The Big Bang Model - Chapter 12

HideShow resource information
View mindmap
  • The Big Bang Model of the Universe
    • Hubble's Ideas
      • Recessional Velocity is Proportional to Distance
        • The spectra from galaxies all show redshift.
          • The amount of redshift gives the recessional velocity.
          • HUBBLES LAW: v=H0d where v = recessional velocity,      H0 = Hubble's Constant,      d = distance
            • UNITS:          v = km/s        d = Mpc      H0 = (km/s) / (Mpc)
              • Mpc is a megaparsec. 1Mpc = 3.09E+22m
            • SI Unit for H0 is 1/s therefore...       v = m/s       d=m
        • When Hubble plotted the recessional velocity of galaxies against their distance from Earth (Cepheid Variables) he found that they were proportional.
      • The Universe is Expanding
        • By showing that objects in the Universe are moving away from each other, Hubble's work is strong evidence that the Universe is expanding.
          • The rate of expansion depends on the value of H0.
        • The way cosmologists tend to look at this, the galaxies aren't actually moving through space away from us.
          • Instead, space itself is expanding and light waves are being stretched along with it.
            • This is called cosmological redshift to distinguish it from redshift produced by sources that are moving through space.
        • The Universe is expanding uniformly away from us, creating the illusion that we are at the centre of the universe.
      • The Age and Observable Size of the Universe depend on H0.
        • If the Universe has been expanding at the same rate for its whole life, the age of the Universe is                    t = 1/H0
          • This is only an estimate as it is unlikely that the universe has been expanding at the same rate.
        • Since no on know the exact value of H0, we can only guess the universe's age.
          • Approx. 14 billion years old.
        • The absolute size of the Universe is unknown. There is a limit on the observable size of the Universe.
          • This is a sphere, where radius = maximum distance that light can travel during its age (radius approx. 14 billion light years).
      • Evidence: The Red Shift  of Galaxies
        • If you assume that the Universe has always been expanding, if you trace back far enough it can be implied that the universe must once have been contained in a single point.
    • Evidence: Cosmic Microwave Background Radiation
      • Properties of the Cosmic Microwave Background Radiation
        • Cosmic Background Explorer set up to look at spectrum.
          • Continuous spectrum corresponding to a temperature of 2.73k
        • Radiation is ISOTROPIC AND HOMOGENOUS - same intensity whichever direction you look at it
        • Very tiny fluctuations in temperature, at the limit of COBE detection.
          • Due to tiny energy density variations in the early universe and are needed for the initial seeding of galaxy formation.
        • Also shows a Doppler Shift
          • Milky Way is rushing towards an unknown mass (GREAT ATTRACTOR) at over a million miles per hour.
      • Penzias and Wilson, 1960's
      • HBBM predicts that EM radiation was produced in the very early Universe. This radiation should still be observed today.
      • Because the Universe has expanded,, the wavelengths have been stretched and are in the microwave region.
      • The Universe started off very hot and very dense (perhaps as an infinitely hot, infinitely dense singularity)and has been expanded.
      • Widely accepted
      • Since Hubble's findings were published,the redshifts of other objects have been measured and fit with his predictions.
    • Evidence: the amount of Helium in the Universe
      • The HBB Model also explains the large amount of helium in the Universe.
      • The early Universe had to have been very hot and at some point it must have been hot enough for hydrogen fusion to occur.
      • This means that, together with the theory of the synthesis of heavier elements in stars, the relative abundances of all of the elements can be accounted for.


No comments have yet been made

Similar Physics resources:

See all Physics resources »See all Cosmology resources »