In 1942, in a squash court beneath the stadium at the University of Chicago, physicist Enrico Fermi and his colleagues produced a controlled nuclear chain reaction using uranium. Fermi had relied on the 1939 work of physicists Lise Meitner and Otto Frisch, who showed how the uranium nucleus breaks into two pieces, unleashing tremendous energy. In the 1942 experiment, metal rods absorbed the neutrons, allowing Fermi to control the rate of reaction. Author Alan Weismann explains, “Less than three years later, in a New Mexico desert, they did just the opposite. The nuclear reaction this time [which included plutonium] was intended to go completely out of control. Immense energy was released, and within a month, the act was repeated twice, over two Japanese cities. . . . Ever since, the human race has been simultaneously terrified and fascinated by the double deadliness of nuclear fission: fantastic destruction followed by slow torture.”
The Manhattan Project, led by the U.S., was the codename for a project conducted during World War II to develop the first atomic bomb. Physicist Leó Szilárd had been so concerned about German scientists creating nuclear weapons that he approached Albert Einstein to obtain his signature for a letter sent to President Roosevelt in 1939, alerting him to this danger. Note that a second kind of nuclear weapon (an “H-bomb”) uses nuclear fusion reactions.
SEE ALSO Radioactivity (1896), E = mc2 (1905), Nucleus (1911), Little Boy Atomic Bomb (1945).
LEFT: Lise Meitner was part of the team that discovered nuclear fission (1906 photo). RIGHT: Calutron (mass spectrometer) operators in the Y-12 plant at Oak Ridge, Tennessee, during World War II. The calutrons were used to refine uranium ore into fissile material. Workers toiled in secrecy during the Manhattan Project effort to construct an atomic explosive.
1945
Little Boy Atomic Bomb • Clifford A. Pickover
J. Robert Oppenheimer (1904–1967), Paul Warfield Tibbets, Jr. (1915–2007)
On July 16, 1945, American physicist J. Robert Oppenheimer watched the first detonation of an atomic bomb in the New Mexico deserts, and he recalled a line from the Bhagavad Gita, “Now I become Death, the destroyer of worlds.” Oppenheimer was the scientific director of the Manhattan Project, the World War II effort to develop the first nuclear weapon.
Nuclear weapons are exploded as a result of nuclear fission, nuclear fusion, or a combination of both processes. Atomic bombs generally rely on nuclear fission in which certain isotopes of uranium or plutonium split into lighter atoms, releasing neutrons and energy in a chain reaction. Thermonuclear bombs (or hydrogen bombs) rely on fusion for a portion of their destructive power. In particular, at very high temperatures, isotopes of hydrogen combine to form heavier elements and release energy. These high temperatures are achieved with a fission bomb to compress and heat fusion fuel.
Little Boy was the name of the atomic bomb dropped on Hiroshima, Japan on August 6, 1945, by the bomber plane Enola Gay, piloted by Colonel Paul Tibbets. Little Boy was about 9.8 feet long (3.0 meters) and contained 140 pounds (64 kilograms) of enriched uranium. After release from the plane, four radar altimeters were used to detect the altitude of the bomb. For greatest destructive power, the bomb was to explode at an altitude of 1,900 feet (580 meters). When any two of the four altimeters sensed the correct height, a cordite charge was to explode in the bomb, firing one mass of uranium-235 down a cylinder into another mass to create a self-sustaining nuclear reaction. After the explosion, Tibbets recalled the “awful cloud . . . boiling up, mushrooming terrible and incredibly tall.” Over a period of time, as many as 140,000 people were killed—roughly half due the immediate blast and the other half due to gradual effects of the radiation. Oppenheimer later noted, “The deep things in science are not found because they are useful; they are found because it was possible to find them.”
SEE ALSO Von Guericke’s Electrostatic Generator (1660), Radioactivity (1896), Energy from the Nucleus (1942).
Little Boy on trailer cradle in pit, August 1945. Little Boy was about 9.8 feet (3.0 meters) long. Over a period of time, Little Boy may have killed as many as 140,000 people.
1945
Uranium Enrichment • Marshall Brain
Imagine the following situation faced by engineers working on the Manhattan Project in 1942. The uranium that comes out of the ground is almost entirely U-238. But mixed in with the U-238 atoms is the occasional U-235 atom (less than 1 percent). The U-235 atoms are what engineers need to build a nuclear bomb. How is it possible to separate the U-235 atoms from the U-238 atoms?
There are lots of processes that engineers use in factories to separate one thing from another. Oil refineries use different boiling and condensation temperatures. Quarries use sieves to separate different sizes of gravel. If salt and sand mix together, water can chemically dissolve the salt to separate it. But separating U-235 from U-238 is difficult because the atoms are nearly identical.
People came up with many different ideas for performing the separation: thermal, magnetic, centrifuge, etc. The method they settled on as the best means of separation at the time is called gaseous diffusion and it involves two steps: Turn solid uranium into a gas called uranium hexafluoride, and let the gas diffuse though hundreds of micro-porous membranes, which have a slight preference for letting U-235 atoms through instead of U-238 atoms.
While this sounds simple, engineering a structure to perform the operation reliably turned out to be a gigantic engineering challenge. The K-25 building—the first full-scale gaseous diffusion plant, at Oak Ridge, Tennessee—came online in 1945, cost $500 million at the time ($8 billion today) and used a noticeable percentage of the nation’s electricity. The building was enormous—one of the largest in the world, with something like fifty enclosed acres holding thousands of diffusion chambers along with their pumps, seals, valves, temperature controls, etc. One of the biggest problems was the highly corrosive nature of uranium hexafluoride. Newly developed materials like Teflon helped block its action.
With an unprecedented level of secrecy and a speed that boggles the mind, engineers built K-25 (and other plants) and brought them online to purify the uranium for the first atomic bombs. After World II, the gaseous diffusion process kept purifying uranium until it was replaced by more efficient centrifuges.
SEE ALSO Atomic Nucleus (1911), Energy from the Nucleus (1942), Little Boy Atomic Bomb (1945).
Gas centrifuges used to produce enriched uranium. This photograph is of the US gas centrifuge plant in Piketon, Ohio, from 1984.
1946
ENIAC • Clifford A. Pickover
John Mauchly (1907–1980), J. Presper Eckert (1919–1995)
ENIAC, short for Electronic Numerical Integrator and Computer, was built at the University of Pennsylvania by American scientists John Mauchly and J. Presper Eckert. This device was the first electronic, reprogrammable, digital computer that could be used to solve a large range of computing problems. The original purpose of ENIAC was to calculate artillery firing tables for the U.S. Army; however, its first important application involved the design of the hydrogen bomb.
ENIAC was unveiled in 1946, having cost nearly $500,000, and it was in nearly continuous use until it was turned off on October 2, 1955. The machine contained more than 17,000 vacuum tubes and around 5 million hand-soldered joints. An IBM card reader and card punch machine were used for input and output. In 1997, a team of engineering students led by Professor Jan Van der Spiegel created a “replica” of the 30-ton ENIAC on a single integrated circuit!
Other important electrical computing machines of the 1930s and 1940s include the American Atanasoff-Berry Computer (demonstrated in December, 1939), the German Z3 (demonstrated in May, 1941), and the British Colossus computer (demonstrated in 1943); however, these machines were either not fully electronic or not general purpose.
The authors of the ENIAC patent (No. 3,120,606; filed in 1947) write, “With the advent of everyday use of elaborate calculations, speed has become paramount to such a high degree that there is no machine on the market today capable of satisfying
the full demand of modern computational methods. . . . The present invention is intended to reduce to seconds such lengthy computations. . . .”
Today, computer use has invaded most areas of mathematics, including numerical analysis, number theory, and probability theory. Mathematicians, of course, increasingly use computers in their research and in their teaching, sometimes using computer graphics to gain insight. Famous mathematical proofs have been done with the aid of the computer.
SEE ALSO Antikythera Mechanism (c. 125 BCE) Slide Rule (1621), Babbage Mechanical Computer (1822), Turing Machines (1936), Transistor (1947).
U.S. Army photo of ENIAC, the first electronic, reprogrammable, digital computer that could be used to solve a large range of computing problems. Its first important application involved the design of the hydrogen bomb.
1946
Stellar Nucleosynthesis • Clifford A. Pickover
Fred Hoyle (1915–2001)
“Be humble for you are made of dung. Be noble for you are made of stars.” This old Serbian proverb serves to remind us today that all the elements heavier than hydrogen and helium would not exist in any substantial amounts in the universe were it not for their production in stars that eventually died and exploded and scattered the elements into the universe. Although light elements such as helium and hydrogen were created in the first few minutes of the Big Bang, the subsequent nucleosynthesis (atomic-nucleus creation) of the heavier elements required massive stars with their nuclear fusion reactions over long periods of time. Supernova explosions rapidly created even heavier elements due to an intense burst of nuclear reactions during the explosion of the core of the star. Very heavy elements, like gold and lead, are produced in the extremely high temperatures and neutron flux of a supernova explosion. The next time you look at the golden ring on a friend’s finger, think of supernova explosions in massive stars.
Pioneering theoretical work into the mechanism with which heavy nuclei were created in stars was performed in 1946 by astronomer Fred Hoyle who showed how very hot nuclei could assemble into iron.
As I write this entry, I touch a saber-tooth tiger skull in my office. Without stars, there could be no skulls. As mentioned, most elements, like calcium in bones, were first cooked in stars and then blown into space when the stars died. Without stars, the tiger racing across the savanna fades away, ghostlike. There are no iron atoms for its blood, no oxygen for it to breathe, no carbon for its proteins and DNA. The atoms created in the dying ancient stars were blown across vast distances and eventually formed the elements in the planets that coalesced around our Sun. Without these supernova explosions, there are no mist-covered swamps, computer chips, trilobites, Mozarts, or the tears of a little girl. Without exploding stars, perhaps there could be a heaven, but there is certainly no Earth.
SEE ALSO Sun-Centered Universe (1543), E = mc2 (1905), Atomic Nucleus (1911).
The Moon passing in front of the Sun, captured by NASA’s STEREO-B spacecraft on February 25, 2007, in four wavelengths of extreme ultraviolet light. Because the satellite is farther from the Sun than the Earth, the Moon appears smaller than usual.
1947
Hologram • Clifford A. Pickover
Dennis Gabor (1900–1979)
Holography, the process by which a three-dimensional image can be recorded and later reproduced, was invented in 1947 by physicist Dennis Gabor. In his Nobel Prize acceptance speech for the invention, he said of holography, “I need not write down a single equation or show an abstract graph. One can, of course, introduce almost any amount of mathematics into holography, but the essentials can be explained and understood from physical arguments.”
Consider an object such as a pretty peach. Holograms can be stored on photographic film as a record of the peach from many viewpoints. To produce a transmission hologram, a beam-splitter is used to divide the laser light into a reference beam and an object beam. The reference beam does not interact with the peach and is directed toward the recording film with a mirror. The object beam is aimed at the peach. The light reflected off the peach meets the reference beam to create an interference pattern in the film. This pattern of stripes and whorls is totally unrecognizable. After the film is developed, a 3D image of the peach can be reconstructed in space by directing light toward the hologram at the same angle used for the reference beam. The finely spaced fringes on the hologram film act to diffract, or deflect, the light to form the 3D image.
“Upon seeing your first hologram,” write physicists Joseph Kasper and Steven Feller, “you are certain to feel puzzlement and disbelief. You may place your hand where the scene apparently lies, only to find nothing tangible is there.”
Transmission holograms employ light shining through the developed film from behind, and reflection holograms make use of light shining on the film with the light source in front of the film. Some holograms require laser light for viewing, while rainbow holograms (such as those with a reflective coating commonly seen on credit cards) can be viewed without the use of lasers. Holography can also be used to optically store large amounts of data.
SEE ALSO Newton’s Prism (1672), Wave Nature of Light (1801), Laser (1960).
The hologram on the 50 euro banknote. Security holograms are very difficult to forge.
1947
Photosynthesis • Derek B. Lowe
Melvin Calvin (1911–1997), Samuel Goodnow Wildman (1912–2004), Andrew Alm Benson (1917–2015), James Alan Bassham (1922–2012)
Photosynthesis is the quiet, unnoticed chemistry that is keeping everyone and everything on Earth alive. Our planet’s atmosphere didn’t even have much oxygen until photosynthetic microbes began cranking it out as a waste product (gradually killing off the planet’s original microbial inhabitants or driving them into hiding). Photosynthesis not only produces the oxygen we breathe, but it also helps regulate the amount of carbon dioxide in the air. And as if making our atmosphere breathable were not enough, photosynthesis underpins the global food chain for almost every living organism, including humankind.
The strange thing is, the whole process depends on what appears to be one of the clunkiest enzymes ever seen. In 1947, Samuel Goodnow Wildman reported his discovery of a large, extremely abundant enzyme in spinach leaves that turned out to be a key player. Referred to by the laboratory nickname Rubisco, which is short for ribulose biscarboxylase oxygenase (and no wonder), it is an essential part of the Calvin cycle—the plant world’s equivalent of the Krebs cycle of cellular respiration—discovered by American biochemist Melvin Calvin, working with compatriots James Alan Bassham, a chemist, and Andrew Alm Benson, a biologist. (Instead of mitochondria, plant cells have other ancient interlopers called chloroplasts to perform this work.)
Rubisco, probably the most abundant protein on Earth, can account for up to half the protein weight of a plant. The reason there’s so much of it is that it’s an incredibly slow enzyme. Instead of zipping through thousands of molecular changes per second, it processes three. It may be that this bizarrely low rate is a trade-off against its ability to tell carbon dioxide from oxygen; this is still an open question. After several billion years of evolutionary pressure, odds are that there must be good reasons for such an important enzyme to be so strange, but many research groups are putting that to the test by seeing what happens if they try to improve it for use in artificial photosynthesis.
SEE ALSO Nitrogen Cycle and Plant Chemistry (1837), Cellular Respiration (1937), Green Revolution (1961).
The green chloroplasts—where the Rubisco enzyme does its slow, strange work—are clearly visible inside these plant cells.
1947
Transistor • Clifford A. Pickover
Julius Edgar Lilienfeld (1882–1963), John Bardeen (1908–1991), Walter Houser Brattain (1902–1987), William Bradford Shockley (1910–1989)
A thousand years from now, when our ancestors reflect upon history, they will mark December 16, 1947 as the start of humankind’s Information Age—the day on which Bell Telephone Laboratories physicists Joh
n Bardeen and Walter Brattain connected two upper electrodes to a piece of specially treated germanium that sat on a third electrode (a metal plate attached to a voltage source). When a small current was introduced through one of the upper electrodes, another much stronger current flowed through the other two electrodes. The transistor was born.
Given the magnitude of the discovery, Bardeen’s reaction was rather sedate. That evening, walking in through the kitchen door of his home, he mumbled to his wife, “We discovered something important today,” and he said no more. Their fellow scientist William Shockley understood the device’s great potential and also contributed to the knowledge of semiconductors. Later, when Shockley was angered by being left out of the Bell Lab’s transistor patent that had only the names of Bardeen and Brattain, he created a better transistor design.
A transistor is a semiconductor device that may be used to amplify or switch electronic signals. The conductivity of a semiconductor material can be controlled by introduction of an electrical signal. Depending on the transistor design, a voltage or current applied to one pair of the transistor’s terminals changes the current flowing through another terminal.
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