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In general relativity, a black hole is a region of space in which the gravity well is so deep that gravitational time dilation halts time completely forming an event horizon, a one-way surface into which objects can fall, but out of which nothing can appear. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black-body in thermodynamics.Thermodynamics of Black Holes,P.C.W Davies, Rep. Prog. Phys Vol. 41(1978), pp.1313-1355. Quantum analysis of black holes shows them to possess a temperature and Hawking radiation.

Despite its invisible interior, a black hole can reveal its presence through interaction with other matter. A black hole can be inferred by tracking the movement of a group of stars that orbit a region in space which looks empty. Alternatively, one can see gas falling into a relatively small black hole, from a companion star. This gas spirals inward, heating up to very high temperatures and emitting large amounts of radiation that can be detected from earthbound and earth-orbiting telescopes. Such observations have resulted in the scientific consensus that, barring a breakdown in our understanding of nature, black holes exist in our universe.

Category: File - :Universe expansion2.png|thumb|According to the Big Bang model, the Universe expanded from an extremely dense and hot state and continues to expand today. A common analogy explains that space itself is expanding, carrying galaxies with it, like raisins in a rising loaf of bread. The graphic scheme above is an artist's concept illustrating the expansion of a portion of a flat Universe.

The Big Bang is the cosmological model of the initial conditions and subsequent development of the Universe that is supported by the most comprehensive and accurate explanations from current scientific evidence and observation.

As used by cosmologists, the term Big Bang generally refers to the idea that the Universe has expanded from a primordial hot and dense initial condition at some finite time in the past (currently estimated to have been approximately 13.7 billion years ago

), and continues to expand to this day.

Georges Lemaître proposed what became known as the Big Bang theory of the origin of the Universe, although he called it his "hypothesis of the primeval atom". The framework for the model relies on Albert Einstein's general relativity and on simplifying assumptions (such as homogeneity and isotropy of space). The governing equations had been formulated by Alexander Friedmann. After Edwin Hubble discovered in 1929 that the distances to far away galaxies were generally proportional to their redshifts, as suggested by Lemaître in 1927, this observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity.

If the distance between galaxy clusters is increasing today, everything must have been closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures,

and large particle accelerators have been built to experiment on and test such conditions, resulting in significant confirmation of the theory, but these accelerators have limited capabilities to probe into such high energy regimes. Without any evidence associated with the earliest instant of the expansion, the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the Universe since that instant. The observed abundances of the light elements throughout the cosmos closely match the calculated predictions for the formation of these elements from nuclear processes in the rapidly expanding and cooling first minutes of the Universe, as logically and quantitatively detailed according to Big Bang nucleosynthesis.

Fred Hoyle is credited with coining the term Big Bang during a 1949 radio broadcast. It is popularly reported that Hoyle, who favored an alternative "steady state" cosmological model, intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models.

Hoyle later helped considerably in the effort to understand stellar nucleosynthesis, the nuclear pathway for building certain heavier elements from lighter ones. After the discovery of the cosmic microwave background radiation in 1964, and especially when its spectrum (i.e., the amount of radiation measured at each wavelength) sketched out a blackbody curve, most scientists were fairly convinced by the evidence that some Big Bang scenario must have occurred.

A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes. In their astronomical role they differ from optical telescopes in that they operate in the radio frequency portion of the electromagnetic spectrum where they can detect and collect data on radio sources. Radio telescopes are typically large parabolic ("dish") antennas used singly or in an array. Radio observatories are preferentially located far from major centers of population in order to avoid electromagnetic interference (EMI) from radio, TV, radar, and other EMI emitting devices. This is similar to the locating of optical telescopes to avoid light pollution, with the difference being that radio observatories are often placed in valleys to further shield them from EMI as opposed to clear air mountain tops for optical observatories.

'Hubbles law' describes the observation in physical cosmology that the velocity at which various galaxies are receding from the Earth is proportional to their distance from us. The law was first formulated by Edwin Hubble in 1929Hubble, Edwin, "A Relation between Distance and Radial Velocity among Extra-Galactic Nebulae" (1929) Proceedings of the National Academy of Sciences of the United States of America, Volume 15, Issue 3, pp. 168-173 (Full article, PDF) after nearly a decade of observations. The recession velocity of the objects was inferred from their redshifts, many measured much earlier by Vesto Slipher (1917) and related to velocity by him. It is considered the first observational basis for the expanding space paradigm and today serves as one of the pieces of evidence most often cited in support of the Big Bang model.

The law is often expressed by the equation v = H0D, with H0 the constant of proportionality (the Hubble constant) between the distance D to a galaxy and its velocity v. The SI unit of H0 is s-1 but it is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy one Megaparsec away. The reciprocal of H0 is the Hubble time.

The most recent observational determination of the proportionality constant obtained in 2009 by using the Hubble Space Telescope yielded a value of H0 = .

The results agree closely with an earlier measurement of H0 =  obtained in 2001 also by Hubble. In August 2006, a less-precise figure was obtained independently using data from NASA's Chandra X-ray Observatory: H0 = 77 (km/s)/Mpc or about 2.5×10?18 s?1 with an uncertainty of ± 15%. NASA summarizes existing data to indicate a constant of 70.8 ± 1.6 (km/s)/Mpc if space is assumed to be flat, or 70.8 ± 4.0 (km/s)/Mpc otherwise.

In quantum mechanics, the Heisenberg uncertainty principle states that certain pairs of physical properties, like position and momentum, cannot both be known to arbitrary precision. That is, the more precisely one property is known, the less precisely the other can be known. This statement has been interpreted in two different ways. According to Heisenberg its meaning is that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle with any degree of accuracy or certainty. According to others (for instance BallentineL.E. Ballentine, The statistical interpretation of quantum mechanics, Rev. Mod. Phys. 42, 358-381 (1970).) this is not a statement about the limitations of a researcher's ability to measure particular quantities of a system, but it is a statement about the nature of the system itself as described by the equations of quantum mechanics.

In quantum mechanics, a particle is described by a wave. The position of the particle is regarded as being where the wave amplitude is greatest and the momentum is determined by the wavelength. The position is uncertain to the degree that the wave is spread out (well-defined wavelength), but the momentum is certain (well-defined) only to the degree that the wavelength is well-defined. Thus, position and momentum for a particle have opposite requirements for good definition, so that both position and wavelength cannot simultaneously be well-defined.

The only kind of wave with a definite position is concentrated at one point, and such a wave has an indefinite wavelength. Conversely, the only kind of wave with a definite wavelength is an infinite regular periodic oscillation over all space, which has no definite position. So in quantum mechanics, there are no states that describe a particle with both a definite position and a definite momentum. The more precise the position, the less precise the momentum.

The uncertainty principle can be restated in terms of measurements, which involves collapse of the wavefunction. When the position is measured, the wavefunction collapses to a narrow bump near the measured value, and the momentum wavefunction becomes spread out. The particle's momentum is left uncertain by an amount inversely proportional to the accuracy of the position measurement. The amount of left-over uncertainty can never be reduced below the limit set by the uncertainty principle, no matter what the measurement process.

This means that the uncertainty principle is related to the observer effect, with which it is often conflated. The uncertainty principle sets a lower limit to how small the momentum disturbance in an accurate position experiment can be, and vice versa for momentum experiments.

A mathematical statement of the principle is that every quantum state has the property that the root mean square (RMS) deviation of the position from its mean (the standard deviation of the X-distribution):

:\Delta X = \sqrt{\langle(X - \langle X\rangle)^2\rangle} \,

times the RMS deviation of the momentum from its mean (the standard deviation of P):

:\Delta P = \sqrt{\langle(P - \langle P \rangle)^2\rangle} \,

can never be smaller than a fixed fraction of Planck's constant:

:\Delta X \Delta P \ge {\hbar \over 2}.

Any measurement of the position with accuracy \scriptstyle \Delta X collapses the quantum state making the standard deviation of the momentum \scriptstyle \Delta P larger than \scriptstyle \hbar/2\Delta x.