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Cosmology The Origin and Future of the Universe Part 3

Cosmology The Origin and Future of the Universe Part 3. Why there is matter in the Universe? and The critical density of the Universe. Why there is matter in the Universe?.

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Cosmology The Origin and Future of the Universe Part 3

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  1. CosmologyThe Origin and Future of the UniversePart 3 Why there is matter in the Universe? and The critical density of the Universe

  2. Why there is matter in the Universe? • In the beginning, long ago, in the early stages of the Big Bang, highly energetic photons created massive X-particle/X-anti-particle pairs and vice versa • At this time and at the temperatures that then existed, this process was reversible

  3. Why there is matter in the Universe? • Temperatures began to fall and the unstable X-particles and X-anti-particles decayed • There are two decay possibilities: i) X-particle  quark + quark or anti-quark + anti-lepton ii) X-anti-particle  anti-quark + anti-quark or quark + lepton

  4. Why there is matter in the Universe? • What are quarks and leptons? a) Quarks are fundamental particles of matter and are constituent particles of neutrons, protons and other hadrons (baryons & mesons) b) leptons are fundamental particles of matter which have no strong interactions (electrons & neutrinos)

  5. Why there is matter in the Universe? • Now, the proportion of X-particles which decayed into quarks was about 1 part in a billion larger than the proportion of X-anti-particles that decayed into anti-quarks • Consequently there were more quarks than anti-quarks and more leptons than anti-leptons

  6. Why there is matter in the Universe? • As particle – anti-particle pairs annihilate each other, this results in photons and protons being produced in the ratio of one billion to one • Hence, there is the existence of matter in the Universe

  7. The Critical Density of the Universe • If a galaxy of mass m is at a distance r from the location of the Big Bang then its velocity is given by: • V = H0r where H0 is the Hubble constant • The kinetic energy of the galaxy is therefore: • E = ½ m (H0r)2

  8. The Critical Density of the Universe • The net gravitational force acting on the galaxy is due to the mass of the Universe within a sphere of radius r. This mass is equal to: • M = 4/3 пr3р where р is the density of the Universe

  9. The Critical Density of the Universe • The net gravitational force acting on the galaxy is given by: • F = G(Mm/r2) • The work which must be done by the galaxy to escape from the rest of the Universe is: • G(Mm/r) • This is the integral from infinity to r of G(Mm/r2) with respect to dr

  10. The Critical Density of the Universe • The critical density рc of the Universe at which the galaxy has just enough kinetic energy to escape is given by: • ½ m (H0r)2 = G(m/r)(4/3 пr3рc) • Therefore: • рc = (3H02)/8пG

  11. The Critical Density of the Universe • However! • It is important to realize that these calculations have been done using Newton’s gravitational theory and not the general theory of relativity

  12. Your task for next week! • You should produce a Power Point presentation lasting about 10 minutes which deals with one of the following topics: • Stars and their formation • The death of a star • Reading radiation from the stars • Thermonuclear reactions • X-ray pulsars

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