Topic 1: The Origin of the Universe
I.
Structure, Composition, and Age
 The universe as we currently know it comprises all space and time, and all matter and energy in it.
It is made up of following:
 4.6% baryonic matter ~ “ordinary” matter consisting of protons, electrons, and neutrons: atoms, planets, stars,
galaxies, nebulae, and other bodies.
 24% cold dark matter ~ matter that has gravity but does not emit light.
 71.4% dark energy ~ a source of anti-gravity; a force that counteracts gravity and causes the universe to expand.
 Hydrogen, helium, and lithium are the three most abundant elements.
 Stars which are the building block of galaxies are born out of clouds of gas and dust in galaxies. Instabilities within the
clouds eventually results into a protostar
 protostar ~ the hot core of a future star as thermonuclear reactions set in.
 Most stars such as the Sun belong to the so called “main sequence stars”. In the cores of such stars hydrogen atoms are
fused through thermonuclear reactions (nucleosynthesis) to make helium atoms.
 Energy produced from this reaction are enormous. Nucleosynthesis requires very high temperature. The minimum
temperature for H fusion is 5x100 oC.
 The remaining dust and gas may end up as they are or as planets, asteroids, or other bodies in the accompanying planetary
systems.
 A galaxy is a cluster of billions of star and clusters of galaxies form superclusters. In between the clusters is practically an
empty space. This organization of matter in the universe suggest that it is indeed clumpy at a certain scale. But at large
scale, it appears homogeneous and isotropic.
 Based on recent data, the universe is 13.8 billion years old.
 The diameter of the universe is possibly infinite but should be at least 91 billion light-years (1 light year = 9.4607 x 1012
km). It’s density is 4.5 x 10-31 g/cm3.
II.
Theories about the Origin of the Universe
A. Non – Scientific Thoughts
 Ancient Egyptians believed in many gods and myths which narrate that the world arose from an infinite sea at the first
rising of the sun.
 The Kuba people of Central Africa tell the story of a creator god Mbombo (or Bumba) who, alone in a dark and watercovered Earth, felt an intense stomach pain and then vomited the stars, sun, and moon. Mbombo, also called Bumba,
is the creator god in the religion and mythology of the Kuba of Central Africa. In the Mbombo creation myth, Mbombo
was a giant in form and white in color.
B. Scientific thoughts
1. Steady State Theory
 It is proposed by Hermann Bondi, Thomas Gold, and Fred Hoyle,
suggests that the universe has always been there and will always be
present. It also conveys that the universe always looks the same in any
time or space but continuously expands while simultaneously creating
matter, maintaining the density of the universe; hence, the name Steady
State.
 The Steady State Theory is so simple that it was widely accepted even before the proposal of the Big Bang
Theory. The discovery of the cosmic background radiation significantly supported the explanations given by the
Big Bang Theory, which led many scientists to reject the Steady
State Theory.
2. Big Bang Theory
 The most accepted theory about the origin of the universe is the Big
Bang Theory. Georges Lemaître, a Belgian priest, is considered as
the first proponent of the Big Bang Theory. The theory was supported
by other scientists such as Edwin Hubble, Arno Penzias, and Robert Wilson who presented pieces of evidence
to support it.
 The Big Bang Theory states that the universe started as a “singularity”—an area predicted to be in the core of a
black hole with a very high temperature and density, which compressed matter with its intense gravitational
pressure.
3. Oscillating Universe Theory
 The Oscillating Universe Theory, also referred to as the Pulsating Universe Theory, discusses that the universe
is expanding and will contract once all the energy after the Big Bang is used up. This theory, proposed by Richard
Tolman, can be described as the combination of the Big Bang and the Big Crunch.
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 The Big Crunch occurs when the universe expands and eventually reverses, then collapses causing a
singularity or the formation of another Big Bang.
 The Oscillating Universe Theory suggests that once the universe reverses and attains the point of singularity,
another universe will be born. This is referred to as the Big Bounce.
 Tolman theorized that the universe may be first in the cycle and could be a result of a previous Big Bounce event.
 Just like in the Steady State Theory, scientists discovered many loopholes in the Oscillating Universe Theory
because it was said that for the universe to collapse, energy must be present. This theory suggests that the
universe will collapse on its own after it reaches its full expansion, which violates some laws of physics.
III.
Evidences that Support the Big Bang Theory
1. Discovery of primordial elements
 From time zero (13.8 billion years ago) until 10-43 second later, all matter and energy in the universe existed as a hot,
dense, tiny state.
 It then underwent extremely rapid, exponential inflation until10-32 second later after which and until 10 seconds from
time zero, conditions allowed the existence of only quarks, hadrons, and leptons.
 Then, nucleosynthesis took place and produced protons, neutrons, atomic nuclei, and then hydrogen, helium, and
lithium until 20 minutes after time zero when sufficient cooling did not allow further nucleosynthesis.
 From then on until 380,000 years, the cooling universe entered a matter-dominated period when photons decoupled
from matter and light could travel freely as still observed today in the form of cosmic microwave background radiation.
 As the universe continued to cool down, matter collected into clouds giving rise to only stars after 380,000 years and
eventually galaxies would form after 100 million years from time zero during which, through nucleosynthesis in stars,
carbon and elements heavier than carbon were produced.
 From 9.8 billion years until the present, the universe became dark-energy dominated and underwent accelerating
expansion. At about 9.8 billion years after the big bang, the solar system was formed.
2. Discovery of Red Shift by Edwin Hubble.
 In 1929, Edwin Hubble announced his significant discovery of the “redshift” and its interpretation that galaxies are
moving away from each other, hence as evidence for an expanding universe.
 He observed that spectral lines of starlight made to pass through a prism are shifted toward the red part of the
electromagnetic spectrum, i.e., toward the band of lower frequency; thus, the inference that the star or galaxy must be
moving away for us.
 Red shift as evidence for an expanding universe. The positions of the absorptions lines for helium for light coming
from the Sun are shifted towards the end as compared with those for a distant star. Thus evidence for expansion
contradicted the previously
held view of a static and
unchanging universe
 Electromagnetic Spectrum
3. Doppler Effect of Light
 The redshift is due to the Doppler Effect phenomena similar of that of sound waves: to a stationary observer, the
frequency or pitch of a receding source decreases as it moves away.
4. Detection of the Cosmic Microwave Background Radiation.
 There is a pervasive cosmic microwave background (CMB)
radiation in the universe. Its accidental discovery in 1964 by Arno
Penzias and Robert Woodrow Willson earned them the physics
Nobel Prize in 1978.
 It can be observed as strikingly uniform faint glow in the
microwave band coming all directions-blackbody radiation with an
average temperature of about 2.7 degrees above absolute zero.
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