BIG BANG

BIG BANG THEORY

OVERVIEW

Big bang theory is the prevailing cosmological model that describes the early development of the universe.According to the theory the big bang will be approximately 13.798(+-)0.037 billion years ago, which is thus considered the age of the universe.
At this time the universe was in an extremely hot and dense state and began expanding rapidly.

• After the initial expansion , the universe cooled sufficiently to allow energy to be converted in to various subatomic particles, including protons, neutrons and electrons.
• Though simple atomic nuclei formed within the first three minutes after the big bang.
• While the scientific community was once divided between supporters of two different expanding universe theories- the big bang and the study state theory, observational conformation of the big bang scenario came with the discovery of cosmic microwave background radiation in 1964.
• And later when its spectrum was found to match that of thermal radiation from a black body.
• Since then , astrophysicists have incorporated observational and theoretical in to the big bang model.
• The parametrization as the Lambda CDM model serves as the framework for current investigations of theoritical cosmology.

Timeline of the bigbang:

• Extrapolation of the expansion of the universe backwards in time using general relativity yields and infinite density and temperature at a finite time in the past.
• This singularity signals the breakdown of the general relativity.
• How closely we can extrapolate towards the singularity is debated- certainly no closer than the end of the planck epoch.
• All of this cosmic evolution after the inflationary epoch can be rigorously and modeled by the ACDM model of cosmology.
• Which uses the independant frameworks of quantum mechanics and Einsteins general relativity.
• As noted above, there is no well supported model describing the action prior to 10(-15) seconds or so.

Underlying assumptions:

• If the large scale universe appears isotrophic as viewed from earth, the cosmological principle can be derived from the simpler copernican principle.
• Which states that there is no preferred observer or vantage point.
• To this end the cosmological principle has been confirmed to a level 10(-5) via observations of the CMB.
• The universe has been measured to be homogenous on the largest scales at the 10% level.

FLRW metric :

• The big bang is not an exploision of the matter moving outward to fill an empty universe.
• Instead , space itself expands with time everywhere and increases the physical distance between two comoving points.
• Because the FLRW metric assumes a uniform distribution of mass and energy , it applies in our universe only inlarge scales  - local concerntrations to our matters such as galaxy are gravitationally bound and as such do not experience the large scale expansion of space.

Horizons :

• Our understanding of the universe back to very early times suggests that there is a past horizon recedes in space.
• If the expansion of the universe continues to accelerate , there is a future horizon as well.

Etymology :

• Fred hoyle is credited with coining the term " Big bang " during a 1949 radio broadcast.
• It is popularly reported that hoyle, who favoured an alternative "steady state" cosmological model .
• Intended this to be pejorative, but hoyle explicitly denied this and said it was just striking image meant to highlight the difference between the two models.

Development :

• Scientific process in big bang cosmology have been made since the late 1990's since the result of advances in telescope technology as well as the analysis of data from satellites such as cobe, the Hubble space telescope WMAP.
  
  
  
  
  
  
  
  
  
  
  
• Cosmologists have fairly precise and accurate measurements of many of the parameters of the big bang model and have made the unexpected discovery that the expansion of the universe appears to be accelerating.

Observational evidence:

• The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law.
• Most recent evidence includes observations of galaxy formation and evolution and the distribution of large scale cosmic structures.
• These are sometimes called the four pillars of the big bang theory.

Problems:

Horizon problem:

• The horizon problems results from the premise that information cannot travel faster than the light.
• Heisenberg's uncertainity principle , predicts that during the inflationary phase there would be quantum thermal fluctuations , which would be magnified with cosmic scale.
• These fluctuations serves as seeds of all current structure of the universe.
• If inflation occured, exponential expansion would push large regions of space well beyond our observable horizon.

Magnetic monopoles:

• The magnetic monopole objection was raised in late 1970's.
• Grand unification theories predicted topological defects in space that would manifest as magnetic monopoles.
  
  
  
  
  
  
  
  
  
  
  
  
  
• This problem is also resolved by cosmic inflation , which removes all point defects from the observable universe in the same way that it drives the geometry to flatness.

Religious and Philosophical interpretations :

• As a relevant to the origin of the universe, the big bang significant bearing on religion and philosophy.
•  As a result it became one of the liveliest areas in the discourse between science and religion.
• Some believe the big bang implies a creator, while others argue the bigbang cosmology makes the notion of creator    superfluous.

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