The big bang theory


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The big bang theory

  1. 1. Friday, 23 July 2010
  2. 2. The Universe The Big Bang Friday, 23 July 2010
  3. 3. 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) Friday, 23 July 2010
  4. 4. Key idea 1: General Relativity 2 E = mc E= energy m = mass c = speed of light Gravity is not really a ‘field’, but a distortion Albert Einstein’s theories of time and space Friday, 23 July 2010
  5. 5. Key Idea 2: The cosmological Principle • Matter is evenly distributed (on average) • The temperature of the cosmic microwave background Distribution of galaxies over a 30° section of the sky radiation is very uniform Friday, 23 July 2010
  6. 6. 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 Friday, 23 July 2010
  7. 7. 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. Friday, 23 July 2010
  8. 8. Evidence - Background radiation The early universe was a very hot place As 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. Friday, 23 July 2010
  9. 9. ‘Heat’? Expansion = Originally, cooling = lower the energy universe was very Today, the hot radiation is much colder, High heat = only 2.725° high above absolute energy zero (- 273.16°C) Microwaves Friday, 23 July 2010
  10. 10. 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) Friday, 23 July 2010
  11. 11. 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! Friday, 23 July 2010