String theory
Superstring theory
Theory String theory Superstring theory Bosonic string theory M-theory (simplified) Type I string Type II string F-theory Heterotic string String field theory
Concepts Strings Branes D-brane Calabi–Yau manifold Holographic principle T-duality S-duality Kac–Moody algebra E8 Lie group
Related Topics Supersymmetry Supergravity Quantum gravity
Scientists Duff Green Greene Gross Kaku Maldacena Mandelstam Polchinski Polyakov Ramond Scherk Schwarz Sen Susskind Townsend Vafa Veneziano Witten
v t e

In theoretical physics, M-theory is an extension of string theory in which 11 dimensions are identified. Because the dimensionality exceeds that of superstring theories in 10 dimensions, proponents believe that the 11-dimensional theory unites all five string theories (and supersedes them). Though a full description of the theory is not known, the low-entropy dynamics are known to be supergravity interacting with 2- and 5-dimensional membranes.

This idea is the unique supersymmetric theory in eleven dimensions, with its low-entropy matter content and interactions fully determined, and can be obtained as the strong coupling limit of type IIA string theory because a new dimension of space emerges as the coupling constant increases.

Drawing on the work of a number of string theorists (including Ashoke Sen, Chris Hull, Paul Townsend, Michael Duff and John Schwarz), Edward Witten of the Institute for Advanced Study suggested its existence at a conference at USC in 1995, and used M-theory to explain a number of previously observed dualities, initiating a flurry of new research in string theory called the second superstring revolution.

In the early 1990s, it was shown that the various superstring theories were related by dualities which allow the description of an object in one super string theory to be related to the description of a different object in another super string theory. These relationships imply that each of the super string theories is a different aspect of a single underlying theory, proposed by Witten, and named "M-theory".

Originally the letter M in M-theory was taken from membrane, a construct designed to generalize the strings of string theory. However, as Witten was more skeptical about membranes than his colleagues, he opted for "M-theory" rather than "Membrane theory". Witten has since stated that the different interpretations of the M can be a matter of taste for the user, such as magic, mystery, and mother theory.^[1]

M-theory (and string theory) has been criticized for lacking predictive power or being untestable. Further work continues to find mathematical constructs that join various surrounding theories. However, the tangible success of M-theory can be questioned, given its current incompleteness and limited predictive power.

History and development[link]

Prior to May 1995[link]

Before 1995 there were five known consistent superstring theories (henceforth referred to as string theories), which were given the names Type I string theory, Type IIA string theory, Type IIB string theory, heterotic SO(32) (the HO string) theory, and heterotic E₈×E₈ (the HE string) theory. The five theories all share essential features that relate them to the name of string theory. Each theory is fundamentally based on vibrating, one-dimensional strings at approximately the length of the Planck length. Calculations have also shown that each theory requires more than the normal four spacetime dimensions (although all extra dimensions are in fact spatial). When the theories are analyzed in detail, significant differences appear.

Type I string theory and supplements[link]

The Type I string theory has vibrating strings like the rest of the string theories. These strings vibrate both in closed loops, so that the strings have no ends, and as open strings with two loose ends. The open loose strings are what separates the Type I string theory from the other four string theories. This was a feature that the other string theories did not contain.

String vibrational patterns[link]

The calculations of the String Vibrational Patterns show that the list of string vibrational patterns and the way each pattern interacts and influences others vary from one theory to another. These and other differences hindered the development of the string theory as being the theory that united quantum mechanics and general relativity successfully. Attempts by the physics community to eliminate four of the theories, leaving only one string theory, have not been successful.

M-theory[link]

M-theory attempts to unify the five string theories by examining certain identifications and dualities. Thus each of the five string theories become special cases of M-theory.

As the names suggest, some of these string theories were thought to be related to each other. In the early 1990s, string theorists discovered that some relations were so strong that they could be thought of as an identification.

Type IIA and Type IIB[link]

The Type IIA string theory and the Type IIB string theory were known to be connected by T-duality; this essentially meant that the IIA string theory description of a circle of radius R is exactly the same as the IIB description of a circle of radius 1/R, where distances are measured in units of the Planck length.

This was a profound result. First, this was an intrinsically quantum mechanical result; the identification did not hold in the realm of classical physics. Second, because it is possible to build up any space by gluing circles together in various ways, it would seem that any space described by the IIA string theory can also be seen as a different space described by the IIB theory. This implies that the IIA string theory can identify with the IIB string theory: any object which can be described with the IIA theory has an equivalent, although seemingly different, description in terms of the IIB theory. This suggests that the IIA string theory and the IIB string theory are really aspects of the same underlying theory.

Other dualities[link]

There are other dualities between the other string theories. The heterotic SO(32) and the heterotic E₈×E₈ theories^[2][3] are also related by T-duality; the heterotic SO(32) description of a circle of radius R is exactly the same as the heterotic E₈×E₈ description of a circle of radius 1/R. This implies that there are really only three superstring theories, which might be called (for discussion) the Type I theory, the Type II theory, and the heterotic theory.

There are still more dualities, however. The Type I string theory is related to the heterotic SO(32) theory by S-duality; this means that the Type I description of weakly interacting particles can also be seen as the heterotic SO(32) description of very strongly interacting particles. This identification is somewhat more subtle, in that it identifies only extreme limits of the respective theories. String theorists have found strong evidence that the two theories are really the same, even away from the extremely strong and extremely weak limits, but they do not yet have a proof strong enough to satisfy mathematicians. However, it has become clear that the two theories are related in some fashion; they appear as different limits of a single underlying theory.

Only two string theories[link]

Given the above commonalities there appear to be only two string theories: the heterotic string theory (which is also the type I string theory) and the type II theory. There are relations between these two theories as well, and these relations are in fact strong enough to allow them to be identified.

Last step[link]

This last step is best explained first in a certain limit. In order to describe our world, strings must be extremely tiny objects. So when one studies string theory at low energies, it becomes difficult to see that strings are extended objects — they become effectively zero-dimensional (pointlike). Consequently, the quantum theory describing the low energy limit is a theory that describes the dynamics of these points moving in spacetime, rather than strings. Such theories are called quantum field theories. However, since string theory also describes gravitational interactions, one expects the low-energy theory to describe particles moving in gravitational backgrounds. Finally, since superstring string theories are supersymmetric for supersymmetry is needed for consistency, one expects to see supersymmetry appearing in the low-energy approximation. These three facts imply that the low-energy approximation to a superstring theory is a supergravity theory.

Supergravity theories[link]

The possible supergravity theories were classified by Werner Nahm in the 1970s. In 10 dimensions, there are only two supergravity theories, which are denoted Type IIA and Type IIB. This similar denomination is not a coincidence; the Type IIA string theory has the Type IIA supergravity theory as its low-energy limit and the Type IIB string theory gives rise to Type IIB supergravity. The heterotic SO(32) and heterotic E₈×E₈ string theories also reduce to Type IIA and Type IIB supergravity in the low-energy limit. This suggests that there may indeed be a relation between the heterotic/Type I theories and the Type II theories.

In 1994, Edward Witten outlined the following relationship: The Type IIA supergravity (corresponding to the heterotic SO(32) and Type IIA string theories) can be obtained by dimensional reduction from the single unique eleven-dimensional supergravity theory. This means that if one studied supergravity on an eleven-dimensional spacetime that looks like the product of a ten-dimensional spacetime with another very small one-dimensional manifold, one gets the Type IIA supergravity theory. (And the Type IIB supergravity theory can be obtained by using T-duality.) However, eleven-dimensional supergravity is not consistent on its own — it does not make sense at extremely high energy, and likely requires some form of completion. It seems plausible, then, that there is some quantum theory — which Witten dubbed M-theory — in eleven-dimensions which gives rise at low energies to eleven-dimensional supergravity, and is related to ten-dimensional string theory by dimensional reduction. Dimensional reduction to a circle yields the Type IIA string theory, and dimensional reduction to a line segment yields the heterotic SO(32) string theory.

Same underlying theory[link]

M-theory would implement the notion that all of the different string theories are different special cases.

Recent developments[link]

In late 2007, Bagger and Lambert set off renewed interest in M-theory with the discovery of a candidate Lagrangian description of coincident M2-branes, based on a non-associative generalization of Lie Algebra, Nambu 3-algebra or Filippov 3-algebra. Practitioners hope the Bagger–Lambert–Gustavsson action will provide the long-sought microscopic description of M-theory.

Nomenclature[link]

When Edward Witten named M-theory, he did not specify what the M stood for—perhaps because the nascent theory was not fully defined. Some, including Sheldon Glashow, speculate that Witten chose the letter because it resembles an inverted W. According to Witten, "M can stand variously for 'magic', 'mystery', or 'matrix', according to one's taste."^[4]

Faced with this ambiguous initial, countless scientists and commentators have offered their own expansions of the M—some sincere, others facetious. M should stand for membrane, say some.^[who?] Meanwhile, Michio Kaku, Michael Duff, Neil Turok, and others suggest mother or master (i.e., the "mother of all theories" or the "master theory").^[5]

Although Witten coined the term M-theory to refer to his model of an eleven-dimensional universe, other scientists have generalized the moniker for application to any of various meta-theories involving string theory and brane cosmology. (Ashoke Sen proposed u-theory (ur, 'über', 'ultimate', 'underlying', or perhaps 'unified') as a more distinctive appellation.)^{[citation needed]} When unqualified, M-theory now usually denotes this more general definition, rather than the one Witten originally advanced.

M-theory and membranes[link]

In the standard string theories, strings are assumed to be the single fundamental constituent of the universe. M-theory adds another fundamental constituent - membranes. Like the tenth spatial dimension, the approximate equations in the original five superstring models proved too weak to reveal membranes.

P-branes[link]

A membrane, or brane, is a multidimensional object, usually called a P-brane, with P referring to the number of dimensions in which it exists. The value of 'P' can range from zero to nine, thus giving branes dimensions from zero (0-brane ≡ point particle) to nine - five more than the world we are accustomed to inhabiting. The inclusion of p-branes does not render previous work in string theory wrong on account of not taking note of these P-branes. P-branes are much more massive ("heavier") than strings, and when all higher-dimensional P-branes are much more massive than strings, they can be ignored, as researchers had done unknowingly in the 1970s.

Strings with "loose ends"[link]

Shortly after Witten's breakthrough in 1995, Joseph Polchinski of the University of California, Santa Barbara discovered a fairly obscure feature of string theory. He found that in certain situations the endpoints of strings (strings with "loose ends") would not be able to move with complete freedom as they were attached, or stuck within certain regions of space. Polchinski then reasoned that if the endpoints of open strings are restricted to move within some p-dimensional region of space, then that region of space must be occupied by a p-brane. These type of "sticky" branes are called Dirichlet-P-branes, or D-P-branes. His calculations showed that the newly discovered D-P-branes had exactly the right properties to be the objects that exert a tight grip on the open string endpoints, thus holding down these strings within the p-dimensional region of space they fill.

Strings with closed loops[link]

Not all strings are confined to p-branes. Strings with closed loops, like the graviton, are completely free to move from membrane to membrane. Of the four force carrier particles, the graviton is unique in this way. Researchers speculate that this is the reason why investigation through the weak force, the strong force, and the electromagnetic force have not hinted at the possibility of extra dimensions. These force carrier particles are strings with endpoints that confine them to their p-branes. Further testing is needed in order to show that extra spatial dimensions indeed exist through experimentation with gravity.

Membrane interactions[link]

One of the reasons M-theory is so difficult to formulate is that the numbers of different types of membranes in the various dimensions increases exponentially. For example once one gets to 3 dimensional surfaces, one has to deal with solid objects with knot-shaped holes, and then one needs the whole of knot theory just to classify them. Since M-theory is thought to operate in 11 dimensions this problem then becomes very difficult. But just like string theory, in order for the theory to satisfy causality, the theory must be local, and so the topology changing must occur at a single point. The basic orientable 2-brane interactions are easy to show. Orientable 2-branes are tori with multiple holes cut out of them.

Matrix theory[link]

The original formulation of M-theory was in terms of a (relatively) low-energy effective field theory, called 11-dimensional Supergravity. Though this formulation provided a key link to the low-energy limits of string theories, it was recognized that a full high-energy formulation (or "UV-completion") of M-theory was needed.

Analogy with water[link]

For an analogy, the supergravity description is like treating water as a continuous, incompressible fluid. This is effective for describing long-distance effects such as waves and currents, but inadequate to understand short-distance/high-energy phenomena such as evaporation, for which a description of the underlying molecules is needed. What, then, are the underlying degrees of freedom of M-theory?

BFSS model[link]

Banks, Fischler, Shenker and Susskind (BFSS) conjectured that Matrix theory could provide the answer. They demonstrated that a theory of 9 very large matrices, evolving in time, could reproduce the supergravity description at low energy, but take over for it as it breaks down at high energy. While the supergravity description assumes a continuous space-time, Matrix theory predicts that, at short distances, non-commutative geometry takes over, somewhat similar to the way the continuum of water breaks down at short distances in favor of the graininess of molecules.

IKKT model[link]

Another matrix string theory equivalent to Type IIB string theory was constructed in 1996 by Ishibashi, Kawai, Kitazawa, and Tsuchiya.

Mysterious duality[link]

A conjecture developed by Cumrun Vafa, Amer Iqbal, and Andrew Neitzke in 2001,^[6] called "mysterious duality", concerns a set of mathematical similarities between objects and laws describing M-theory on k-dimensional tori (i.e. type II superstring theory on T^{k − 1} for k > 0) on one side, and geometry of del Pezzo surfaces (for example, the cubic surfaces) on the other side. The main observation is that the large diffeomorphisms of del Pezzo surfaces match the Weyl group of the U-duality group of the corresponding compactification of M-theory. The elements of the second homology of the del Pezzo surfaces are mapped to various BPS objects of different dimensions in M-theory.

The complex projective plane P²(C) is related to M-theory in 11 dimensions. When k points are blown-up, the del Pezzo surface describes M-theory on a k-torus, and the exceptional del Pezzo surface, namely P¹(C) × P¹(C), is connected with type IIB string theory in 10 dimensions.

See also[link]

• AdS/CFT correspondence

Notes[link]

References[link]

• Rovelli, Carlo. "[2]"

Further reading[link]

• Brian Greene has written books explaining string theory and M-theory for the layperson:
  • The Elegant Universe. New York: Vintage. 1999. ISBN 0-375-70811-1. Link at Google Books. 
  • The Fabric of the Cosmos: Space, Time, and the Texture of Reality. New York: Alfred A. Knopf. 2004. ISBN 0-375-41288-3. 
• Kaku, Michio (1999). Strings, Conformal Fields, and M-Theory. New York: Springer. ISBN 0-387-98892-0. Link at Google Books. 
• Hawking, Stephen (2001). The Universe in a Nutshell. New York: Bantam Spectra. ISBN 0-553-80202-X. Link at Google Books. 
• Hawking S.; Mlodinow L. (2010). The Grand Design. London: Bantam Press. ISBN 978-0-593-05830-5. Link at Google Books. 

External links[link]

• The Elegant Universe — a three-hour miniseries with Brian Greene on the series Nova (original PBS broadcast dates: October 28, 8–10 p.m. and November 4, 8–9 p.m., 2003). Various images, texts, videos and animations explaining string theory and M-theory.
• Superstringtheory.com — the "Official String Theory Web Site", created by Patricia Schwarz. Excellent references on string theory and M-theory for the layperson and expert.
• Basics of M-Theory by A. Miemiec and I. Schnakenburg is a lecture note on M-Theory published in Fortsch.Phys. 54:5–72, 2006.
• M-Theory-Cambridge
• M-Theory-Caltech
• String Theory, Super Gravity and M-Theory on Sci-Q Sundays with Dr. Michio Kaku; The Science Channel
• Brian Greene on string theory at TED 2005
• Peter Woit's blog on physics in general, and string theory in particular

This article contains Japanese text. Without proper rendering support, you may see question marks, boxes, or other symbols instead of kanji and kana.

Michio Kaku (加来 道雄, Kaku Michio^?, born January 24, 1947) 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, a co-founder of string field theory,^[1] a futurist, and a "communicator" and "popularizer" of science. He has written several books about physics and related topics; he has made frequent appearances on radio, television, and film; and he writes extensive online blogs and articles. He has written two New York Times best sellers, Physics of the Impossible (2008) and Physics of the Future (2011). He has hosted several TV specials for BBC-TV, the Discovery Channel, and the Science Channel.

Early life and education[link]

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^{[citation needed]}. 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 parents' garage for a science fair project.^[2] 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 individual training at Fort Lewis, Washington.^[3] However, the Vietnam War ended before he was deployed as an infantryman.

Academic career[link]

Kaku became a visiting professor at the Institute for Advanced Study in Princeton,^[4] and New York University.^[5] He currently holds the Henry Semat Chair and Professorship in theoretical physics at the City College of New York.^[6]

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.^[7] In 1974, along with Prof. Keiji Kikkawa of Osaka University, he authored the first papers describing string theory in a field form.^[8][9]

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

Popular science[link]

Kaku is most widely known as a popularizer of science.^[10] He has written books and appeared on many television programs as well as film. He also hosts a weekly radio program.

Books[link]

Kaku is the author of various popular science books.

• Hyperspace (1994)
• Beyond Einstein (with Jennifer Thompson) (1995)
• Visions: How Science Will Revolutionize the 21st Century^[11] (1998)
• Einstein's Cosmos (2004)
• Parallel Worlds (2004)
• Physics of the Impossible (2008)
• Physics of the Future (2011)

Hyperspace was a best-seller and was voted one of the best science books of the year by both The New York Times^[10] and The Washington Post. Parallel Worlds was a finalist for the Samuel Johnson Prize for non-fiction in the UK.^[12]

Radio[link]

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.^{[citation needed]} 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.^[13]

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.

Television and film[link]

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.

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.^{[citation needed]}

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 deals 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 science fiction 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.^[14]

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.^[15]

He is pictured in Symphony of Science's newest song (as of September 6, 2011), 'The Quantum World.'

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.^[16]

Social policy advocacy[link]

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.^[17] He was critical of the Cassini–Huygens space probe because of the 72 pounds (33 kg) 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.^[18] 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.^{[citation needed]} 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[link]

Kaku is married to Shizue Kaku and has two daughters.^[19]

Bibliography[link]

References[link]

External links[link]

Wikimedia Commons has media related to: Michio Kaku

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Stephen Hawking
Stephen Hawking at NASA, 1980s
Born	Stephen William Hawking (1942-01-08) 8 January 1942 (age 70) Oxford, England, United Kingdom
Residence	United Kingdom
Nationality	British
Fields	Mathematics Theoretical physics
Institutions	Cambridge University California Institute of Technology Perimeter Institute for Theoretical Physics
Alma mater	Oxford University Cambridge University
Doctoral advisor	Dennis Sciama
Other academic advisors	Robert Berman
Known for	Black holes Theoretical cosmology Quantum gravity Hawking radiation
Influences	Dikran Tahta
Notable awards	Albert Einstein Award (1978) Wolf Prize (1988) Prince of Asturias Award (1989) Copley Medal (2006) Presidential Medal of Freedom (2009)
Spouse	Jane Hawking (m. 1965–1991, divorced) Elaine Mason (m. 1995–2006, divorced)

Stephen William Hawking, CH, CBE, FRS, FRSA (born 8 January 1942) is a British theoretical physicist, cosmologist, and author. His 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).

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 between 1979 and 2009. Subsequently, he became research director at the university's Centre for Theoretical Cosmology.

Hawking has a motor neurone disease related to amyotrophic lateral sclerosis, a condition that has progressed over the years. He is now almost completely paralysed and communicates through a speech generating device. He has been married twice and has three children. Hawking has achieved success with works of popular science in which he discusses his own theories and cosmology in general; these include A Brief History of Time, which stayed on the British Sunday Times best-sellers list for a record-breaking 237 weeks.

Early life and education[link]

Stephen Hawking was born on 8 January 1942 to Frank Hawking, a research biologist, and Isobel Hawking.^[1] He has two younger sisters, Philippa and Mary, and an adopted brother, Edward.^[2] Although Hawking's parents were living in North London, he was born in Oxford as his parents felt it was safer to stay in Oxford for the later stages of the pregnancy. (London was under attack at the time by the Luftwaffe).^[3]

When his father became head of the division of parasitology at the National Institute for Medical Research^[1] in 1950, Hawking and his family moved to St Albans, Hertfordshire.^[3] Hawking attended St Albans High School for Girls from 1950 to 1953 (At that time, boys could attend the girls' school until the age of 10).^[2] and then from the age of 11, he attended St Albans School, where he was a good, but not exceptional, student.^[3]

Inspired by his mathematics teacher, Hawking 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, applications were not accepted from students who wished to study that discipline. Hawking therefore applied to read natural sciences with an emphasis in Physics. He was accepted and gained a scholarship.^[3] While at Oxford, he coxed a rowing team, which, he stated, helped relieve his immense boredom at the university.^[4] His physics tutor, Robert Berman, later said "It was only necessary for him to know that something could be done, and he could do it without looking to see how other people did it. ... his mind was completely different from all of his contemporaries".^[3]

Hawking's unimpressive study habits resulted in a final examination score on the borderline between first and second class honours, making an "oral examination" necessary.^[3] Berman said of the oral examination: "And of course the examiners then were intelligent enough to realize they were talking to someone far more clever than most of themselves".^[3] After receiving his B.A. degree at Oxford in 1962, he left for graduate work at Trinity Hall, Cambridge.^[3]

Career[link]

1962-1975[link]

Hawking in Cambridge

Hawking with string theorists David Gross and Edward Witten

Although Hawking started developing symptoms of amyotrophic lateral sclerosis as soon as he arrived at Cambridge and did not distinguish himself in his first two years at Cambridge, he returned to working on his PhD after the disease had stabilised and with the help of his doctoral tutor, Dennis William Sciama.^[5]

When Hawking began his graduate studies In the 1960s, there was much debate in the physics community about the opposing theories of the creation of the universe: big bang, and steady state.^[5] Hawking and his Cambridge friend and colleague, Roger Penrose, showed in 1970 that if the universe obeys general relativity and if the universe fits any of the Friedmann models, then the universe must have begun as a singularity.^[6] This work showed that, far from being mathematical curiosities which appear only in special cases, singularities are a fairly generic feature of general relativity.^[7]

Hawking's work with Brandon Carter, Werner Israel and D. Robinson, strongly supported John Wheeler's no-hair theorem – that any black hole is fully described by the three properties of mass, angular momentum, and electric charge.^[8] With Bardeen and Carter, he proposed the four laws of black hole mechanics, drawing an analogy with thermodynamics.^[9] 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.^[6]

Hawking was elected one of the youngest Fellows of the Royal Society in 1974,^[10] and in the same year 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.^[11] He continues to have ties with Caltech, spending a month each year there since 1992.^[12]

1975-present[link]

The mid to late 1970s were a period of growing fame and success for Hawking, his work was now much talked about, he was appearing in popular television documentaries and in 1979 he was made the Lucasian Professor of Mathematics at the University of Cambridge, a post he held for 30 years until his retirement in 2009.^[13][14] Hawking's inaugural lecture as Lucasian Professor of Mathematics had the title "Is the end in sight for Theoretical Physics" and promoted the idea that supergravity would help resolve many of the outstanding problems physicists were studying. ^[14]

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.^[15] 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.^[16]

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.^[17] 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.^[18]

Thorne–Hawking–Preskill bet[link]

U.S. President Barack Obama talks with Stephen Hawking in the Blue Room of the White House before a ceremony presenting him and 15 others the Presidential Medal of Freedom on 12 August 2009. The Medal of Freedom is the United States' highest civilian honour.

In 1997 Hawking made a public scientific wager with Thorne and John Preskill of Caltech concerning the black hole information paradox.^[19] Thorne and Hawking argued that since general relativity made it impossible for black holes to radiate, and lose information, the mass-energy and information carried by Hawking Radiation must be "new", and must not originate from inside the black hole event horizon. Since this contradicted the idea under quantum mechanics of microcausality, quantum mechanics would need to be rewritten. Preskill argued the opposite, that since quantum mechanics suggests that the information emitted by a black hole relates to information that fell in at an earlier time, the view of black holes given by general relativity must be modified in some way.^[20] The winner of the bet was to receive an encyclopedia of the loser's choice, from which information may be accessed.^[19]

In 2004, Hawking announced that he was conceding the bet, and that he now believed that black hole horizons should fluctuate and leak information, in doing so providing Preskill with a copy of Total Baseball.^[19] Comparing the useless information obtainable from a black hole to "burning an encyclopedia", Hawking commented, "I gave John an encyclopedia of baseball, but maybe I should just have given him the ashes".^[19]

Recognition[link]

Acclaim[link]

On 19 December 2007, a statue of Hawking by artist Ian Walters was unveiled at the Centre for Theoretical Cosmology, University of Cambridge.^[21] 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.^[22] The 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.^[23]

Awards and honours[link]

Personal life[link]

Stephen Hawking being presented by his daughter Lucy Hawking at the lecture he gave for NASA's 50th anniversary

Hawking has stated that, having been diagnosed with ALS during an early stage of his graduate work, he did not see much point in obtaining a doctorate if he were to die soon after. Hawking later said that the real turning point was his 1965 marriage to Jane Wilde, a language student.^[29] Jane cared for him until 1990 when the couple separated.^[1] They had three children: Robert, Lucy, and Timothy.^[1] Hawking married his personal care assistant, Elaine Mason, in 1995; ^[1] the couple divorced In October 2006^[30] amid claims by former nurses that she had abused him.^[31] In 1999, Jane Hawking published a memoir, Music to Move the Stars, detailing the marriage and its breakdown; in 2010 she published a revised version, Travelling to Infinity, My Life with Stephen.^[32]

Hawking supports the children's charity SOS Children's Villages UK^[33] and has stated that his view on how to live life is to "seek the greatest value of our action".^[34] He strongly opposed the Iraq War, calling it "a war crime" and "based on two lies" at a demonstration in Trafalgar Square, where he participated in a public reading of the names of Iraqi war victims.^[35][36]

Hawking has named his secondary school mathematics teacher Dikran Tahta as an inspiration.^[37] He maintains his connection with St Albans School, giving his name to one of the four houses and to an extracurricular science lecture series.^[38]

Illness[link]

Hawking on 5 May 2006, during the press conference at the Bibliothèque nationale de France to inaugurate the Laboratory of Astronomy and Particles in Paris and the French release of his work God Created the Integers

Hawking has a motor neurone disease that is related to amyotrophic lateral sclerosis (ALS), a condition that has progressed over the years. He is now almost completely paralysed and communicates through a speech generating device. Hawking's illness has progressed more slowly than typical cases of ALS: survival for more than 10 years after diagnosis is uncommon.^[39][40]

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.^[4] 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. 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. During a visit to 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.^[41] A speech generating device was built in Cambridge, using software from an American company, that enabled Hawking to write onto a computer with small movements of his body, and then have a voice synthesiser speak what he typed.^[42]

The particular voice synthesiser hardware he uses, which has an American English accent, is no longer being produced. Asked why he has still kept the same voice after so many years, Hawking stated that he has not heard a voice he likes better and that he identifies with it even though the synthesiser is both large and fragile by current standards. Although a mid-2009 corporate press release said that he had chosen NeoSpeech's VoiceText speech synthesiser as his new voice,^[43] a 30 December 2011 interview with Hawking's technician indicates that Hawking is still using an older synthesiser containing a card "which dates back to the 1980s" and that any upgrade would have to be the same voice, otherwise "it wouldn't be Stephen's voice any more".^[44]

For lectures and media appearances, Hawking appears to speak fluently through his synthesiser; however when preparing answers his system produces words at a rate of about one per minute.^[44] 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.^[44] During a TED Conference talk, it took him seven minutes to provide a brief answer to a question.^[45]

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".^[42]

In popular culture[link]

Hawking in 2007, experiencing weightlessness

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,^[46] and appeared on the Discovery Channel special Alien Planet.^[47] He has also played himself in several episodes of The Simpsons and Futurama, and has had an action figure made of his Simpsons likeness.^[48] The 2004 BBC4 TV film Hawking dealt with his early life and the onset of his illness. He was portrayed by Benedict Cumberbatch. 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.^[49] 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)". On 5 April 2012 he appeared as a guest star in an episode of The Big Bang Theory.^[50]

Space and spaceflight[link]

At the celebration of his 65th birthday on 8 January 2007, Hawking announced his plan to take a zero-gravity flight that year, with an intention to later take a sub-orbital spaceflight. Billionaire Richard Branson pledged to pay all expenses for a future flight on Virgin Galactic's space service, costing an estimated £100,000.^[51] 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.^[52] He became the first quadriplegic to float in zero gravity. The fee is normally US$3,750 for 10 to 15 plunges, but Hawking was not required to pay. Hawking was quoted before the flight saying:

Many people have asked me why I am taking this flight. I am doing it for many reasons. First of all, I believe that life on Earth is at an ever-increasing risk of being wiped out by a disaster such as sudden nuclear war, a genetically engineered virus, or other dangers. I think the human race has no future if it doesn't go into space. I therefore want to encourage public interest in space.^[53]

In an interview with The Daily Telegraph, he suggested that space was the Earth's long term hope.^[54] He continued this theme at a 2008 Charlie Rose interview.^[55]

Hawking has indicated that he is almost certain that alien life exists in other parts of the universe, "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".^[56] 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 has also warned that a few of these species might be intelligent and threaten Earth.^[57] "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.^[56] He has advocated that, rather than try to establish contact, humans should try to avoid contact with alien life forms.^[56] At a George Washington University lecture in honour of NASA's fiftieth anniversary, Hawking discussed the existence of extraterrestrial life, believing that "primitive life is very common and intelligent life is fairly rare".^[58]

Religious views[link]

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."^[59] In the same book he suggested the existence of God was unnecessary to explain the origin of the universe.^[60] In the Channel 4 documentary Genius of Britain, in his 2010 book The Grand Design, and in interviews with the Telegraph, Hawking has clarified that he does not believe in a "personal" God.^[61] 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."^[61] He adds, "Because there is a law such as gravity, the Universe can and will create itself from nothing."^[62]

His ex-wife, Jane, has described him as an atheist.^[63] 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."^[64] In an interview published in The Guardian newspaper, Hawking regarded the concept of Heaven as a myth, believing that there is "no heaven or afterlife" and that such a notion was a "fairy story for people afraid of the dark."^[59][65] 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."^[66]

Philosophical views[link]

At Google’s Zeitgeist Conference in 2011, Hawking said that "philosophy is dead." He believes philosophers "have not kept up with modern developments in science" and that scientists "have become the bearers of the torch of discovery in our quest for knowledge.” He said that philosophical problems can be answered by science, particularly new scientific theories which "lead us to a new and very different picture of the universe and our place in it”.^[67]

Publications[link]

Hawking's first popular science book, A Brief History of Time, was published on 1 April 1988. It stayed on the British Sunday Times best-sellers list for a record-breaking 237 weeks.^[68] A Brief History of Time was followed by The Universe in a Nutshell (2001). 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, updated his earlier works to make them accessible to a 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 Lucy Hawking described as "a bit like Harry Potter but without the magic."^[69]

Popular[link]

• A Brief History of Time, (1988)
• Black Holes and Baby Universes and Other Essays, (1994)
• The Universe in a Nutshell, (2001)
• On The Shoulders of Giants. The Great Works of Physics and Astronomy, (2002)
• A Briefer History of Time, (2005)
• God Created the Integers: The Mathematical Breakthroughs That Changed History, (2005)^[70]
• The Grand Design, (2010)^[70]

Children's fiction[link]

These are co-written with his daughter Lucy.

• George's Secret Key to the Universe, (2007)
• George's Cosmic Treasure Hunt, (2009)^[70]
• George and the Big Bang, (2011)

Films and series[link]

• A Brief History of Time (1991)
• Stephen Hawking's Universe (1997)
• Horizon: The Hawking Paradox^[71] (2005)
• Masters of Science Fiction (2007)
• Stephen Hawking: Master of the Universe^[72] (2008)
• Into the Universe with Stephen Hawking^[73] (2010)
• Brave New World with Stephen Hawking

See also[link]

• Many-worlds interpretation, or flexiverse
• Gibbons–Hawking ansatz
• Gibbons–Hawking space

References[link]