The Science Book

A PARADIGM SHIFT 249

LIFE ITSELF IS
A PROCESS OF
OBTAINING
KNOWLEDGE

KONRAD LORENZ (1903–1989)

IN CONTEXT A mong the first to conduct These cranes and geese, hatched and
scientific 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—within a critical period
describes inherited behavior learned, but Spalding thought that after hatching. The mother’s
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 “fixed action
“hardwired”—such as the tendency pattern” 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—the study goslings, which adopted him as
behavior in birds. of animal behavior—accepts 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 modified Lorenz was awarded the Nobel
by experience. Prize in Physiology in 1973. ■
AFTER
1976 British zoologist Imprinting geese
Richard Dawkins publishes In the 1930s, Austrian biologist
The Selfish 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 “imprinting.” He studied the
way that greylag geese imprint on,
2000s New research reveals or follow, the first eligible moving
growing evidence of the stimulus they see—usually their
importance of teaching among
many species of animal, from See also: Charles Darwin 142–49 ■ Gregor Mendel 166–71 ■
insects to killer whales. Thomas Hunt Morgan 224–25

250

95 PERCENT
OF THE UNIVERSE
IS MISSING

FRITZ ZWICKY (1898–1974)

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
first proposed by Swiss astronomer Virial theorem, which allowed him
BEFORE Fritz Zwicky. In 1922–23, Edwin to calculate the overall mass from
1923 Edwin Hubble confirms Hubble had realized that “nebulae” the relative velocities of individual
the true nature of galaxies were in fact distant galaxies. cluster galaxies. To Zwicky’s
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 first of all energy. 26.8 percent of all energy.
detailed catalogue of galaxy
clusters. Subsequent studies Just 4.9 percent of the universe’s energy is accounted for
of galaxy clusters have by visible matter.
repeatedly confirmed the
existence of dark matter.

1950s–present 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 236–41 ■ Georges Lemaître 242–45

Rotational velocity Measured
[km/s]
Calculated
200

100

50,000 100,000

Distance from center of galaxy (light years)

If our galaxy’s mass distribution matched that of its visible matter, Fritz Zwicky
then stars in the galaxy’s outer disk would move more slowly at greater
distances from the massive center. Vera Rubin’s 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’s 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 “dark matter.” or rogue planets, have not been Aside from his work on
borne out by research. It is now dark matter, Zwicky is also
Zwicky’s 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 first 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—they 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 “supernovae” 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 “missing become clear that even dark By showing that one class
mass” fell substantially. matter is dwarfed by “dark energy.” 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.236–41), and its nature also provided a means of
finally recognized in the 1970s, is still unknown—it 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 fifth fundamental force known of Hubble’s Law, paving the
in the Milky Way and measured as “quintessence.” 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’s visible confines, in a amounting to 26.8 percent, and
region known as the galactic halo. normal matter a mere 4.9 percent. ■ 1934 On Supernovae
(with Walter Baade)
1957 Morphological Astronomy

252

A UNIVERSAL
COMPUTING
MACHINE

ALAN TURING (1912–1954)

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.
“decision problem,” 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…, 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 finite number of
computers, using some of A Compare the first pair of numbers. times; and yields a finished result,
Turing’s 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 first 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 first 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, finish. procedures. His work was initially

1946 The first general-purpose
electronic programmable
computer, ENIAC, based
partly on Turing’s concepts,
is unveiled.

A PARADIGM SHIFT 253

See also: Donald Michie 286–91 ■ Yuri Manin 317

theoretical—an 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.” showed a prodigious talent for
mathematics at school. He
The a-machine Now known as the Universal earned a first class degree in
To help envisage the situation, Turing Machine (UTM), this device mathematics from Kings
Turing conceived a hypothetical had an infinite store (memory) College, Cambridge, in 1934,
machine. The “a-machine” (“a” 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 first 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. ■ fully functioning computer
the rules. It then moves to one known as the “Bombe” 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
configuration 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—it seems
undertaking. He added, “We 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 infinitely 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 (1901–1994)



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 figured 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 Schrödinger in Zurich.
have definite combining He had already decided that he Electrons orbit an atomic nucleus in
power, which determines the wanted to research the bonding various ways—in 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 Kekulé 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—it forms four bonds Hybridization of orbitals quantum mechanics designated
with other atoms. When he returned to the US, the first two as “1s-electrons”:
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—
chemist Gilbert Lewis shows of five rules for interpreting the like a balloon inflated 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’s rules. At the same two “2s-electrons.” The 2s shell
time, he was turning his attention is like another, bigger balloon
AFTER to the bonding between atoms in outside the first. Lastly, there are
1938 British mathematician covalent molecules (molecules in “p-orbitals,” 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— 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 modified occupy two of these orbitals—
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 “clouds” of probability
The nature of the densities. It was no longer quite
chemical bond reflects 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 Kekulé 160–65 ■ Max Planck 202–05 ■ Erwin Schrödinger 226–33 ■ Harry Kroto 320–21

bonding. Bonds could either be By 1935, I felt I had an Diamond is pure carbon, and in
strong “sigma” 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 “pi” 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’s 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’s atomic orbitals closest neighboring atoms were atoms to bond to other atoms is
could combine, or “hybridize,” 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 first These stick out from the nucleus
orbitals could hybridize to form structures to be resolved by in one plane, with angles of 120°
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°. 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° apart. This is consistent ❯❯

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. infinite lattice held together by
The remaining two covalent carbon–carbon 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 Kekulé when he
first 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’s 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° 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 specific 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 first 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–O) is first 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–C bonds and O–O 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—a strong bond. element (strictly speaking in Pauling took great interest
a particular compound) is a in biological molecules,
Sodium chloride was the first 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 fluorine; the least electronegative was awarded the Nobel Peace
structure comprises an infinite (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, fluoride, each fluorine 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: infinite ionic compound Cs+F-. his enthusiasm for alternative
lattices of one type of ion with medicine. He championed the
different ions filling 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 first 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. ■

AN AWESOME

POWER

IS LOCKED INSIDE THE NUCLEUS

OF AN ATOM

J. ROBERT OPPENHEIMER (1904–1967)



262 J. ROBERT OPPENHEIMER

IN CONTEXT Splitting the nucleus of an atom of uranium
releases three neutrons. 
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’s famous
mass-energy equivalence Each time a nucleus is split, a fraction of its mass is
equation E = mc2 describes turned into energy. 
how tiny masses “store” 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’s experiments absorbing neutrons explosion (nuclear bomb).
splitting lithium nuclei (nuclear fission reactor).
with protons hint at the
enormous energy locked An awesome power is locked inside the
inside the nucleus. nucleus of an atom.

1939 Leó Szilárd spots that
a single fission event of
uranium-235 releases three
neutrons and suggests that
a chain reaction is possible.

AFTER
1954 The USSR’s Obninsk
Nuclear Power Plant goes into
operation. It is the first nuclear
power station to generate
electricity for a country’s
national grid.

I n 1938, the world stood at the and this compulsion took the newly to be computed. Oppenheimer’s
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 scientific drive that theoretical physics. At Göttingen modern chemistry, but the final
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–Oppenheimer 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
scientific project the world had put it, “why molecules are Fission and black holes
seen—the Manhattan Project—but molecules.” 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’s varied professional ambitious mathematical exercise Fritz Strassmann “split the atom”
life had been characterized by a as a dizzying range of possibilities in their Berlin laboratory. They had
ruthless drive to “be where it’s at” for each electron in a molelcule had been firing neutrons at uranium,

A PARADIGM SHIFT 263

See also: Marie Curie 190–95 ■ Ernest Rutherford 206–13 ■ Albert Einstein 214–21

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–Wheeler theory nuclei contain 92 protons and
remembered the line from of nuclear fission. 143 neutrons. The Bohr–Wheeler
the Hindu scripture: “Now theory incorporated the finding that
I am become Death, the All the atoms of the same low-energy neutrons could cause
destroyer of worlds.” element have nuclei with the same fission 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 ❯❯

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 fission 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
figured out the basic mechanism (Ba), an atom of krypton (Kr), and three
of nuclear fission, recognizing how more neutrons. The three neutrons can
uranium was split into barium and then go on to cause fission 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–Frisch paper in the journal
Nature, set the East Coast scientific
community ablaze with excitement.
Conversations between Bohr and

264 J. ROBERT OPPENHEIMER

saw the potential for making a realize the horrific consequences We have made a thing, a most
weapon of awesome power—to his for a world heading toward war. terrible weapon, that has
mind “a good, honest, practical Pondering Rutherford’s lecture,
way” to use the new science. But Szilárd saw that the “secondary altered abruptly and profoundly
while laboratories in East Coast neutrons” emerging from the first the nature of the world. And
universities raced to replicate the fission event could themselves by so doing we have raised
results of early fission experiments, create further fission 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 fission. Szilárd J. Robert Oppenheimer
collapsing under their own gravity later recalled, “There was little
to form black holes. doubt in my mind that the world smaller facilities, it employed
was headed for grief.” 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 £16 bn, in
already in the air. As early as 1913, the US showed that the chain 2014 money)—all in top secrecy.
H. G. Wells wrote of “tapping the reaction was indeed possible,
internal energy of atoms” to make prompting Szilárd and another Early in 1941, the decision
“atomic bombs.” In his novel The Hungarian emigré, Edward Teller, was taken to pursue five
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 fissionable 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
fission 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 first.
of harnessing this energy as
“moonshine,” since the process Birth of Big Science
was so inefficient 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 Leó Szilárd 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 Göttingen 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 influential friends Gravitational Contraction
wherever he went. However, he

A PARADIGM SHIFT 265

On August 9, 1945, the plutonium
bomb “Fat Man” 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 first
controlled chain reaction involving
nuclear fission was carried out on a
squash court at the University of
Chicago. Enrico Fermi’s Chicago
Pile-1 was the prototype for the
reactors that would enrich uranium
and create the newly discovered
plutonium—an 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’s research into secret the bomb was dropped, and many him, “I feel I have blood on my
weapons, Oppenheimer approved Los Alamos scientists felt a public hands.” 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—after 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’s final stages—the be sure to surrender. However, ability to influence public policy.
construction of an atomic bomb. while Hiroshima was believed by
“Site Y” would see the highest some to be a necessary evil, the By then, Oppenheimer had
concentration of Nobel laureates detonation of a plutonium device— overseen the advent of the
ever gathered in one place. called “Fat Man”—over Nagasaki military–industrial 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 scientific 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 “problem scientists must now consider. ■
of engineering.” However, it was
Oppenheimer’s 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 “Little
Boy” 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–PRESENT

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 first 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 flourish, and that this
field of science, from telescopes to set up an ingenious experiment process had produced the complex
chemical analysis. New technology to find 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 first 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— proposal. American microbiologist
Artificial Intelligence, has emerged. American James Watson and Briton Michael Syvanen showed how
CERN’s Large Hadron Collider—a Francis Crick—in a race against genes can jump from one species
particle accelerator—is the biggest rival teams in the US and Soviet to another, while in the 1990s, the
piece of scientific equipment ever Union, figured out the molecular old Lamarckian idea that acquired
made. Powerful microscopes have structure of deoxyribonucleic acid, characteristics can be passed
allowed the first 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 artificial 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’s theory of a
New particles had predicted was detected by constantly splitting multiverse
In physics, the strangeness of CERN’s Large Hadron Collider. was at first 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 “theory of everything”—a Future directions
explained quantum interactions theory that would unite all four Deep puzzles remain to be solved,
in terms of exchange of “virtual” 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)—took 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 “electroweak” 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. ■
hidden dimensions in addition to

270

WE ARE MADE
OF STARDUST

FRED HOYLE (1915–2001)

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 first developed Bethe’s 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’s 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—the death throes
1863 English astronomer E = mc2. Eddington developed a of massive stars. The elements
William Huggins’ spectrum model of star structure in terms of needed for life are made in stars. ■
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
1905–10 Astronomers in the he did not figure out the physics of
US and Sweden analyze stars’ the nuclear reactions involved.
luminosity and group them
into dwarfs and giants. Making heavier elements Space isn’t remote at all.
In 1939, German-born US physicist It’s only an hour’s 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 identified two routes—a slow, Fred Hoyle
1934 Fritz Zwicky coins the low-temperature chain that
term “supernova” for a massive dominates in stars like our Sun, and
star’s explosive end. a rapid, high-temperature cycle that
dominates in more massive stars.
AFTER
2013 Deep-sea fossils reveal See also: Marie Curie 190–95 ■ Albert Einstein 214–21 ■
what may be biological traces Ernest Rutherford 206–13 ■ Georges Lemaître 242–45 ■ Fritz Zwicky 250–51
of iron from a supernova.

FUNDAMENTAL BUILDING BLOCKS 271

JUMPING GENES

BARBARA MCCLINTOCK (1902–1992)

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 refined as new variety, which she reported in 1951.
discoveries were made about the
BEFORE particles of inheritance, identified 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 “particles”— chromosomes. In the 1930s, X-shaped structures marked
later called genes. American geneticist Barbara locations where chromosome pairs
McClintock first 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 shuffled
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’s Exchanging genes This shuffling of genes—called
fruit fly experiments confirm McClintock was studying genetic recombination—produces
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’s are enhanced. ■
AFTER genes. A kernel is a seed—a single
1953 James Watson and offspring—so studying many cobs
Francis Crick’s 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 first human genome that, during sexual reproduction,
is published, cataloguing the
location of 20,000–25,000 See also: Gregor Mendel 166–71 ■ Thomas Hunt Morgan 224–25 ■
genes on humans’ 23 pairs James Watson and Francis Crick 276–83 ■ Michael Syvanen 318–19
of chromosomes.

272

THE STRANGE
THEORY OF LIGHT
AND MATTER

RICHARD FEYNMAN (1918–1988)

IN CONTEXT O ne of the questions to particles interacted through the
arise from the quantum exchange of quanta, or “photons,”
BRANCH mechanics of the 1920s of electromagnetic energy—the
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’s uncertainty principle,
mass can behave like a wave. quantum electrodynamics (QED), and this allows fluctuations in
explained the interaction of the amount of energy available
1927 Werner Heisenberg particles through the exchange of in “empty” space. Such photons
shows there is an inherent electromagnetism. It has proved are sometimes called “virtual”
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 confirmed their
such as the position and it a “strange” 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 field theories
1927 Paul Dirac applies are known as “gauge bosons.”
quantum mechanics to fields Messenger particles
rather than single particles. Paul Dirac made the first step However, there were problems
toward a theory of QED based on with QED. Most significantly,
AFTER the idea that electrically charged its equations often generated
Late 1950s Julian Schwinger nonsensical infinite 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 first 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 “color charge.” Path of second electron

Space

FUNDAMENTAL BUILDING BLOCKS 273

See also: Erwin Schrödinger 226–33 ■ Werner Heisenberg 234–35 ■
Paul Dirac 246–47 ■ Sheldon Glashow 292–93

Particles interact by This exchange can
exchanging photons. happen in many different

ways, each with its
own probability.

The “strange theory Summing the Richard Feynman
of light and matter” 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 fixing 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 “strange” 1942, Feynman worked under
and others took Bethe’s 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 flair for
subject approachable through his description of reality even if it feels communicating his ideas. He
invention of “Feynman diagrams”— 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—the strong nuclear force
work. The key breakthrough was has been successfully described Key works
to find 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 unified 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. ■ Theory of Light and Matter
1985 Surely You’re Joking,
Mr. Feynman?

274

LIFE IS NOT
A MIRACLE

HAROLD UREY (1893–1981)
STANLEY MILLER (1930–2007)

IN CONTEXT Earth’s 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, “But if…we 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
“some warm little pond.” 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…” 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’s 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–Miller
experiment, advances in chemistry
AFTER and astronomy had analyzed the
1961 Spanish biochemist atmospheres on the other, lifeless
Joan Oró adds further likely planets in the solar system. In the
chemicals to the Urey–Miller 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’s 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: Jöns Jakob Berzelius 119 ■ Friedrich Wöhler 124–25 ■ FUNDAMENTAL BUILDING BLOCKS 275
Charles Darwin 142–49 ■ Fred Hoyle 270
Harold Urey and
Stanley Miller

Laboratory apparatus replicated Gases (Earth’s atmosphere) Harold Clayton Urey was born
the effect of lightning on early Earth’s 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’s oceans) column the Manhattan Project’s
development of the first 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’s 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 first prolonged experiment to experiment to the journal Science,
test the Oparin–Haldane theory. In which published it as “Production Stanley Lloyd Miller was
a closed series of connected glass of amino acids under possible born in Oakland, CA. After
flasks, sealed from the atmosphere, primitive earth conditions.” 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’s “warm little pond” may Berkeley, he was a teaching
in Earth’s primitive atmosphere— have generated the first 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 “just turning on the spark in a basic professor in San Diego.
around all the flasks in the closed prebiotic experiment will yield
loop. In one of the flasks was a pair amino acids.” 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—one of the experiment had produced at least Acids under Possible Primitive
hypothetical triggers for primordial 25 amino acids—more than are Earth Conditions
reactions. The sparks provided found in nature. Since Earth’s 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—and 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. ■

WE WISH TO SUGGEST A

STRUCTURE

FOR THE SALT OF

DEOXYRIBOSE

NUCLEIC ACID (DNA)

JAMES WATSON (1928–)
FRANCIS CRICK (1916–2004)



278 JAMES WATSON AND FRANCIS CRICK

IN CONTEXT I n April 1953, the answer to on the challenge of DNA’s 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 scientific journal,
BEFORE Nature. The article explained both DNA was the hot topic of the
1869 Friedrich Miescher first how genetic instructions are held day, and an understanding of its
identifies 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 first time, the double-helix and the Soviet Union were vying
of DNA as sugars, phosphates, structure of deoxyribose nucleic to be the first to “crack” DNA’s
and four types of base. acid (DNA), the molecule that three-dimensional shape—the
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’s code is cracked: popularly thought, nor were Crick
three DNA bases of code for and Watson the first to find 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 artificially made Flemming had reported that “X”-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 “central
genetics, Watson moved to dogma”: that genetic data flow
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 142–49 ■ Gregor Mendel 166–71 ■ Thomas Hunt Morgan 224–25 ■ Barbara McClintock 271 ■
Linus Pauling 254–59 ■ Craig Venter 324–25

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—a huge molecule
able to replicate. consisting of repeating units, or
monomers—was 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’s
The structure of DNA is a double helix. crystals. A crystal’s 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’s 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—Mendel had been information. The next step was to patterns of spots, lines, and blurs
the first to suggest that there were look at the constituent molecules were captured on photographic
units of heredity that came in pairs of chromosomes—molecules that film. Working backward from those
(which would later be called genes). might be candidates for genes. patterns, it was possible to figure
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 ❯❯
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…that the
cell to each of its daughter cells. The Russian-American biochemist twenty amino acids and the
The ensuing Sutton–Boveri theory Phoebus Levene and others four bases, are, with minor
proposed that chromosomes are gradually identified 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—including 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 figure out the shapes and substance in blood—have 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—
alpha-helix. the viruses that infect bacteria.
Pauling in the lead Crick, 37 years old, was a
The British research team at the Pauling’s 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’s 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’s
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’s
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’s draft reports One of Franklin’s considerations
data from others, including the on her theoretical models for DNA’s was whether the structural
results of chemical experiments structure were key to Watson and “backbone,” a chain of phosphate
that gave information about the Crick’s 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 scientific 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
“photo 51,” which became key to recognized their significance, and access to Franklin’s 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’s
diffraction image of DNA that backbones were on the outside,
resembled an “X” seen through the From this point, the exact with the bases pointing inward and
slats of a Venetian blind—fuzzy 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 shuffled
the sharpest and most informative discovery are conflicting. Franklin around cardboard shapes that
of DNA’s 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—adenine, 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’s 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’s 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’s
image at various times. giant molecule. first rule. This stated that in DNA,
the amounts of guanine and
Cardboard models cytosine are equal, as are the
Also working at King’s 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 findings 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 fit
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. ❯❯

282 JAMES WATSON AND FRANCIS CRICK

These are human male chromosomes. the pieces to fit together, producing cell how to make the particular
Before Crick and Watson’s 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’s 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 “unzipped”
and their angles, and other data— each other, like the uprights of a by undoing the bonds, which then
all approximate and subject to “twisted ladder,” connected by exposes the code of bases as a
ranges of errors. Their final 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 configurations 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—which in turn told the could be made from one unzipped

FUNDAMENTAL BUILDING BLOCKS 283

half of the double helix; then, “for 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 significance 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.” The award, however, combinations of either adenine–thymine
was surrounded in controversy. or cytosine–guanine.
Second, when the whole length In the preceding years, Rosalind
of the double helix was unzipped, Franklin had received little official 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—resulting in two lengths that helped to direct Watson phosphate
of DNA that were identical to the and Crick’s 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’s the prizes are not awarded
life—and 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.
“Secret of life”
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’s 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 “the secret of life”— genetic “code.” By 1964, scientists
or so Watson later recalled in his figured 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 specific
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 specific 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—a sequence
of more than 20,000 genes. Crick
and Watson’s discovery had paved
the way for genetic engineering
and gene therapy. ■

284

EVERYTHING
THAT CAN
HAPPEN HAPPENS

HUGH EVERETT III (1930–1982)

IN CONTEXT A card finely 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
infinity of inhabited worlds.
is consistent with (2 × 2 × 2 × 2).
1924–27 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. figure to sci-fi 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.232–33).
1980s A principle known mechanics changed scientists’
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’s work was inspired by to exist in any number of possible
interpretation may work. the embarrassing flaw at the heart states of location, velocity, and
of quantum mechanics. Although spin, or “superpositions,” as
2000s Swedish cosmologist it can explain interactions at the described by Erwin Schrödinger’s
Max Tegmark describes an most fundamental level of matter, wave function, but the phenomenon
infinity 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 202–05 ■ Werner Heisenberg 234–35 ■ Erwin Schrödinger 226–33

“Multiverse” 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’s idea was to explain do, in fact, occur. Reality peels
seems to “shunt” it into one state what happens to the quantum itself, or splits, into new worlds,
or another, forcing it to “choose” superpositions. He presumed but since we inhabit a world where
its option. In the world we’re 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 definite heads or tails, and not (unobserved) collapse—why should outcomes are inaccessible to us,
one, the other, and both at once. nature “choose” 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’s 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 “collapse” 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 find together. While he was studying An effect known as “decoherence”—
it unsatisfactory since it reveals mathematics at Princeton, he whereby quantum objects “leak”
nothing about the mechanism drifted into physics. MWI—his their superposition information—is
of wave function collapse. This answer to the riddle at the heart a mechanism by which MWI might
bothered Schrödinger, too. For him, of quantum mechanics—was be proved to work. ■
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, “Either the wave function, as trip to Copenhagen in 1959 to the US defense industry, but
given by the Schrödinger equation, discuss the idea with Niels Bohr today MWI is regarded as a
is not everything, or is not right.” was a disaster—Bohr rejected mainstream interpretation of
quantum theory—too 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 (1923–2007)



288 DONALD MICHIE C omputers in 1961 were Can machines think? The
mostly mainframes short answer is “Yes: 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
Artificial intelligence know them today were several were done by a human being.”
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 artificial symmetrical to, each other.
program to play tic-tac-toe by intelligence— 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 “artificial task, too—the game of tic-tac-toe,
intelligence” 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 “tit-tat-to.” 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’s main version of example, a green bead meant O
1968 MacHack, the first 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’s Deep Blue computer. grid with various arrangements using the matchbox for no Os or
of Os and Xs, corresponding to Xs in the grid—the “first move”
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 “V” shape. To
and error. combinations but some can be play, the tray was removed from
the box, jiggled, and tilted so the
…a 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’s color
determined the position of
Reinforcing positive MENACE’s first 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…

FUNDAMENTAL BUILDING BLOCKS 289

See also: Alan Turing 252–53

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 “V” 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 first 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 “punished” 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’s second O. The same permutation of Xs and Os Michie’s goal was that MENACE
opponent placed their second X. cropped up, the beads designating would “learn from experience.” For
And so on, recording MENACE’s 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 “reward.” 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, identified by the code number Colossus, the world’s first electronic Controlling variables
and slightly open tray. The tray programmable computer, was made in Michie considered potential
also received three extra “bonus” 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’s 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—and 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 ❯❯

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’s first 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 “complicate the problem Michie simulated this by having then notch up some wins. To
unnecessarily.” 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’s 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—those 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—had three of each kind of wins. At one point in a series of
a principle: machine learning works bead. For MENACE’s 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’s
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—usually 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 ‘“Essentially, the animal makes
contributed less to the final defeat— 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
final one increases. Therefore as produced the ‘desired’ 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 artificial 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 artificial 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 first 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.” 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’ brains. thought might possibly solve
biology, surgery, genetics, and computer chess…It 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 artificial 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 “industrial-strength a reminder or “memo.” If the same
tools” 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
artificial 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. ■

292

THE UNITY OF
FUNDAMENTAL
FORCES

SHELDON GLASHOW (1932–)

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 fields, a force is
Physics Greeks. Physicists currently “felt” by the exchange of a gauge
recognize four fundamental forces— boson, such as the photon, which
BEFORE gravity, electromagnetism, and carries electromagnetic interaction.
1820 Hans Christian Ørsted 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—an
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. “electroweak” force. Discovering changing quarks (the particles
this was an important step on that protons and neutrons are made
1933 Enrico Fermi’s theory the way to finding a “Theory of from) from one kind to another.
of beta decay describes the Everything” that would explain the
weak force. relationship between all four forces.

1954 The Yang–Mills theory The weak force Decay of particles via the weak force
lays the mathematical The weak force was first invoked drives the Sun’s proton–proton 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’t 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 “charm” 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’s Super Proton carrying particles that mediate
Synchrotron in Switzerland. interaction via the weak force.

FUNDAMENTAL BUILDING BLOCKS 293

See also: Marie Curie 190–95 ■ Ernest Rutherford 206–13 ■
Peter Higgs 298–99 ■ Murray Gell-Mann 302–07

A “Theory of Everything” 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 “superforce.”
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–, 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’s particle by massless photons of light), while In the 1960s, Glashow
accelerator in 1983. the weak force barely reaches extended Murray Gell-Mann’s
across an atomic nucleus and is quark model, adding a
Unification some 10 million times weaker. property known as “charm”
In the 1960s, two physicists, Their unification 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 field (pp.298–99) into Bang, all four fundamental forces theory, disputing its place
Glashow’s theory. The resultant may coalesce into one “superforce.” in physics due to its lack of
Weinberg–Salam model, or unified The search continues for evidence testable predictions, and
of such a Theory of Everything. ■ describing it as a “tumor.”

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 (1928–2005)

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’s atmosphere. disastrous warming first came
BEFORE to widespread scientific and
1824 Joseph Fourier suggests Its concentration in the public attention in the 1950s.
that Earth’s 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’s 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’s 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 findings 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’s average temperature Keeling measured CO2 in several
increased by 1°F (0.5°C) 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
scientific 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 ■ Joseph Fourier 122–23 ■ Robert FitzRoy 150–55

Parts per million Carbon Dioxide Concentration Keeling’s 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 “At the South Pole the concentration
350 fluctuation (shown has increased at the rate of about
340 by the blue line) is 1.3 ppm per year…the 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).” In other
words, humans are at least part
1960 1970 1980 1990 2000 2010 of the cause. ■

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…as
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 first 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 first concrete evidence
and began soaking up CO2 again. that the concentration of CO2 in
The level dropped to a minimum in Earth’s atmosphere is increasing.
October, when northern plants died

Charles Keeling Born in Scranton, Pennsylvania, was to be a lifetime’s 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’s 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 traffic, so he monitoring the atmosphere.
went camping in the wilderness
at Big Sur and found small but Key work
significant variations there, too.
This inspired him to begin what 1997 Climate Change and
Carbon Dioxide: An Introduction

296

THE BUTTERFLY
EFFECT

EDWARD LORENZ (1917–2008)

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—the mass of a planet,
behavior of systems. Certain its position, velocity, and so on—
BEFORE phenomena in nature, such as future configurations can be
1687 Newton’s three laws of
motion hold that the universe According to Newton’s Calculating the
is predictable. laws, the universe can trajectories of pool
balls after a break should
1880s Henri Poincaré shows be predicted. be possible if we have all
that the motion of three or the data about the
more bodies interacting …because 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 final distribution of accurate our data, it is
1970s Chaos theory is used balls to vary wildly. impossible to replicate
to model traffic flow, digital
encryption, function, and in These minute a pool break…
designs for cars and aircraft. uncertainties forbid us
from knowing how a Accurate predictions
1979 Benoît 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 62–69 ■ Benoît 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, figures 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 first strides toward chaos dependence on initial conditions the weather for the US Army
theory were taken in the 1880s, was named the “butterfly effect”— Air Corps. After the war,
when French mathematician Henri the idea that a small change in a he studied meteorology at
Poincaré worked on the “three-body system, as trivial as a teaspoonful Massachusetts Institute
problem.” Poincaré showed that for of air molecules moved by a of Technology (MIT).
a planet with a satellite orbiting a butterfly flapping its wings in
star—an Earth-Moon-Sun system— Brazil, can be amplified over time Lorenz’s 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—and one of the
complex to calculate, Poincaré Edward Lorenz defined the great “eureka” 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—traffic systems, stock almost identical starting
in the field until the 1960s, when market fluctuations, the flow of conditions. His seminal 1963
scientists began to use new, fluids and gases, the growth of paper showed that perfect
powerful computers to predict the galaxies—and they have all been weather prediction was a pipe
weather. Surely, they reasoned, modeled using chaos theory. ■ 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’s 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–)

IN CONTEXT Imagine a room of physicists at
a cocktail party. This is like the Higgs field,
BRANCH
Physics which fills everything, even a vacuum.

BEFORE A tax collector enters In walks Peter Higgs. The
1964 Peter Higgs, François the party, and travels physicists would like to talk to
Englert, and Robert Brout unimpeded to the bar at the
describe a field 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 “field”
of physicists predict the “field” 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 field to formulate T he great scientific 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’s 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.