Teory BIG BANG

The night sky presents the viewer with a picture of a
calm and unchanging Universe. So the 1929 discovery by
Edwin Hubble that the Universe is in fact expanding at
enormous speed was revolutionary. Hubble noted that
galaxies outside our own Milky Way were all moving
away from us, each at a speed proportional to its
distance from us. He quickly realized what this meant
that there must have been an instant in time (now
known to be about 14 billion years ago) when the entire
Universe was contained in a single point in space. The
Universe must have been born in this single violent
event which came to be known as the "Big Bang."
Astronomers combine mathematical models with
observations to develop workable theories of how the
Universe came to be. 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 Edwin Hubble's work of measuring
the expansion of the Universe. 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?"
Background Radiation
According to the theories of physics, if we were to look
at the Universe one second after the Big Bang, what we
would see is a 10-billion degree sea of neutrons,
protons, electrons, anti-electrons (positrons), photons,
and neutrinos. 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.
Before this "recombination" occurred, the Universe
would have been opaque because the free electrons
would have caused light (photons) to scatter the way
sunlight scatters from the water droplets in clouds. But
when the free electrons were absorbed to form neutral
atoms, the Universe suddenly became transparent.
Those same photons - the afterglow of the Big Bang
known as cosmic background radiation - can be
observed today.
Missions Study Cosmic Background Radiation
NASA has launched two missions to study the cosmic
background radiation, taking "baby pictures" of the
Universe only 400,000 years after it was born. The first of
these was the Cosmic Background Explorer (COBE).
In 1992, the COBE team announced that they had
mapped the primordial hot and cold spots in cosmic
background radiation. These spots are related to the
gravitational field in the early Universe and form the
seeds of the giant clusters of galaxies that stretch
hundreds of millions of light years across the Universe.
This work earned NASA's Dr. John C. Mather and George
F. Smoot of the University of California the 2006 Nobel
Prize for Physics.
The second mission to examine the cosmic background
radiation was the Wilkinson Microware Anisotropy
Probe (WMAP). With greatly improved resolution
compared to COBE, WMAP surveyed the entire sky,
measuring temperature differences of the microwave
radiation that is nearly uniformly distributed across the
Universe. The picture shows a map of the sky, with hot
regions in red and cooler regions in blue. By combining
this evidence with theoretical models of the Universe,
scientists have concluded that the Universe is "flat,"
meaning that, on cosmological scales, the geometry of
space satisfies the rules of Euclidean geometry (e.g.,
parallel lines never meet, the ratio of circle
circumference to diameter is pi, etc).
A third mission, Planck , led by the European Space
Agency with significant participation from NASA, was.
launched in 2009. Planck is making the most accurate
maps of the microwave background radiation yet. With
instruments sensitive to temperature variations of a few
millionths of a degree, and mapping the full sky over 9
wavelength bands, it measures the fluctuations of the
temperature of the CMB with an accuracy set by
fundamental astrophysical limits.
Inflation
One problem that arose
from the original COBE
results, and that persists
with the higher-
resolution WMAP data,
was that the Universe
was too homogeneous.
How could pieces of the
Universe that had never
been in contact with
each other have come to
equilibrium at the very
same temperature? This
and other cosmological
problems could be
solved, however, if there
had been a very short
period immediately after
the Big Bang where the Universe experienced an
incredible burst of expansion called "inflation." For this
inflation to have taken place, the Universe at the time of
the Big Bang must have been filled with an unstable
form of energy whose nature is not yet known. Whatever
its nature, the inflationary model predicts that this
primordial energy would have been unevenly distributed
in space due to a kind of quantum noise that arose
when the Universe was extremely small. This pattern
would have been transferred to the matter of the
Universe and would show up in the photons that began
streaming away freely at the moment of recombination.
As a result, we would expect to see, and do see, this
kind of pattern in the COBE and WMAP pictures of the
Universe.
But all this leaves unanswered the question of what
powered inflation. One difficulty in answering this
question is that inflation was over well before
recombination, and so the opacity of the Universe before
recombination is, in effect, a curtain drawn over those
interesting very early events. Fortunately, there is a way
to observe the Universe that does not involve photons at
all. Gravitational waves, the only known form of
information that can reach us undistorted from the
instant of the Big Bang, can carry information that we
can get no other way. Two missions that are being
considered by NASA, LISA and the Big Bang Observer,
will look for the gravitational waves from the epoch of
inflation.
Dark Energy
During the years following Hubble and COBE, the picture
of the Big Bang gradually became clearer. But in 1996,
observations of very distant supernovae required a
dramatic change in the picture. It had always been
assumed that the matter of the Universe would slow its
rate of expansion. Mass creates gravity, gravity creates
pull, the pulling must slow the expansion. But
supernovae observations showed that the expansion of
the Universe, rather than slowing, is accelerating.
Something, not like matter and not like ordinary energy,
is pushing the galaxies apart. This "stuff" has been
dubbed dark energy, but to give it a name is not to
understand it. Whether dark energy is a type of
dynamical fluid, heretofore unknown to physics, or
whether it is a property of the vacuum of empty space,
or whether it is some modification to general relativity is
not yet known.