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A Singularity at the beginning of time might have created the universe.
Singularity is a scientific term for what is popularly known as a black hole. Singularity occurs when matter in our universe is compressed to infinitely small proportions, a mathematical point. When this happens, the gravitational force becomes dominant and causes spacetime to fold in on itself, creating the spherical event horizon, which separates the singularity from the rest of the universe.
Because nothing, not even light, can escape from beyond the event horizon, we currently have no information about what this region of the singularity is like. Moreover, the only mathematical properties we can currently apply to a black hole include only mass (measured by the strength of the gravitational pull), volume (calculated in three dimensions using the Schwarzschild Radius), electrical charge, temperature* (see notes), and spin.
Current theoretical limitations of the singularity.
Although we possess compelling observational evidence for the existence of spatial singularities, and despite sophisticated mathematical models which deal with the properties of the collapsing mass before it implodes into infinity, no current theory can explain either precisely how the singularity itself originates or exactly what takes place within the event horizon. The efforts to unify Einstein's relativity and quantum mechanics within a single theoretical framework should aleviate many mathematical difficulties and contribute much towards our understanding of this phenomenon.
Detailed discussion on the singularity.
The definition of singularities as points where space-time curvature reaches infinity is the most intuitive. However, singularities can exist even if the curvature of space-time is finite everywhere. Not all geometries whose metric tensor blows up at some point must be actual geometric singularities; some of them are merely coordinate singularities and may be removed by a redefinition of coordinates.
Singularity: More generally, a space-time is considered singular if:
The Big Bang cosmological model of the universe contains a gravitational singularity at the start of time (t=0). At the "Big Bang Singularity," the model predicts that the density of the universe and the curvature of space-time are paradoxically infinite. However, the basic Big Bang model does not include quantum effects, so its predictions are valid only shortly after the projected singularity.
A singularity certainly exists within a black hole, where General relativity predicts a region of infinite curvature. In a non-rotating black hole, the singularity occurs at a single point in the model coordinates, and is called a "point singularity". In a rotating black hole, the singularity occurs on a ring, and is called a "ring singularity". Rotating black holes are sometimes referred to as Kerr black holes. Such a singularity may also theoretically become a wormhole**(see notes).
This type of singularity may result either after a type II supernova or when a super-dense neutron star becomes unstable and implodes due to its own gravitational forces.
Until the early 1990s, it was widely believed that General relativity hides every singularity behind an event horizon, making naked singularities impossible. This is referred to as the cosmic censorship hypothesis. However, in 1991 Shapiro and Teukolsky performed computer simulations of a rotating plane of dust which indicated that General relativity *might* allow for "naked" singularities. What these objects would actually look like is unknown. Nor is it known if singularities would still arise if the simplifying assumptions used to make the simulation were removed.
The singularity is an object that challenges many conventions in physics. This does not mean that it does not exist, but it does mean that it would take a new view and a few new theories about physics to explain its existence properly. It is believed that a theory of quantum gravity, a theory that unifies General relativity with quantum mechanics, will eventually provide a better description of what actually occurs where General relativity breaks down in a singularity. However, as of 2006, no theory of Quantum gravity has been experimentally confirmed. There are, however, a handful of promising theories in development. For more reading on the subject, see string theory (there are five of them!), M-Theory (proposes to unify the string theories), theory of Everything.
Notes about the singularity.
Before Steven Hawking came up with the concept of Hawking Radiation, the question of black holes having entropy was avoided. However, this concept demonstrates that black holes can radiate energy, which conserves entropy and solves the incompatibility problems with the second law of thermodynamics. Entropy, however, implies heat and therefore temperature. The loss of energy also suggests that black holes do not last forever, but rather "evaporate," slowly losing energy over millennia... Small black holes tend to be hotter and large, massive ones tend to be colder.
If a rotating singularity is given a uniform electrical charge, a repellent force results, causing a ring singularity to form. The effect may be a stable wormhole, a non-point-like puncture in Spacetime which may be connected to a second ring singularity on the other end. Suggested Reading
1. "The Elegant Universe" by Brian Greene. This book is relatively easy to understand and contains everything you need to know about string theory and related topics.
Shapiro, S. L., and Teukolsky, S. A.: Formation of Naked Singularities: The Violation of Cosmic Censorship, Phys. Rev. Lett. 66, 994-997 (1991) Wald, Robert M.: General Relativity, ch. 9, University of Chicago Press (1984).
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