After the Big Bang! (தமிழ்)
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on Aug 3, 2019
Visaipalagai
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The Big Bang theory is
the prevailing cosmological model (Big Bang) for the observable universe from
the earliest known periods through its subsequent large-scale evolution. The
model describes how the universe expanded from a very high-density and
high-temperature state, and offers a comprehensive explanation for a broad
range of phenomena, including the abundance of light elements, the cosmic
microwave background (CMB), large scale structure and Hubble's law (the farther
away galaxies are, the faster they are moving away from Earth). If the observed
conditions are extrapolated backwards in time using the known laws of physics,
the prediction is that just before a period of very high density there was a
singularity which is typically associated with the Big Bang. Current knowledge
is insufficient to determine if the singularity was primordial.
Since Georges Lemaître
first noted in 1927 that an expanding universe could be traced back in time to
an originating single point, scientists have built on his idea of cosmic
expansion. The scientific community was once divided between supporters of two
different theories, the Big Bang and the Steady State theory, but a wide range
of empirical evidence has strongly favored the Big Bang which is now
universally accepted. In 1929, from analysis of galactic redshifts, Edwin
Hubble concluded that galaxies are drifting apart; this is important
observational evidence for an expanding universe. In 1964, the cosmic microwave
background radiation was discovered, which was crucial evidence in favor of the
hot Big Bang model, since that theory predicted the existence of background
radiation throughout the universe before it was discovered.
The known physical laws
of nature can be used to calculate the characteristics of the universe in
detail back in time to an initial state of extreme density and temperature.
Detailed measurements of the expansion rate of the universe place the Big Bang
at around 13.8 billion years ago, which is thus considered the age of the
universe. After its initial expansion, the universe cooled sufficiently to
allow the formation of subatomic particles, and later atoms. Giant clouds of
these primordial elements (mostly hydrogen, with some helium and lithium) later
coalesced through gravity, eventually forming early stars and galaxies, the
descendants of which are visible today. Astronomers also observe the
gravitational effects of dark matter surrounding galaxies. Most of the matter
in the universe seems to be in the form of dark matter, and Big Bang theory and
various observations indicate that it is not conventional baryonic matter
(atoms). It is still not known exactly what dark matter is. More recently,
measurements of the redshifts of supernovae indicate that the expansion of the
universe is accelerating, an observation attributed to dark energy's existence.
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