Big Bang

Big Bang.

These words were first aired on a BBC radio show when Sir Fred Hoyle was describing the two theories of creation of the universe at that time: Dynamic evolving model and Steady state model. He used these two words to describe the Dynamic evolving model of the universe which he opposed throughout his life even when there were much observational evidence and almost every scientist accepted it.

At first Einstein was also in favor of the steady state model. He used cosmological constant so that the equations do not predict a collapsing universe.

But Alexander Friedmann used equations of general relativity to show that different values of cosmological constant give rise to different fate of universe,

1.      It expands and then contracts

2.      Continuous expansion

3.      Neither collapses nor expands

Even though Einstein found Friedmann’s calculations correct, he refused to believe in such a dynamical universe. So Friedmann’s work didn’t become popular.

Later Georges Lemaitre rediscovered all these facts without knowing Friedmann had already gone through same thought process. Using the concept of radioactive decay Lemaitre speculated that on a greater scale a similar process might have given birth to the universe. By extrapolating backwards in time the universe began in a small compact region from which it exploded outward he found all the stars squeezed into a super compact universe, which he called primeval atom.

In his words,

“The evolution of the universe can be likened to a display of fireworks that has just ended: some few wisps, ashes and smoke. Standing on a well-cooled cinder, we see the fading of the suns, and try to recall the vanished brilliance of the origins of the worlds.”

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But at that time there were no observational evidence to these theories. Later when Edwin Hubble using his observational data (of red shifted galaxies) & drew a graph which showed a linear relationship between the distance and velocity of galaxies, scientists concluded that if galaxies are moving away from us, in past they must have been closer to each other.

 v = Hd

Using this equation, if we know the speed of a galaxy, its distance can be calculated. And we can also evaluate the time when the galaxies were closer to each other. As the measurements became more accurate, age of the universe came out bigger and it was concluded between 10 – 20 billion years.

Ralph Alpher and Robert Herman proposed that the oldest light in the universe which spread everywhere 300000 years after the creation can be taken as the test for big bang model.

Later Robert Wilson and Arno Penzias detected signal from space which was proved to be the echo from the big bang: the cosmic microwave background radiation (oldest light in the universe). Since steady state model does not predict this radiation, it was now clear that the universe started billions of years ago with Big Bang.

But still scientists including Fred Hoyle along with Jayant Vishnu Narlikar were working on steady state model, and developed it to a new Quasi-steady state model.

Since the CMB radiation detected is just a few thousand years older than the universe’s creations. So any density variation at that time would have given rise to the density variation later like galaxies. After many efforts and other experiments COBE (Cosmic Background Explorer Satellite) was launched on 18 Nov. 1989. COBE had four detectors and its main purpose was to observe the density variations in CMB radiation. Later WMAP (Wilkinson Microwave Anisotropy Probe) launched in 2001, provided more data and thus the age of the universe was calculated to be 13.8 billion years and it also became known that universe 23% Dark Matter, 73% Dark Energy, 4% Ordinary Matter.