The Big Bang Astronomers combine mathematical models with observations to develop workable theories of how the Universe came to be. One of the goals has long been to decide whether the Universe will expand forever, or whether it will someday stop, turn around, and collapse in a "Big Crunch? Then, as time went on, we would see the Universe cool, the neutrons either decaying into protons and electrons or combining with protons to make deuterium an isotope of hydrogen. As it continued to cool, it would eventually reach the temperature where electrons combined with nuclei to form neutral atoms.

Building Blocks of Matter: General relativity is a metric theory of gravity, now verified to high precision via observations of the binary pulsar. The cosmological principle has also been verified to exquisite precision, as far as this can be achieved. The cosmological principle asserts that the universe is statistically isotropic and homogeneous for any observer.

The cosmic microwave background has demonstrated isotropy to a level of order 1 part inThere is no preferred direction such as might be associated with the geometrical center of the universe. Homogeneity has been demonstrated by galaxy redshift surveys that provide three-dimensional maps of the universe, given the strong empirical correlation discovered by Edwin Hubble in between redshift and distance.

Humankind definitely does not inhabit a fractal universe of vanishingly low density in the mean, as some have argued. One can set a limit on any large-scale nonuniformities of approximately 10 percent; otherwise, excessive perturbations would be induced in the Hubble diagram of galaxy redshift versus distance.

In Einstein found a static cosmological model that could only be prevented from collapsing under the relentless tug of gravity by invoking a repulsion force.

This force was enshrined as the cosmological constant, a term that has no counterpart and no effect in Newtonian gravity, but is important only on cosmological scales.

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In modern parlance, one identifies the cosmological constant with the energy of the vacuum, and its introduction leads to the Einstein static universe. In fact, Einstein had overlooked the only true cosmological solution to the field equations that satisfied the cosmological principle and that did not require the introduction of a cosmological constant.

The expanding universe was much later dubbed the Big Bang for the simple reason that it expanded from a pointlike singularity of infinite density. It was realized at the outset that this singularity was a mathematical artifact indicative of missing physics that was only supplied half a century later.

Space itself was uniform, unbounded, and expanding. There was no center and no edge to space. The Big Bang theory indeed predicted the expansion of the universe, a result that many scientists in the early decades of the twentieth century, including Hubble himself, found too radical to accept.

The equations that describe the evolution of the universe come from Einstein's theory of general relativity. To describe expansion, one introduces the scale factor a t. This can be cast in the form of a cosmic energy equation: The first term on the left describes the kinetic energy of a shell of matter, and the second term is its gravitational potential energy.

There are three distinct solutions in the absence of the cosmological constant term. These are conveniently described by the curvature of space that in the Newtonian limit corresponds to the total energy of an arbitrarily placed expanding shell of matter. The shell may have either zero total energy, in which case space is flat; negative energy, in which case space is positively curved like a spheroidal surface; or positive energy, which results in space being negatively curved like the surface of a hyperboloid.

The constant -k represents the total energy of the shell per unit mass and may be -1, 0, or -1, corresponding to a universe of negative, zero, or positive energy. The flat and negatively curved spaces are infinite, and only the positively curved space is finite.

This is the density of the flat or Einsteinâ€”de Sitter universe and is equal to Here, H0 is Hubble's constant. Because of the matter content, a universe without a cosmological constant is decelerating.

At early times, the three spaces are indistinguishable. Only at late times do they deviate from one another, the negative-energy spatially closed model decelerating more strongly than the other models before reaching its maximum extent and then recollapsing to a future singularity.

To further examine the deceleration, one may apply conservation of mass-energy that leads to and an equation can now be derived for the deceleration of the universe: The latter is measured by identifying a class of luminous variable stars, Cepheids, that were used to establish the size of the Milky Way galaxy and, more recently, the distances to its nearest neighbor galaxies.

Hubble used the brightest stars in more distant galaxies as his basic distance indicators.

He explored a region that extends to the Virgo cluster of galaxies. With hindsight, one knows that Hubble's distance indicators were erroneous, since he could not distinguish HII regions from stars. It is also known that the region between the Earth and the Virgo cluster, where Hubble's galaxies were located, is dominated by random motions.

The uniformity of the universe only becomes manifest beyond Virgo. Nevertheless, Hubble in announced his discovery of the redshift-distance law. The redshift was produced by the Doppler effect and resulted in a systematic displacement toward longer wavelengths for a receding galaxy. Blueshifts would be indicative of approach; only a few of the nearest galaxies have blue-shifted spectra.While the Big Bang model is well established in cosmology, it is likely to be refined.

The Big Bang theory, built upon the equations of classical general relativity, indicates a singularity at the origin of cosmic time; this infinite energy density is regarded as impossible in physics. The Big Bang Theory It is always a mystery about how the universe began, whether if and when it will end.

Astronomers construct hypotheses called cosmological models that try to find the answer. There are two types of models: Big Bang and Steady State. The Big Bang Theory says that the CMB would be mostly the same, no matter where you look.

Examining the CMB also gives astronomers clues as to the composition of the universe. The mathematical underpinnings of the Big Bang theory include Albert Einstein's general theory of relativity along with standard theories of fundamental particles.

Today NASA spacecraft such as the Hubble Space Telescope and the Spitzer Space Telescope continue measuring the expansion of the Universe. Org provides the latest news on astronomy, space, earth an analysis of the big bang theory in astronomy science and space exploration.

The Big Bang is the dominant (and highly supported) theory of the origin of the universe. In essence, this theory states that the universe began from an initial point or singularity which has expanded over billions of years to form the universe as we now know it.

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What Is the Big Bang Theory?