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From 10 Seconds After the Big Bang to Now
Eric Biehn
Math 89S Seminar
Professor Hubert Bray
Duke University
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Introduction
Humans were not around for the big bang. There are obviously no written accounts of it, and it
occurred billions of years ago, so how could we possibly understand it? What gives human
beings the audacity to say that we can describe what happened billions of years ago, when we’ve
only been around as a species for a couple of million years ourselves? As it turns out, when we
look into the night sky, we are essentially gazing billions of years back in time to the light from
events that happened during some of the earliest stages of the creation of the universe. While we
can’t exactly see back to the very beginning, we can use the laws of physics and other techniques
and theories in order to get a good sense of what happened. It is difficult for one to wrap his or
her head around the concept behind the big bang, but it is still accepted by most scientists. For
the first 10 seconds after the birth of our universe, a seemingly impossible amount of processes
and events occured to begin the creation of everything we know today. But let’s worry about
that another time. For now, we’re going to focus on the creation of the universe from 10 seconds
after the big bang to the present day.
Photon Epoch and Nucleosynthesis
The Photon Epoch occurred approximately 10 seconds after the big bang. At this point in time,
the universe was a plasma consisting of free-flying protons, electrons, and neutrons. The
temperature was high enough for the photons to collide and interact with other particles,
typically electrons, however it is too high to allow the formation of atomic nuclei [1]. The
photons collide with energized electrons to create a “Lorentz Force”, which accelerates the
electrons and causes vibration. A new photon is omitted in a different direction because the
vibration causes a new electromagnetic oscillation. Photons could not travel freely due to the
constant collisions between particles, therefore the universe was opaque [4].
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Nucleosynthesis occurred in the first minutes of the photon epoch. By definition,
nucleosynthesis is when lighter nuclei fuse together to form a new, heavier nuclei. Initially, the
leftover matter in the universe consisted of protons, electrons and neutrons. However, as the
universe began to cool, these particles were finally able to form larger and more complex atomic
nuclei through nucleosynthesis. During this period, many isotopes of elements were formed
such as Deuterium, which is a hydrogen isotope consisting of 1 proton and 1 neutron. There
were also isotopes of helium, such as He-3, consisting of 2 protons and 1 neutron, and He-4,
consisting of 2 protons and 2 neutrons [5].
Figure 1
This diagram shows a pathway in which a deuterium nucleus collides with a neutron which
forms tritium, and then a proton to form He-4.
http://aether.lbl.gov/www/tour/elements/early/early_a.html
A strong argument for the big bang theory involves the makeup of the universe which is
predicted to be 76% of Hydrogen-1, slightly less than 24% helium-4, about 0.01% of deuterium,
and a small amount of other elements. This is almost exactly what has been seen in the universe
today, which provides compelling evidence for the big bang theory [5].
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Recombination
Approximately 378,000 years after the big bang, the universe had finally cooled enough to allow
atoms to form. Ions and electrons were able to combine and form atoms, thus beginning the
“recombination epoch”. Primarily hydrogen and helium atoms were created from the
recombination effects [2]. The epoch of recombination marks the first interval in the
development of the universe that can still be observed today. Previously, the plasma that
dominated the universe scattered the radiation so that the photons from that period were not able
to escape and freely travel. However, as time passed, charged particles bonded to neutral
atoms. As a result, photons did not interact with the charged particles, therefore these photons
could now travel freely. These photons allow astronomers to study the “cosmic microwave
background” of the recombination period [2].
Dark Ages
The monumental emergence of detectable light in the universe comes to a halt with another
period of darkness, appropriately referred to as the “Dark Ages” of the universe. The dark ages
mark the period before the formation of galactic structures, which formed a few hundred million
years after the big bang.
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Figure 2
This diagram shows the chronology of the universe. The dark ages are shown as the dark period
before the formation of structures.
https://en.wikipedia.org/wiki/Chronology_of_the_universe
It is important to point out that the dark ages were not entirely “dark”. Electrons and photons
decoupled from each other. Instead of individual forms of light such as stars, the universe was
made up of neutral hydrogen clouds. At this point in time, the density of the universe is much
lower than it previously had been because the universe had finally expanded enough to allow a
better distribution. Also, the temperature had cooled down to about 3000K compared to the
billions of degrees Kelvin that it was at the big bang [3]. The relatively recent decoupling
allowed matter to assemble due to the effects of gravity; thus resulting in both ordinary and dark
matter concentrations to grow more massive while also becoming denser. This began the
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formation of the cosmic web, which was the substructure of both regular and dark matter which
eventually gave way to the formation of stars and galaxies. The cosmic web was formed by the
gravitational pull of dark matter structures to ordinary matter which caused regions of high
matter and high density areas to form [3]. The densest buildups eventually became the first stars
and structures, which brings us to the end of the dark ages and to the beginning of the creation of
the stars and galaxies of our universe.
Large Scale Structure Formation
When we look up into the night sky, some of the light visible to us originates from the first
structures that formed from the various clumps of high density areas which were able to form
into stars and galaxies. As structures in the universe began to form, small structures were
thought to have formed before larger ones, which follows the “bottom-up theory”. There is also
the less-accepted “top-down theory” stating that matter formed in a large clump which
eventually broke into smaller pieces. The first stars that are thought to have formed, referred to
as Population III stars, were thought to be large formations of hydrogen and helium. Population
III stars were intensely hot with virtually no other metals, and they are thought to have formed
about 560 million years after the big bang [3]. While no population III stars have been observed,
this is thought to be the case because these stars had such high masses. The high concentration
of mass exhausted the stars’ fuel very quickly, therefore the only things we can observe today are
the remnants of them such as white dwarfs, neutron stars, or black holes. Thus, when these stars
quickly collapsed, they formed supernovas which led to a new generation of stars forming from
the remnants [3]. The next generation included many stars that were typically
smaller. Population II stars eventually began to form, followed by Population I stars. Population
II stars are primarily composed of hydrogen and helium, and they also contain small traces of
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heavier elements. Population I stars are composed of heavier and more diverse elements because
they formed later after the big bang, therefore these elements were more abundant in the
universe. However, hydrogen and helium are still by far the most abundant gases found in
population I stars [9]. The initial generations were formed in galaxies of very low mass, but the
generations that formed later were created in higher-density galaxies. Galaxies, like stars, were
also formed by even-larger collapses of matter, with gas and dust rotating in a disk formation to
eventually form galactic disks. Galaxy clusters, which are large clusters of galaxies, further
prove the “bottom-up” theory because the smaller components eventually congregated together
to form a larger cluster. The filaments composed of mainly dark matter that formed during the
dark ages determined the string-like patterns of galaxies. Galaxies formed along these filaments,
and when the filaments intersected, a galaxy cluster arose. A typical cluster contains hundreds of
thousands of galaxies. Furthermore, this pattern lead to galaxy superclusters forming, which are
large congregations of galaxy clusters. These are some of the largest structures in the known
universe, potentially spanning from 100 million light years to a billion light years across [10].
Figure 3
This figure, shown below, highlights the filament structures in the universe that large-scale
structures formed on.
http://cosmicweb.uchicago.edu/filaments.html
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The Solar System
The solar system formed about 4.6 billion years ago stemming from a gravitational disturbance
to a molecular cloud (also known as a nebula) which now makes up our home solar system. The
molecular cloud was initially several light years across. The nebula had a net rotation, and as it
continued to collapse, the angular momentum was conserved which caused the nebula to rotate
faster and faster. As the nebula continued to collapse, most of the mass formed near the center,
which eventually became the sun. The gravitational potential energy eventually turned into
kinetic energy, and through collisions between the particles the energy turned into heat. There
was such a great buildup of heat in the center, with temperatures exceeding 10 million Kelvin,
that nuclear reaction began to occur due to the particles colliding so violently, and the extreme
buildup of mass in the center finally became the Sun [11].
While about 99.8% of the total mass in the solar system was used to form the sun, there was still
a remaining disk of matter which eventually become planets, moons, asteroids, and other
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structures. A flat accretion disk of the remaining dust and gas formed around the sun, with the
small grains of dust within the disk eventually forming into planets [7]. Atoms and molecules
began to stick together to form ball-like structures, and these structures eventually grew to be
about a mile wide. At this point, the structures were able to attract surrounding objects due to
gravity instead of relying on random collisions. For another 10 to 100 million years, further
collisions lead to the eventual formation of the 8 planets in our solar system [7].
Figure 4
This figure shows the spinning disk of matter which eventually became the structures of the solar
system.
http://www.sci-news.com/space/science-half-water-earth-older-than-sun-02173.html
The definition of a planet is a spherical body that orbits the sun and has cleared the area around
itself of smaller objects [7]. The inner 4 planets (Mercury, Venus, Earth, and Mars) are rocky
and smaller than the 4 outer planets (Jupiter, Saturn, Uranus, and Neptune) which are gaseous
with a rocky core. It is believed that stellar winds from the sun blew off the gases surrounding
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the 4 inner planets, thus causing the 4 to be small and terrestrial. Separating the inner and outer
planets is an asteroid belt of small bodies that remains from the beginning of the solar system
[7]. It is theorized that this is due to Jupiter’s extreme gravitational pull influencing this region,
and as a result another planet could not take shape. These collective processes eventually formed
the solar system that our home planet Earth inhabits today.
Conclusion
Through remarkable scientific and technological achievements, scientists have been able to
slowly uncover the mysteries behind the origins of our universe. However, there are still many
things we do not know. As science further progresses, more and more secrets will eventually be
revealed about the beginnings of the universe. But in the meantime, anyone can go outside on a
clear night, look up at the sky, and speculate on the unanswered questions of the universe’s
origins as we sail through space on this tiny rock we call home.
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Sources
"The Photon Epoch." Highbrow. Web. 27 Sept. 2016. [1]
"Epoch Of Recombination." Epoch Of Recombination. Web. 27 Sept. 2016. [2]
Esa. "History of Cosmic Structure Formation." European Space Agency. Web. 27 Sept. 2016. [3]
"Our Universe Part 10: Photon Epoch." Scientific Explorer. Web. 27 Sept. 2016. [4]
Hillyard, William. "The Early Universe - Photon Epoch." The Early Universe - Photon Epoch.
Web. 27 Sept. 2016.[5]
Britt, Griswold. “How Did Structures Form In the Universe.” NASA. Web. 27 Sept. 2016.l [6]
Brown, Cynthia. “How Our Solar System Formed”. Khan Academy, Web. 27 Sept. 2016. [7]
Gibson, Carl. “Evolution of proto-galaxy-clusters to their present form.’ UCSD, Web. 27 Sept.
2016. [8]
"Populations I and II." Encyclopedia Britannica Online. Encyclopedia Britannica, Web. 27 Sept.
2016. [9]
“Formations of Structures in the Universe.” NASA, Web. 27 Sept. 2016. [10]
"Solar System Formation." Windows to the Universe. Web. 27 Sept. 2016. [11]