Lesson 1: The Universe and Solar System
Origin of the Universe
The science of cosmology provides
several hypotheses explaining the beginning of
the universe based on its present physical and
chemical properties. There are numerous
versions, but the most widely accepted ones
are based on current scientific observations
and available evidences that support the
claims. Among the theories that have been
thoroughly investigated and have gained the
most support include the big bang theory, the
cosmic inflation theory, and the steady state
theory.
BIG BANG THEORY
 The best-supported theory of our
universe's origin centers on an event known as
the big bang. This theory was born of the
observation that other galaxies are moving
away from our own at great speed in all
directions, as if they had all been propelled by
an ancient explosive force.
 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 received major boosts from
Edwin Hubble's observations that galaxies are
speeding away from us in all directions, as well
as from the 1960s discovery of cosmic
microwave radiation—interpreted as echoes
of the big bang—by Arno Penzias and Robert
Wilson.
 In the recent past, astronomers have
based their new findings on the beginning of
the universe through cosmic microwave
background (CMB). CMB is a thermal radiation
used in observational cosmology because it is
considered the oldest light in the universe. It can
be detected as a glow which is believed to be
remnant from an early stage of development of
the universe. Because of this belief, the big
bang theory gained the most support from the
scientific community among the various
theories on the origin of the universe.
 Some scientist speculate through the
CMB evidence that when the universe was
young, before the stars and planets even
existed, the universe was denser and hotter
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(around 5.5 billion degrees Celsius) and filled
with a uniform glow from a white for of
hydrogen plasma. The universe also contained
basic particles of neutrons, electrons and
protons. Then the space expanded and cooled
because of the expansion. When the universe
got cooler, the neutron, electron and proton
particles decayed or combined. Overtime,
those particles created neutral atoms which
allowed light to shine through. The light is the
CMB, also referred to as “afterglow” of the big
bang. The CMB was believed to have been
released 380 000 years after the big bang.
COSMIC INFLATION THEORY
 The most recent cosmic inflation theory
id proposed by physicists Alan Guth and Andrei
Linde in the 1980’s According to the cosmic
inflation theory of Guth and Linde, the early
universe went under rapid expansion in spacetime.
 The theory states that the early universe
was a rapidly expanding bubble of pure
vacuum energy. It did not have any matter or
radiation. After the expansion and cooling due
to the inflation, the potential energy was
converted into kinetic energy of matter and
radiation. Then a big bang occurred because
of the extremely hot dense condition of the
matter. Seconds after the explosion, matter
began to clump together. Eventually, stars were
formed, and then the galaxies soon flowed. The
universe continued to expand up to the present
time.
STEADY STATE THEORY
 The steady state theory states that the
universe is always expanding. It also states that
new matter is constantly formed as the universe
continues to expand. The other bodies
eventually became out of sight as a
consequence of their increasing distance and
rate of recession. This theory further claims that
the universe has no beginning or end in time,
and even though it is expanding, its
appearance remains the same overtime.
 This theory was proposed by Sir James
Hopwood Jeans in 1920. It gained popularity
after it was revised by Sir Fred Hoyle, Sir Hermann
Bondi, and Thomas Gold in 1948 as an
EARTH SCIENCE | Universe
alternative to the big bang theory. However,
toward the middle of 1960s, pieces of evidence
that would contradict the steadiness or the
unchanging state of the universe were brought
out. One of these pieces of evidence was when
galactic bodies such as quasars and radio
galaxies were found a long way from the sun at
far distances in space (and found none
nearby); it disproved the idea that similar bodies
are created and found everywhere. Hence,
distant objects in space are considered ancient
and the younger universes are found nearer.
This implies that the universe is actually dynamic
(and not steady). In cosmology, the steady
state theory is now considered obsolete.
Structure, Composition and Age
STRUCTURE
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The universe can be defined as space and
all the matter and energy in it.
Throughout the universe, there are areas
where galaxies are densely concentrated.
These areas are called clusters and
superclusters.
Clusters contain as many as several
thousand galaxies.
Super clusters can be made up of 10 or
more clusters of galaxies.
The universe also contains huge spherical
areas where very little matter exists. These
areas are called voids.
Astronomers have begun to think of the
universe as having a structure similar to soap
bubbles.
Clusters and superclusters are located
along the thin bubble walls.
The interior of the bubbles are voids. It takes
light hundreds of millions of years to cross
the largest voids.
COMPOSITION
Dark energy
 It represents about 74 % of the matterenergy of the Universe.
 It is an unknown kind of energy
responsible for the acceleration of the
expansion of the Universe.
 Dark energy acts as a repulsive force
against the gravity and for some
scientists it is similar to the cosmological
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constant which Einstein had introduced
in his equations, although today it
acquires a different meaning.
Others scientists attribute it to energy
fields of the vacuum that they call
quintessence (the name that Aristotle
gave to the fifth element which formed
the skies)
Visible matter
 This is the matter which forms galaxies,
stars, cosmic dust, etc. It is formed by:
- 75% Hydrogen
- 20 % Helium
- 5% the rest of the chemical elements
 It is distributed in a heterogeneous
way in the Universe.
 It is concentrated in determinate places
while other remains empty of it.
 The general structure of the Universe is
formed by huge empty spaces (similar
to bubbles) separated by filaments of
matter (galaxies).
 These filaments present nodes, galaxy
groups called galaxy super clusters
within which there are other smaller
groups called galaxy clusters.
 Visible matter represents only around
4% of the total of the matter-energy of
the Universe, so that it is possible that the
empty regions do not be so empty.
 Astronomers suppose that they can be
filled by other type of matter called dark
matter.
Dark matter
 It represents the 22% left of the total of
the matter-energy of the Universe.
 Its nature is still unknown because it does
not emit or absorb electromagnetic
energy (light, radio waves, etc) which
allow us detect it and its existence only
can be put in evidence indirectly
through its gravitational effects over
galaxies.
AGE
In 2012, WMAP estimated the age of the
universe to be 13.772 billion years, with an
uncertainty of 59 million years. In 2013, Planck
measured the age of the universe at 13.82
billion years.
EARTH SCIENCE | Universe