166 Chapter 3 The Universe Was Born With a Big Bang
Three Pieces of Evidence for the Big Bang Theory
At first, most scientists considered the Big Bang theory to be outlandish. But over time,
observations were made that supported the theory, and more scientists began to endorse it.
Evidence of the Big Bang, Exhibit A: Cosmic Microwave Background Radiation
In 1964, the US company Bell Laboratories made an accidental discovery while moni-
toring radio waves reflected from radio balloons. It determined that the background
interference or “noise” in the data was being caused by a microwave signal of a specific
wavelength that was coming from all directions in space. This signal is now known as
cosmic microwave background radiation (CMBR). Scholars who advocated the Big Bang
theory hypothesized that this radiation was caused by the temperature of space (approxi-
mately 3,000 Kelvin (K), a temperature equivalent to almost 5,000ºF) in the era when
electrons and protons, which had been flying around freely until then, began to com-
bine (approximately 380,000 years after the Big Bang). According to the hypothesis,
atoms were created, space became transparent to radiation, and the electro magnetic
waves that were emitted have now reached their current places in space due to the
subsequent expansion of the universe. They exist with a frequency distribution that
indicates a constant absolute temperature of 3 K. Observations of a temperature of
2.725 K support this hypothesis magnificently.
The CMBR, examined carefully by the Cosmic Background Explorer (COBE)
satellite launched by NASA in 1989, has helped to advance astronomers’ knowledge of
the early universe. The accidental discoverers of CMBR were awarded the Nobel Prize
in Physics in 1978.
Evidence of the Big Bang, Exhibit B: WMAP Satellite Measurements
The Wilkinson Microwave Anisotropy Probe (WMAP), which was launched in 2001 and
operated until 2010, observed cosmic microwave background radiation temperatures
across the entire sky. When its data were analyzed, it became apparent that more than
72 percent of the gravitational sources or structures in the universe consist of dark
energy (energy held by the vacuum between the visible heavenly bodies), and matter
makes up no more than the remaining approximately 28 percent. Incidentally, most
of the matter is dark matter, while baryonic matter that we are familiar with (that
is, “normal” matter consisting of protons, neutrons, and electrons) accounts for only
approximately 4.6 percent. This result is consistent with the inflation theory, which
asserts that there was a sudden expansion immediately after the universe was born.
Evidence of the Big Bang, Exhibit C: Chemical Composition of Stars
Various observations have demonstrated that the chemical composition of stars is
hydrogen:helium = 3:1. The most logical explanation for why hydrogen and helium are
present in such large quantities and in a specific ratio ties in nicely with the Big Bang
theory. Hydrogen and helium are the lightest of all the chemical elements. The rela-
tive abundance in stars of the lightest element followed by the next-lightest element is
consistent with the hypothesis that the universe began with an explosion. An explosion
would result in high temperatures, which in turn would cause matter to organize in a
way that would produce many small particles and fewer large ones.
Thr Pieces of Evidence for the Big Bang Theory 167
I don't
understand this
very we...
H...
What’s
wrong?
We, first there
was a bming
explosion and
the universe was
born, right?
So after that, didn't
the maer that was
blown up fly around
in tiny pieces?
No, that's not
what haened.
When the
Universe suenly
expanded due to
inflation, only light
was generated, not
maer.
More aurately,
what exploded were
light particles caed
photons. Since these are
indestructible, they were
not broken into pieces.
Are photons
one of the
elementary
particles?
168 Chapter 3 The Universe Was Born With a Big Bang
Elementary
particle? What
language is she
speaking? Grk?
Chinese?
We talked about
elementary
particles in the
chronology
of the universe
earlier!
In short, how
does the big
bang dier
from a normal
explosion...
Gloria!
U...I
have no
idea!
SWSH
Kanta! Pa!
I don't
know
either!
It figures...
get ready,
Profeor!
This is a lile diicult to explain.
Elementary particles are the
smaest indivisible units that
constitute maer. Formerly,
scientists thought that atoms
were elementary particles, but
cuently, quarks or leptons
have this distinction.
Photons are claified as one
of the gauge particles, which
are particles that propagate
forces betwn elementary
particles. Quarks are thought
to have bn generated from
photons in the early universe.
Molecule
Atom
Quarks and leptons are
elementary particles claified
as fermions, and photons are
elementary particles claified
as bosons.
Huh?
Quark Photon
Lepton
Elementary particle

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