucleic Acid near Northampton in Britain. He 1968 The Double Helix developed antisubmarine mines","FUNDAMENTAL BUILDING BLOCKS 279 See also: Charles Darwin 142\u201349 \u25a0 Gregor Mendel 166\u201371 \u25a0 Thomas Hunt Morgan 224\u201325 \u25a0 Barbara McClintock 271 \u25a0 Linus Pauling 254\u201359 \u25a0 Craig Venter 324\u201325 DNA carries genetic It encodes genetic called bases. By the end of the information and must be information in a series of 1940s, the basic formula of DNA as bases along its structure. a giant polymer\u2014a huge molecule able to replicate. consisting of repeating units, or monomers\u2014was clear. By 1952, experiments with bacteria had shown that DNA itself, and not its rival candidates, the proteins inside chromosomes, was the physical embodiment of genetic information. A double helix could X-ray images of the Tricky research tools both carry genetic structure show that it has The competing researchers were using several advanced research information and provide a a helix shape. tools, including X-ray diffraction way to replicate. crystallography, in which X-rays were passed through a substance\u2019s The structure of DNA is a double helix. crystals. A crystal\u2019s unique geometry in terms of its atomic were preparing to divide. In 1900, biologist Thomas Hunt Morgan content made the X-ray beams Gregor Mendel\u2019s experiments showed that chromosomes were diffract, or bend, as they passed with heredity in pea plants were indeed the carriers of hereditary through. The resulting diffraction rediscovered\u2014Mendel had been information. The next step was to patterns of spots, lines, and blurs the \ufb01rst to suggest that there were look at the constituent molecules were captured on photographic units of heredity that came in pairs of chromosomes\u2014molecules that \ufb01lm. Working backward from those (which would later be called genes). might be candidates for genes. patterns, it was possible to \ufb01gure At about the same time as Mendel out the structural details within the was being rediscovered, breeding New pairs of genes crystal. This was not an easy task. experiments by American physician In the 1920s, two types of candidate X-ray crystallography has been \u276f\u276f Walter Sutton and, independently, molecules were discovered: proteins by German biologist Theodor Boveri called histones, and nucleic acids, It is one of the more striking revealed that sets of chromosomes which had been described generalizations of (the rod-shaped structures that chemically in 1869 as nuclein by carry genes) pass from a dividing Swiss biologist Friedrich Miescher. biochemistry\u2026that the cell to each of its daughter cells. The Russian-American biochemist twenty amino acids and the The ensuing Sutton\u2013Boveri theory Phoebus Levene and others four bases, are, with minor proposed that chromosomes are gradually identi\ufb01ed the main the carriers of genetic material. ingredients of DNA in increasing reservations, the same detail as nucleotide units, each throughout Nature. Soon, more scientists were made up of a deoxyribose sugar, a Francis Crick investigating these mysterious phosphate, and one of four subunits X-shaped bodies. In 1915, American","280 JAMES WATSON AND FRANCIS CRICK likened to studying the myriad in molecular biology when they By this time, James Watson was light patterns cast by a crystal correctly proposed that many working at the Cavendish chandelier on the ceiling and biological molecules\u2014including Laboratory. He was only 25 years walls of a large room, and using hemoglobin, the oxygen-carrying old, but he had the enthusiasm of them to \ufb01gure out the shapes and substance in blood\u2014have a youth and two degrees in zoology, positions of each piece of glass in corkscrew-like helix shape. Pauling and had studied the genes and the chandelier. named this molecular model the nucleic acids of bacteriophages\u2014 alpha-helix. the viruses that infect bacteria. Pauling in the lead Crick, 37 years old, was a The British research team at the Pauling\u2019s breakthrough had biophysicist with an interest in the Cavendish Laboratory was eager narrowly beaten the Cavendish brain and neuroscience. He had to beat the American researchers, Laboratory and it looked as though studied proteins, nucleic acids, and led by Linus Pauling. In 1951, the precise shape of DNA\u2019s other giant molecules in living Pauling and his colleagues Robert structure was within his grasp. things. He had also observed the Corey and Herman Branson had Then, early in 1953, Pauling Cavendish team racing to beat already achieved a breakthrough proposed that the structure of DNA Pauling to the alpha-helix idea, and was in the form of a triple helix. later analyzed their mistaken suppositions and dead-end exploratory efforts. Both Watson and Crick also had experience of X-ray crystallography, albeit in different areas, and together they soon began musing on two questions that fascinated them both: how does DNA as a physical molecule encode genetic information, and how is this information translated into the parts of a living system? Crucial crystal pictures Watson and Crick knew of Pauling\u2019s success with the alpha-helix model of proteins, in which the molecule twisted along a single corkscrew path, repeating its main structure every 3.6 turns. They also knew that the latest research evidence did not seem to support Pauling\u2019s triple helix model for DNA. This led them to wonder whether the elusive model was one that was neither a single nor a triple helix. The two conducted hardly any experiments This X-ray diffraction photograph of DNA was obtained by Rosalind Franklin in 1953, and was the biggest clue to cracking DNA. The helical structure of DNA was ascertained from the pattern of spots and bands.","FUNDAMENTAL BUILDING BLOCKS 281 themselves. Instead they collected Rosalind Franklin\u2019s draft reports One of Franklin\u2019s considerations data from others, including the on her theoretical models for DNA\u2019s was whether the structural results of chemical experiments structure were key to Watson and \u201cbackbone,\u201d a chain of phosphate that gave information about the Crick\u2019s discovery of the double helix, and deoxyribose sugar subunits, angles of the links, or bonds, but she received little recognition in was in the center with the bases between the various ingredient her lifetime. projecting outward, or the other atoms and subgroups of DNA. way around. Another colleague They also pooled their joint In early 1953, in what was perhaps who provided help was Austrian- knowledge of X-ray crystallography a break with scienti\ufb01c protocol, born British biologist Max Perutz, and approached those researchers Wilkins showed the images taken by who would win the Nobel prize in who had made the highest-quality Franklin and Gosling, without their Chemistry in 1962 for his work on images of DNA and other similar permission or knowledge, to James the structure of hemoglobin and molecules. One such image was Watson. The American immediately other proteins. Perutz also had \u201cphoto 51,\u201d which became key to recognized their signi\ufb01cance, and access to Franklin\u2019s unpublished their achieving their breakthrough. took the implications straight back reports and passed them on to the to Crick. Suddenly their work was on ever-networking Watson and Crick. Photo 51 was an X-ray the right path. They pursued the idea that DNA\u2019s diffraction image of DNA that backbones were on the outside, resembled an \u201cX\u201d seen through the From this point, the exact with the bases pointing inward and slats of a Venetian blind\u2014fuzzy to sequence of events becomes perhaps connecting to each other our eyes, but at that time, among unclear, and later accounts of the in pairs. They cut out and shuf\ufb02ed the sharpest and most informative discovery are con\ufb02icting. Franklin around cardboard shapes that of DNA\u2019s X-ray pictures. Some had described in unpublished draft represented these molecular debate surrounds the identity of reports her thoughts about the subunits: phosphates and sugars in the photographer who took this structure and shape of DNA. These the backbone, and the four types of historic picture. It came from the were also incorporated by Watson base\u2014adenine, thymine, guanine, laboratory of a British biophysicist and Crick as they struggled with and cytosine. named Rosalind Franklin, an their various proposals. The main expert in X-ray crystallography, idea, derived from Pauling\u2019s alpha- In 1952, Watson and Crick had and her graduate student Raymond helix model and supported by met Erwin Chargaff, an Austrian- Gosling, at King\u2019s College, London. Wilkins, centered on some form of born biochemist, who had devised Each has been credited with the repeating helical pattern for the what became known as Chargaff\u2019s image at various times. giant molecule. \ufb01rst rule. This stated that in DNA, the amounts of guanine and Cardboard models cytosine are equal, as are the Also working at King\u2019s was amounts of adenine and thymine. Maurice Wilkins, a physicist who Experiments had sometimes shown was interested in molecular biology. that all four amounts were roughly equal, and sometimes not. The We have discovered the latter \ufb01ndings came to be seen as secret of life. errors in methodology, and equal amounts of all four bases came to Francis Crick be accepted as the rule of thumb. Making the pieces \ufb01t By splitting the base quantities into two sets of pairs, Chargaff had shed light on the structure of DNA. Watson and Crick now began to think of adenine as only and always linking to thymine, and guanine to cytosine. \u276f\u276f","282 JAMES WATSON AND FRANCIS CRICK These are human male chromosomes. the pieces to \ufb01t together, producing cell how to make the particular Before Crick and Watson\u2019s discovery, an elegant double helix in which protein or other molecule that was it had been known that chromosomes the pairs of bases linked along the the physical manifestation of the carry genes that pass from a dividing middle. Unlike the protein alpha- genetic data and had a particular cell to a daughter cell. helix, which had 3.6 subunits in role in the cell\u2019s fabric and function. one complete turn, DNA had about In assembling the cardboard 10.4 subunits per turn. Zip and unzip pieces for their 3-D jigsaw, Watson Each pair of bases is connected and Crick were juggling a vast The model that Watson and by what chemists call hydrogen amount of data, working from Crick described consisted of two bonds. These are made and broken mathematics, X-ray images, their helical or corkscrew phosphate- relatively easily, so the sections of own knowledge of chemical bonds sugar backbones curling around the double-helix can be \u201cunzipped\u201d and their angles, and other data\u2014 each other, like the uprights of a by undoing the bonds, which then all approximate and subject to \u201ctwisted ladder,\u201d connected by exposes the code of bases as a ranges of errors. Their \ufb01nal pairs of bases serving as rungs. template for making a copy. breakthrough came when they The sequence of bases worked like realized that making slight letters in a sentence, carrying small This zip-unzip allowed two adjustments to the con\ufb01gurations units of information that combined processes to occur. First, a mirror of thymine and guanine allowed to make an overall instruction, complementary copy of nucleic acid or gene\u2014which in turn told the could be made from one unzipped","FUNDAMENTAL BUILDING BLOCKS 283 half of the double helix; then, \u201cfor their discoveries concerning A DNA molecule is a double helix carrying its genetic information the molecular structure of nucleic formed by base pairs attached to a as the sequence of bases, it would acids and its signi\ufb01cance for backbone made of sugar-phosphates. leave the cell nucleus to become information transfer in living The base pairs always match up in involved in the protein production. material.\u201d The award, however, combinations of either adenine\u2013thymine was surrounded in controversy. or cytosine\u2013guanine. Second, when the whole length In the preceding years, Rosalind of the double helix was unzipped, Franklin had received little of\ufb01cial Base pairs each part would act as a template credit for producing the key X-ray to build a new complementary images and for writing the reports Sugar- partner\u2014resulting in two lengths that helped to direct Watson phosphate of DNA that were identical to the and Crick\u2019s research. She died of backbone original and to each other. In this ovarian cancer in 1958, at only 37, way, DNA was copied as cells and was therefore ineligible Adenine Thymine divided into two for growth and for the Nobel Prize in 1962, since Guanine Cytosine repair throughout an organism\u2019s the prizes are not awarded life\u2014and as sperm and eggs, the posthumously. Some said the sex cells, carried their quotient of award should have been made the genes to make a fertilized egg, earlier, with Franklin as one of so beginning the next generation. the co-recipients, but the rules allow a maximum of three. \u201cSecret of life\u201d On February 28, 1953, elated by Following their momentous their discovery, Watson and Crick work, Watson and Crick became went for lunch to The Eagle, one of world celebrities. They continued Cambridge\u2019s oldest inns, where their research in molecular biology colleagues from the Cavendish and and received great numbers of other laboratories often met. Crick awards and honors. Now that the is said to have startled drinkers by structure of DNA was known, the announcing that he and Watson next big challenge was to solve the had discovered \u201cthe secret of life\u201d\u2014 genetic \u201ccode.\u201d By 1964, scientists or so Watson later recalled in his \ufb01gured out how sequences of its book, The Double Helix, though bases were translated into the Crick denied this really happened. amino acids that make up speci\ufb01c proteins and other molecules that In 1962, Watson, Crick, and are the building blocks of life. Wilkins were awarded the Nobel Prize in Physiology or Medicine Today, scientists can identify base sequences for all the genes of I never dreamed that in my an organism, collectively known as lifetime my own genome its genome. They can manipulate DNA to move genes around, delete would be sequenced. them from speci\ufb01c lengths of DNA, James Watson and insert them into others. In 2003, the Human Genome Project, the largest international biological research project ever, announced that it had completed the mapping of the human genome\u2014a sequence of more than 20,000 genes. Crick and Watson\u2019s discovery had paved the way for genetic engineering and gene therapy. \u25a0","284 EVERYTHING THAT CAN HAPPEN HAPPENS HUGH EVERETT III (1930\u20131982) IN CONTEXT A card \ufb01nely balanced on Quantum theory allows its edge will fall faceup both outcomes to happen. BRANCH Physics and cosmology or facedown. So each card fall results in its own possible world. BEFORE 1600 Italian philosopher A quantum theory in Repeat the experiment Giordano Bruno is burned at which nature does not four times and we have the stake for his belief in an decide between outcomes created 16 parallel worlds in\ufb01nity of inhabited worlds. is consistent with (2 \u00d7 2 \u00d7 2 \u00d7 2). 1924\u201327 Niels Bohr and observation. Werner Heisenberg seek to resolve the measurement Everything that can happen happens. paradox of wave-particle duality by invoking a wave H ugh Everett III is a cult bizarre results that seem to function collapse. \ufb01gure to sci-\ufb01 enthusiasts be at odds with experiment, because his many-worlds a dichotomy at the heart of the AFTER interpretation (MWI) of quantum measurement paradox (pp.232\u201333). 1980s A principle known mechanics changed scientists\u2019 as decoherence attempts to ideas about the nature of reality. In the quantum world, provide a mechanism by subatomic particles are allowed which the many-worlds Everett\u2019s work was inspired by to exist in any number of possible interpretation may work. the embarrassing \ufb02aw at the heart states of location, velocity, and of quantum mechanics. Although spin, or \u201csuperpositions,\u201d as 2000s Swedish cosmologist it can explain interactions at the described by Erwin Schr\u00f6dinger\u2019s Max Tegmark describes an most fundamental level of matter, wave function, but the phenomenon in\ufb01nity of universes. quantum mechanics also produces of many possibilities disappears as 2000s In quantum computer theory, computational power is sourced from superpositions that are not in our universe.","FUNDAMENTAL BUILDING BLOCKS 285 See also: Max Planck 202\u201305 \u25a0 Werner Heisenberg 234\u201335 \u25a0 Erwin Schr\u00f6dinger 226\u201333 \u201cMultiverse\u201d is an installation of 41,000 LED lights at the National Gallery of Art in Washington DC. It was inspired by the many-worlds interpretation. soon as it is observed. The very Many worlds The MWI says that all possibilities act of measuring a quantum system Everett\u2019s idea was to explain do, in fact, occur. Reality peels seems to \u201cshunt\u201d it into one state what happens to the quantum itself, or splits, into new worlds, or another, forcing it to \u201cchoose\u201d superpositions. He presumed but since we inhabit a world where its option. In the world we\u2019re the objective reality of the only one outcome occurs, this familiar with, a coin toss results in wave function and removed the is what we see. Other possible a de\ufb01nite heads or tails, and not (unobserved) collapse\u2014why should outcomes are inaccessible to us, one, the other, and both at once. nature \u201cchoose\u201d a particular version since there can be no interference of reality every time someone between worlds and we are fooled Copenhagen fudge makes a measurement? He then into thinking that something is lost In the 1920s, Niels Bohr and Werner asked another question: what then every time we measure something. Heisenberg attempted to sidestep happens to the various options the measurement problem with available to quantum systems? While Everett\u2019s theory is not what became known as the accepted by all, it removes a Copenhagen interpretation. It holds Hugh Everett III theoretical block to interpreting that the act of making an observation quantum mechanics. MWI does on a quantum system causes the Born in Washington DC, Hugh not mention parallel universes, wave function to \u201ccollapse\u201d into Everett was a precocious boy. but they are its logical prediction. the single outcome. Although At 12, he wrote to Einstein It has been criticized for being this remains a widely accepted asking what held the universe untestable, but this may change. interpretation, many theorists \ufb01nd together. While he was studying An effect known as \u201cdecoherence\u201d\u2014 it unsatisfactory since it reveals mathematics at Princeton, he whereby quantum objects \u201cleak\u201d nothing about the mechanism drifted into physics. MWI\u2014his their superposition information\u2014is of wave function collapse. This answer to the riddle at the heart a mechanism by which MWI might bothered Schr\u00f6dinger, too. For him, of quantum mechanics\u2014was be proved to work. \u25a0 any mathematical formulation of the subject of his PhD in 1957, the world had to have an objective and led to him being pilloried for everything that Everett said. reality. As Irish physicist John Bell proposing multiple universes. A Discouraged, he left physics for put it, \u201cEither the wave function, as trip to Copenhagen in 1959 to the US defense industry, but given by the Schr\u00f6dinger equation, discuss the idea with Niels Bohr today MWI is regarded as a is not everything, or is not right.\u201d was a disaster\u2014Bohr rejected mainstream interpretation of quantum theory\u2014too late for Everett, an alcoholic, who died at just 51. A lifelong atheist, he asked for his ashes to be thrown out with the trash. Key works 1956 Wave Mechanics Without Probability 1956 The Theory of the Universal Wave Function","A PERFECT GAME OF TIC-TAC-TOE DONALD MICHIE (1923\u20132007)","","288 DONALD MICHIE C omputers in 1961 were Can machines think? The mostly mainframes short answer is \u201cYes: there are IN CONTEXT the size of a room. machines which can do what Minicomputers would not arrive BRANCH until 1965 and microchips as we we would call thinking, if it Arti\ufb01cial intelligence know them today were several were done by a human being.\u201d BEFORE years in the future. With computer 1950 Alan Turing suggests hardware so huge and specialized, Donald Michie a test to measure machine British research scientist Donald intelligence (the Turing Test). Michie decided to use simple rotated to give others, and 1955 American programmer physical objects for a small project some are mirror images of, or Arthur Samuel improves his on machine learning and arti\ufb01cial symmetrical to, each other. program to play tic-tac-toe by intelligence\u2014 matchboxes and This made 304 permutations writing one that learns to play. glass beads. He selected a simple an adequate working number. 1956 The term \u201carti\ufb01cial task, too\u2014the game of tic-tac-toe, intelligence\u201d is coined by also known as noughts-and- In each matchbox box were American John McCarthy. crosses. Or, as Michie called it beads of nine different kinds, 1960 American psychologist \u201ctit-tat-to.\u201d The result was the distinguished by color. Each Frank Rosenblatt makes a Matchbox Educable Noughts color of bead corresponded to computer with neural networks And Crosses Engine (MENACE). MENACE putting its O on a certain that learn from experience. one of the nine squares. For AFTER Michie\u2019s main version of example, a green bead meant O 1968 MacHack, the \ufb01rst chess MENACE comprised 304 in the lower left square, a red one program to achieve a good matchboxes glued together in a designated O in the central square, level of skill, is created by chest-of-drawers arrangement. and so on. American Richard Greenblatt. A code number on each box was 1997 World chess champion keyed into a chart. The chart Mechanics of the game Garry Kasparov is defeated by showed drawings of the 3x3 game MENACE opened the game IBM\u2019s Deep Blue computer. grid with various arrangements using the matchbox for no Os or of Os and Xs, corresponding to Xs in the grid\u2014the \u201c\ufb01rst move\u201d Animals learn by possible layout permutations as box. In the tray of each matchbox experience of trial the game progressed. There are were two extra pieces of card at actually 19,683 possible layout one end forming a \u201cV\u201d shape. To and error. combinations but some can be play, the tray was removed from the box, jiggled, and tilted so the \u2026a perfect game of Machines can be V was at the lower end. The beads tic-tac-toe. built that change with randomly rolled down and one nestled into the apex of the V. each experience. Thus chosen, this bead\u2019s color determined the position of Reinforcing positive MENACE\u2019s \ufb01rst O in the grid. outcomes in a simple This bead was then put aside, and the tray replaced in its box mechanical system, but left slightly open. machines can play\u2026","FUNDAMENTAL BUILDING BLOCKS 289 See also: Alan Turing 252\u201353 State Each of the 304 of play matchboxes in MENACE represented a possible Bead state of the board. The indicating beads inside the boxes move represented each possible move for that state. The bead at the bottom of the \u201cV\u201d determined the move. As games went on, winning beads were reinforced and losing ones removed, allowing MENACE to learn from its experience. Next, the opponent positioned The chances of choosing that bead, For a draw, each bead from that their \ufb01rst X. For the second turn and so the same move and another game was replaced in its relevant of MENACE, the matchbox was possible win, were increased. box, along with a small reward, selected that corresponded to one bonus bead of the same the positions of the X and O If MENACE lost it was color. This increased the chances on the grid at this time. Again the \u201cpunished\u201d by not receiving of that bead being selected if the matchbox was opened, the tray back the removed beads, which same permutation came around shaken and tilted, and the color represented the losing sequence again, but not as much as the of the randomly selected bead of moves. But this was still win with three bonus beads. determined the position of positive. In future games, if the MENACE\u2019s second O. The same permutation of Xs and Os Michie\u2019s goal was that MENACE opponent placed their second X. cropped up, the beads designating would \u201clearn from experience.\u201d For And so on, recording MENACE\u2019s the same move as the previous time given permutations of Os and Xs, sequence of beads and so moves. were either fewer in number or when a certain sequence of moves absent, thereby lessening the had been successful, it should Win, lose, draw chance of another loss. gradually become more likely, while Eventually there came a result. moves that led to losses would If MENACE won, it received become less likely. It should reinforcement or a \u201creward.\u201d progress by trial and error, adapt The removed beads showed the with experience, and with more sequence of winning moves. Each games, become more successful. of these beads was put back in its box, identi\ufb01ed by the code number Colossus, the world\u2019s \ufb01rst electronic Controlling variables and slightly open tray. The tray programmable computer, was made in Michie considered potential also received three extra \u201cbonus\u201d 1943 to crack codes at Bletchley Park problems. What if the selected beads of the same color. As a in England. Michie trained staff to bead from a tray decreed that consequence, in a future game, if use the computer. MENACE\u2019s O should be placed the same permutation of Os and on a square already occupied Xs occurred on the grid, this by an O or X? Michie accounted matchbox would come into play for this by ensuring that each again\u2014and it had more of the matchbox contained only beads beads that previously led to a win. corresponding to empty squares for its particular permutation. So the \u276f\u276f","290 DONALD MICHIE box for the permutation of O top left Expert knowledge is intuitive; Human vs MENACE and X bottom right did not contain it is not necessarily accessible So what were the results? Michie beads for putting the next O on was MENACE\u2019s \ufb01rst opponent those squares. Michie considered to the expert himself. in a tournament of 220 games. that putting beads for all nine Donald Michie MENACE began shakily but soon possible O positions in every box settled down to draw more often, would \u201ccomplicate the problem Michie simulated this by having then notch up some wins. To unnecessarily.\u201d It meant MENACE different numbers of beads for counter, Michie began to stray would not only learn to win or draw, each move. So for MENACE\u2019s from safe options and employ it would also have to learn the rules second move (third move overall), unusual strategies. MENACE took as it went along. Such start-up each box that could be called upon time to adapt but then began conditions might lead to one or two to play\u2014those with permutations to cope with these too, coming early disasters that collapsed the of one O and one X already in the back to achieve more draws, then whole system. This demonstrated grid\u2014had three of each kind of wins. At one point in a series of a principle: machine learning works bead. For MENACE\u2019s third move, 10 games, Michie lost eight. best starting simple and gradually there were two beads of each kind, add more sophistication. and for its fourth (seventh move MENACE provided a simple overall), just one. A fatal choice example of machine learning Michie also pointed out that on the fourth move would result and how altering variables could when MENACE lost, its last move in removal of the only bead affect the outcome. Michie\u2019s was the 100 percent fatal one. The specifying that position on the description of MENACE was, in move before contributed to the loss, grid. Without that bead, the same fact, part of a longer account that as though backing the machine into situation could not recur. went on to compare its performance a corner, but less so\u2014usually it still with trial-and-error animal learning, left open the possibility of escaping as Michie explained: defeat. Working back toward the start of the game, each earlier move \u2018\u201cEssentially, the animal makes contributed less to the \ufb01nal defeat\u2014 more-or-less random movements that is, as moves accumulate, the and selects, in the sense that it probability that each becomes the subsequently repeats, those which \ufb01nal one increases. Therefore as produced the \u2018desired\u2019 result. This the total number of moves grows, it description seems tailor-made becomes more important to get rid for the matchbox model. Indeed, of choices that have proved fatal. MENACE constitutes a model of trial-and-error learning in so pure Donald Michie Born in 1923 in Rangoon, Burma Intelligence and Perception. (Myanmar), Michie won a He worked on the FREDDY scholarship to Oxford in 1942, but series of visually-enabled, instead assisted in the war effort teachable research robots. In by joining the code-breaking addition, he ran a series of teams at Bletchley Park, becoming prestigious arti\ufb01cial intelligence a close colleague of the computing projects and founded the pioneer Alan Turing. Turing Institute in Glasgow. In 1946, he returned to Oxford Michie continued as an to study mammalian genetics. active researcher into his However, he had a growing eighties. He died in a car interest in arti\ufb01cial intelligence, accident while traveling and by the 1960s it had become to London in 2007. his main pursuit. He moved to the University of Edinburgh in 1967, Key work and became the \ufb01rst Chairman of the Department of Machine 1961 Trial and Error","FUNDAMENTAL BUILDING BLOCKS 291 a form, that when it shows elements learn in ways perhaps not even New computer technology has led to of other categories of learning guessed at by their human a rapid development in AI, and in 1997, we may reasonably suspect originators. Michie demonstrated the chess machine Deep Blue defeated these of contamination with that careful application of world champion Garry Kasparov. a trial-and-error component.\u201d human intelligence empowered The computer learned strategy by machines to make themselves analyzing thousands of past games. Turning point smarter. Recent developments Before developing MENACE, in AI use similar principles to He had this concept that Donald Michie had pursued a develop networks that mirror the he wanted to try out that he distinguished research career in neural networks of animals\u2019 brains. thought might possibly solve biology, surgery, genetics, and computer chess\u2026It was the embryology. After MENACE, he Michie also conceived the idea of reaching a steady state. moved into the fast-developing notion of memoization, in which area of arti\ufb01cial intelligence (AI). the result of each set of inputs in a Kathleen Spracklen He developed his machine learning machine or computer was stored as ideas into \u201cindustrial-strength a reminder or \u201cmemo.\u201d If the same tools\u201d applied in hundreds of set of inputs recurred, the device situations, including assembly would at once activate the memo lines, factory production, and steel and recall the answer, rather than mills. As computers spread, his recalculating afresh, thereby saving arti\ufb01cial intelligence work was time and resources. He contributed used to design computer programs the memoization technique to and control structures that could computer programming languages such as POP-2 and LISP. \u25a0","292 THE UNITY OF FUNDAMENTAL FORCES SHELDON GLASHOW (1932\u2013) IN CONTEXT T he idea of forces of nature, Messenger particles or fundamental forces, goes In the quantum mechanical BRANCH back at least to the ancient description of \ufb01elds, a force is Physics Greeks. Physicists currently \u201cfelt\u201d by the exchange of a gauge recognize four fundamental forces\u2014 boson, such as the photon, which BEFORE gravity, electromagnetism, and carries electromagnetic interaction. 1820 Hans Christian \u00d8rsted the two nuclear forces, weak and A boson is emitted by one particle discovers that magnetism and strong interactions, which hold and absorbed by a second. Normally, electricity are aspects of the together the subatomic particles neither particle is fundamentally same phenomenon. inside the nucleus of an atom. changed by this interaction\u2014an We now know that the weak force electron is still an electron after 1864 James Clerk Maxwell and the electromagnetic force are absorbing or emitting a photon. The describes electromagnetic different manifestations of a single weak force breaks this symmetry, waves in a set of equations. \u201celectroweak\u201d force. Discovering changing quarks (the particles this was an important step on that protons and neutrons are made 1933 Enrico Fermi\u2019s theory the way to \ufb01nding a \u201cTheory of from) from one kind to another. of beta decay describes the Everything\u201d that would explain the weak force. relationship between all four forces. 1954 The Yang\u2013Mills theory The weak force Decay of particles via the weak force lays the mathematical The weak force was \ufb01rst invoked drives the Sun\u2019s proton\u2013proton fusion groundwork for unifying the to explain beta decay, a type of reaction, turning hydrogen into helium. four fundamental forces. nuclear radiation in which a Without it, the Sun wouldn\u2019t shine. neutron turns into a proton inside AFTER the nucleus, emitting electrons or 1974 A fourth kind of positrons in the process. In 1961, quark, the \u201ccharm\u201d quark, is a graduate student at Harvard, discovered, revealing a new Sheldon Glashow, was given the underlying structure to matter. ambitious brief to unify the theories of weak and electromagnetic 1983 The force-carrying W interactions. Glashow fell short of and Z bosons are discovered this, but did describe the force- in CERN\u2019s Super Proton carrying particles that mediate Synchrotron in Switzerland. interaction via the weak force.","FUNDAMENTAL BUILDING BLOCKS 293 See also: Marie Curie 190\u201395 \u25a0 Ernest Rutherford 206\u201313 \u25a0 Peter Higgs 298\u201399 \u25a0 Murray Gell-Mann 302\u201307 A \u201cTheory of Everything\u201d suggests an explanation of the unity of the fundamental forces. It is proposed that, at stupendously high temperatures just after Sheldon Glashow the Big Bang, all four forces were united as one \u201csuperforce.\u201d Sheldon Lee Glashow was At a temperature of about 1032K, gravity born in New York in 1932, separated from the other forces. the son of Russian Jewish immigrants. He attended high At about 1027K, the strong nuclear force separated. school with his friend Steven Weinberg and upon graduating At about 1015K, the electromagnetic and weak forces separated. in 1950, they both studied physics at Cornell University. So what kind of boson might be electroweak theory, brought weak Glashow earned his PhD from involved? Glashow guessed that interaction and electromagnetic Harvard, where he came up the bosons associated with the force together as a single force. with a description of the W weak force had to be relatively and Z bosons. After Harvard, massive because the force operates This was an astounding result, he went to the University of over miniscule ranges and heavy since the weak and electromagnetic California at Berkeley in 1961, particles do not travel far. He forces operate in entirely different and later returned to join proposed two charged bosons, spheres. The electromagnetic force the faculty at Harvard as a W+ and W\u2013, and a third neutral extends to the very edge of the professor of physics in 1967. Z boson. The W and Z force-carriers visible universe (the force is carried were detected by CERN\u2019s particle by massless photons of light), while In the 1960s, Glashow accelerator in 1983. the weak force barely reaches extended Murray Gell-Mann\u2019s across an atomic nucleus and is quark model, adding a Uni\ufb01cation some 10 million times weaker. property known as \u201ccharm\u201d In the 1960s, two physicists, Their uni\ufb01cation opens up the and predicting a fourth quark, American Steven Weinberg and tantalizing possibility that, under which was discovered in Pakistani Abdus Salam, working certain high-energy conditions 1974. In recent years, he has independently, incorporated the such as those just after the Big been heavily critical of string Higgs \ufb01eld (pp.298\u201399) into Bang, all four fundamental forces theory, disputing its place Glashow\u2019s theory. The resultant may coalesce into one \u201csuperforce.\u201d in physics due to its lack of Weinberg\u2013Salam model, or uni\ufb01ed The search continues for evidence testable predictions, and of such a Theory of Everything. \u25a0 describing it as a \u201ctumor.\u201d Key works 1961 Partial Symmetries of Weak Interactions 1988 Interactions: A Journey Through the Mind of a Particle Physicist 1991 The Charm of Physics","294 WE ARE THE CAUSE OF GLOBAL WARMING CHARLES KEELING (1928\u20132005) IN CONTEXT Carbon dioxide T he realization that carbon is a greenhouse gas dioxide (CO2) levels in BRANCH the atmosphere are not Meteorology that traps heat in only rising but might also cause Earth\u2019s atmosphere. disastrous warming \ufb01rst came BEFORE to widespread scienti\ufb01c and 1824 Joseph Fourier suggests Its concentration in the public attention in the 1950s. that Earth\u2019s atmosphere makes air is rising in line with Past scientists had assumed that the planet warmer. fossil fuel consumption. the concentration of CO2 in the atmosphere varied from time to 1859 Irish physicist John Earth\u2019s temperature time, but was always around Tyndall proves that carbon is rising. 0.03 percent, or 300 parts per dioxide (CO2), water vapor, million (ppm). In 1958, American and ozone trap heat in We are the geochemist Charles Keeling began Earth\u2019s atmosphere. cause of global to measure the concentration of CO2 using a sensitive instrument 1903 Swedish chemist Svante warming. he had developed. It was his Arrhenius suggests that the \ufb01ndings that alerted the world CO2 released by burning to the relentless rise of CO2 and, fossil fuel might be causing by the late 1970s, to the human atmospheric warming. role in accelerating the so-called greenhouse effect. 1938 British engineer Guy Callendar reports that Regular measurements Earth\u2019s average temperature Keeling measured CO2 in several increased by 1\u00b0F (0.5\u00b0C) places: Big Sur in California, the between 1890 and 1935. Olympic peninsula in Washington State, and the high mountain AFTER forests of Arizona. He also recorded 1988 The Intergovernmental measurements at the South Pole Panel on Climate Change and from aircraft. In 1957, Keeling (IPCC) is set up to assess founded a meteorological station at scienti\ufb01c research and 10,000 ft (3,000 m) above sea level guide global policy. on the top of Mauna Loa in Hawaii.","FUNDAMENTAL BUILDING BLOCKS 295 See also: Jan Ingenhousz 85 \u25a0 Joseph Fourier 122\u201323 \u25a0 Robert FitzRoy 150\u201355 Parts per million Carbon Dioxide Concentration Keeling\u2019s graph CO2 is a greenhouse gas, helping plots the rising to trap heat from the Sun, so 390 levels of CO2 in the increasing CO2 concentration is 380 atmosphere year likely to lead to global warming. 370 after year. The Keeling found the following: 360 small annual \u201cAt the South Pole the concentration 350 \ufb02uctuation (shown has increased at the rate of about 340 by the blue line) is 1.3 ppm per year\u2026the observed 330 due to seasonal rate of increase is nearly that to 320 changes in CO2 be expected from the combustion 310 uptake by plants. of fossil fuel (1.4 ppm).\u201d In other words, humans are at least part 1960 1970 1980 1990 2000 2010 of the cause. \u25a0 Keeling measured the carbon back for winter. Third, crucially, The demand for energy is dioxide level at the station regularly, the concentration was increasing certain to increase\u2026as and discovered three things. inexorably. Cores of polar ice an ever larger population contained bubbles of air, which strives to improve its First, there was a daily variation showed that during most of locally. The concentration was at the time since 9000 BCE, the CO2 standard of living. a minimum midafternoon, when concentration varied from 275 to Charles Keeling green plants were at their most 285 ppm by volume. In 1958, active in soaking up CO2. Second, Keeling measured 315 ppm; by there was annual variation globally. May 2013, the average concentration The northern hemisphere had more exceeded 400 ppm for the \ufb01rst time. land for plants to grow, and the The increase from 1958 to 2013 level of CO2 rose slowly during the was 85 ppm, meaning that the northern winter when plants were concentration had increased by not growing. It reached a peak in 27 percent in 55 years. This May before plants started to grow was the \ufb01rst concrete evidence and began soaking up CO2 again. that the concentration of CO2 in The level dropped to a minimum in Earth\u2019s atmosphere is increasing. October, when northern plants died Charles Keeling Born in Scranton, Pennsylvania, was to be a lifetime\u2019s work. Charles Keeling was an In 1956, he joined the Scripps accomplished pianist as well Institution of Oceanography in as a scientist. In 1954, as La Jolla, California, where he a postdoctoral fellow in worked for 43 years. geochemistry at the California Institute of Technology (Caltech), In 2002, Keeling received he developed a new instrument the National Medal of Science, to measure carbon dioxide in America\u2019s highest award for atmospheric samples. He found lifetime achievement in science. that the concentration varied Since his death, his son Ralph hour by hour at Caltech, probably has taken over his work because of all the traf\ufb01c, so he monitoring the atmosphere. went camping in the wilderness at Big Sur and found small but Key work signi\ufb01cant variations there, too. This inspired him to begin what 1997 Climate Change and Carbon Dioxide: An Introduction","296 THE BUTTERFLY EFFECT EDWARD LORENZ (1917\u20132008) IN CONTEXT M uch of the history of planetary motion, lend themselves science has been readily to this schema. With a BRANCH devoted to developing description of the initial Meteorology simple models that predict the conditions\u2014the mass of a planet, behavior of systems. Certain its position, velocity, and so on\u2014 BEFORE phenomena in nature, such as future con\ufb01gurations can be 1687 Newton\u2019s three laws of motion hold that the universe According to Newton\u2019s Calculating the is predictable. laws, the universe can trajectories of pool balls after a break should 1880s Henri Poincar\u00e9 shows be predicted. be possible if we have all that the motion of three or the data about the more bodies interacting \u2026because the gravitationally is generally many, tiny differences balls and table. chaotic and unpredictable. in the initial setup will cause But no matter how AFTER the \ufb01nal distribution of accurate our data, it is 1970s Chaos theory is used balls to vary wildly. impossible to replicate to model traf\ufb01c \ufb02ow, digital encryption, function, and in These minute a pool break\u2026 designs for cars and aircraft. uncertainties forbid us from knowing how a Accurate predictions 1979 Beno\u00eet Mandelbrot system will change. of chaotic phenomena discovers the Mandelbrot set, which shows how complex are impossible. patterns can be created using very simple rules. 1990s Chaos theory is thought of as a subset of complexity science, which seeks to explain complex natural phenomena.","FUNDAMENTAL BUILDING BLOCKS 297 See also: Isaac Newton 62\u201369 \u25a0 Beno\u00eet Mandelbrot 316 calculated. However, the behavior Lorenz was astounded when the Edward Lorenz of many processes, such as waves computer returned hugely different crashing on a beach, smoke rising outcomes each time. Checking his Born in West Hartford, from a candle, or weather patterns, \ufb01gures again, he found that the Connecticut, in 1917, Edward is chaotic and unpredictable. Chaos program had rounded up the Norton Lorenz received his theory seeks to explain such numbers from six decimal places MSc in mathematics from unpredictable phenomena. to three. This tiny alteration to the Harvard in 1940. During initial state had a major impact World War II he served as a Three-body problem on the end result. This sensitive meteorologist, forecasting The \ufb01rst strides toward chaos dependence on initial conditions the weather for the US Army theory were taken in the 1880s, was named the \u201cbutter\ufb02y effect\u201d\u2014 Air Corps. After the war, when French mathematician Henri the idea that a small change in a he studied meteorology at Poincar\u00e9 worked on the \u201cthree-body system, as trivial as a teaspoonful Massachusetts Institute problem.\u201d Poincar\u00e9 showed that for of air molecules moved by a of Technology (MIT). a planet with a satellite orbiting a butter\ufb02y \ufb02apping its wings in star\u2014an Earth-Moon-Sun system\u2014 Brazil, can be ampli\ufb01ed over time Lorenz\u2019s discovery of there is no solution for a stable to create unpredictable outcomes, sensitive dependency on orbit. Not only was the gravitational such as a tornado in Texas. initial conditions (SDIC) was interaction between bodies far too accidental\u2014and one of the complex to calculate, Poincar\u00e9 Edward Lorenz de\ufb01ned the great \u201ceureka\u201d moments in found that tiny differences in initial limits of predictability, explaining science. Running simple conditions resulted in large and that the impossibility of knowing computer simulations of unpredictable changes. However, what will happen is actually weather systems he found his work was largely forgotten. written into the rules that govern a that his model was churning chaotic system. Not only weather, out wildly different outcomes, A surprise discovery but many real-world systems are despite being supplied with Few further developments occurred chaotic\u2014traf\ufb01c systems, stock almost identical starting in the \ufb01eld until the 1960s, when market \ufb02uctuations, the \ufb02ow of conditions. His seminal 1963 scientists began to use new, \ufb02uids and gases, the growth of paper showed that perfect powerful computers to predict the galaxies\u2014and they have all been weather prediction was a pipe weather. Surely, they reasoned, modeled using chaos theory. \u25a0 dream. Lorenz remained given enough data on the state of physically and academically the atmosphere at a given time Here, turbulence forms at the tip of a active all his life, contributing and enough computational power vortex left in the wake of an aircraft\u2019s academic papers, and hiking to crunch the data, it should be wing. Study of the critical point beyond and skiing until shortly before possible to know how weather which a system creates turbulence was his death in 2008. systems evolve. Working on key to the development of chaos theory. the assumption that ever-larger Key work computers would increase the range of predictions, Edward 1963 Deterministic Lorenz, an American meteorologist Nonperiodic Flow at the Massachusetts Institute of Technology (MIT), tested simulations involving just three simple equations. He ran the simulation several times, each time inputting the same initial state and expecting to see the same results.","298 A VACUUM IS NOT EXACTLY NOTHING PETER HIGGS (1929\u2013) IN CONTEXT Imagine a room of physicists at a cocktail party. This is like the Higgs \ufb01eld, BRANCH Physics which \ufb01lls everything, even a vacuum. BEFORE A tax collector enters In walks Peter Higgs. The 1964 Peter Higgs, Fran\u00e7ois the party, and travels physicists would like to talk to Englert, and Robert Brout unimpeded to the bar at the describe a \ufb01eld that gives far end of the room. him, so they gather around, mass to all elementary and impeding his progress. force-carrying particles. The taxman has Peter Higgs interacts 1964 Three separate teams little interaction with the strongly with the \u201c\ufb01eld\u201d of physicists predict the \u201c\ufb01eld\u201d of physicists and is and moves slowly through existence of a new massive analogous to a particle of particle (the Higgs boson). the room. He is like a low mass. high-mass particle. AFTER 1966 Physicists Steven A vacuum is not exactly nothing. Weinberg and Abdus Salam use the Higgs \ufb01eld to formulate T he great scienti\ufb01c event of boson gives mass to all things in the electroweak theory. 2012 was the announcement the universe, and is the missing from scientists at the Large piece that completes the standard 2010 CERN\u2019s Large Hadron Hadron Collider (LHC) at CERN in model of physics. Its existence had Collider reaches full power. Switzerland that a new particle had been hypothesized by six physicists, The search begins for the been found, and that it might be among them Peter Higgs, in 1964. Higgs boson. the elusive Higgs boson. The Higgs Finding the Higgs boson was of 2012 Scientists at CERN announce the discovery of a new particle matching the description of the Higgs boson."]