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Sunday, April 1, 2012


THE BIG BANG: Hubble’s law suggests that at some time in the past, all the matter in the universe was far more concentrated than it is today. It was then blown apart on an immense explosion called the big bang, giving all observable matter more or less the velocities that we observe today. The matter in the ball was thrown out into many fragments. These fragments turn into galaxies. Later within the galaxies stars and planets were formed. According to Hubble law, matter at a distance r away from us travelling with speed v=H₀r. The time t needed to travel a distance r is given by, t= r/v.
Therefore, t=r/ H₀r= 1/ H₀= 4.3*10¹⁷s =1.4*10¹ᴼyears.
By this hypothesis, the big bang occurred about 14 billion years ago. It assumes that all the speeds are constant after the big bang; that is it neglects any changes in the expansion rate due to gravitational attraction or other effects.
The events that went on during succeeding time after the big bang are summarized as follows:
1.       Initial expansion began about 14 billion years ago. Cosmologists refer to this event as the initial singularity because at this time the volume of the universe was zero and density of mass energy was infinite.
2.       At t=10⁻⁴³s the temperature of the universe was about 10³²k, the averse energy per particle was about 10¹⁹GeV. The entire universe was much smaller than a proton. The concept of space and time come to have their present meanings and law of physics as we them become applicable.
3.       At t=10⁻³⁵s the temperature has decreased to about 10²⁷k and average energy to about 10¹⁴GeV. The universe has undergone a tremendously rapid inflation increasing the size by a factor of about 10³ᴼ.
4.       At t=10⁻³²s the universe was a mixture of quarks, leptons and mediating bosons (gluons, photons, and weak bosons W⁻⁺ and zᴼ).
5.       At t=10⁻⁶s the temperature was about 10¹³k and typical energies were 1GeV. At this time quarks began to bind together to form nucleons and antinucleons. Also there were still enough photons of sufficient energy to energy to produce nucleon-anti nucleon pairs to balance the process of nucleon anti nucleon annihilation.
6.       At t=1 min the universe has now cooled enough so that protons and neutrons in colliding, can stick together to form the low mass nuclei H², He³, He⁴, and Li⁷ the predicted relative abundance of these nuclides are just what we observe in the universe today. There is plenty of radiation present but light cannot travel far before it interacts with a nucleus. The universe is opaque.
7.       At t=300,000 years, the temperature now fallen to about 10⁴ k and electrons can stick to bear nucleus when they collide forming atoms. Because light does not interact appreciably with uncharged particles such as neutral atoms, the light is now free to travel great distances. Atoms of hydrogen and helium under the influence of gravity begin to clump together, starting the formation of galaxies and stars.

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