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By: rose_aries15

Year 2

H62BPA: Presentation Skills

University of Nottingham, Malaysia Campus.

THE BIG BANG THEORY

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PremiseHistory & DevelopmentProblems & EvidenceExpansion of the UniverseCommon MisconceptionsSummary

Content

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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.

Premise

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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. 

Premise

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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.

Premise

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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.

Premise

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PremiseThe 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.

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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

History & Development

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History & Development- Einstein (1879–1955)

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.

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History & Development- Alexander Friedmann (1888-1925)

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.

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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

History & Development- Alexander Friedmann

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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.

History & Development- Alexander Friedmann

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History & Development- Edwin Hubble (1889-1953)

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.

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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

History & Development- Edwin Hubble (1889-1953)

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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.

Problems & Evidence

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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.”

Problems & Evidence

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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.

Problems & Evidence

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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.

Problems & Evidence

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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.

Expansion of the Universe

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Expansion of the UniverseOn 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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Expansion of the Universe 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.

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A Giant ExplosionI’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. 

Common Misconceptions

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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. 

Common Misconceptions

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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. 

Summary