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A Tipler cylinder, also called a Tipler time machine, is a
hypothetical A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...
object theorized to be a potential mode of time travel—although results have shown that a Tipler cylinder could only allow time travel if its length were infinite or with the existence of negative energy.


Discovery

The Tipler cylinder was discovered as a solution to the equations of general relativity by
Willem Jacob van Stockum Willem Jacob van Stockum (20 November 1910 – 10 June 1944) was a Dutch mathematician who made an important contribution to the early development of general relativity. Biography Van Stockum was born in Hattem in the Netherlands. His father wa ...
in 1936 and Kornel Lanczos in 1924, but not recognized as allowing
closed timelike curves In mathematical physics, a closed timelike curve (CTC) is a world line in a Lorentzian manifold, of a material particle in spacetime, that is "closed", returning to its starting point. This possibility was first discovered by Willem Jacob van St ...
until an analysis by Frank Tipler Available in GIF format here: page
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/ref> in 1974. Tipler showed in his 1974 paper, "Rotating Cylinders and the Possibility of Global Causality Violation" that in a spacetime containing a "...sufficiently large rotating cylinder..." which was spinning along its longitudinal
axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis *Axis (mathematics), a designator for a Cartesian-coordinate ...
, the cylinder should create a frame-dragging effect. This frame-dragging effect warps spacetime in such a way that the light cones of objects in the cylinder's proximity become tilted, so that part of the light cone then points backwards along the time axis on a
spacetime diagram A spacetime diagram is a graphical illustration of the properties of space and time in the special theory of relativity. Spacetime diagrams allow a qualitative understanding of the corresponding phenomena like time dilation and length contracti ...
. Therefore, a spacecraft accelerating sufficiently in the appropriate direction can travel backwards through time along a
closed timelike curve In mathematical physics, a closed timelike curve (CTC) is a world line in a Lorentzian manifold, of a material particle in spacetime, that is "closed", returning to its starting point. This possibility was first discovered by Willem Jacob van ...
. CTCs are associated, in Lorentzian manifolds which are interpreted physically as spacetimes, with the possibility of causal anomalies such as a person going back in time and potentially shooting their own grandfather, although paradoxes might be avoided using some constraint such as the
Novikov self-consistency principle The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture and Larry Niven's law of conservation of history, is a principle developed by Russian physicist Igor Dmitriyevich Novikov in the mid-1980s. Novikov inten ...
. They appear in some of the most important exact solutions in general relativity, including the Kerr vacuum (which models a
rotating black hole A rotating black hole is a black hole that possesses angular momentum. In particular, it rotates about one of its axes of symmetry. All celestial objects – planets, stars (Sun), galaxies, black holes – spin. Types of black holes Ther ...
) and the van Stockum dust (which models a cylindrically symmetrical configuration of rotating pressureless fluid or dust).


Practicality

An objection to the practicality of building a Tipler cylinder was discovered by Stephen Hawking, who argued that according to general relativity it is impossible to build a time machine in any finite region that satisfies the weak energy condition, meaning that the region contains no exotic matter with negative energy. The Tipler cylinder, on the other hand, does not involve any negative energy. Tipler's original solution involved a cylinder of infinite length, which is easier to analyze mathematically, and although Tipler suggested that a finite cylinder might produce closed timelike curves if the rotation rate were fast enough, he did not prove this. But Hawking comments "it can't be done with positive energy density everywhere! I can prove that to build a finite time machine, you need negative energy." Hawking's argument appears in his 1992 paper on the
chronology protection conjecture The chronology protection conjecture is a hypothesis first proposed by Stephen Hawking that laws of physics beyond those of standard general relativity prevent time travel on all but microscopic scales - even when the latter theory states that it ...
(though the argument is distinct from the conjecture itself, since the argument asserts that classical general relativity predicts a finite region containing closed timelike curves can only be created if there is a violation of the weak energy condition in that region, whereas the conjecture predicts that closed timelike curves will prove to be impossible in a future theory of
quantum gravity Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics; it deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the vi ...
which replaces general relativity). In the paper, he examines "the case that the causality violations appear in a finite region of spacetime without curvature singularities" and proves that " ere will be a
Cauchy horizon In physics, a Cauchy horizon is a light-like boundary of the domain of validity of a Cauchy problem (a particular boundary value problem of the theory of partial differential equations). One side of the horizon contains closed space-like geodes ...
that is compactly generated and that in general contains one or more closed null geodesics which will be incomplete. One can define geometrical quantities that measure the Lorentz boost and area increase on going round these closed null geodesics. If the causality violation developed from a noncompact initial surface, the averaged weak energy condition must be violated on the Cauchy horizon."


In fiction

* ''
Steins;Gate ''Steins;Gate'' is a 2009 science fiction visual novel game developed by 5pb. and Nitroplus. It is the second game in the ''Science Adventure'' series, following ''Chaos;Head''. The story follows a group of students as they discover and develop ...
'' is a visual novel which mentions Tipler cylinders with the topic of time travel and John Titor. * John DeChancie's ''Starrigger'' series uses vertically-aligned Tipler cylinders (called
Kerr Kerr may refer to: People * Kerr (surname) * Kerr (given name) Places ;United States * Kerr Township, Champaign County, Illinois * Kerr, Montana, A US census-designated place *Kerr, Ohio, an unincorporated community * Kerr County, Texas Other ...
–Tipler objects) to create spacetime gateways along an intergalactic highway. *
Larry Niven Laurence van Cott Niven (; born April 30, 1938) is an American science fiction writer. His best-known works are ''Ringworld'' (1970), which received Hugo, Locus, Ditmar, and Nebula awards, and, with Jerry Pournelle, ''The Mote in God's Eye'' ...
's short story, "Rotating Cylinders and the Possibility of Global Causality Violation", borrows its title from Tipler's paper. * Poul Anderson includes it in his novel ''The Avatar''. * Vernor Vinge in the novel ''Marooned in Realtime'' (although the object is described as being a naked black hole). *
Kris Straub The kris, or ''keris'' in the Indonesian language, is an asymmetrical dagger with distinctive blade-patterning achieved through alternating laminations of iron and nickelous iron (''pamor''). Of Javanese origin, the kris is famous for its disti ...
's ''Starslip'' comic includes a Tipler cylinder created as a work of art (comic 569), which also causes time travel. * Ian Douglas has a Tipler cylinder created by aliens of unknown origin in ''Singularity'', the third book of the ''Star Carrier'' series. *'' Star Trek Online'' uses a device by the same name which enables the player to reverse time several (up to 7~13 secs.) seconds within a localised field. (The specificity of thirteen seconds of time reversal, along with the device having a beryllium core, are references to the science fiction comedy ''
Galaxy Quest ''Galaxy Quest'' is a 1999 American science fiction comedy film directed by Dean Parisot and written by David Howard and Robert Gordon. A parody of and homage to science-fiction films and series, especially ''Star Trek'' and its fandom, the f ...
''.) * In his '' Warstrider'' series of novels, William H. Keith uses a Tipler cylinder with a length-to-width ratio of 512 that allows travel to and from the core of the Milky Way galaxy. * In Terry Pratchett's '' Discworld'' series, the "procrastinators" used by the History Monks are considered to be a type of Tipler cylinder. * The ''greens'', a race of parasite aliens, tried to build a Tipler cylinder in the '' Lifeline'' mobile game series. This is explained in the ''Halfway To Infinity'' game. * A Tipler cylinder is used as a plot device in Chuck Grossart's story " The Phoenix Descent". * Episode 9 of the webseries ''Ask Weathersby'' mentions the Tipler cylinder, discussing time travel. * In "The Miracle of Christmas", Episode 2.11 of the American TV series ''
Timeless Timeless (or atemporal) or timelessness (or atemporality) may refer to: * Agelessness, the condition of being unaffected by the passage of time * Akal (Sikh term), timelessness in Sikhism * Eternity, timeless existence or infinite duration * Im ...
'', a Tipler cylinder is mentioned as being added to an upgraded time machine. * In season 2 episode 14 of "Gabby Duran & the Unsittables - Zeke to the Future" a Tipler's Infinity Cylinder is mentioned as a possible time travel device. * In "Doctor Who", in the opening scene, his time-travelling Tardis is making its way through something most think to be a 'wormhole', but is actually, unbeknownst to most, a Tipler cylinder.


References

;Notes ;Bibliography # Frank Jennings Tipler
''Causality Violation in General Relativity''
Ph.D. thesis at the University of Maryland, College Park (1976). Source: Dissertation Abstracts International, Vol. 37–06, Section B, pg. 2923. Also available as Dissertation 76–29,018 from Xerox University Microfilms, Ann Arbor, MI. # Penrose, Roger. "The Question of Cosmic Censorship." ''
Journal of Astrophysics and Astronomy The ''Journal of Astrophysics and Astronomy'' is a peer-reviewed scientific journal of astrophysics and astronomy established in 1980. It is co-published bimonthly by Springer India, the Indian Academy of Sciences, and Astronomical Society of I ...
'' Vol. 20 (September, 1999): 233. # Wald, Robert (ed). ''Black Holes and Relativistic Stars''. University of Chicago Press, 1998. {{Time travel Megastructures Physics in fiction Time travel devices