• The Big Bang
• The origins of the theory
• Various phenomena explained by the Big
• The expanding universe
• The discovery of the expanding universe
• Cosmic microwave background radiation
• Galactic evolution and distribution
• Evidence for the Big Bang theory
• Speculative physics beyond the Big Bang
• Magnetic monopoles
• The future according to the Big Bang
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
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
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
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 UNIVERSE
The 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
EXPLAINED BY BIG BANG THEORY:
In 1929, Edwin Hubble, an astronomer at
Caltech, made a critical discovery that the universe
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.
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
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 SPACE
This 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
In 1964 Arno Penzias and Robert Wilson serendipitously discovered the cosmic
background radiation, an omnidirectional signal in
the microwave band. 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, 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. The Planck space probe was launched in May 2009. Other ground
and balloon based cosmic microwave background experiments are on going.
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
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
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
• 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
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.
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. 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
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 light
Quantum gravity (QG) is a field of theoretical physics that seeks to
describe the force of gravity according to the principles of quantum
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.
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
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