## Gravitational singularity |

A **gravitational singularity**, **spacetime singularity** or simply **singularity** is a location in ^{[1]}^{[2]}

Gravitational singularities are mainly considered in the context of

General relativity predicts that any object collapsing beyond a certain point (for ^{[3]} The ^{[4]} The termination of such a geodesic is considered to be the singularity.

The initial state of the ^{[5]} In this case the universe did not collapse into a black hole, because currently-known calculations and density limits for gravitational collapse are usually based upon objects of relatively constant size, such as stars, and do not necessarily apply in the same way to ^{[6]} but in general, quantum mechanics does not permit particles to inhabit a space smaller than their ^{[7]}

Many theories in physics have

Some theories, such as the theory of ^{[8]} This is also true for such classical unified field theories as the

There are different types of singularities, each with different physical features which have characteristics relevant to the theories from which they originally emerged, such as the different shape of the singularities, *conical and curved*. They have also been hypothesized to occur without Event Horizons, structures which delineate one spacetime section from another in which events cannot affect past the horizon; these are called *naked.*

A conical singularity occurs when there is a point where the limit of every

An example of such a conical singularity is a ^{[9]}

Solutions to the equations of

An example is the

While in a non-rotating black hole the singularity occurs at a single point in the model coordinates, called a "point singularity", in a rotating black hole, also known as a ^{[10]}

More generally, a spacetime is considered singular if it is *t*=0), where all time-like geodesics have no extensions into the past. Extrapolating backward to this hypothetical time 0 results in a universe with all spatial dimensions of size zero, infinite density, infinite temperature, and infinite spacetime curvature.

Until the early 1990s, it was widely believed that ^{[11]}^{[12]}^{[13]}

Disappearing event horizons exist in the ^{[14]} that the coordinate (which is not the radius) of the event horizon is, , where , and . In this case, "event horizons disappear" means when the solutions are complex for , or . However, this corresponds to a case where exceeds (or in

Similarly, disappearing event horizons can also be seen with the ^{[15]} that the singularities occur at , where , and . Of the three possible cases for the relative values of and , the case where causes both to be complex. This means the metric is regular for all positive values of , or in other words, the singularity has no event horizon. However, this corresponds to a case where exceeds (or in Planck units, ), i.e. the charge exceeds what is normally viewed as the upper limit of its physically possible values. Also, actual astrophysical black holes are not expected to possess any appreciable charge.

Before ^{[16]} All known black hole candidates are so large that their temperature is far below that of the cosmic background radiation, which means they will gain energy on net by absorbing this radiation. They cannot begin to lose energy on net until the background temperature falls below their own temperature. This will occur at a ^{[citation needed]}

- 0-dimensional singularity:
magnetic monopole - 1-dimensional singularity:
cosmic string - 2-dimensional singularity:
domain wall Fuzzball (string theory) Penrose-Hawking singularity theorems White hole

**^**"Blackholes and Wormholes".**^**Claes Uggla (2006). "Spacetime Singularities".*Einstein Online*.**2**(1002). Archived from the original on 2017-01-24. Retrieved 2015-10-20.**^**Curiel, Erik & Peter Bokulich. "Singularities and Black Holes".*Stanford Encyclopedia of Philosophy*. Center for the Study of Language and Information, Stanford University. Retrieved 26 December 2012.**^**Moulay, Emmanuel. "The universe and photons" (PDF). FQXi Foundational Questions Institute. Retrieved 26 December 2012.**^**Wald, p. 99**^**Hawking, Stephen. "The Beginning of Time".*Stephen Hawking: The Official Website*.Cambridge University . Retrieved 26 December 2012.**^**Zebrowski, Ernest (2000).*A History of the Circle: Mathematical Reasoning and the Physical Universe*. Piscataway NJ:Rutgers University Press . p. 180.ISBN 978-0813528984 .**^**Rodolfo Gambini; Javier Olmedo; Jorge Pullin (2014). "Quantum black holes in Loop Quantum Gravity".*Classical and Quantum Gravity*.**31**(9): 095009. arXiv:arXiv:1310.5996 .2014CQGra..31i5009G .10.1088/0264-9381/31/9/095009 .**^**Copeland, Edmund J; Myers, Robert C; Polchinski, Joseph (2004). "Cosmic F- and D-strings".*Journal of High Energy Physics*.**2004**(6): 013. arXiv:arXiv:hep-th/0312067 .2004JHEP...06..013C .10.1088/1126-6708/2004/06/013 .**^**If a rotating singularity is given a uniform electrical charge, a repellent force results, causing aring singularity to form. The effect may be a stablewormhole , a non-point-like puncture in spacetime that may be connected to a second ring singularity on the other end. Although such wormholes are often suggested as routes for faster-than-light travel, such suggestions ignore the problem of escaping the black hole at the other end, or even of surviving the immensetidal forces in the tightly curved interior of the wormhole.**^**M. Bojowald (2008). "Loop Quantum Cosmology".*Living Reviews in Relativity*.**11**(4): 4.2008LRR....11....4B .10.12942/lrr-2008-4 . PMCPMC 5253914 .the original on 2015-12-21.**^**R. Goswami; P. Joshi (2008). "Spherical gravitational collapse in N-dimensions".*Physical Review D*.**76**(8): 084026. arXiv:arXiv:gr-qc/0608136 .2007PhRvD..76h4026G .10.1103/PhysRevD.76.084026 .**^**R. Goswami; P. Joshi; P. Singh (2006). "Quantum evaporation of a naked singularity".*Physical Review Letters*.**96**(3): 031302. arXiv:arXiv:gr-qc/0506129 .2006PhRvL..96c1302G .10.1103/PhysRevLett.96.031302 .16486681 .**^**Hobson, et al.,*General Relativity an Introduction for Physicists*, Cambridge University Press 2007, p. 300-305**^**Hobson, et al.,*General Relativity an Introduction for Physicists*, Cambridge University Press 2007, p. 320-325**^**LoPresto, M. C. (2003). "Some Simple Black Hole Thermodynamics".*The Physics Teacher*.**41**(5): 299–301.10.1119/1.1571268 .

Hawking, S. W. ;Penrose, R. (1970), "The Singularities of Gravitational Collapse and Cosmology",*Proc. R. Soc. A*,**314**(1519): 529–548,1970RSPSA.314..529H ,10.1098/rspa.1970.0021 (Free access.)- Shapiro, Stuart L.;
"Formation of naked singularities: The violation of cosmic censorship" (PDF)..Physical Review Letters **66**(8): 994–997.1991PhRvL..66..994S .10.1103/PhysRevLett.66.994 .10043968 . Robert M. Wald (1984). .*General Relativity*University of Chicago Press .ISBN 0-226-87033-2 .Misner, Charles W. ;Thorne, Kip ;Wheeler, John Archibald (1973). .*Gravitation*W. H. Freeman .ISBN 0-7167-0344-0 . §31.2 The nonsingularity of the gravitational radius, and following sections; §34 Global Techniques, Horizons, and Singularity Theorems

- Roger Penrose(1996). "Chandrasekhar, Black Holes, and Singularities".
*ias.ac.in*. - Roger Penrose (1999). "The Question of Cosmic Censorship".
*ias.ac.in*. - Τ. P. Singh. "Gravitational Collapse, Black Holes and Naked Singularities".
*ias.ac.in*.

byThe Elegant Universe Brian Greene . This book provides alayman 's introduction to string theory, although some of the views expressed are already becoming outdated. His use of common terms and his providing of examples throughout the text help the layperson understand the basics of string theory.

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