Embedded diagram of a Schwarzschild wormhole (see also below)

In physics, a wormhole is a hypothetical topological feature of spacetime that would be, fundamentally, a "shortcut" through spacetime. For a simple visual explanation of a wormhole, consider spacetime visualized as a two-dimensional (2D) surface. If this surface is folded along a third dimension, it allows one to picture a wormhole "bridge". (Please note, though, that this is merely a visualization displayed to convey an essentially unvisualisable structure existing in 4 or more dimensions. The parts of the wormhole could be higher-dimensional analogues for the parts of the curved 2D surface; for example, instead of mouths which are circular holes in a 2D plane, a real wormhole's mouths could be spheres in 3D space.) A wormhole is, in theory, much like a tunnel with two ends each in separate points in spacetime.

There is no observational evidence for wormholes, but on a theoretical level there are valid solutions to the equations of the theory of general relativity which contain wormholes. Because of its robust theoretical strength, a wormhole is also known as one of the great physics metaphors for teaching general relativity. The first type of wormhole solution discovered was the Schwarzschild wormhole which would be present in the Schwarzschild metric describing an eternal black hole, but it was found that this type of wormhole would collapse too quickly for anything to cross from one end to the other. Wormholes which could actually be crossed, known as traversable wormholes, would only be possible if exotic matter with negative energy density could be used to stabilize them. (Many physicists such as Stephen Hawking,^[1] Kip Thorne,^[2] and others^[3][4][5] believe that the Casimir effect is evidence that negative energy densities are possible in nature.) Physicists have not found any natural process which would be predicted to form a wormhole naturally in the context of general relativity, although the quantum foam hypothesis is sometimes used to suggest that tiny wormholes might appear and disappear spontaneously at the Planck scale,^[6][7] and stable versions of such wormholes have been suggested as dark matter candidates.^[8][9] It has also been proposed that if a tiny wormhole held open by a negative-mass cosmic string had appeared around the time of the Big Bang, it could have been inflated to macroscopic size by cosmic inflation.^[10]

The American theoretical physicist John Archibald Wheeler coined the term wormhole in 1957; however, in 1921, the German mathematician Hermann Weyl already had proposed the wormhole theory, in connection with mass analysis of electromagnetic field energy.^[11]

This analysis forces one to consider situations...where there is a net flux of lines of force, through what topologists would call "a handle" of the multiply-connected space, and what physicists might perhaps be excused for more vividly terming a "wormhole".

—John Wheeler in Annals of Physics

Definition[link]

The basic notion of an intra-universe wormhole is that it is a compact region of spacetime whose boundary is topologically trivial but whose interior is not simply connected. Formalizing this idea leads to definitions such as the following, taken from Matt Visser's Lorentzian Wormholes.

If a Minkowski spacetime contains a compact region Ω, and if the topology of Ω is of the form Ω ~ R x Σ, where Σ is a three-manifold of the nontrivial topology, whose boundary has topology of the form ∂Σ ~ S², and if, furthermore, the hypersurfaces Σ are all spacelike, then the region Ω contains a quasipermanent intra-universe wormhole.

Characterizing inter-universe wormholes is more difficult. For example, one can imagine a 'baby' universe connected to its 'parent' by a narrow 'umbilicus'. One might like to regard the umbilicus as the throat of a wormhole, but the spacetime is simply connected. For this reason wormholes have been defined geometrically, as opposed to topologically, as regions of spacetime that constrain the incremental deformation of closed surfaces. For example, in Enrico Rodrigo’s The Physics of Stargates a wormhole is defined informally as

a region of spacetime containing a "world tube" (the time evolution of a closed surface) that cannot be continuously deformed (shrunk) to a world line [(the time evolution of a point)].

Schwarzschild wormholes[link]

An artist's impression of a wormhole from an observer's perspective, crossing the event horizon of a Schwarzschild wormhole which bridges two different universes. The observer originates from the right, and another universe becomes visible in the center of the wormhole’s shadow once the horizon is crossed, the observer seeing light that has fallen into the black hole interior region from the other universe; however, this other universe is unreachable in the case of a Schwarzschild wormhole, as the bridge always collapses before the observer has time to cross it, and everything that has fallen through the event horizon of either universe is inevitably crushed in the singularity.

Lorentzian wormholes known as Schwarzschild wormholes or Einstein-Rosen bridges are connections between areas of space that can be modeled as vacuum solutions to the Einstein field equations, and which are now understood to be intrinsic parts of the maximally extended version of the Schwarzschild metric describing an eternal black hole with no charge and no rotation. Here, "maximally extended" refers to the idea that the spacetime should not have any "edges": for any possible trajectory of a free-falling particle (following a geodesic) in the spacetime, it should be possible to continue this path arbitrarily far into the particle's future or past, unless the trajectory hits a gravitational singularity like the one at the center of the black hole's interior. In order to satisfy this requirement, it turns out that in addition to the black hole interior region which particles enter when they fall through the event horizon from the outside, there must be a separate white hole interior region which allows us to extrapolate the trajectories of particles which an outside observer sees rising up away from the event horizon. And just as there are two separate interior regions of the maximally extended spacetime, there are also two separate exterior regions, sometimes called two different "universes", with the second universe allowing us to extrapolate some possible particle trajectories in the two interior regions. This means that the interior black hole region can contain a mix of particles that fell in from either universe (and thus an observer who fell in from one universe might be able to see light that fell in from the other one), and likewise particles from the interior white hole region can escape into either universe. All four regions can be seen in a spacetime diagram which uses Kruskal–Szekeres coordinates.

In this spacetime, it is possible to come up with coordinate systems such that if you pick a hypersurface of constant time (a set of points that all have the same time coordinate, such that every point on the surface has a space-like separation, giving what is called a 'space-like surface') and draw an "embedding diagram" depicting the curvature of space at that time, the embedding diagram will look like a tube connecting the two exterior regions, known as an "Einstein–Rosen bridge". Note that the Schwarzschild metric describes an idealized black hole that exists eternally from the perspective of external observers; a more realistic black hole that forms at some particular time from a collapsing star would require a different metric. When the infalling stellar matter is added to a diagram of a black hole's history, it removes the part of the diagram corresponding to the white hole interior region, along with the part of the diagram corresponding to the other universe.^[12]

The Einstein–Rosen bridge was discovered by Albert Einstein and his colleague Nathan Rosen, who first published the result in 1935. However, in 1962 John A. Wheeler and Robert W. Fuller published a paper showing that this type of wormhole is unstable, and that it will pinch off too quickly for light (or any particle moving slower than light) that falls in from one exterior region to make it to the other exterior region.

Before the stability problems of Schwarzschild wormholes were apparent, it was proposed that quasars were white holes forming the ends of wormholes of this type.^{[citation needed]}

While Schwarzschild wormholes are not traversable, their existence inspired Kip Thorne to imagine traversable wormholes created by holding the 'throat' of a Schwarzschild wormhole open with exotic matter (material that has negative mass/energy).

Traversable wormholes[link]

Image of a traversable wormhole which connects the place in front of the physical institutes of Tübingen University with the sand dunes near Boulogne sur Mer in the north of France. The image is calculated with 4D raytracing in a Morris-Thorne wormhole metric, but the gravitational effects on the wavelength of light have not been simulated.^[13]

Lorentzian traversable wormholes would allow travel from one part of the universe to another part of that same universe very quickly or would allow travel from one universe to another. The possibility of traversable wormholes in general relativity was first demonstrated by Kip Thorne and his graduate student Mike Morris in a 1988 paper. For this reason, the type of traversable wormhole they proposed, held open by a spherical shell of exotic matter, is referred to as a Morris-Thorne wormhole. Later, other types of traversable wormholes were discovered as allowable solutions to the equations of general relativity, including a variety analyzed in a 1989 paper by Matt Visser, in which a path through the wormhole can be made where the traversing path does not pass through a region of exotic matter. However, in the pure Gauss–Bonnet gravity (a modification to general relativity involving extra spatial dimensions which is sometimes studied in the context of brane cosmology) exotic matter is not needed in order for wormholes to exist—they can exist even with no matter.^[14] A type held open by negative mass cosmic strings was put forth by Visser in collaboration with Cramer et al.,^[10] in which it was proposed that such wormholes could have been naturally created in the early universe.

Wormholes connect two points in spacetime, which means that they would in principle allow travel in time, as well as in space. In 1988, Morris, Thorne and Yurtsever worked out explicitly how to convert a wormhole traversing space into one traversing time.^[2] However, according to general relativity it would not be possible to use a wormhole to travel back to a time earlier than when the wormhole was first converted into a time machine by accelerating one of its two mouths.^[15]

Raychaudhuri's theorem and exotic matter[link]

To see why exotic matter is required, consider an incoming light front traveling along geodesics, which then crosses the wormhole and re-expands on the other side. The expansion goes from negative to positive. As the wormhole neck is of finite size, we would not expect caustics to develop, at least within the vicinity of the neck. According to the optical Raychaudhuri's theorem, this requires a violation of the averaged null energy condition. Quantum effects such as the Casimir effect cannot violate the averaged null energy condition in any neighborhood of space with zero curvature,^[16] but calculations in semiclassical gravity suggest that quantum effects may be able to violate this condition in curved spacetime.^[17] Although it was hoped recently that quantum effects could not violate an achronal version of the averaged null energy condition,^[18] violations have nevertheless been found,^[19] thus eliminating a basis on which traversable wormholes could be rendered unphysical.

Faster-than-light travel[link]

The impossibility of faster-than-light relative speed only applies locally. Wormholes allow superluminal (faster-than-light) travel by ensuring that the speed of light is not exceeded locally at any time. While traveling through a wormhole, subluminal (slower-than-light) speeds are used. If two points are connected by a wormhole, the time taken to traverse it would be less than the time it would take a light beam to make the journey if it took a path through the space outside the wormhole. However, a light beam traveling through the wormhole would always beat the traveler. As an analogy, running around to the opposite side of a mountain at maximum speed may take longer than walking through a tunnel crossing it.

Time travel[link]

The theory of general relativity predicts that if traversable wormholes exist, they could allow time travel.^[2] This would be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox. However, time connects differently through the wormhole than outside it, so that synchronized clocks at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around.^[20] This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry.

For example, consider two clocks at both mouths both showing the date as 2000. After being taken on a trip at relativistic velocities, the accelerated mouth is brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2005 while the stationary mouth's clock read 2010. A traveler who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2005, in the same region but now five years in the past. Such a configuration of wormholes would allow for a particle's world line to form a closed loop in spacetime, known as a closed timelike curve.

It is thought that it may not be possible to convert a wormhole into a time machine in this manner; the predictions are made in the context of general relativity, but general relativity does not include quantum effects. Some analyses^[who?] using the semiclassical approach to incorporating quantum effects into general relativity indicate that a feedback loop of virtual particles would circulate through the wormhole with ever-increasing intensity, destroying it before any information could be passed through it, in keeping with the chronology protection conjecture. This has been called into question by the suggestion that radiation would disperse after traveling through the wormhole, therefore preventing infinite accumulation. The debate on this matter is described by Kip S. Thorne in the book Black Holes and Time Warps, and a more technical discussion can be found in The quantum physics of chronology protection by Matt Visser.^[21] There is also the Roman ring, which is a configuration of more than one wormhole. This ring seems to allow a closed time loop with stable wormholes when analyzed using semiclassical gravity, although without a full theory of quantum gravity it is uncertain whether the semiclassical approach is reliable in this case.

Inter-Universe travel[link]

A possible resolution to the paradoxes resulting from wormhole-enabled time travel rests on the Many Worlds Interpretation of quantum mechanics. In 1991 David Deutsch showed that quantum theory is fully consistent (in the sense that the so-called density matrix can be made free of discontinuities) in spacetimes with closed timelike curves.^[22] However, later it was shown that such model of closed time like curve can have internal inconsistencies as it will lead to strange phenomena like distinguishing non orthogonal quantum states and distinguishing proper and improper mixture.^[23][24] Accordingly, the destructive positive feedback loop of virtual particles circulating through a wormhole time machine, a result indicated by semi-classical calculations, is averted. A particle returning from the future does not return to its universe of origination but to a parallel universe. This suggests that a wormhole time machine with an exceedingly short time jump is a theoretical bridge between contemporaneous parallel universes.^[25] Because a wormhole time-machine introduces a type of nonlinearity into quantum theory, this sort of communication between parallel universes is consistent with Joseph Polchinski’s discovery of an “Everett phone” in Steven Weinberg’s formulation of nonlinear quantum mechanics.^[26]

Metrics[link]

Theories of wormhole metrics describe the spacetime geometry of a wormhole and serve as theoretical models for time travel. An example of a (traversable) wormhole metric is the following:

Failed to parse (Missing texvc executable; please see math/README to configure.): ds^2= - c^2 dt^2 + dl^2 + (k^2 + l^2)(d \theta^2 + \sin^2 \theta \, d\phi^2).

One type of non-traversable wormhole metric is the Schwarzschild solution (see the first diagram):

Failed to parse (Missing texvc executable; please see math/README to configure.): ds^2= - c^2 \left(1 - \frac{2GM}{rc^2}\right)dt^2 + \frac{dr^2}{1 - \frac{2GM}{rc^2}} + r^2(d \theta^2 + \sin^2 \theta \, d\phi^2).

In fiction[link]

Wormholes are a common element in science fiction as they allow interstellar (and sometimes interuniversal) travel within human timescales.

See also[link]

• Black hole
• Closed timelike curve
• Faster-than-light
• Exotic star
• Krasnikov tube
• Non-orientable wormhole
• Self-consistency principle
• Retrocausality
• Ring singularity
• Roman ring
• White hole

Notes[link]

References[link]

External links[link]

• White Holes and Wormholes

External links[link]

• What exactly is a 'wormhole'? answered by Richard F. Holman, William A. Hiscock and Matt Visser.
• Why wormholes? by Matt Visser.
• Wormholes in General Relativity by Soshichi Uchii.
• White holes and Wormholes provides a very good description of Schwarzschild wormholes with graphics and animations, by Andrew J. S. Hamilton.
• Questions and Answers about Wormholes a comprehensive wormhole FAQ by Enrico Rodrigo.
• Large Hadron Collider – Theory on how the collider could create a small wormhole, possibly allowing time travel into the past.
• animation that simulates traversing a wormhole
• renderings and animations of a Morris-Thorne wormhole
• N.A.S.A's current theory on wormhole creation

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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]

Bibliography[link]