Big Bang(Book review)

The Big Bang model of the universe is perhaps the most important and glorious scientific achievement of the 20^th century. It has evolved over several decades and stood the test of time and observational evidence.

Here is a brief description of events that lead to the acceptance of the Big Bang Model

1.        1915 Albert Einstein developed his General Theory of Relativity, which gave a new theory of gravity that explained high-gravity environments better than Newton’s theory of gravity.
   2.       The gravitational implications of the Theory of Relativity meant that everything in universe attracted each other and so the universe should collapse into a singularity. Einstein hated this conclusion and added a “cosmological constant” to the theory with an anti gravitational effect that would act against the attraction and stop the universe from collapsing.
   3.       FriedMann and George Lemaitre ignored the “cosmological constant” and proposed an expanding universe that explained why there was no gravitational collapse. They were both ignored as there was no observational evidence and Einstein vehemently opposed their models.
   4.       The scientist community mostly believed in a static universe.
   5.       Edwin Hubble observed that majority of the galaxies were racing away from us (red shifted). He publishes his famous paper where he shows that the velocity by which the galaxies are receding is directly proportional to their distance (Hubble’s law), possibly implying that all the galaxies started from the same point in spacetime.
   
   
   a.                  Extrapolating the observational results back in time showed that the all the matter in the universe should have started in the same place 1.8 billion years ago.
   
   
   6.       Einstein changes side and supported Big Bang after viewing Hubble’s observations, but he was concerned that the age of the universe calculated as per Hubble’s observation was less than some rocks found on earth that were 3.6 billion years old.
   7.       The major supporters of the Big Bang Gamow, Alpher and Herman came up with a mathematical model of Big Bang using which they were able to explain the relative abundance of Hydrogen (90%) and Helium (9%) atoms in the universe. They failed to explain the formation of heavier elements by nucleosynthesis as they were stuck in the 5 nucleon crevasse.
   8.       Gamov, Alpher and Herman continued their work on the model and predicted CMB (Cosmic Background Radiation) that should be released 300,000 years or so after the moment of creation if the Big Bang model were true.
   a.       Thus discovering the CMB would prove that there was a Big Bang
   b.      They were ignored as theoretical astronomers and nobody searched for the CMB.
   9.       Baade and Sandage detected an error in Hubble’s calculations and recalibrated the age of the universe to 5.5 billion years.
   a.       One hurdle in the Big Bang was resolved.
   10.   Fred-Hoyle over came the 5 nucleon crevasse by predicting the existence of an excited state of carbon (which was never identified before). This was proved later by observation.
   a.       The nucleosynthesis issue with Big Bang was solved.
   11.   Penzias and Wilson accidentally discovered CMB after about 20 years of it being predicted (by Gamov, Alpher and Herman); providing compelling evidence on the Big Bang.
   a.       At this point nearly all cosmologists switched sides to Big Bang
   
   
   12.   The only problem that the non supporters of Big Bang highlighted was that the CMB that arrived from different directions (as observed from earth) did not show any variations in wavelength. This implied that the average density of the particles that resulted from the BigBang was relatively the same which couldn’t justify the observed matter concentration in the galaxies.
   13.   Every attempt to find any variation in the CMB from earth failed.
   14.   1992 the detectors mounted on top of the COBE satellite (headed by scientists George Smoot and John Mather) discovered the variations in the CMB radiation coming from different parts of the sky. COBE indicated tiny variations in density in the early universe, which would have seeded the formation of the galaxies.
   15.   George Smoot and John Mather, received the Nobel Prize in Physics in 2006 for their work on the project.
   a.       Here the Nobel Prize committee’s comment is work noting, "the COBE-project can also be regarded as the starting point for cosmology as a precision science"
   16.   Later the WMAP satellite was deployed that was designed to measure the CMB radiation at thrity-five times better resolution than COBE. The mappings generated by WMAP further confirmed CMB variations and provided convincing evidence that could lead to the observed concentration of matter in the universe.  WMAP also:
   a.       Estimated the age of the universe to be 13.7 billion years with an error of 0.2 billion years
   b.      Identified the composition of universe as 23% dark matter, 73% dark energy and 4% ordinary matter.