Lesson 1: The Universe and Solar System (around 5.

5 billion degrees Celsius) and filled

with a uniform glow from a white for of
Origin of the Universe hydrogen plasma. The universe also contained
basic particles of neutrons, electrons and
The science of cosmology provides protons. Then the space expanded and cooled
several hypotheses explaining the beginning of because of the expansion. When the universe
the universe based on its present physical and got cooler, the neutron, electron and proton
chemical properties. There are numerous particles decayed or combined. Overtime,
versions, but the most widely accepted ones those particles created neutral atoms which
are based on current scientific observations allowed light to shine through. The light is the
and available evidences that support the CMB, also referred to as “afterglow” of the big
claims. Among the theories that have been bang. The CMB was believed to have been
thoroughly investigated and have gained the released 380 000 years after the big bang.
most support include the big bang theory, the
cosmic inflation theory, and the steady state
theory. COSMIC INFLATION THEORY

BIG BANG THEORY  The most recent cosmic inflation theory

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