- explain briefly the Big Bang theory
- describe the available evidence supporting the Big Bang theory
We have learned in Unit 9 Lesson 1 that the
nature of the universe is anything but simple. Observing is one thing –
explaining what is seen can be altogether different.
Depiction of the Wilkinson Microwave Anisotropy
Probe (WMAP) satellite used to gather data to help
in the understanding of the Big Bang
there are several theories as to how the universe began and has since
evolved, one theory is widely accepted by astronomers: the Big Bang theory
The Big Bang theory states that at one point in the past (now estimated
to be 13.7 billion years ago), all the material which currently makes
up the universe was exploded outward from a single point. At the time
of initial explosion, the universe was extremely hot, and very dense.
Matter and energy were indistinct. This initial state of high density
and temperature is known as a singularity.
Did You Know ?
name of the Big Bang theory came about by accident! Dr. Fred Hoyle, a
British astronomer and defender of competing ideas on the origin of the
universe, was making fun of the theory during a radio interview for the
BBC. He referred to it sarcastically as “this big bang idea…” and the
According to the Big Bang theory, the timeline of the universe is then divided into three sections. The first, the very early universe
is still poorly understood. There are no experiments on Earth which can
test the conditions which existed at this point in time, so the theory
remains speculative. It is thought that during this time, which lasted
much less than one second, the four forces we know today (gravity,
electromagnetism, strong and weak nuclear forces) were all initially
one force, and broke apart during this epoch.
expansion of gigantic proportions, called inflation, occurred as well
during this time. Inflation served to flatten the universe and spread
radiation (matter/energy) out in all directions, and only lasted a very
short time. However, this expansion may have been the beginning of
structure in the universe as we know it. Finally, the initial creation
of matter arose during this time, known as baryogenesis
. During baryogenesis
the amount of matter and antimatter became unbalanced, allowing for
more matter than antimatter to exist. If the matter and antimatter had
remained balanced, the particles would have annihilated each other.
Matter would not have been created, and you would not be here reading
In the second epoch, the early universe
the universe continued to expand, but at a much slower rate than during
inflation. As the universe expanded, it began to cool, and matter and
energy began to de-couple. For the first 300,000 years, photons
dominated the universe, interacting with newly-formed protons and
electrons. It was also during this time that the initial elements were
formed; the early universe was composed of 75% hydrogen, 25% helium and
trace amounts of lithium, the first three elements on the periodic
table. Small structure began to form, based on gravitational
interactions with the new particles.
The final stage of universe evolution began at about 300,000
years after the Big Bang and is continuing today. Structure formation
small scales. It is thought that quasars
formed first – very early, very
bright, active galaxies with little structure. Stars and galaxies formed next,
eventually evolving into galaxy clusters and superclusters. The larger stars
produced elements heavier than hydrogen, helium and lithium which previously
existed, and the evolution continues to this day.
According to the Big Bang theory of universe evolution, a large explosion resulting from
Did You Know ?
a singularity caused a massive expansion, eventually leading to structure in the universe
as we see it today.
every billion antiparticles which existed before baryogenesis, there
were a billion-plus-one normal particles. This means that for every 1
billion annihilations of particles and antiparticles, one particle
survived. That may not sound like a lot, but those one-in-a-billion
particles are what currently make up all matter in the universe!
It may sound far-fetched, but the majority of the
developments in this theory are supported – and in some cases initiated
– by actual observations made in the past century. the most notable of
these observations being the current expansion of the universe. What
caused all of the galaxies to be moving further and further away from
each other? An initial explosion and subsequent inflationary period
could have caused this, as modeled in the Big Bang theory.
exists another “ubiquitous” observation that supports this theory.
During baryogenesis, radiation freely streamed throughout the entire
universe (which was smaller at the time). This radiation continues to
stream through space to this day, but does so at a much lower
temperature, due to the expansion and cooling of the universe. In 1964,
remnants of this radiation were discovered at a temperature of 2.7K –
only 2.3K shy of a predicted value of 5K! Since then, the radiation has
been mapped in all directions away from the Earth, using both ground
and space-based observatories. It has been found to have nearly the
same temperature in all directions, consistent with radiation that
would have existed shortly after the Big Bang, and with the estimated
rate of expansion of the universe.
Astronomers from the University
of Toronto and the Canadian Institute
for Theoretical Astrophysics (CITA) contributed to the science behind
BOOMERanG: a balloon observation station which flew above Antarctica
and measured the cosmic microwave background radiation. Its goal was to measure
differences in the temperature of the microwave background, in an effort to
determine what the universe was like at the end of the early universe period.
The Big Bang also correctly predicts the percentage of early elements
found in the universe, as well as the distribution and structure of
galaxies and galaxy clusters. There are, however, some aspects of the
nature of the universe which the Big Bang does not model very well, and
these will be discussed in the following Module.
Representation of the expansion of the universe, the inflationary epoch
represented by the dramatic expansion.