2. Premise
History & Development
Problems & Evidence
Expansion of the Universe
Common Misconceptions
Summary
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3. Discoveries in astronomy and physics have shown
beyond a reasonable doubt that our universe did
have a beginning: It all started with an explosion
known as the Big Bang (BB).
The Big Bang theory and the term BB generally
refers to the idea that this mysterious universe has
expanded from a very hot and dense initial condition
at some time in the past, and it continues to expand.
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4. The Big Bang theory is basically an effort to explain
what happened at the very beginning of our
universe.
Prior to the moment when the universe began, there
was nothing; during and after that moment there was
something: our universe. The big bang theory
explains what happened during and after that
moment.
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5. According to the standard theory, our universe
sprang into existence as singularity around 13.7
billion years ago. Singularities are zones which defy
our current understanding of physics.
A singularity is a point where the predictable nature
of physics breaks down because the curvature
predicted by general relativity at that point is infinite.
They are thought to exist at the core of black holes.
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6. Black holes are areas of intense gravitational
pressure. The pressure is thought to be so intense
that finite matter is actually squished into infinite
density. These zones of infinite density are called
"singularities”.
After the initial appearance of our universe as
singularity, it apparently inflated (the "Big Bang"),
expanded and cooled - going from very, very small
and very, very hot, to the size and temperature of
our current universe.
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7. 7
The universe continues to
expand and cool to this day
and we are inside of it:
incredible creatures living
on a unique planet, circling
a beautiful star clustered
together with several
hundred billion other stars
in a galaxy soaring through
the cosmos, all of which is
inside a universe which
appeared out of nowhere.
This is the Big Bang theory.
8. The Big Bang theory developed from observations of the
structure of the Universe and from theoretical considerations.
In 1912, Vesto Slipher measured the first Doppler shift of a
"spiral nebula" (spiral nebula is the obsolete term for spiral
galaxies), and soon discovered that almost all such nebulae
were receding from Earth. He did not grasp the cosmological
implications of this fact, and indeed at the time it was highly
controversial whether or not these nebulae were "island
universes" outside our Milky Way.
Other scientists who contributed to the research of the
expanding universe include:
• Albert Einstein
• Alexander Friedmann
• Edwin Hubble
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9. 9
In 1915, Einstein predicted
that the universe is
expanding and he came up
with 10 field equations to
support his general theory
of relativity.
However, since Einstein
believed in a static
universe, he modified his
equations and put in a
cosmological constant to
make the universe static.
10. 10
10 years later,
Alexander Friedmann, a
Russian cosmologist
and mathematician,
read Einstein’s work but
thought that the
cosmological constant
was wrong. So, he tried
to solve Einstein’s
equations.
11. Alexander then derived the Friedmann equations
from Albert Einstein's equations of general relativity,
showing that the Universe might be expanding in
contrast to the static Universe model advocated by
Einstein at that time.
Friedmann’s math proposed two models:
• Closed Universe
• Open Universe
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12. Closed Universe: According to Alexander, time and
space have a beginning and an end. They both
began with a big bang and will end when gravity
stops the universe and pulls everything back into
one point – the big squeeze. The universe is finite
and the expanding universe is due to space
expanding.
Open Universe: According to this part of the theory,
the universe began with a big bang and will continue
to expand forever. Time and space have no end.
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13. 13
In 1924, Edwin Hubble's
measurement of the great
distance to the nearest spiral
nebulae showed that these
systems were indeed other
galaxies.
Hubble painstakingly
developed a series of
distance indicators using the
100-inch (2,500 mm) Hooker
telescope at Mount Wilson
Observatory.
14. This allowed him to estimate distances to galaxies
whose red shifts had already been measured, mostly
by Slipher. In 1929, Hubble discovered a correlation
between distance and recession velocity—now
known as Hubble’s Law or Hubble’s Constant (Ho).
Hubble’s Law explained the rate at which the
universe is expanding and the constant (Ho) is used
to estimate the size of the universe
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15. In the 1920s and 1930s almost every major
cosmologist preferred an eternal steady
state Universe and several complained that the
beginning of time implied by the Big Bang imported
religious concepts into physics.
This objection was later repeated by supporters of
the steady state theory. This perception was
enhanced by the fact that one of the originators of
the Big Bang theory, Monsignor Georges Lemaître,
was a Roman Catholic priest.
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16. Arthur Eddington agreed with Aristotle that the universe
did not have a beginning in time and that matter is
eternal. A beginning in time was "repugnant" to him.
Lemaître, however, said,
“If the world has begun with a single quantum, the
notions of space and time would altogether fail to have
any meaning at the beginning; they would only begin to
have a sensible meaning when the original quantum had
been divided into a sufficient number of quanta. If this
suggestion is correct, the beginning of the
world happened a little before the beginning of space and
time.”
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17. During the 1930s, other ideas were proposed
as non-standard cosmologies to explain Hubble's
observations, including the Milne model,
the oscillatory Universe (originally suggested by
Friedmann, but advocated by Albert Einstein
and Richard Tolman)and Fritz Zwicky's tired light
hypothesis.
However, it was then criticized by supporters of the
steady state theory that if the universe was really
initially very hot as the Big Bang suggests, we
should be able to find some remnant of this heat.
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18. In 1965, Radio astronomers Arno Penzias and Robert Wilson
discovered a 2.725 degree Kelvin Cosmic Microwave
Background radiation (CMB) which pervades the observable
universe. This is thought to be the remnant which scientists
were looking for to support the Big Bang Theory. Penzias and
Wilson shared the Nobel Prize for Physics for their discovery
in 1978.
Significant progress in Big Bang cosmology has been made
since the late 1990s as a result of advances
in telescope technology as well as the analysis of data from
satellites such as COBE, the Hubble Space
Telescope and WMAP. Cosmologists now have fairly precise
and accurate measurements of many of the parameters of the
Big Bang model, and have made the unexpected discovery
that the expansion of the Universe appears to be
accelerating.
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19. Observations of distant galaxies show that these
objects are red shifted - the light emitted from them
has been shifted to longer wavelengths.
This can be seen by taking a frequency spectrum of
an object and matching the spectroscopic pattern
of emission lines or absorption lines corresponding
to atoms of the chemical elements interacting with
the light.
These red shifts are uniformly isotropic, distributed
evenly among the observed objects in all directions.
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20. 20
On the left is a spectrum of
the transmitted frequency of
light from a star.
The right spectrum is the
observed frequency of the
star from Earth.
The spectral lines are
observed to be shifted
towards the red end.
This shows that the star is
moving away from us
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If the red shift is interpreted as
a Doppler shift, the
recessional velocity of the object
can be calculated.
For some galaxies, it is possible
to estimate distances via
the cosmic distance ladder. When
the recessional velocities are
plotted against these distances, a
linear relationship known
as Hubble's law is observed:
v = H0D, where
• v is the recessional velocity of
the galaxy or other distant object,
• D is the moving distance to the
object, and
• H0 is Hubble's constant.
22. A Giant Explosion
I’m sure that when I talk about the Big Bang, many of
you imagine a huge explosion (I know I did!).
Well, Experts say that there was no explosion; there
was (and continues to be) an expansion. Rather than
imagining a balloon popping and releasing its
contents, imagine a balloon expanding: an
infinitesimally small balloon expanding to the size of
our current universe.
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23. Another misconception is that we tend to image the
singularity as a little fireball appearing somewhere in
space. According to the many experts however, space
didn't exist prior to the Big Bang. In 1968 and 1970,
papers were published in which Einstein's Theory of
General Relativity was extended to include
measurements of time and space.
According to calculations, time and space had a finite
beginning that corresponded to the origin of matter and
energy. The singularity didn't appear in space; rather,
space began inside of the singularity. Prior to the
singularity, nothing existed, not space, time, matter, or
energy - nothing.
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24. We have made a first attempt at explaining the
answers that science has revealed about our
universe. Our understanding of the Big Bang, the
first atoms and the age of the universe is obviously
incomplete. As time wears on, more discoveries are
made, leading to infinite questions which require yet
more answers. Unsatisfied with our base of
knowledge, research is being conducted around the
world at this very moment to further our minimal
understanding of the unimaginably complex
universe.
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