The entry is arbitrarily dated as 1984, the date of an important breakthrough in superstring theory by physicists Michael Green and John Schwarz. M-theory, an extension of string theory, was developed in the 1990s.
SEE ALSO Maxwell’s Equations (1861), String Theory (1919), Standard Model (1961), Quantum Electrodynamics (1948).
Particle accelerators provide information on subatomic particles to help physicists develop a Theory of Everything. Shown here is the Cockroft-Walton generator, once used at Brookhaven National Laboratory to provide the initial acceleration to protons prior to injection into a linear accelerator and then a synchrotron.
1987
Mitochondrial Eve • Michael C. Gerald with Gloria E. Gerald
Allan Wilson (1934–1991), Rebecca L. Cann (b. 1951), Mark Stoneking (b. 1956)
A 1987 paper in the prestigious journal Nature reported that “all mitochondrial DNA stems from one woman” and that she had lived in Africa some 200,000 years ago. The paper, authored by Rebecca L. Cann, Mark Stoneking, and their doctoral advisor, Allan Wilson, at the University of California, Berkeley, aroused intense interest and controversy for many reasons, and it continues to do so.
The authors referred to the samples they analyzed as “mitochondrial DNA,” whereas the press dubbed them “mitochondrial Eve”—far more memorable, but also subject to misinterpretation. This Eve was not the single and only woman living at the time, as was said of the Eve of Genesis. In addition, the literal Biblical interpretation computed the age of humans to a time measured in thousands of years, not 200,000 years. Moreover, many evolutionists believed that humans evolved in separate parts of the world at about the same time, rather than the “Out of Africa” theory, in which anatomically modern humans originated in Africa and then migrated worldwide.
Cann and her colleagues analyzed mitochondrial DNA (mtDNA) and not nuclear DNA (nDNA), the latter responsible for transmitting the color of our eyes, racial characteristics, and susceptibility of certain diseases; mtDNA only codes for manufacturing proteins and performing other mitochondrial functions. Present in all cells of our body, nDNA is a merger of our mother’s and father’s DNA (recombination), whereas mtDNA is derived virtually exclusively from the maternal side with few if any mtDNA contributed from the sperm. Closely related individuals have almost identical mtDNA, with occasional mutations arising over thousands of years. It is assumed that the fewer the number of mutations, the shorter the period of time since common ancestors diverged.
Proponents of mitochondrial Eve do not suggest that this Eve was the first woman or only woman living at the time. Rather they estimate that some catastrophic event occurred, dramatically reducing Earth’s population to some 10,000–20,000, and that only this Eve had an unbroken line of female descendants. Eve was said to be the most recent common ancestor from whom all living humans descended.
SEE ALSO Darwin’s Theory of Natural Section (1859), Cellular Respiration (1937), Endosymbiont Theory (1967).
Adam and Eve, completed c.1537 by the German Renaissance painter Lucas Cranach the Younger (1515–1586).
1990
Domains of Life • Michael C. Gerald with Gloria E. Gerald
Carl Linnaeus (1707–1778), Ernst Haeckel (1834–1919), C. B. van Niel (1897–1985), Roger Y. Stanier (1916–1982), Carl Woese (1928–2012), George E. Fox (b. 1945)
An impetus for classification came during the seventeenth century when new plants and animals were arriving in Europe. In 1735, Carl Linnaeus, a pioneer in the science of taxonomy (also called systematics), developed a hierarchical system of biological nomenclature in which the highest rank, inclusive of all lower levels, was the kingdom, and these were two: animal and vegetable (plant). With the growing realization that unicellular organisms were unaccounted for, in 1866 Ernst Haeckel proposed the addition of a third kingdom, Protista.
In the 1960s, Roger Y. Stanier and C. B. van Niel devised a four-kingdom classification system based on the distinction between prokaryotic and eukaryotic cells, with the latter having a cell membrane enclosing its nucleus. Furthermore, they proposed a higher and more inclusive rank termed superdomain or empire. The Empire Prokarya encompassed the Kingdom Monera (bacteria), and the Empire Eukarya included the Kingdoms Plantae, Animalia, and Protista.
Until the mid-1970s, all classifications were based on the outward appearance of cells, namely their anatomy, morphology, embryology, and cell structure. In 1977, Carl Woese and George E. Fox at the University of Illinois at Urbana-Champaign classified organisms based on a comparison of their genes at a molecular level. In particular, they compared the nucleotide sequences in a subunit of ribosomal rRNA, the molecules that undergo evolutionary changes. In 1990, they introduced the concept of three domains of cellular life: the Domain Archaea, a disparate collection of prokaryotic organisms, among the most ancient found on Earth and capable of adapting to extreme environments (extremophiles); the Domain Bacteria; and the Domain Eukarya, which was subdivided into Kingdoms Fungi (yeasts, molds), Plantae (flowering plants, ferns), and Animalia (vertebrates, invertebrates). More recently, their Protista Kingdom has been subdivided into more discrete kingdoms. The final chapter on classification has not been written, with systems proposed that contain two to eight kingdoms.
SEE ALSO Linnaean Classification of Species (1735), Darwin’s Theory of Natural Section (1859), Endosymbiont Theory (1967).
The rainbow colors in the Grand Prismatic Spring in Yellowstone National Park, Wyoming—the world’s third largest hot spring—result from resident thermophilic microbes (extremophiles of the Kingdom Archaea) that favor temperatures ranging from 1,880°F (870°C) at the center to 1,470°F (640°C) at the rim.
1990
Hubble Telescope • Clifford A. Pickover
Lyman Strong Spitzer, Jr. (1914–1997)
“Since the earliest days of astronomy,” write the folks at the Space Telescope Science Institute, “since the time of Galileo, astronomers have shared a single goal—to see more, see farther, see deeper. The Hubble Space Telescope’s launch in 1990 sped humanity to one of its greatest advances in that journey.” Unfortunately, ground-based telescope observations are distorted by the Earth’s atmosphere that makes stars seem to twinkle and that partially absorbs a range of electromagnetic radiation. Because the Hubble Space Telescope (HST) orbits outside of the atmosphere, it can capture high-quality images.
Incoming light from the heavens is reflected from the telescope’s concave main mirror (7.8 feet [2.4 meters] in diameter) into a smaller mirror that then focuses the light through a hole in the center of the main mirror. The light then travels toward various scientific instruments for recording visible, ultraviolet, and infrared light. Deployed by NASA using a space shuttle, the HST is the size of a Greyhound bus, powered by solar arrays, and uses gyroscopes to stabilize its orbit and point at targets in space.
Numerous HST observations have led to breakthroughs in astrophysics. Using the HST, scientists were able to determine the age of the universe much more accurately than ever before by allowing scientists to carefully measure distance to Cepheid variable stars. The HST has revealed protoplanetary disks that are likely to be the birthplaces of new planets, galaxies in various stages of evolution, optical counterparts of gamma-ray bursts in distance galaxies, the identity of quasars, the occurrence of extrasolar planets around other stars, and the existence of dark energy that appears to be causing the universe to expand at an accelerating rate. HST data established the prevalence of giant black holes at the centers of galaxies and the fact that the masses of these black holes are correlated with other galactic properties.
In 1946, American astrophysicist Lyman Spitzer, Jr. justified and promoted the idea of a space observatory. His dreams were realized in his lifetime.
SEE ALSO Telescope (1608), Hubble’s Law of Cosmic Expansion (1929), Space Satellite (1957), Dark Energy (1998).
Astronauts Steven L. Smith and John M. Grunsfeld appear as small figures as they replace gyroscopes inside the Hubble Spac
e Telescope (1999).
1990
World Wide Web • Marshall Brain
Robert Cailliau (b. 1947), Tim Berners-Lee (b. 1955)
In the mid-1980s, the Internet existed, and people were using it. The number of host computers connected to the Internet in 1987 was about 10,000. However, nearly every person using the Internet at that time was affiliated with the universities, companies, and research organizations that provided the host computers. The public had no access.
At this time, people were using a variety of Internet tools to move information around. E-mail and FTP (File Transfer Protocol) were two of the most common. A person could upload a file to a FTP server and then send e-mail to people telling them that they could download the file. People could connect to computers remotely using Telnet. It all worked, but the Internet was a bit technical and cumbersome.
Then, in 1990, everything began to change, when British computer scientist Tim Berners-Lee and Belgian computer scientist Robert Cailliau, proposed a “hypertext project” for the “WorldWideWeb.” The World Wide Web was born, and it made the Internet incredibly easy to use as an information tool. On the one hand it was so simple, but on the other hand it was so incredibly powerful. As a result, the web has changed so many things, including the way goods are bought and sold, the way news and information are delivered, the way we educate people, the way people communicate. In addition, it utterly leveled the playing field. Suddenly, anyone could publish information to millions of people.
There were four core ideas that had to be engineered simultaneously for the web to work: 1) the web server, which holds web pages for people to access, 2) the web browser, which can gather and assemble web pages from servers so people can view them, 3) the web markup language, called HTML (Hypertext Markup Language), which allows people to create web pages, and 4) the web protocol, named HTTP (Hypertext Transfer Protocol), which allows for communication between server and browser. Once a web server existed with a web page in HTML on it, and someone had a web browser, the web was born. And then it spread like wildfire because engineers made accessing the Internet trivially easy.
SEE ALSO Telephone (1876), ENIAC (1946), ARPANET (1969).
The World Wide Web, for which resources such as Web pages are identified by URLs (Uniform Resource Locators), continues to change society in unprecedented ways.
1994
Global Positioning System (GPS) • Marshall Brain
Ivan A. Getting (1912–2003), Roger L. Easton (1912–2014), Bradford Parkinson (b. 1935)
If you were an engineer working on the Global Positioning System (GPS), you were doing something incredible. You were proposing the creation of a new sense that could become available to every human being on the planet. Humans come equipped with the normal senses: vision, hearing, smell, taste, and touch. But humans definitely do not come equipped with a sense of direction, especially at night, especially on the open oceans, especially in bad weather where clouds, fog, and rain obscure every landmark.
The GPS engineers, a team including Ivan Getting, Roger Easton, and Bradford Parkinson, who were working for the United States Department of Defense, proposed to change all of that. By 1994, they had created a ubiquitous, instantaneous, and precise system by which any human could locate his or her exact position on the planet with roughly 30-foot (10 meter) accuracy, anytime, anywhere.
One of the most audacious parts of the proposed system would be the cost—approximately $12 billion for a constellation of 24 satellites funded by the US military that went into orbit between 1989 and 1994. Another audacious part was the technology. This new GPS system demanded small, accurate atomic clocks that could operate unattended for years in orbit—two of them per satellite. These clocks are not simple devices. And then there was the technique the engineers devised to determine location. A GPS receiver would need to be able to see at least four satellites overhead, know exactly where each is in orbit, and then determine exactly how far away each one is. Using the distance and location of the four satellites, the receiver could triangulate its exact position and altitude on earth. It could also derive the exact time with atomic clock accuracy without needing to have its own atomic clock.
Here on Earth, the arrival of the cheap consumer GPS receiver combined with the arrival of the cheap, pocket cell phone to make it seem like we were living in the future. It is an amazing pair of capabilities for any human to have.
SEE ALSO Atomic Clocks (1955), Space Satellite (1957), Saturn V Rocket (1967).
Photo of the iPhone 5 smartphone running the Google Maps app (a Web-based service displaying street maps and more).
1998
Dark Energy • Clifford A. Pickover
“A strange thing happened to the universe five billion years ago,” writes science-journalist Dennis Overbye. “As if God had turned on an antigravity machine, the expansion of the cosmos speeded up, and galaxies began moving away from one another at an ever faster pace.” The cause appears to be dark energy—a form of energy that may permeate all of space and that is causing the universe to accelerate its expansion. Dark energy is so abundant that it accounts for nearly three-quarters of the total mass-energy of the universe. According to astrophysicist Neil deGrasse Tyson and astronomer Donald Goldsmith, “If cosmologists could only explain where the dark energy comes from . . . they could claim to have uncovered a fundamental secret of the universe.”
Evidence of the existence of dark energy came in 1998, during astrophysical observations of certain kinds of distant supernovae (exploding stars) that are receding from us at an accelerating rate. In the same year, American cosmologist Michael Turner coined the term dark energy.
If the acceleration of the universe continues, galaxies outside our local supercluster of galaxies will no longer be visible, because their recessional velocity will be greater than the speed of light. According to some scenarios, dark energy may eventually exterminate the universe in a cosmological Big Rip as matter (in forms that range from atoms to planets) is torn apart. However, even without a Big Rip, the universe may become a lonely place. Tyson writes, “Dark energy . . . will, in the end, undermine the ability of later generations to comprehend their universe. Unless contemporary astrophysicists across the galaxy keep remarkable records . . . future astrophysicists will know nothing of external galaxies. . . . Dark energy will deny them access to entire chapters from the book of the universe. . . . [Today] are we, too, missing some basic pieces of the universe that once was, [thus] leaving us groping for answers we may never find?”
SEE ALSO Hubble’s Law of Cosmic Expansion (1929), Dark Matter (1933), Cosmic Microwave Background (1965), Cosmic Inflation (1980).
SNAP (which stands for Supernova Acceleration Probe, a cooperative venture between NASA and the U.S. Department of Energy) is a proposed space observatory for measuring the expansion of the Universe and for elucidating the nature of dark energy.
1998
International Space Station • Jim Bell
Early-twentieth-century rocket pioneers such as Konstantin Tsiolkovsky and Robert Goddard were among the first to work out the technical details of orbiting stations and habitats in space. For most of the century, however, the idea of a human outpost in Earth orbit was only realized in science fiction books, magazines, TV shows, and movies. In the 1970s the Soviet Union launched the first of nine long-duration Salyut space research modules, followed up in the 1980s by the orbital assembly of their Mir space station—the first long-duration, multicrew outpost in space.
NASA’s plans to launch a US space station (called Freedom) in the 1980s never materialized, due to cost overruns and technical delays. The fall of the Soviet Union in 1991, technical problems with the Mir station, and the high cost of launching and operating space vehicles in general all compelled NASA, Russia, and other space-faring nations to pool resources toward the design and operation of a joint International Space Station (ISS), begun in 1993.
The first component of the new ISS was a Russian electrical power, propu
lsion, and storage module called Zarya, launched into low Earth orbit (about 230 miles [370 kilometers] above the surface) on a Russian Proton rocket in November 1998. The second component, a US docking, airlock, and research module called Unity, was launched and connected to Zarya a few weeks later by the crew of the space shuttle Endeavour. Fifteen more launches of shuttles and Russian Proton and Progress rockets over the next 13 years added additional solar panels, living quarters, laboratories, airlocks, and docking ports. Completed in 2011, the ISS now spans the area of a US football field, with a total mass of more than 920,000 pounds (420,000 kilograms), making it the largest artificial satellite ever constructed. In addition to the United States and Russia, the European, Japanese, and Canadian space agencies are also key partners.
The ISS is primarily an international research laboratory designed to take advantage of its unique microgravity, orbital environment to enable space-related medical, engineering, and astrophysical research. But it also serves an important role as an outpost for a permanent human presence in space, a place where we can learn how to live and work there, and how best to prepare to venture further beyond low Earth orbit for deep space voyages of exploration.
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