In philosophy and logic, the concept of a possible world is used to express modal claims. The concept of possible worlds is common in contemporary philosophical discourse and has also been disputed.

Possibility, necessity, and contingency

Those theorists who use the concept of possible worlds consider the ''actual'' world to be one of the many possible worlds. For each distinct way the world could have been, there is said to be a distinct possible world; the actual world is the one we in fact live in. Among such theorists there is disagreement about the nature of possible worlds; their precise ontological status is disputed, and especially the difference, if any, in ontological status between the actual world and all the other possible worlds. One position on these matters is set forth in David Lewis's modal realism (see below). There is a close relation between propositions and possible worlds. We note that every proposition is either true or false at any given possible world; then the ''modal status'' of a proposition is understood in terms of the ''worlds in which it is true'' and ''worlds in which it is false''. The following are among the assertions we may now usefully make:

True propositions are those that are ''true in the actual world'' (for example: "Richard Nixon became President in 1969")

False propositions are those that are ''false in the actual world'' (for example: "Ronald Reagan became President in 1969")

Possible propositions are those that are ''true in at least one possible world'' (for example: "Hubert Humphrey became President in 1969")

Contingent propositions are those that are ''true in some possible worlds and false in others'' (for example: "Richard Nixon became President in 1969" is ''contingently true'' and "Hubert Humphrey became President in 1969" is ''contingently false'')

Necessarily true propositions (usually simply called necessary propositions) are those that are ''true in all possible worlds'' (for example: "2 + 2 = 4"; "all bachelors are unmarried")

Impossible propositions (or ''necessarily false propositions'') are those that are ''true in no possible world'' (for example: "Melissa and Toby are taller than each other at the same time")

The idea of possible worlds is most commonly attributed to Gottfried Leibniz, who spoke of possible worlds as ideas in the mind of God and used the notion to argue that our actually created world must be "the best of all possible worlds". However, scholars have also found implicit traces of the idea in the works of Al-Ghazali (''The Incoherence of the Philosophers''), Averroes (''The Incoherence of the Incoherence''), Fakhr al-Din al-Razi (''Matalib al-'Aliya'') and John Duns Scotus. The modern philosophical use of the notion was pioneered by David Lewis and Saul Kripke.

Formal semantics of modal logics

A semantics for modal logic was first introduced in the 1950s work of Saul Kripke and his colleagues. A statement in modal logic that is ''possible'' is said to be true in at least one possible world; a statement that is ''necessary'' is said to be true in all possible worlds.

From modal logic to philosophical tool

From this groundwork, the theory of possible worlds became a central part of many philosophical developments, from the 1960s onwards – including, most famously, the analysis of counterfactual conditionals in terms of "nearby possible worlds" developed by David Lewis and Robert Stalnaker. On this analysis, when we discuss what ''would'' have happened ''if'' some set of conditions ''were'' the case, the truth of our claims is determined by what is true at the nearest possible world (or the ''set'' of nearest possible worlds) where the conditions obtain. (A possible world W₁ is said to be near to another possible world W₂ in respect of R to the degree that the same things happen in W₁ and W₂ in respect of R; the more different what happens in two possible worlds in a certain respect, the "further" they are from one another in that respect.) Consider this conditional sentence: "If George W. Bush hadn't become president of the U.S. in 2001, Al Gore would have." The sentence would be taken to express a claim that could be reformulated as follows: "In all nearest worlds to our actual world (nearest in relevant respects) where George W. Bush didn't become president of the U.S. in 2001, Al Gore became president of the U.S. then instead." And on this interpretation of the sentence, if there is some nearest world to the actual world (nearest in relevant respects) where George W. Bush didn't become president but Al Gore didn't either, then the claim expressed by this counterfactual would be false.

Today, possible worlds play a central role in many debates in philosophy, including especially debates over the Zombie Argument, and physicalism and supervenience in the philosophy of mind. Many debates in the Philosophy of religion have been reawakened by the use of possible worlds. Intense debate has also emerged over the ontological status of possible worlds, provoked especially by David Lewis's defense of modal realism, the doctrine that talk about "possible worlds" is best explained in terms of innumerable, ''really existing'' worlds beyond the one we live in. The fundamental question here is: ''given'' that modal logic works, and that some possible-worlds semantics for modal logic is correct, ''what has to be true'' of the world, and just what ''are'' these possible worlds that we range over in our interpretation of modal statements? Lewis argued that what we range over are real, concrete ''worlds'' that exist just as unequivocally as our actual world exists, but that are distinguished from the actual world simply by standing in no spatial, temporal, or causal relations with the actual world. (On Lewis's account, the only "special" property that the ''actual'' world has is a relational one: that ''we'' are in it. This doctrine is called "the indexicality of actuality": "actual" is a merely indexical term, like "now" and "here".) Others, such as Robert Adams and William Lycan, reject Lewis's picture as metaphysically extravagant, and suggest in its place an interpretation of possible worlds as consistent, maximally complete sets of descriptions of or propositions about the world, so that a "possible world" is conceived of as a complete ''description'' of ''a way the world could be'' – rather than a ''world that is that way''. (Lewis describes their position, and similar positions such as those advocated by Alvin Plantinga and Peter Forrest, as "''ersatz'' modal realism", arguing that such theories try to get the benefits of possible worlds semantics for modal logic "on the cheap", but that they ultimately fail to provide an adequate explanation.) Saul Kripke, in ''Naming and Necessity'', took explicit issue with Lewis's use of possible worlds semantics, and defended a ''stipulative'' account of possible worlds as purely ''formal'' (logical) entities rather than either really existent worlds or as some set of propositions or descriptions.

Possible-world theory in literary studies

Possible worlds theory in literary studies uses concepts from possible-world logic and applies them to worlds that are created by fictional texts, fictional universe. In particular, possible-world theory provides a useful vocabulary and conceptual framework with which to describe such worlds. However, a literary world is a specific type of possible world, quite distinct from the possible worlds in logic. This is because a literary text houses its own system of modality, consisting of actual worlds (actual events) and possible worlds (possible events). Thus, a literary universe is granted autonomy in much the same way as the actual universe.

Literary critics, such as Marie-Laure Ryan, Lubomir Dolezel, and Thomas Pavel, have used possible-worlds theory to address notions of literary truth, the nature of fictionality, and the relationship between fictional worlds and reality. Taxonomies of fictional possibilities have also been proposed where the likelihood of a fictional world is assessed. Possible-world theory is also used within narratology to divide a specific text into its constituent worlds, possible and actual. In this approach, the modal structure of the fictional text is analysed in relation to its narrative and thematic concerns.

See also

Standard translation, an embedding of modal logics into first-order logic which captures their possible world semantics

n-universes

References

Further reading

D.M. Armstrong, ''A World of States of Affairs'' (1997. Cambridge: Cambridge University Press) ISBN 0-521-58948-7

John Divers, ''Possible Worlds'' (2002. London: Routledge) ISBN 0-415-15556-8

Paul Herrick, ''The Many Worlds of Logic (1999. Oxford: Oxford University Press) Chapters 23 and 24. ISBN 978-0-19-515503-7

David Lewis, ''On the Plurality of Worlds'' (1986. Oxford & New York: Basil Blackwell) ISBN 0-631-13994-X

Michael J. Loux [ed.] ''The Possible and the Actual'' (1979. Ithaca & London: Cornell University Press) ISBN 0-8014-9178-9

G.W. Leibniz, ''Theodicy'' (2001. Wipf & Stock Publishers) ISBN 978-0875484372

Brian Skyrms "Possible Worlds, Physics and Metaphysics" (1976. Philosophical Studies 30)

External links

"Possible worlds: what they are good for and what they are" — Alexander Pruss

Category:Possibility Category:Modal logic Category:Concepts in logic

da:Mulig verden de:Mögliche Welt fr:Mondes possibles hu:Lehetséges világok ja:可能世界論 pt:Mundo possível sr:Могући свет fi:Mahdolliset maailmat sv:Möjlig värld zh:可能世界

Coordinates	28°36′36″N77°13′48″N
name	Michio Kaku
birth date	January 24, 1947
birth place	San Jose, California, United States
residence	New York City, New York, United States
nationality	American
field	Theoretical physics
work institutions	City University of New YorkNew York UniversityInstitute for Advanced Study
alma mater	Harvard University (B.S., 1968)University of California, Berkeley (Ph.D.,1972)
doctoral advisor	Stanley Mandelstam
known for	String field theory, Popular science
footnotes	}}

is an American theoretical physicist, the Henry Semat Professor of Theoretical Physics in the City College of New York of City University of New York, the co-founder of string field theory, and a "communicator" and "popularizer" of science. He has written several books on physics and related topics, he has made frequent appearances on radio, television, and film, and he writes extensive online blogs and articles.

Early life and education

Kaku was born in San Jose, California to Japanese immigrant parents. His grandfather came to the United States to take part in the clean-up operation after the 1906 San Francisco Earthquake. His father was born in California but was educated in Japan and spoke little English. Both his parents were put in the Tule Lake War Relocation Center, where they met and where his two brothers were born.

At Cubberley High School in Palo Alto, Kaku assembled an atom smasher in his parent's garage for a science fair project. At the National Science Fair in Albuquerque, New Mexico, he attracted the attention of physicist Edward Teller, who took Kaku as a protégé, awarding him the Hertz Engineering Scholarship. Kaku graduated ''summa cum laude'' from Harvard University in 1968 and was first in his physics class. He attended the Berkeley Radiation Laboratory at the University of California, Berkeley and received a Ph.D. in 1972, and in 1972 he held a lectureship at Princeton University.

During the Vietnam War, Kaku completed his U.S. Army basic training at Fort Benning, Georgia and his advanced infantry training at Fort Lewis, Washington. However, the Vietnam War ended before he was deployed as an infantryman.

Academic career

Kaku became a visiting professor at the Institute for Advanced Study in Princeton, and New York University. He currently holds the Henry Semat Chair and Professorship in theoretical physics at the City College of New York.

Kaku has had over 70 articles published in physics journals such as Physical Review, covering topics such as superstring theory, supergravity, supersymmetry, and hadronic physics. In 1974, along with Prof. Keiji Kikkawa of Osaka University, he authored the first papers describing string theory in a field form.

Kaku is the author of several textbooks on string theory and quantum field theory.

Popular science

Kaku is most widely known as a popularizer of science. He has written books and appeared on many television programs as well as film. He also hosts a weekly radio program.

Books

Kaku is the author of various popular science books.

''Physics of the Future''

''Physics of the Impossible''

''Hyperspace''

''Einstein's Cosmos''

''Parallel Worlds''

''Beyond Einstein'' (with Jennifer Thompson)

''Hyperspace'' was a best-seller and was voted one of the best science books of the year by both ''The New York Times'' and ''The Washington Post''. ''Parallel Worlds'' was a finalist for the Samuel Johnson Prize for non-fiction in the UK.

Radio

Kaku is the host of the weekly, one-hour radio program ''Explorations'', produced by the Pacifica Foundation's WBAI in New York. "Explorations" is syndicated to community and independent radio stations and makes previous broadcasts available on the program's website. Kaku defines the show as dealing with the general topics of science, war, peace, and the environment.

In April 2006, Kaku began broadcasting ''Science Fantastic'' on 90 commercial radio stations, the only nationally syndicated science program on commercial radio in the United States. It is syndicated by Talk Radio Network and now reaches 130 radio stations and America's Talk on XM. The program is formatted as a live listener call-in show, focusing on "futurology," which he defines as the future of science. Featured guests include Nobel laureates and top researchers on the topics of string theory, time travel, black holes, gene therapy, aging, space travel, artificial intelligence, and SETI. When Kaku is busy filming for television, ''Science Fantastic'' goes on hiatus, sometimes for several months. Kaku is also a frequent guest on many programs, where he is outspoken in all areas and issues he considers of importance, such as the program "Coast to Coast AM," where on 30 November 2007, he reaffirmed his belief that there is a 100% probability of extraterrestrial life in the universe.

Kaku has appeared on ''The Opie and Anthony Show'' a number of times, discussing popular fiction such as ''Back to The Future'', ''Lost,'' and the theories behind time-travel that these and other fictional entertainment focus on. Steven G. Spruill's novel ''The Janus Equation'', which describes the time travel of a post-op transsexual mating with her past self and thereby becoming father and mother to her present self, prompted Dr. Kaku's comment: "Well, you're in deep doo doo if that happens."

Television and film

Kaku has appeared in many forms of media and on many programs and networks, including ''Good Morning America'', ''The Screen Savers'', ''Larry King Live'', ''60 Minutes'', ''Nightline'', ''20/20'', ''Naked Science'', CNN, ABC News, CBS News, NBC News, Al Jazeera English, Fox News Channel, The History Channel, ''Conan'', The Science Channel, The Discovery Channel, TLC, ''Countdown with Keith Olbermann'', ''The Colbert Report'', ''The Art Bell Show'' and its successor, ''Coast To Coast AM'', ''BBC World News America'', ''The Opie & Anthony Show'', ''The Covino & Rich Show'', ''Head Rush'', ''The Late Show with David Letterman'', and ''Real Time with Bill Maher.

We Are the Guinea Pigs (1980)

Borders (1989)

''Synthetic Pleasures'' (1995)

Einstein Revealed (1996)

''Future Fantastic'' (1996)

''Stephen Hawking's Universe'' (1997)

Bioperfection: Building a New Human Race (1998)

Exodus Earth (1999)

Me & Isaac Newton (1999)

Space: The Final Junkyard (1999)

''Big Questions'' (2001)

''Parallel Universes'' (2001)

''Horizon'': "Time travel" (2003)

Robo sapiens (2003)

Brilliant Minds: Secret Of The Cosmos (2003)

''Nova'': "The Elegant Universe" (2003)

''Hawking'' (2004)

''The Screen Savers'' (2004)

''Unscrewed with Martin Sargent'' (2004)

''Alien Planet (2005)

''ABC News'' "UFOs: Seeing Is Believing" (2005)

''HARDtalk Extra'' (2005)

''Last Days on Earth'' (2005)

Obsessed & Scientific (2005)

''Horizon'': "Einstein's Unfinished Symphony" (2005)

Prophets of Science Fiction (2006)

''Time'' (2006)

''2057'' (2007)

''The Universe'' (2007)

Futurecar (2007)

''Attack of the Show!'' (2007)

''Visions of the Future'' (2008)

''Horizon'': "The President's Guide to Science" (2008)

Stephen Hawking: Master of the Universe (2008)

''Horizon'': "Who's Afraid of a Big Black Hole" (2009–2010)

''Sci Fi Science: Physics of the Impossible'' (2009–2010)

''Horizon'': "What Happened Before the Big Bang?" (2010)

''GameTrailers TV With Geoff Keighley'': "The Science of Games" (2010)

''How the Universe Works'' (2010)

''Through the Wormhole'' (2011)

In 1999, Kaku was one of the scientists profiled in the feature-length film ''Me and Isaac Newton'', directed by Michael Apted. It played theatrically in the United States, was later broadcast on national TV, and won several film awards.

In 2005, Kaku appeared in the short documentary ''Obsessed & Scientific.'' The film is about the possibility of time travel and the people who dream about it. It screened at the Montreal World Film Festival and a feature film expansion is in development talks. Kaku also appeared in the ABC documentary ''UFOs: Seeing Is Believing'', in which he suggested that while he believes it is extremely unlikely that extraterrestrials have ever actually visited Earth, we must keep our minds open to the possible existence of civilizations a million years ahead of us in technology, where entirely new avenues of physics open up. He also discussed the future of interstellar exploration and alien life in the Discovery Channel special ''Alien Planet'' as one of the multiple speakers who co-hosted the show, and Einstein's Theory of Relativity on The History Channel.

In February 2006, Kaku appeared as presenter in the BBC-TV four-part documentary ''Time'' which seeks to explore the mysterious nature of time. Part one of the series concerns personal time, and how we perceive and measure the passing of time. The second in the series deal with cheating time, exploring possibilities of extending the lifespan of organisms. The geological time covered in part three explores the ages of the earth and the sun. Part four covers the topics of cosmological time, the beginning of time and the events that occurred at the instant of the big bang.

On January 28, 2007, Kaku hosted the Discovery Channel series ''2057.'' This three-hour program discussed how medicine, the city, and energy could change over the next 50 years.

In 2008, Kaku hosted the three-hour BBC-TV documentary ''Visions of the Future'', on the future of computers, medicine, and quantum physics, and he appeared in several episodes of the History Channel's ''Universe'' series.

On December 1, 2009, he began hosting a 12-episode weekly TV series for the Science Channel at 10 pm, called ''Sci Fi Science: Physics of the Impossible'', based on his best-selling book. Each 30-minute episode discusses the scientific basis behind imaginative schemes, such as time travel, parallel universes, warp drive, star ships, light sabers, force fields, teleportation, invisibility, death stars, and even superpowers and flying saucers. Each episode includes interviews with the world's top scientists working on prototypes of these technologies, interviews with sci-fi fans, clips from science fiction movies, and special effects and computer graphics. Although these inventions are impossible today, the series discusses when these technologies might become feasible in the future.

In 2010, he began to appear in a series on the website Gametrailers.com called ''Science of Games'', discussing the scientific aspects of various popular video games such as ''Mass Effect 2'' and ''Star Wars: The Force Unleashed''.

Kaku is popular in mainstream media because of his knowledge and his accessible approach to presenting complex subjects in science. While his technical writings are confined to theoretical physics, his public speaking and media appearances cover a broad range of topics, from the Kardashev scale to more esoteric subjects such as wormholes and time travel. In January 2007, Kaku visited Oman. While there, he talked at length to select members of that country's decision makers. In an interview with local media, Dr Kaku elaborated on his vision of mankind's future. Kaku considers climate change and terrorism as serious threats in man's evolution from a Type 0 civilization to Type 1.

On October 11, 2010, Michio Kaku appeared in the BBC program "What Happened Before the Big Bang" (along with Laura Mersini-Houghton, Andrei Linde, Roger Penrose, Lee Smolin, Neil Turok, and other notable cosmologists and physicists), where he propounded his theory of the universe created out of nothing.

Social policy advocacy

Kaku has publicly stated his concerns over matters including the anthropogenic cause of global warming, nuclear armament, nuclear power and the general misuse of science. He was critical of the Cassini–Huygens space probe because of the of plutonium contained in the craft for use by its radioisotope thermoelectric generator. Conscious of the possibility of casualties if the probe's fuel were dispersed into the environment during a malfunction and crash as the probe was making a 'sling-shot' maneuver around earth, Kaku publicly criticized NASA's risk assessment. He has also spoken on the dangers of space junk and called for more and better monitoring. Kaku is generally a vigorous supporter of the exploration of outer space, believing that the ultimate destiny of the human race may lie in extrasolar planets; but he is critical of some of the cost-ineffective missions and methods of NASA.

Kaku credits his anti-nuclear war position to programs he heard on the Pacifica Radio network, during his student years in California. It was during this period that he made the decision to turn away from a career developing the next generation of nuclear weapons in association with Edward Teller and focused on research, teaching, writing and media. Kaku joined with others such as Helen Caldicott, Jonathan Schell, Peace Action and was instrumental in building a global anti-nuclear weapons movement that arose in the 1980s, during the administration of U.S. President Ronald Reagan.

Kaku was a board member of Peace Action and on the board of radio station WBAI-FM in New York City where he originated his long running program, ''Explorations,'' that focused on the issues of science, war, peace and the environment.

His remark from an interview in support of SETI, "We could be in the middle of an intergalactic conversation...and we wouldn't even ''know''.", is used in the third Symphony of Science installment "Our Place in the Cosmos".

Personal life

Kaku is married to Shizue Kaku and has one daughter.

Bibliography

References

External links

Getting Physical: Dr. Michio Kaku Explains Einstein's Genius

Russia Takes Aim at Asteroids, op-ed on asteroid defense, Wall St. Journal, Jan. 5, 2010

''The Skeptics' Guide To The Universe'' interview

Michio Kaku on National Public Radio

Category:City College of New York faculty Category:American physicists Category:American radio personalities Category:City University of New York faculty Category:Princeton University faculty Category:Futurologists Category:Harvard University alumni Category:American academics of Japanese descent Category:American people of Japanese descent Category:Japanese-American civil rights activists Category:Pacifica Radio Category:String theorists Category:Theoretical physicists Category:University of California, Berkeley alumni Category:People from San Jose, California Category:1947 births Category:Living people

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Coordinates	28°36′36″N77°13′48″N
name	Carl Sagan
birth date	November 09, 1934
birth place	Brooklyn, New York City, U.S.
residence	United States
nationality	American
death date	December 20, 1996
death place	Seattle, Washington, U.S.
death cause	Pneumonia
education	Rahway High School
alma mater	University of Chicago,Cornell University
field	Astronomy, Astrophysics, Cosmology, Astrobiology, Space science, Planetary science
work institutions	Cornell University Harvard University Smithsonian Astrophysical Observatory University of California, Berkeley
alma mater	University of Chicago (B.A.), (B.Sc.), (M.Sc.), (Ph.D.)
known for	Search for Extra-Terrestrial Intelligence (SETI) ''Cosmos: A Personal Voyage'' ''Cosmos'' Voyager Golden Record Pioneer plaque ''Contact'' ''Pale Blue Dot''
prizes	Oersted Medal (1990) NASA Distinguished Public Service Medal (twice) Pulitzer Prize for General Non-Fiction (1978) National Academy of Sciences Public Welfare Medal (1994) }}

Carl Edward Sagan () (November 9, 1934 December 20, 1996) was an American astronomer, astrophysicist, cosmologist, author, science popularizer, and science communicator in the space and natural sciences. During his lifetime, he published more than 600 scientific papers and popular articles and was author, co-author, or editor of more than 20 books. In his works, he advocated skeptical inquiry and the scientific method. He pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI).

Sagan became world-famous for his popular science books and for the award-winning 1980 television series ''Cosmos: A Personal Voyage'', which he narrated and co-wrote. A book to accompany the program was also published. Sagan also wrote the novel ''Contact'', the basis for the 1997 film of the same name.

Early life

Carl Sagan was born in Brooklyn, New York City, to a Ukrainian Jewish family. His father, Sam Sagan, was an immigrant garment worker from Kamenets-Podolsk, Ukraine; his mother, Rachel Molly Gruber, a housewife. Carl was named in honor of Rachel's biological mother, Chaiya Clara, in Sagan's words, "the mother she never knew." Sagan graduated from Rahway High School in Rahway, New Jersey, in 1951.

He had one sister, Carol, and the family lived in a modest apartment near the Atlantic Ocean, in Bensonhurst, a Brooklyn neighborhood. According to Sagan, they were Reform Jews, the most liberal of the three main Jewish groups. Both Sagan and his sister agree that their father was not especially religious, but that their mother "definitely believed in God, and was active in the temple ... and served only Kosher meat." During the height of the Depression, his father had to accept a job as a theater usher.

According to biographer Keay Davidson, Sagan's "inner war" was a result of his close relations with both his parents, who were in many ways "opposites." Sagan traced his later analytical urges to his mother, a woman who had known "extreme poverty as a child," and had grown up almost homeless in New York City during World War I and the 1920s. She had her own intellectual ambitions as a young woman, but they were blocked by social restrictions, because of her poverty, her being a woman and wife, and her Jewish religion. Davidson notes that she therefore "worshiped her only son, Carl. He would fulfill her unfulfilled dreams."

However, his "sense of wonder" came from his father, who was a "quiet and soft-hearted escapee from the Czar." In his free time, he gave apples to the poor, or helped soothe labor-management tensions within New York's "tumultuous" garment industry. Although he was "awed" by Carl's "brilliance, his boyish chatter about stars and dinosaurs," he took his son's inquisitiveness in stride, as part of his growing up. In his later years as a writer and scientist, Sagan would often draw on his childhood memories to illustrate scientific points, as he did in his book, ''Shadows of Forgotten Ancestors''. Sagan describes his parents' influence on his later thinking:

:''My parents were not scientists. They knew almost nothing about science. But in introducing me simultaneously to skepticism and to wonder, they taught me the two uneasily cohabiting modes of thought that are central to the scientific method.''

1939 World's Fair

Sagan recalls that one of his best experiences was when he was four or five years old, his parents took him to the 1939 New York World's Fair. The exhibits became a turning point in his life. He later recalled the moving map of the "America of Tomorrow" exhibit: "It showed beautiful highways and cloverleaves and little General Motors cars all carrying people to skyscrapers, buildings with lovely spires, flying buttresses — and it looked great!" At other exhibits, he remembered how a flashlight that shined on a photoelectric cell created a cracking sound, and how the sound from a tuning fork became a wave on an oscilloscope. He also witnessed the future media technology that would replace radio: television. Sagan wrote:

:''Plainly, the world held wonders of a kind I had never guessed. How could a tone become a picture and light become a noise?''

He also saw one of the Fair's most publicized events, the burial of a time capsule at Flushing Meadows, which contained mementos of the 1930s to be recovered by Earth's descendants in a future millennium. "The time capsule thrilled Carl," writes Davidson. As an adult, Sagan and his colleagues created similar time capsules, but ones that would be sent out into the galaxy. These were the Pioneer plaque and the ''Voyager Golden Record'' records, all of which were spinoffs of Sagan's memories of the World Fair.

World War II

During World War II, Sagan's family worried about the fate of their European relatives. Sagan, however, was generally unaware of the details of the ongoing war. He writes, "Sure, we had relatives who were caught up in the Holocaust. Hitler was not a popular fellow in our household ... But on the other hand, I was fairly insulated from the horrors of the war." His sister, Carol, said that their mother "above all wanted to protect Carl ... She had an extraordinarily difficult time dealing with World War II and the Holocaust." Sagan's book, ''The Demon-Haunted World'' (1996), included his memories of this conflicted period in his life, where his family dealt with the realities of the war in Europe, but tried to prevent it from undermining his optimistic spirit.

Inquisitiveness about nature

Soon after entering elementary school, he began to express a strong inquisitiveness about nature. Sagan recalled taking his first trips to the public library alone, at the age of five, when his mother got him a library card. He wanted to learn what stars were, since none of his friends or their parents could give him a clear answer: :''I went to the librarian and asked for a book about stars ... And the answer was stunning. It was that the Sun was a star but really close. The stars were suns, but so far away they were just little points of light ... The scale of the universe suddenly opened up to me. It was a kind of religious experience. There was a magnificence to it, a grandeur, a scale which has never left me. Never ever left me.''

About the time he was six or seven, he and a close friend took trips to the American Museum of Natural History in New York City. While there, they went to the Hayden Planetarium and walked around the museum's exhibits of space objects, such as meteorites, and displays of dinosaurs and animals in natural settings. Sagan writes about those visits: :''I was transfixed by the dioramas — lifelike representations of animals and their habitats all over the world. Penguins on the dimly lit Antarctic ice; ... a family of gorillas, the male beating his chest, ... an American grizzly bear standing on his hind legs, ten or twelve feet tall, and staring me right in the eye.''

His parents helped nurture his growing interest in science by buying him chemistry sets and reading materials. His interest in space, however, was his primary focus, especially after reading science fiction stories by writers such as Edgar Rice Burroughs, which stirred his imagination about life on other planets, such as Mars. According to biographer Ray Spangenburg, these early years as Sagan tried to understand the mysteries of the planets, became a "driving force in his life, a continual spark to his intellect, and a quest that would never be forgotten."

Education and scientific career

He attended the University of Chicago, where he participated in the Ryerson Astronomical Society, received a bachelor of arts with general and special honors in 1954, a bachelor of science in 1955, and a master of science in physics in 1956 before earning a PhD in astronomy and astrophysics in 1960. During his time as an undergraduate, Sagan worked in the laboratory of the geneticist H. J. Muller. From 1960 to 1962 Sagan was a Miller Fellow at the University of California, Berkeley. From 1962 to 1968, he worked at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

Sagan lectured and did research at Harvard University until 1968, when he moved to Cornell University in Ithaca, New York. He became a full Professor at Cornell in 1971, and he directed the Laboratory for Planetary Studies there. From 1972 to 1981, Sagan was the Associate Director of the Center for Radio Physics and Space Research at Cornell.

Sagan was associated with the American space program from its inception. From the 1950s onward, he worked as an advisor to NASA, where one of his duties included briefing the Apollo astronauts before their flights to the Moon. Sagan contributed to many of the robotic spacecraft missions that explored the solar system, arranging experiments on many of the expeditions. He conceived the idea of adding an unalterable and universal message on spacecraft destined to leave the solar system that could potentially be understood by any extraterrestrial intelligence that might find it. Sagan assembled the first physical message that was sent into space: a gold-anodized plaque, attached to the space probe Pioneer 10, launched in 1972. Pioneer 11, also carrying another copy of the plaque, was launched the following year. He continued to refine his designs; the most elaborate message he helped to develop and assemble was the Voyager Golden Record that was sent out with the Voyager space probes in 1977. Sagan often challenged the decisions to fund the Space Shuttle and Space Station at the expense of further robotic missions.

Sagan taught a course on critical thinking at Cornell University until he died in 1996 from pneumonia, a few months after finding that he was in remission of myelodysplastic syndrome.

Scientific achievements

Sagan's contributions were central to the discovery of the high surface temperatures of the planet Venus. In the early 1960s no one knew for certain the basic conditions of that planet's surface, and Sagan listed the possibilities in a report later depicted for popularization in a Time-Life book, ''Planets''. His own view was that Venus was dry and very hot as opposed to the balmy paradise others had imagined. He had investigated radio emissions from Venus and concluded that there was a surface temperature of . As a visiting scientist to NASA's Jet Propulsion Laboratory, he contributed to the first Mariner missions to Venus, working on the design and management of the project. Mariner 2 confirmed his conclusions on the surface conditions of Venus in 1962.

Sagan was among the first to hypothesize that Saturn's moon Titan might possess oceans of liquid compounds on its surface and that Jupiter's moon Europa might possess subsurface oceans of water. This would make Europa potentially habitable for life. Europa's subsurface ocean of water was later indirectly confirmed by the spacecraft Galileo. Sagan also helped solve the mystery of the reddish haze seen on Titan, revealing that it is composed of complex organic molecules constantly raining down onto the moon's surface.

He further contributed insights regarding the atmospheres of Venus and Jupiter as well as seasonal changes on Mars. Sagan established that the atmosphere of Venus is extremely hot and dense with pressures increasing steadily all the way down to the surface. He also perceived global warming as a growing, man-made danger and likened it to the natural development of Venus into a hot, life-hostile planet through a kind of runaway greenhouse effect. Sagan and his Cornell colleague Edwin Ernest Salpeter speculated about life in Jupiter's clouds, given the planet's dense atmospheric composition rich in organic molecules. He studied the observed color variations on Mars' surface and concluded that they were not seasonal or vegetational changes as most believed but shifts in surface dust caused by windstorms.

Sagan is best known, however, for his research on the possibilities of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation.

He is also the 1994 recipient of the Public Welfare Medal, the highest award of the National Academy of Sciences for "distinguished contributions in the application of science to the public welfare." He was denied membership in the Academy, reportedly because his media activities made him unpopular with many other scientists.

Sagan's ability to convey his ideas allowed many people to better understand the cosmos — simultaneously emphasizing the value and worthiness of the human race, and the relative insignificance of the Earth in comparison to the universe. He delivered the 1977 series of Royal Institution Christmas Lectures in London. He hosted and, with Ann Druyan, co-wrote and co-produced the highly popular thirteen-part PBS television series ''Cosmos: A Personal Voyage'' modeled on Jacob Bronowski's ''The Ascent of Man''.

Sagan was a proponent of the search for extraterrestrial life. He urged the scientific community to listen with radio telescopes for signals from intelligent extraterrestrial life-forms. So persuasive was he that by 1982 he was able to get a petition advocating SETI published in the journal ''Science'' and signed by 70 scientists including seven Nobel Prize winners. This was a tremendous turnaround in the respectability of this controversial field. Sagan also helped Dr. Frank Drake write the Arecibo message, a radio message beamed into space from the Arecibo radio telescope on November 16, 1974, aimed at informing extraterrestrials about Earth.

Sagan was chief technology officer of the professional planetary research journal ''Icarus'' for twelve years. He co-founded the ''Planetary Society'', the largest space-interest group in the world, with over 100,000 members in more than 149 countries, and was a member of the SETI Institute Board of Trustees. Sagan served as Chairman of the Division for Planetary Science of the American Astronomical Society, as President of the Planetology Section of the American Geophysical Union, and as Chairman of the Astronomy Section of the American Association for the Advancement of Science.

At the height of the Cold War, Sagan became involved in public awareness efforts for the effects of nuclear war when a mathematical climate model suggested that a substantial nuclear exchange could upset the delicate balance of life on Earth. He was one of five authors — the "S" of the "TTAPS" report as the research paper came to be known. He eventually co-authored the scientific paper hypothesizing a global nuclear winter following nuclear war. He also co-authored the book ''A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race'', a comprehensive examination of the phenomenon of nuclear winter.

''Cosmos'' covered a wide range of scientific subjects including the origin of life and a perspective of our place in the universe. The series was first broadcast by the Public Broadcasting Service in 1980, winning an Emmy and a Peabody Award. It has been broadcast in more than 60 countries and seen by over 500 million people, making it the most widely watched PBS program in history. In addition, ''Time'' magazine ran a cover story about Sagan soon after the show broadcast, referring to him as "creator, chief writer and host-narrator of the new public television series Cosmos, [and] takes the controls of his fantasy spaceship."

Sagan also wrote books to popularize science, such as ''Cosmos'', which reflected and expanded upon some of the themes of ''A Personal Voyage'', and became the best-selling science book ever published in English; ''The Dragons of Eden: Speculations on the Evolution of Human Intelligence'', which won a Pulitzer Prize; and ''Broca's Brain: Reflections on the Romance of Science''. Sagan also wrote the best-selling science fiction novel ''Contact'' in 1985, based on a film treatment he wrote with his wife in 1979, but he did not live to see the book's 1997 motion picture adaptation, which starred Jodie Foster and won the 1998 Hugo Award for Best Dramatic Adaption.

thumb|left|Pale Blue Dot: Earth is a bright pixel when photographed from "Voyager 1" six billion kilometers out (past Pluto). Sagan encouraged NASA to generate this image. He wrote a sequel to ''Cosmos,'' ''Pale Blue Dot: A Vision of the Human Future in Space'', which was selected as a notable book of 1995 by ''The New York Times''. He appeared on PBS' Charlie Rose program in January 1995. Sagan also wrote an introduction for the bestselling book by Stephen Hawking, ''A Brief History of Time''. Sagan was also known for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of scientific skepticism and against pseudoscience, such as his debunking of the Betty and Barney Hill abduction. To mark the tenth anniversary of Sagan's passing, David Morrison, a former student of Sagan, recalled "Sagan's immense contributions to planetary research, the public understanding of science, and the skeptical movement" in ''Skeptical Inquirer''.

Sagan hypothesized in January 1991 that enough smoke from the 1991 Kuwaiti oil fires "might get so high as to disrupt agriculture in much of South Asia ..." He later conceded in ''The Demon-Haunted World'' that this prediction did not turn out to be correct: "it ''was'' pitch black at noon and temperatures dropped 4°–6°C over the Persian Gulf, but not much smoke reached stratospheric altitudes and Asia was spared." A 2007 study noted that modern computer models have been applied to the Kuwait oil fires, finding that individual smoke plumes are not able to loft smoke into the stratosphere, but that smoke from fires covering a large area, like some forest fires or the burning of cities that would be expected to follow a nuclear strike, would loft significant amounts of smoke into the stratosphere.

In his later years Sagan advocated the creation of an organized search for near Earth objects that might impact the Earth. When others suggested creating large nuclear bombs that could be used to alter the orbit of a NEO that was predicted to hit the Earth, Sagan proposed the Deflection Dilemma: If we create the ability to deflect an asteroid away from the Earth, then we also create the ability to deflect an asteroid towards the Earth — providing an evil power with a true doomsday bomb.

Billions and billions

From ''Cosmos'' and his frequent appearances on ''The Tonight Show Starring Johnny Carson'', Sagan became associated with the catchphrase "billions and billions". Sagan stated that he never actually used the phrase in the ''Cosmos'' series. The closest that he ever came was in the book ''Cosmos'', where he talked of "billions ''upon'' billions": }}

However, his frequent use of the word ''billions'', and distinctive delivery emphasizing the "b" (which he did intentionally, in place of more cumbersome alternatives such as "billions with a 'b'", in order to distinguish the word from "millions" in viewers' minds), made him a favorite target of comic performers, including Johnny Carson, Gary Kroeger, Mike Myers, Bronson Pinchot, Penn Jillette, Harry Shearer, and others. Frank Zappa satirized the line in the song "Be In My Video", noting as well "atomic light". Sagan took this all in good humor, and his final book was entitled ''Billions and Billions'' which opened with a tongue-in-cheek discussion of this catchphrase, observing that Carson himself was an amateur astronomer and that Carson's comic caricature often included real science.

The popular perception of his characterization of large cosmic quantities continued to be a sense of wonderment at the vastness of space and time, as in his phrase "The total number of stars in the Universe is larger than all the grains of sand on all the beaches of the planet Earth." However, this famous saying was widely misunderstood, as he was in fact referring to the world being at a "critical branch point in history" as in the following quote from ''Cosmos: A Personal Voyage'', Episode 8: "Journeys in Space and Time":

"Those worlds in space are as countless as all the grains of sand on all the beaches of the earth. Each of those worlds is as real as ours and every one of them is a succession of incidents, events, occurrences which influence its future. Countless worlds, numberless moments, an immensity of space and time. And our small planet at this moment, here we face a critical branch point in history: what we do with our world, right now, will propagate down through the centuries and powerfully affect the destiny of our descendants. It is well within our power to destroy our civilization and perhaps our species as well."

Sagan units

As a humorous tribute to him, a ''sagan'' has been defined as a unit of measurement equal to at least four billion, since the lower bound of a number conforming to the constraint of ''billions and billions'' must be two billion plus two billion.

Social concerns

Sagan believed that the Drake equation, on substitution of reasonable estimates, suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations highlighted by the Fermi paradox suggests technological civilizations tend to destroy themselves rather quickly. This stimulated his interest in identifying and publicizing ways that humanity could destroy itself, with the hope of avoiding such a cataclysm and eventually becoming a spacefaring species. Sagan's deep concern regarding the potential destruction of human civilization in a nuclear holocaust was conveyed in a memorable cinematic sequence in the final episode of ''Cosmos'', called "Who Speaks for Earth?" Sagan had already resigned from the Air Force Scientific Advisory Board and voluntarily surrendered his top secret clearance in protest over the Vietnam War. Following his marriage to his third wife (novelist Ann Druyan) in June 1981, Sagan became more politically active — particularly in opposing escalation of the nuclear arms race under President Ronald Reagan.

In March 1983, Reagan announced the Strategic Defense Initiative — a multi-billion dollar project to develop a comprehensive defense against attack by nuclear missiles, which was quickly dubbed the "Star Wars" program. Sagan spoke out against the project, arguing that it was technically impossible to develop a system with the level of perfection required, and far more expensive to build than for an enemy to defeat through decoys and other means — and that its construction would seriously destabilize the nuclear balance between the United States and the Soviet Union, making further progress toward nuclear disarmament impossible.

When Soviet leader Mikhail Gorbachev declared a unilateral moratorium on the testing of nuclear weapons, which would begin on August 6, 1985 — the 40th anniversary of the atomic bombing of Hiroshima — the Reagan administration dismissed the dramatic move as nothing more than propaganda, and refused to follow suit. In response, American anti-nuclear and peace activists staged a series of protest actions at the Nevada Test Site, beginning on Easter Sunday in 1986 and continuing through 1987. Hundreds of people were arrested, including Sagan, who was arrested on two separate occasions as he climbed over a chain-link fence at the test site.

Personal life and beliefs

Sagan was married three times — in 1957, to biologist Lynn Margulis, mother of Dorion Sagan and Jeremy Sagan; in 1968, to artist Linda Salzman, mother of Nick Sagan; and in 1981, to author Ann Druyan, mother of Alexandra Rachel (Sasha) Sagan and Samuel Democritus Sagan. His marriage to Druyan continued until his death in 1996.

Isaac Asimov described Sagan as one of only two people he ever met whose intellect surpassed his own. The other, he claimed, was the computer scientist and artificial intelligence expert Marvin Minsky.

Sagan wrote frequently about religion and the relationship between religion and science, expressing his skepticism about the conventional conceptualization of God as a sapient being. For example:

Some people think God is an outsized, light-skinned male with a long white beard, sitting on a throne somewhere up there in the sky, busily tallying the fall of every sparrow. Others — for example Baruch Spinoza and Albert Einstein — considered God to be essentially the sum total of the physical laws which describe the universe. I do not know of any compelling evidence for anthropomorphic patriarchs controlling human destiny from some hidden celestial vantage point, but it would be madness to deny the existence of physical laws.

In another description of his view of God, Sagan emphatically writes:

The idea that God is an oversized white male with a flowing beard who sits in the sky and tallies the fall of every sparrow is ludicrous. But if by God one means the set of physical laws that govern the universe, then clearly there is such a God. This God is emotionally unsatisfying... it does not make much sense to pray to the law of gravity.

Despite his criticism of religion, Sagan denied that he was an atheist, saying "An atheist has to know a lot more than I know. An atheist is someone who knows there is no god. By some definitions atheism is very stupid." In reply to a question in 1996 about his religious beliefs, Sagan answered, "I'm agnostic." Sagan maintained that the idea of a creator of the universe was difficult to prove or disprove and that the only conceivable scientific discovery that could challenge it would be an infinitely old universe. According to his last wife, Ann Druyan, he was not a believer: }}

In 2006, Ann Druyan edited Sagan's 1985 Glasgow ''Gifford Lectures in Natural Theology'' into a book, ''The Varieties of Scientific Experience: A Personal View of the Search for God'', in which he elaborates on his views of divinity in the natural world. Sagan is also widely regarded as a freethinker or skeptic; one of his most famous quotations, in ''Cosmos'', was, "Extraordinary claims require extraordinary evidence" (called the "Sagan Standard" by some). This was based on a nearly identical statement by fellow founder of the Committee for the Scientific Investigation of Claims of the Paranormal, Marcello Truzzi, "An extraordinary claim requires extraordinary proof." This idea originated with Pierre-Simon Laplace (1749–1827), a French mathematician and astronomer who said, "The weight of evidence for an extraordinary claim must be proportioned to its strangeness."

Late in his life, Sagan's books elaborated on his skeptical, naturalistic view of the world. In ''The Demon-Haunted World: Science as a Candle in the Dark'', he presented tools for testing arguments and detecting fallacious or fraudulent ones, essentially advocating wide use of critical thinking and the scientific method. The compilation ''Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium'', published in 1997 after Sagan's death, contains essays written by Sagan, such as his views on abortion, and his widow Ann Druyan's account of his death as a skeptic, agnostic, and freethinker.

Sagan warned against humans' tendency towards anthropocentrism. He was the faculty adviser for the Cornell Students for the Ethical Treatment of Animals. In the ''Cosmos'' chapter "Blues For a Red Planet", Sagan wrote, "If there is life on Mars, I believe we should do nothing with Mars. Mars then belongs to the Martians, even if the Martians are only microbes."

Sagan was a user and advocate of marijuana. Under the pseudonym "Mr. X", he contributed an essay about smoking cannabis to the 1971 book ''Marihuana Reconsidered''. The essay explained that marijuana use had helped to inspire some of Sagan's works and enhance sensual and intellectual experiences. After Sagan's death, his friend Lester Grinspoon disclosed this information to Sagan's biographer, Keay Davidson. The publishing of the biography, ''Carl Sagan: A Life'', in 1999 brought media attention to this aspect of Sagan's life. Not long after his death, widow Ann Druyan had gone on to preside over the board of directors of NORML, a foundation dedicated to reforming cannabis laws.

In 1994, engineers at Apple Computer code-named the Power Macintosh 7100 "Carl Sagan" in the hope that Apple would make "billions and billions" with the sale of the PowerMac 7100. The name was only used internally, but Sagan was concerned that it would become a product endorsement and sent Apple a cease and desist letter. Apple complied, but engineers retaliated by changing the internal codename to "BHA" for "Butt-Head Astronomer". Sagan then sued Apple for libel, a form of defamation, in federal court. The court granted Apple's motion to dismiss Sagan's claims and opined in dicta that a reader aware of the context would understand Apple was "clearly attempting to retaliate in a humorous and satirical way", and that "It strains reason to conclude that Defendant was attempting to criticize Plaintiff's reputation or competency as an astronomer. One does not seriously attack the expertise of a scientist using the undefined phrase 'butt-head'." Sagan then sued for Apple's original use of his name and likeness, but again lost. Sagan appealed the ruling. In November 1995, an out of court settlement was reached and Apple's office of trademarks and patents released a conciliatory statement that "Apple has always had great respect for Dr. Sagan. It was never Apple's intention to cause Dr. Sagan or his family any embarrassment or concern."

Sagan briefly served as an adviser on Stanley Kubrick's film ''2001: A Space Odyssey''. Sagan proposed that the film would suggest, rather than depict, extraterrestrial superintelligence.

Sagan and UFOs

Sagan had some interest in UFO reports from at least 1964 when he had several conversations on the subject with Jacques Vallee. Though quite skeptical of any extraordinary answer to the UFO question, Sagan thought scientists should study the phenomenon, at least because there was widespread public interest in UFO reports.

Stuart Appelle notes that Sagan "wrote frequently on what he perceived as the logical and empirical fallacies regarding UFOs and the abduction experience. Sagan rejected an extraterrestrial explanation for the phenomenon but felt there were both empirical and pedagogical benefits for examining UFO reports and that the subject was, therefore, a legitimate topic of study."

In 1966, Sagan was a member of the Ad Hoc Committee to Review Project Blue Book, the U.S. Air Force's UFO investigation project. The committee concluded Blue Book had been lacking as a scientific study, and recommended a university-based project to give the UFO phenomenon closer scientific scrutiny. The result was the Condon Committee (1966–1968), led by physicist Edward Condon, and in their final report they formally concluded that UFOs, regardless of what any of them actually were, did not behave in a manner consistent with a threat to national security.

Ron Westrum writes that "The high point of Sagan's treatment of the UFO question was the AAAS's symposium in 1969. A wide range of educated opinions on the subject were offered by participants, including not only proponents such as James McDonald and J. Allen Hynek but also skeptics like astronomers William Hartmann and Donald Menzel. The roster of speakers was balanced, and it is to Sagan's credit that this event was presented in spite of pressure from Edward Condon". With physicist Thornton Page, Sagan edited the lectures and discussions given at the symposium; these were published in 1972 as ''UFOs: A Scientific Debate''. Some of Sagan's many books examine UFOs (as did one episode of ''Cosmos'') and he claimed a religious undercurrent to the phenomenon.

Sagan again revealed his views on interstellar travel in his 1980 ''Cosmos'' series. In one of his last written works, Sagan argued that the chances of extraterrestrial spacecraft visiting Earth are vanishingly small. However, Sagan did think it plausible that Cold War concerns contributed to governments misleading their citizens about UFOs, and that "some UFO reports and analyses, and perhaps voluminous files, have been made inaccessible to the public which pays the bills ... It's time for the files to be declassified and made generally available." He cautioned against jumping to conclusions about suppressed UFO data and stressed that there was no strong evidence that aliens were visiting the Earth either in the past or present.

Death

After a long and difficult fight with myelodysplasia, which included three bone marrow transplants, Sagan died of pneumonia at the age of 62 at the Fred Hutchinson Cancer Research Center in Seattle, Washington, on December 20, 1996. He was buried at Lakeview Cemetery in Ithaca, New York.

Posthumous recognition

The 1997 movie ''Contact'', based on Sagan's novel of the same name and finished after his death, ends with the dedication "For Carl".

In 1997, the Sagan Planet Walk was opened in Ithaca New York. It is a walking scale model of the solar system, extending 1.2 km from the center of The Commons in downtown Ithaca, NY, to the Sciencenter, a hands-on museum. The exhibition was created in memory of Carl Sagan, who was an Ithaca resident and Cornell Professor. Professor Sagan had been a founding member of the museum's advisory board.

The landing site of the unmanned Mars Pathfinder spacecraft was renamed the ''Carl Sagan Memorial Station'' on July 5, 1997.

Sagan's son, Nick Sagan, wrote several episodes in the ''Star Trek'' franchise. In an episode of ''Star Trek: Enterprise'' entitled "Terra Prime", a quick shot is shown of the relic rover Sojourner, part of the Mars Pathfinder mission, placed by a historical marker at Carl Sagan Memorial Station on the Martian surface. The marker displays a quote from Sagan: "Whatever the reason you're on Mars, I'm glad you're there, and I wish I was with you." Sagan's student Steve Squyres led the team that landed the Spirit Rover and Opportunity Rover successfully on Mars in 2004.

Asteroid 2709 Sagan is also named in his honor.

On November 9, 2001, on what would have been Sagan's 67th birthday, the NASA Ames Research Center dedicated the site for the Carl Sagan Center for the Study of Life in the Cosmos. "Carl was an incredible visionary, and now his legacy can be preserved and advanced by a 21st century research and education laboratory committed to enhancing our understanding of life in the universe and furthering the cause of space exploration for all time", said NASA Administrator Daniel Goldin. Ann Druyan was at the Center as it opened its doors on October 22, 2006.

Sagan has at least three awards named in his honor:

The Carl Sagan Memorial Award presented jointly since 1997 by the American Astronomical Society (AAS) and the Planetary Society,

The Carl Sagan Medal for Excellence in Public Communication in Planetary Science presented since 1998 by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS) for outstanding communication by an active planetary scientist to the general public — Carl Sagan was one of the original organizing committee members of the DPS, and

The Carl Sagan Award for Public Understanding of Science presented by the Council of Scientific Society Presidents (CSSP) — Sagan himself was the first recipient of the CSSP award in 1993. In 2006, the Carl Sagan Medal was awarded to astrobiologist and author David Grinspoon, the son of Sagan's friend Lester Grinspoon.

On December 20, 2006, the tenth anniversary of Sagan's death, a blogger, Joel Schlosberg, organized a Carl Sagan "blog-a-thon" to commemorate Sagan's death, and the idea was supported by Nick Sagan. Many members of the blogging community participated.

August 2007 the Independent Investigative Group IIG awarded Sagan posthumously a Lifetime Achievement Award. This honor has also been awarded to Harry Houdini and James Randi.

In 2008, Benn Jordan, also known as "The Flashbulb", released the album ''Pale Blue Dot: A Tribute to Carl Sagan''.

In 2009, clips from Carl Sagan's ''Cosmos'' were used as the basis for ''A Glorious Dawn'', the first video produced for the Symphony of Science, an educational music video production by composer John Boswell. Musician Jack White later released this song as a vinyl single under his record label Third Man Records. Additional clips were used in several followup videos which featured Sagan alongside other noted scientists and proponents of rational thinking, such as Richard Dawkins, Richard Feynman, Brian Greene, Lawrence M. Krauss, Bill Nye, and Neil deGrasse Tyson.

In 2010, the 76th anniversary of Carl Sagan's birth, the second "Carl Sagan Day" was celebrated on November 6.

Awards and honors

Annual Award for Television Excellence — 1981 — The Ohio State University — PBS series ''Cosmos''

Apollo Achievement Award — National Aeronautics and Space Administration

NASA Distinguished Public Service Medal — National Aeronautics and Space Administration (twice)

Emmy — Outstanding Individual Achievement — 1981 — PBS series ''Cosmos''

Emmy — Outstanding Informational Series — 1981 — PBS series ''Cosmos''

Exceptional Scientific Achievement Medal — National Aeronautics and Space Administration

Helen Caldicott Leadership Award — Women's Action for Nuclear Disarmament

Hugo Award — 1981 — ''Cosmos''

Humanist of the Year — 1981 — Awarded by the American Humanist Association

In Praise of Reason Award — 1987 — Committee for the Scientific Investigation of Claims of the Paranormal

Isaac Asimov Award — 1994 — Committee for the Scientific Investigation of Claims of the Paranormal

John F. Kennedy Astronautics Award — American Astronautical Society

John W. Campbell Memorial Award — 1974 — ''Cosmic Connection: An Extraterrestrial Perspective''

Joseph Priestley Award — "For distinguished contributions to the welfare of mankind"

Klumpke-Roberts Award of the Astronomical Society of the Pacific — 1974

Konstantin Tsiolkovsky Medal — Awarded by the Soviet Cosmonauts Federation

Locus Award 1986 — ''Contact''

Lowell Thomas Award — Explorers Club — 75th Anniversary

Masursky Award — American Astronomical Society

Miller Research Fellowship — Miller Institute (1960–1962)

Oersted Medal — 1990 — American Association of Physics Teachers

Peabody Award — 1980 — PBS series ''Cosmos''

Prix Galbert — The international prize of Astronautics

Public Welfare Medal — 1994 — National Academy of Sciences

Pulitzer Prize for General Non-Fiction — 1978 — ''The Dragons of Eden''

SF Chronicle Award — 1998 — ''Contact''

Named the "99th Greatest American" on the June 5, 2005, ''Greatest American'' show on the Discovery Channel

Publications

''Planets'' (LIFE Science Library), Sagan, Carl, Jonathan Norton Leonard and editors of Life, Time, Inc., 1966

''Intelligent Life in the Universe'', I.S. Shklovskii coauthor, Random House, 1966, ISBN 1-892803-02-X, 509 pgs (note: republished in 1998 by Emerson-Adams Press)

''UFOs: A Scientific Debate'', Thornton Page coauthor, Cornell University Press, 1972, 310 pgs

''Communication with Extraterrestrial Intelligence''. MIT Press, 1973, 428 pgs

''Mars and the Mind of Man'', Sagan, Carl, et al., Harper & Row, 1973, 143 pgs

''Cosmic Connection: An Extraterrestrial Perspective'', Jerome Agel coauthor, Anchor Press, 1973, ISBN 0-521-78303-8, 301 pgs

''Other Worlds''. Bantam Books, 1975

''Murmurs of Earth: The Voyager Interstellar Record'', Sagan, Carl, et al., Random House, ISBN 0-394-41047-5, 1978

''The Dragons of Eden: Speculations on the Evolution of Human Intelligence''. Ballantine Books, 1978, ISBN 0-345-34629-7, 288 pgs

''Broca's Brain: Reflections on the Romance of Science''. Ballantine Books, 1979, ISBN 0-345-33689-5, 416 pgs

''Cosmos''. Random house, 1980. Random House New Edition, May 7, 2002, ISBN 0-375-50832-5, 384 pgs

''The Cold and the Dark: The World after Nuclear War'', Sagan, Carl et al., Sidgwick & Jackson, 1985

''Comet'', Ann Druyan coauthor, Ballantine Books, 1985, ISBN 0-345-41222-2, 496 pgs

''Contact''. Simon and Schuster, 1985; Reissued August 1997 by Doubleday Books, ISBN 1-56865-424-3, 352 pgs

''A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race'', Richard Turco coauthor, Random House, 1990, ISBN 0-394-58307-8, 499 pgs

''Shadows of Forgotten Ancestors: A Search for Who We Are'', Ann Druyan coauthor, Ballantine Books, October 1993, ISBN 0-345-38472-5, 528 pgs

''Pale Blue Dot: A Vision of the Human Future in Space''. Random House, November 1994, ISBN 0-679-43841-6, 429 pgs

''The Demon-Haunted World: Science as a Candle in the Dark''. Ballantine Books, March 1996, ISBN 0-345-40946-9, 480 pgs (note: the book was first published and copyrighted in 1995 with an errata slip inserted)

''Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium'', Ann Druyan coauthor, Ballantine Books, June 1997, ISBN 0-345-37918-7, 320 pgs

''The Varieties of Scientific Experience: A Personal View of the Search for God'', Carl Sagan (writer) & Ann Druyan (editor), 1985 Gifford lectures, Penguin Press HC, November 2006, ISBN 1-59420-107-2, 304 pgs

References

Further reading

External links

The Carl Sagan Portal

BBC Radio program "Great Lives" on Carl Sagan's life

A Man whose time Has come — Interview with Carl Sagan by Ian Ridpath, New Scientist 1974 July 4

Carl Sagan Prize for Science Popularization

Carl Sagan Medal for Excellence in Public Communication in Planetary Science, presented by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS)

Carl Sagan Center for the Study of Life in the Universe, SETI Institute

Carl Sagan's Life and Legacy as Scientist, Teacher, and Skeptic, Committee for Skeptical Inquiry

Cosmos — Full Episodes and Clips streaming online for free — Hulu, Cosmos online for free

A Tribute to Carl Sagan: Our Place in the Universe, The Skeptics Society

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Coordinates	28°36′36″N77°13′48″N
Name	Stephen Hawking
Birth name	Stephen William Hawking
Birth date	January 08, 1942
Birth place	Oxford, England, United Kingdom
Residence	United Kingdom
Nationality	British
Fields	Applied mathematicsTheoretical physicsCosmology
Workplaces	Cambridge UniversityCalifornia Institute of TechnologyPerimeter Institute for Theoretical Physics
Alma mater	Oxford UniversityCambridge University
Doctoral advisor	Dennis Sciama
Academic advisors	Robert Berman
Doctoral students	Bruce AllenRaphael BoussoFay DowkerMalcolm PerryBernard CarrGary GibbonsHarvey ReallDon PageTim PrestidgeRaymond LaflammeJulian Luttrell
Known for	Black holesTheoretical cosmologyQuantum gravityHawking radiation
Influences	Dikran TahtaAlbert Einstein
Awards
Spouse	Jane Hawking(m. 1965–1991, divorced)Elaine Mason(m. 1995–2006, divorced)
Signature	Hawkingsig.svg }}

Stephen William Hawking, CH, CBE, FRS, FRSA (born 8 January 1942) is a British theoretical physicist and cosmologist, whose scientific books and public appearances have made him an academic celebrity. He is an Honorary Fellow of the Royal Society of Arts, a lifetime member of the Pontifical Academy of Sciences, and in 2009 was awarded the Presidential Medal of Freedom, the highest civilian award in the United States.

Hawking was the Lucasian Professor of Mathematics at the University of Cambridge for 30 years, taking up the post in 1979 and retiring on 1 October 2009. He is now Director of Research at the Centre for Theoretical Cosmology in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge. He is also a Fellow of Gonville and Caius College, Cambridge and a Distinguished Research Chair at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario. He is known for his contributions to the fields of cosmology and quantum gravity, especially in the context of black holes. He has also achieved success with works of popular science in which he discusses his own theories and cosmology in general; these include the runaway best seller ''A Brief History of Time'', which stayed on the British ''Sunday Times'' best-sellers list for a record-breaking 237 weeks.

Hawking's key scientific works to date have included providing, with Roger Penrose, theorems regarding gravitational singularities in the framework of general relativity, and the theoretical prediction that black holes should emit radiation, which is today known as Hawking radiation (or sometimes as Bekenstein–Hawking radiation).

Hawking has a motor neurone disease that is related to amyotrophic lateral sclerosis, a condition that has progressed over the years and has left him almost completely paralysed.

Early life

Stephen Hawking was born on 8 January 1942 to Dr. Frank Hawking, a research biologist, and Isobel Hawking. He had two younger sisters, Philippa and Mary, and an adopted brother, Edward. Though Hawking's parents were living in North London, they moved to Oxford while his mother was pregnant with Stephen, desiring a safer location for the birth of their first child. (London was under attack at the time by the Luftwaffe.) According to Hawking, a German V-2 missile struck only a few streets away.

After Hawking was born, the family moved back to London, where his father headed the division of parasitology at the National Institute for Medical Research. In 1950, Hawking and his family moved to St Albans, Hertfordshire, where he attended St Albans High School for Girls from 1950 to 1953. (At that time, boys could attend the Girls' school until the age of ten.) From the age of eleven, he attended St Albans School, where he was a good, but not exceptional, student. When asked later to name a teacher who had inspired him, Hawking named his mathematics teacher Dikran Tahta. He maintains his connection with the school, giving his name to one of the four houses and to an extracurricular science lecture series. He has visited it to deliver one of the lectures and has also granted a lengthy interview to pupils working on the school magazine, ''The Albanian''.

Hawking was always interested in science. Inspired by his mathematics teacher, he originally wanted to study the subject at university. However, Hawking's father wanted him to apply to University College, Oxford, where his father had attended. As University College did not have a mathematics fellow at that time, it would not accept applications from students who wished to read that discipline. Hawking therefore applied to read natural sciences, in which he gained a scholarship. Once at University College, Hawking specialised in physics. His interests during this time were in thermodynamics, relativity, and quantum mechanics. His physics tutor, Robert Berman, later said in ''The New York Times Magazine'':

Hawking was passing, but his unimpressive study habits resulted in a final examination score on the borderline between first and second class honours, making an "oral examination" necessary. Berman said of the oral examination:

After receiving his B.A. degree at Oxford in 1962, he stayed to study astronomy. He decided to leave when he found that studying sunspots, which was all the observatory was equipped for, did not appeal to him and that he was more interested in theory than in observation. He left Oxford for Trinity Hall, Cambridge, where he engaged in the study of theoretical astronomy and cosmology.

Career

Almost as soon as he arrived at Cambridge, he started developing symptoms of amyotrophic lateral sclerosis (ALS, known colloquially in the United States as Lou Gehrig's disease), a type of motor neurone disease which would cost him almost all neuromuscular control. During his first two years at Cambridge, he did not distinguish himself, but, after the disease had stabilised and with the help of his doctoral tutor, Dennis William Sciama, he returned to working on his PhD.

Hawking was elected as one of the youngest Fellows of the Royal Society in 1974, was created a Commander of the Order of the British Empire in 1982, and became a Companion of Honour in 1989. Hawking is a member of the Board of Sponsors of the ''Bulletin of the Atomic Scientists''.

In 1974, he accepted the Sherman Fairchild Distinguished Scholar visiting professorship at the California Institute of Technology (Caltech) to work with his friend, Kip Thorne, who was a faculty member there. He continues to have ties with Caltech, spending a month each year there since 1992.

Hawking's achievements were made despite the increasing paralysis caused by the ALS. By 1974, he was unable to feed himself or get out of bed. His speech became slurred so that he could be understood only by people who knew him well. In 1985, he caught pneumonia and had to have a tracheotomy, which made him unable to speak at all. A Cambridge scientist built a device that enables Hawking to write onto a computer with small movements of his body, and then have a voice synthesiser speak what he has typed.

Research fields

Hawking's principal fields of research are theoretical cosmology and quantum gravity.

In the late 1960s, he and his Cambridge friend and colleague, Roger Penrose, applied a new, complex mathematical model they had created from Albert Einstein's theory of general relativity. This led, in 1970, to Hawking proving the first of many singularity theorems; such theorems provide a set of sufficient conditions for the existence of a gravitational singularity in space-time. This work showed that, far from being mathematical curiosities which appear only in special cases, singularities are a fairly generic feature of general relativity.

He supplied a mathematical proof, along with Brandon Carter, Werner Israel and D. Robinson, of John Wheeler's no-hair theorem – namely, that any black hole is fully described by the three properties of mass, angular momentum, and electric charge.

Hawking also suggested upon analysis of gamma ray emissions that after the Big Bang, primordial mini black holes were formed. With Bardeen and Carter, he proposed the four laws of black hole mechanics, drawing an analogy with thermodynamics. In 1974, he calculated that black holes should thermally create and emit subatomic particles, known today as Bekenstein-Hawking radiation, until they exhaust their energy and evaporate.

In collaboration with Jim Hartle, Hawking developed a model in which the universe had no boundary in space-time, replacing the initial singularity of the classical Big Bang models with a region akin to the North Pole: one cannot travel north of the North Pole, as there is no boundary. While originally the no-boundary proposal predicted a closed universe, discussions with Neil Turok led to the realisation that the no-boundary proposal is also consistent with a universe which is not closed.

Along with Thomas Hertog at CERN, in 2006 Hawking proposed a theory of "top-down cosmology," which says that the universe had no unique initial state, and therefore it is inappropriate for physicists to attempt to formulate a theory that predicts the universe's current configuration from one particular initial state. Top-down cosmology posits that in some sense, the present "selects" the past from a superposition of many possible histories. In doing so, the theory suggests a possible resolution of the fine-tuning question: It is inevitable that we find our universe's present physical constants, as the current universe "selects" only those past histories that led to the present conditions. In this way, top-down cosmology provides an anthropic explanation for why we find ourselves in a universe that allows matter and life, without invoking an ensemble of multiple universes.

Hawking's many other scientific investigations have included the study of quantum cosmology, cosmic inflation, helium production in anisotropic Big Bang universes, large N cosmology, the density matrix of the universe, topology and structure of the universe, baby universes, Yang-Mills instantons and the S matrix, anti de Sitter space, quantum entanglement and entropy, the nature of space and time, including the arrow of time, spacetime foam, string theory, supergravity, Euclidean quantum gravity, the gravitational Hamiltonian, Brans-Dicke and Hoyle-Narlikar theories of gravitation, gravitational radiation, and wormholes.

At a George Washington University lecture in honour of NASA's fiftieth anniversary, Hawking theorised on the existence of extraterrestrial life, believing that "primitive life is very common and intelligent life is fairly rare."

Losing an old bet

Hawking was in the news in July 2004 for presenting a new theory about black holes which goes against his own long-held belief about their behaviour, thus losing a bet he made with Kip Thorne and John Preskill of Caltech. Classically, it can be shown that information crossing the event horizon of a black hole is lost to our universe, and that thus all black holes are identical beyond their mass, electrical charge and angular velocity (the "no hair theorem"). The problem with this theorem is that it implies the black hole will emit the same radiation regardless of what goes into it, and as a consequence that if a pure quantum state is thrown into a black hole, an "ordinary" mixed state will be returned. This runs counter to the rules of quantum mechanics and is known as the black hole information paradox.

Human spaceflight

At the fiftieth anniversary of NASA in 2008, Hawking gave a keynote speech on the final frontier exhorting and inspiring the space technology community on why we (the human race) explore space.

At the celebration of his sixty-fifth birthday on 8 January 2007, Hawking announced his plan to take a zero-gravity flight in 2007 to prepare for a sub-orbital spaceflight in 2009 on Virgin Galactic's space service. Billionaire Richard Branson pledged to pay all expenses for the latter, costing an estimated £100,000. Stephen Hawking's zero-gravity flight in a "''Vomit Comet''" of Zero Gravity Corporation, during which he experienced weightlessness eight times, took place on 26 April 2007. He became the first quadriplegic to float in zero-gravity. This was the first time in forty years that he moved freely, without his wheelchair. The fee is normally US$3,750 for 10–15 plunges, but Hawking was not required to pay the fee. A bit of a futurist, Hawking was quoted before the flight saying: }} In an interview with ''The Daily Telegraph'', he suggested that space was the Earth's long term hope. He continued this theme at a 2008 Charlie Rose interview.

Existence and nature of extraterrestrial life

Hawking has indicated that he is almost certain that alien life exists in other parts of the universe and uses a mathematical basis for his assumptions. "To my mathematical brain, the numbers alone make thinking about aliens perfectly rational. The real challenge is to work out what aliens might actually be like." He believes alien life not only certainly exists on planets but perhaps even in other places, like within stars or even floating in outer space. He also warns that a few of these species might be intelligent and threaten Earth. Contact with such species might be devastating for humanity. "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans," he said. He advocated that, rather than try to establish contact, humans should try to avoid contact with alien life forms.

Illness

Stephen Hawking is severely disabled by a motor neurone disease known as Amyotrophic lateral sclerosis (ALS), sometimes known as Lou Gehrig's disease. Hawking's illness is markedly different from typical ALS because if confirmed, Hawking's case would make for the most protracted case ever documented. A survival for more than ten years after diagnosis is uncommon for ALS; the longest documented durations, other than Hawking's, are 32 and 39 years and these cases were termed benign because of the lack of the typical progressive course.

When he was young, he enjoyed riding horses. At Oxford, he coxed a rowing team, which, he stated, helped relieve his immense boredom at the university. Symptoms of the disorder first appeared while he was enrolled at University of Cambridge; he lost his balance and fell down a flight of stairs, hitting his head. Worried that he would lose his genius, he took the Mensa test to verify that his intellectual abilities were intact. The diagnosis of motor neurone disease came when Hawking was 21, shortly before his first marriage, and doctors said he would not survive more than two or three years. Hawking gradually lost the use of his arms, legs, and voice, and as of 2009 has been almost completely paralysed.

During a visit to the research centre CERN in Geneva in 1985, Hawking contracted pneumonia, which in his condition was life-threatening as it further restricted his already limited respiratory capacity. He had an emergency tracheotomy, and as a result lost what remained of his ability to speak. He has since used an electronic voice synthesiser to communicate.

The DECtalk DTC01 voice synthesiser he uses, which has an American English accent, is no longer being produced. Asked why he has still kept it after so many years, Hawking mentioned that he has not heard a voice he likes better and that he identifies with it. Hawking is said to be looking for a replacement since, aside from being obsolete, the synthesiser is both large and fragile by current standards. As of mid 2009, he was said to be using NeoSpeech's VoiceText speech synthesiser.

In Hawking's many media appearances, he appears to speak fluently through his synthesiser, but in reality, it is a tedious drawn-out process. Hawking's setup uses a predictive text entry system, which requires only the first few characters in order to auto-complete the word, but as he is only able to use his cheek for data entry, constructing complete sentences takes time. His speeches are prepared in advance, but having a live conversation with him provides insight as to the complexity and work involved. During a TED Conference talk, it took him seven minutes to answer a question.

He describes himself as lucky, despite his disease. Its slow progression has allowed him time to make influential discoveries and has not hindered him from having, in his own words, "a very attractive family." When his wife, Jane, was asked why she decided to marry a man with a three-year life expectancy, she responded, "Those were the days of atomic gloom and doom, so we all had a rather short life expectancy." On 20 April 2009, Cambridge University released a statement saying that Hawking was "very ill" with a chest infection, and was admitted to Addenbrooke's Hospital. The following day, it was reported that his new condition was "comfortable" and he would make a full recovery from the infection.

As popular science advocate

Hawking has played himself on numerous television shows and has been portrayed in many more. He has played himself on a ''Red Dwarf'' anniversary special, played a hologram of himself on the episode "Descent" of ''Star Trek: The Next Generation'', appeared in a skit on ''Late Night with Conan O'Brien'', and appeared on the Discovery Channel special ''Alien Planet''. He has also played himself in several episodes of ''The Simpsons'' and ''Futurama'', and has had an action figure made of his ''Simpsons'' likeness. In 2008, Hawking was the subject of and featured in the documentary series ''Stephen Hawking, Master of the Universe'' for Channel 4. In September 2008, Hawking presided over the unveiling of the 'Chronophage' (time-eating) Corpus Clock at Corpus Christi College Cambridge. His actual synthesiser voice was used on parts of the Pink Floyd song "Keep Talking" from the 1994 album ''The Division Bell'', as well as on Turbonegro's "Intro: The Party Zone" on their 2005 album ''Party Animals'', Wolfsheim's "Kein Zurück (Oliver Pinelli Mix)".

Recognition

Acclaim

On 19 December 2007, a statue of Hawking by renowned late artist Ian Walters was unveiled at the Centre for Theoretical Cosmology, University of Cambridge. In May 2008, the statue of Hawking was unveiled at the African Institute for Mathematical Sciences in Cape Town. The Stephen W. Hawking Science Museum in San Salvador, El Salvador is named in honour of Stephen Hawking, citing his scientific distinction and perseverance in dealing with adversity. Stephen Hawking Building in Cambridge opened on 17 April 2007. The building belongs to Gonville and Caius College and is used as an undergraduate accommodation and conference facility.

Distinctions

Hawking's belief that the lay person should have access to his work led him to write a series of popular science books in addition to his academic work. The first of these, ''A Brief History of Time'', was published on 1 April 1988 by Hawking, his family and friends, and some leading physicists. It surprisingly became a best-seller and was followed by ''The Universe in a Nutshell'' (2001). Both books have remained highly popular all over the world. A collection of essays titled ''Black Holes and Baby Universes'' (1993) was also popular. His book, ''A Briefer History of Time'' (2005), co-written by Leonard Mlodinow, aims to update his earlier works and make them accessible to an even wider audience. In 2007 Hawking and his daughter, Lucy Hawking, published ''George's Secret Key to the Universe'', a children's book focusing on science that has been described as "like ''Harry Potter'', but without the magic." The book includes information on Hawking radiation.

Hawking supports the children's charity SOS Children's Villages UK.

Awards and honours

1975 Eddington Medal

1976 Hughes Medal of the Royal Society

1979 Albert Einstein Medal

1981 Franklin Medal

1982 Order of the British Empire (Commander)

1985 Gold Medal of the Royal Astronomical Society

1986 Member of the Pontifical Academy of Sciences

1988 Wolf Prize in Physics

1989 Prince of Asturias Awards in Concord

1989 Companion of Honour

1999 Julius Edgar Lilienfeld Prize of the American Physical Society

2003 Michelson Morley Award of Case Western Reserve University

2006 Copley Medal of the Royal Society 2008 Fonseca Prize of the University of Santiago de Compostela 2009 Presidential Medal of Freedom, the highest civilian honour in the United States

Personal life

Hawking revealed that he did not see much point in obtaining a doctorate if he were to die soon. Hawking later said that the real turning point was his 1965 marriage to Jane Wilde, a language student. After gaining his PhD at Trinity Hall, he became first a Research Fellow, and later on a Professorial Fellow at Gonville and Caius College. Jane Hawking (née Wilde), Hawking's first wife, cared for him until 1991 when the couple separated, reportedly because of the pressures of fame and his increasing disability. They had three children: Robert, Lucy, and Timothy. Hawking then married his nurse, Elaine Mason (who was previously married to David Mason, the designer of the first version of Hawking's talking computer), in 1995. In October 2006, Hawking filed for divorce from his second wife amid claims by former nurses that she had abused him.

In 1999, Jane Hawking published a memoir, ''Music to Move the Stars'', detailing the marriage and his breakdown; in 2010 she published a revised version, ''Travelling to Infinity, My Life with Stephen''. Hawking's daughter, Lucy, is a novelist. Their oldest son, Robert, emigrated to the United States, married, and has a son. After a period of estrangement, Hawking and his first family were reconciled in 2007.

His view on how to live life is to "seek the greatest value of our action".

Hawking was asked about his IQ in a 2004 newspaper interview, and replied, "I have no idea. People who boast about their I.Q. are losers." Yet when asked "Are you saying you are not a genius?", Hawking replied "I hope I'm near the upper end of the range."

Hawking strongly opposed the US-led Iraq War, calling it "a war crime" and "based on lies". In 2004, he personally attended a demonstration against the war in Trafalgar Square, and participated in a public reading of the names of Iraqi war victims.

Religious views

In his early work, Hawking spoke of "God" in a metaphorical sense, such as in ''A Brief History of Time'': "If we discover a complete theory, it would be the ultimate triumph of human reason—for then we should know the mind of God." In the same book he suggested the existence of God was unnecessary to explain the origin of the universe. His 2010 book ''The Grand Design'' and interviews with the ''Telegraph'' and the Channel 4 documentary ''Genius of Britain'', clarify that he does "not believe in a personal God". Hawking writes, "The question is: is the way the universe began chosen by God for reasons we can't understand, or was it determined by a law of science? I believe the second." He adds, "Because there is a law such as gravity, the Universe can and will create itself from nothing."

His ex-wife, Jane, said during their divorce proceedings that he was an atheist. Hawking has stated that he is "not religious in the normal sense" and he believes that "the universe is governed by the laws of science. The laws may have been decreed by God, but God does not intervene to break the laws." In an interview published in ''The Guardian'' newspaper, Hawking regarded the concept of Heaven as a myth, stating that there is "no heaven or afterlife" and that such a notion was a "fairy story for people afraid of the dark."

Hawking contrasted religion and science in 2010, saying: "There is a fundamental difference between religion, which is based on authority, [and] science, which is based on observation and reason. Science will win because it works."

Selected publications

Technical

''Singularities in Collapsing Stars and Expanding Universes'' with Dennis William Sciama, 1969 Comments on Astrophysics and Space Physics Vol 1 No.1

''The Large Scale Structure of Space-Time'' with George Ellis, 1973, ISBN 0-521-09906-4

''The Nature of Space and Time'' with Roger Penrose, foreword by Michael Atiyah, New Jersey: Princeton University Press, 1996, ISBN 0-691-05084-8

''The Large, the Small, and the Human Mind'', (with Abner Shimony, Nancy Cartwright, and Roger Penrose), Cambridge University Press, 1997, ISBN 0-521-56330-5 (hardback), ISBN 0-521-65538-2 (paperback), Canto edition: ISBN 0-521-78572-3

''Information Loss in Black Holes'', Cambridge University Press, 2005

''God Created the Integers: The Mathematical Breakthroughs That Changed History'', Running Press, 2005 ISBN 0762419229

Popular

''A Brief History of Time'', (Bantam Press 1988) ISBN 055305340X

''Black Holes and Baby Universes and Other Essays'', (Bantam Books 1993) ISBN 0553374117

''The Universe in a Nutshell'', (Bantam Press 2001) ISBN 055380202X

''On The Shoulders of Giants. The Great Works of Physics and Astronomy'', (Running Press 2002) ISBN 076241698X

''A Briefer History of Time'', coauthored with Leonard Mlodinow, (Bantam Books 2005) ISBN 0553804367

''The Grand Design'', coauthored with Leonard Mlodinow, (Bantam Press 2010) ISBN 0553805371

Children's fiction

These are co-written with his daughter Lucy.

''George's Secret Key to the Universe'', (Random House, 2007) ISBN 9780385612708

''George's Cosmic Treasure Hunt'', (Simon & Schuster, 2009) ISBN 9781416986713

Films and series

''A Brief History of Time'' (1991)

''Stephen Hawking's Universe'' (1997)

''Horizon: The Hawking Paradox'' (2005)

''Masters of Science Fiction'' (2007)

''Stephen Hawking: Master of the Universe'' (2008) ''Into The Universe with Stephen Hawking'' (2010) A list of Hawking's publications through the year 2002 is available on his website.

See also

Basic concepts of quantum mechanics

Many-worlds interpretation, or flexiverse

Susskind–Hawking battle – see Black hole information paradox

References

Further reading

A layman's guide to Stephen Hawking

Ferguson, Kitty (1991). ''Stephen Hawking: Quest For A Theory of Everything''. Franklin Watts. ISBN 0-553-29895-X

Highly influential in the field. A much cited centennial survey.

Pickover, Clifford, ''Archimedes to Hawking: Laws of Science and the Great Minds Behind Them'', Oxford University Press, 2008, ISBN 978-0195336115

External links

Stephen Hawking's web site

Stephen Hawking's page on Academia.edu

The Life of Stephen Hawking – slideshow by ''The First Post''

Video: Stephen Hawking – discussion of two views of the universe

Videos: Stephen Hawking's concept of God, The role of God within the no boundary cosmology and Imaginary time

;Dated

Stephen Hawking says universe not created by God

Public Lectures, including debate with Roger Penrose 1996–2006

''Hawking celebrates own brief history'', 7 January 2002, BBC

"Leaping the Abyss", interview in ''Reason'' by Gregory Benford 2002-04-01

2002-03-24

''Black holes turned "inside out"'', 22 July 2004, BBC

''Return of the time lord'', Interview about "A Brief History of Time", 27 September 2005, The Guardian.

Stephen Hawking touches on God and science – Physicist says Pope John Paul told scientists not to study universe's origins msnbc June 2006

Press Release from the Catholic League on misquote of Pope by Hawking 2006-06-16

BBC interview 2008-12-05

Category:1942 births Category:Academics of the University of Cambridge Category:Adams Prize recipients Category:Albert Einstein Medal recipients Category:Alumni of Trinity Hall, Cambridge Category:Alumni of University College, Oxford Category:Calculating prodigies Category:Commanders of the Order of the British Empire Category:Cosmologists Category:English astronomers Category:English theoretical physicists Category:English science writers Category:Fellows of Gonville and Caius College, Cambridge Category:Fellows of the Royal Society Category:People educated at St Albans School, Hertfordshire Category:Honorary Fellows of University College, Oxford Category:Living people Category:Lucasian Professors of Mathematics Category:Members of the Department of Applied Mathematics and Theoretical Physics Category:Members of the United States National Academy of Sciences Category:Members of the Order of the Companions of Honour Category:Members of the Pontifical Academy of Sciences Category:People from Oxford Category:People from St Albans Category:People with motor neurone disease Category:Presidential Medal of Freedom recipients Category:Recipients of the Copley Medal Category:Recipients of the Gold Medal of the Royal Astronomical Society Category:Religious skeptics Category:Wolf Prize in Physics laureates Category:20th-century philosophers Category:21st-century philosophers Category:People educated at St Albans High School for Girls

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