The big bang theory
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Friday, 23 July 2010
description
Copy of ppt used to discuss the big bang theory
Transcript of The big bang theory
Friday, 23 July 2010
The UniverseThe Big Bang
Friday, 23 July 2010
The Big Bang Model
A broadly accepted theory for the origin and evolution of our universe.
12 to 14 billion years ago, the part of the universe we can see today was hot, dense and only a few millimeters across.
It has since expanded into a vast and much cooler cosmos.
Remnants of the original state of the universe can still be seen as ‘background radiation’ (microwave radiation)
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Key idea 1: General Relativity
E = mc
E= energy
m = mass
c = speed of light
Gravity is not really a ‘field’, but a distortion of time and spaceAlbert Einstein’s theories
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Key Idea 2:The cosmological Principle
• Matter is evenly distributed (on average)
• The temperature of the cosmic microwave background radiation is very uniform
Distribution of galaxies over a 30° section of the sky
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Evidence - Expansion
• Edwin Hubble (1929)
• Nearby galaxies are moving away from us at a speed proportional to their distance from us.
Expanding raisin bread model
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Evidence - Light element abundance
One second after the Big Bang...
Temperature of the universe was ~ 10 billion °C
Universe was filled with a sea of neutrons, protons and electrons
As the universe cooled, the neutrons either broke down into protons and electrons or combined with protons to make deuterium (an isotope of hydrogen)
During the first three minutes of the universe, most of the deuterium combined to make helium.
Trace amounts of lithium were also produced at this time.
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Evidence - Background radiation
The early universe was a very hot placeAs it expanded, the gas within it cooled. Thus the universe is filled with electromagnetic radiation that is, literally, the remnant ‘heat’ left over from the Big Bang.This is called the “cosmic microwave background radiation”, or CMB.
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‘Heat’?
Originally, the universe was very hot
High heat = high energy
Expansion = cooling = lower energy
Today, the radiation is much colder, only 2.725° above absolute zero (- 273.16°C)
Microwaves
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Problems with the Big Bang?
• On average the universe is very evenly distributed but ...
• in local areas, this is not so (stars and galaxies exist with very little between them)
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Where will it all end?
• Determined by two competing forces; momentum and gravity
• therefore, two possibilities....
• Not enough matter = not enough gravity...Universe expands (and cools) forever
• Sufficient matter ... gravity overcomes momentum and universe collapses back in on itself (eventually)...the “Big Crunch”.
• At the moment, the expansion is accelerating!
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