THE BIG BANG THEORY

Aishwarya . A

SYNOPSIS :• Etymology• The Big Bang

• The origins of the theory• Various phenomena explained by the Big

Bang theory• The expanding universe

• The discovery of the expanding universe• Cosmic microwave background radiation• Galactic evolution and distribution

SYNOPSIS continued

• Evidence for the Big Bang theory• Speculative physics beyond the Big

Bang theory

• Magnetic monopoles• The future according to the Big Bang

theory• glossary

The Big Bang theory is the prevailing cosmological model for the

early development of the universe. According to the theory, the Big Bang occurred approximately 13.798 ± 0.037 billion years ago, which is thus considered the age of the universe. At this time, the universe was in an extremely hot and dense state and began expanding rapidly. After the initial expansion, the universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and electrons. Though simple atomic nuclei formed within the first three minutes after the Big Bang, thousands of years passed before the first electrically neutral atoms formed. The majority of atoms that were produced by the Big Bang are hydrogen, along with helium and traces of lithium. Giant clouds of these primordial elements later coalesced through gravity to form stars and galaxies, and the heavier elements were synthesized either within stars or during supernovae.

THE BIG BANG

Fred Hoyle is credited with coining the term

"Big Bang" during a 1949 radio broadcast. It is popularly reported that Hoyle, who favoured 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

Etymology

More simply , according to this theory , all matter in

the universe was concentrated as a single extremely dense and hot fire ball. An explosion occurred about 20 billion years ago and the matter was broken into pieces, thrown off in all directions in the form of galaxies, due to continuous movement more and more galaxies will go beyond the boundary and will be lost. Consequently, the number of galaxies per unit volume will go on decreasing and ultimately we will have an empty universe

THE EXPANSION OF UNIVERSEThe graphic scheme above is an artist's concept illustrating the expansion

of a portion of a flat universe.

A Belgian priest named Georges Lemaître first suggested the big bang

theory in the 1920s when he theorized that the universe began from a single primordial atom. The idea subsequently received major boosts by Edwin Hubble's observations that galaxies are speeding away from us in all directions, and from the discovery of cosmic microwave radiation by Arno Penzias and Robert Wilson.

The glow of cosmic microwave background radiation, which is found throughout the universe, is thought to be a tangible remnant of leftover light from the big bang. The radiation is akin to that used to transmit TV signals via antennas. But it is the oldest radiation known and may hold many secrets about the universe's earliest moments.

The big bang theory leaves several major questions unanswered. One is the original cause of the big bang itself. Several answers have been proposed to address this fundamental question, but none has been proven—and even adequately testing them has proven to be a formidable challenge.

The origins of the theory

The big bang theory explains the following phenomena:1. The expansion of the universe;2. The observed microwave background

radiation;3. The observed abundance of the helium in the

universe , formed in the first 100 seconds after the explosion from deuterium at a temperature of 10 kelvin.

VARIOUS PHENOMENA EXPLAINED BY BIG BANG THEORY:

THE EXPANDING UNIVERSE :

THE DISCOVERY OF THE EXPANDING UNIVERSE :

In 1929, Edwin Hubble, an astronomer at Caltech,

made a critical discovery that the universe is expanding.

The ancient Greeks recognized that it was difficult to imagine what an infinite universe might look like. But they also wondered that if the universe were finite, and you stuck out your hand at the edge, where would your hand go? The Greeks' two problems with the universe represented a paradox - the universe had to be either finite or infinite, and both alternatives presented problems.

THE EXPANDING UNIVERSE :

After the rise of modern astronomy, another paradox began to puzzle

astronomers. In the early 1800s, German astronomer Heinrich Olbers argued that the universe must be finite. If the Universe were infinite and contained stars throughout, Olbers said, then if you looked in any particular direction, your line-of-sight would eventually fall on the surface of a star. Although the apparent size of a star in the sky becomes smaller as the distance to the star increases, the brightness of this smaller surface remains a constant. Therefore, if the Universe were infinite, the whole surface of the night sky should be as bright as a star. Obviously, there are dark areas in the sky, so the universe must be finite.

But, when Isaac Newton discovered the law of gravity, he realized that gravity is always attractive.According to Newton’s law of gravitation, Every object in the universe attracts every other object with a force. If the universe truly were finite, the attractive forces of all the objects in the universe should have caused the entire universe to collapse on itself. This clearly had not happened, and so astronomers were presented with a paradox.

When Einstein developed his theory of gravity in the General

Theory of Relativity, he thought he ran into the same problem that Newton did: his equations said that the universe should be either expanding or collapsing, yet he assumed that the universe was static. His original solution contained a constant term, called the cosmological constant, which cancelled the effects of gravity on very large scales, and led to a static universe. After Hubble discovered that the universe was expanding, Einstein called the cosmological constant his "greatest blunder.“

 Between 1912 and 1922, astronomer Vesto Slipher at the Lowell Observatory in Arizona discovered that the spectra of light from many of these objects was systematically shifted to longer wavelengths, or redshifted. A short time later, other astronomers showed that these nebulous objects were distant galaxies.

METRIC EXPANSION OF SPACEThis is an artist's concept of the metric expansion of space, where space

(including hypothetical non-observable portions of the universe) is represented at each time by the circular sections. Note on the left the dramatic expansion

(not to scale) occurring in the inflationary epoch, and at the center the expansion acceleration. The scheme is decorated with WMAP images on the left and with

the representation of stars at the appropriate level of development.

In 1929 Edwin Hubble, working at the Carnegie Observatories in

Pasadena, California, measured the redshifts of a number of distant galaxies. He also measured their relative distances by measuring the apparent brightness of a class of variable stars called Cepheids in each galaxy. When he plotted redshift against relative distance, he found that the redshift of distant galaxies increased as a linear function of their distance. The only explanation for this observation is that the universe was expanding

The expanding universe is finite in both time and space. The reason that the universe did not collapse, as Newton's and Einstein's equations said it might, is that it had been expanding from the moment of its creation. The universe is in a constant state of change. The expanding universe, a new idea based on modern physics, laid to rest the paradoxes that troubled astronomers from ancient times until the early 20th Century.

THE DISCOVERY OF THE EXPANDING UNIVERSE:

In 1964 Arno Penzias and Robert Wilson serendipitously discovered the cosmic

background radiation, an omnidirectional signal in the microwave band.[62] Their discovery provided substantial confirmation of the general CMB predictions: the radiation was found to be consistent with an almost perfect black body spectrum in all directions; this spectrum has been redshifted by the expansion of the universe, and today corresponds to approximately 2.725 K. This tipped the balance of evidence in favor of the Big Bang model, and Penzias and Wilson were awarded a Nobel Prize in 1978.

The surface of last scattering corresponding to emission of the CMB occurs shortly after recombination, the epoch when neutral hydrogen becomes stable. Prior to this, the universe comprised a hot dense photon-baryon plasma sea where photons were quickly scattered from free charged particles. Peaking at around 372±14 kyr,[32] the mean free path for a photon becomes long enough to reach the present day and the universe becomes transparent.

In early 2003 the first results of the Wilkinson Microwave Anisotropy Probe (WMAP) were released, yielding what were at the time the most accurate values for some of the cosmological parameters. The results disproved several specific cosmic inflation models, but are consistent with the inflation theory in general. [64] The Planck space probe was launched in May 2009. Other ground and balloon based cosmic microwave background experiments are on going.

Cosmic microwave background radiation

Cosmic microwave background radiation :

The cosmic microwave background spectrum measured by the FIRAS instrument on the COBE satellite is the most-precisely measured black body spectrum in nature.]The data points and error bars on this graph are obscured by the theoretical curve

Detailed observations of the morphology and distribution of galaxies

and quasars are in agreement with the current state of the Big Bang theory. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the Big Bang, and since then larger structures have been forming, such as galaxy clusters and superclusters. Populations of stars have been aging and evolving, so that distant galaxies (which are observed as they were in the early universe) appear very different from nearby galaxies (observed in a more recent state). Moreover, galaxies that formed relatively recently appear markedly different from galaxies formed at similar distances but shortly after the Big Bang. These observations are strong arguments against the steady-state model. Observations of star formation, galaxy and quasar distributions and larger structures agree well with Big Bang simulations of the formation of structure in the universe and are helping to complete details of the theory.

Galactic evolution and distribution

English: Panoramic view of the entire near-infrared sky reveals the distribution of galaxies beyond the Milky Way. The image is derived from the 2MASS Extended Source Catalog (XSC)—more than 1.5 million galaxies, and the Point Source Catalog (PSC)--nearly 0.5 billion Milky Way stars. The galaxies are color coded by redshift (numbers in parentheses) obtained from the UGC, CfA, Tully NBGC, LCRS, 2dF, 6dFGS, and SDSS surveys (and from various observations compiled by the NASA Extragalactic Database), or photo-metrically deduced from the K band (2.2 μm). Blue/purple are the nearest sources (z < 0.01); green are at moderate distances (0.01 < z < 0.04) and red are the most distant sources that 2MASS resolves (0.04 < z < 0.1). The map is projected with an equal area Aitoff in the Galactic system (Milky Way at center).

First of all, we are reasonably certain that the universe had a beginning. Secondly , Edwin Hubble, in 1929, was able to correlate the distance to objects in the

universe with their velocities -- a relation known as Hubble's Law. According to this law, V μ R or V= HR (i.e.;) the speed of the recession (v) is directly proportional to the distance R. Where H is the Hubble’s constant and the relation is known as the velocity distance law or Hubble’s law. Big Bang theorists later used this information to approximate the age of the Universe at about 15 billion years old, which is consistent with other measurements of the age of the Universe.

The CMB signal detected by Penzias and Wilson, a discovery for which they later won a Nobel Prize, is often described as the “echo” of the Big Bang. Because if the Universe had an origin, it would leave behind a signature of the event, just like an echo heard in a canyon represents a “signature” of the original sound. The difference is that instead of an audible echo, the Big Bang left behind a heat signature throughout all of space.

Another prediction of the Big Bang theory is that the Universe should be receding from us. Specifically, any direction we look out into space, we should see objects moving away from us with a velocity proportional to their distance away from us, a phenomenon known as the red shift.

EVIDENCE FOR THE BIG BANG THEORY

NEW EVIDENCE:• Gravitational waves from inflation put a distinctive

twist pattern in the polarisation of the CMB• This has been using a telescope at the South Pole to

make detailed observations of a small patch of sky.• The aim has been to try to find a residual marker for

"inflation" - the idea that the cosmos experienced an exponential growth spurt in its first trillionth, of a

trillionth of a trillionth of a second.

While the Big Bang model is well established in cosmology, it is likely to be

refined. The equations of classical general relativity indicate a singularity at the origin of cosmic time, although this conclusion depends on several assumptions and the equations break down at any time before the universe reached the Planck temperature. A correct treatment of quantum gravity may avoid the would-be singularity.

It is not known what could have caused the singularity to come into existence (if it had a cause), or how and why it originated, though speculation abounds in the field of cosmogony. Some proposals, each of which entails untested hypotheses, are:

Models including the Hartle–Hawking no-boundary condition, in which the whole of space-time is finite; the Big Bang does represent the limit of time but without the need for a singularity.

Big Bang lattice model, states that the universe at the moment of the Big Bang consists of an infinite lattice of fermions, which is smeared over the fundamental domain so it has rotational, translational and gauge symmetry. The symmetry is the largest symmetry possible and hence the lowest entropy of any state.

Speculative physics beyond the Big Bang theory :

Brane cosmology models, in which inflation is due to the

movement of branes in string theory; the pre-Big Bang model; the ekpyrotic model, in which the Big Bang is the result of a collision between branes and the cyclic model, a variant of the ekpyrotic model in which collisions occur periodically. In the latter model the Big Bang was preceded by a Big Crunch and the universe cycles from one process to the other.

Eternal inflation, in which universal inflation ends locally here and there in a random fashion, each end-point leading to a bubble universe, expanding from its own big bang.

Proposals in the last two categories, see the Big Bang as an event in either a much larger and older universe or in a multiverse.

The magnetic monopole objection was raised in

the late 1970s. Grand unification theories predicted topological defects in space that would manifest as magnetic monopoles. These objects would be produced efficiently in the hot early universe, resulting in a density much higher than is consistent with observations, given that no monopoles have been found. This problem is also resolved by cosmic inflation, which removes all point defects from the observable universe, in the same way that it drives the geometry to flatness.

Magnetic monopoles

Before observations of dark energy, cosmologists considered two scenarios for the future of the universe. If the mass density of the universe were greater than the critical density, then the universe would reach a maximum size and then begin to collapse. It would become denser and hotter again, ending with a state similar to that in which it started—a Big Crunch.[94]

 Alternatively, if the density in the universe were equal to or below the critical density, the expansion would slow down but never stop. Star formation would cease with the consumption of interstellar gas in each galaxy; stars would burn out leaving white dwarfs, neutron stars, and black holes. Very gradually, collisions between these would result in mass accumulating into larger and larger black holes. The average temperature of the universe would asymptotically approach absolute zero—a Big Freeze. Moreover, if the proton were unstable, then baryonic matter would disappear, leaving only radiation and black holes. Eventually, black holes would evaporate by emitting Hawking radiation. The entropy of the universe would increase to the point where no organized form of energy could be extracted from it, a scenario known as heat death.

Modern observations of accelerating expansion imply that more and more of the currently visible universe will pass beyond our event horizon and out of contact with us. The eventual result is not known. The ΛCDM model of the universe contains dark energy in the form of a cosmological constant. This theory suggests that only gravitationally bound systems, such as galaxies, will remain together, and they too will be subject to heat death as the universe expands and cools. Other explanations of dark energy, called phantom energy theories, suggest that ultimately galaxy clusters, stars, planets, atoms, nuclei, and matter itself will be torn apart by the ever-increasing expansion in a so-called Big Rip.

The future according to the Big Bang theory

Deuterium - a heavy isotope of hyrogen containing on proton and one neutron.Red shift - shift toward the red in the spectra of light reaching us from the stars in distant galaxies.The cosmic microwave background radiation- It is a faint glow of light that fills the universe, falling on Earth from every direction with nearly uniform intensity.  Inflation - It is the expansion of space in the early universe at a rate much faster than the speed of lightQuantum gravity (QG) is a field of theoretical physics that seeks to describe the force of gravity according to the principles of quantum mechanics.Cosmogony (or cosmogeny) is any theory concerning the coming into existence(or origin) of either the cosmos (or universe), or the so-called reality of sentient beings.

glossary

string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings.The ekpyrotic universe, or ekpyrotic scenario, is a cosmological model of the origin and shape of the universe.A white dwarf, also called a degenerate dwarf, is a stellar remnant composed mostly of electron-degenerate matter.A neutron star is a type of stellar remnant that can result from the gravitational collapse of a massive star.A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping.Hawking radiation is black body radiation that is predicted to be released by black holes, due to quantum effects near the event horizon.

glossary

Phantom energy is a hypothetical form of 

dark energy that is even more potent than the cosmological constant at increasing the expansion of the universe.

The Big Rip is a cosmological hypothesis first published in 2003, about the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles

glossary