Part 2: Development Of The Theory

The Big BangA Muslim Perspective :The Big BangA Muslim Perspective Part 2: Development of the Theory

Human Curiosity! :Human Curiosity! What existed then at the beginning of the universe? How did it begin, and why? Why did it take the form it did? Who are we? Where did we come from, and why for? Where are we going?

Development of the Big Bang Model :How did this vast cosmos, awesome in beauty and extent, come into being? The general theory of relativity provides the ideas we use to understand space, time and gravity. The theory of relativity predict that our universe should have the big bang, a beginning of time. Development of the Big Bang Model

Is the Universe Static? :Albert Einstein, who in 1915 published the general theory of relativity, was sure that the universe is static, so he introduced a so-called cosmological constant into his equations. This was a new antigravity force assumed to be built into the very fabric of space-time and gives it an inbuilt tendency to expand. This could be made to exactly balance the attraction of all the matter in the universe so that a static universe would result. Is the Universe Static?

The Expansion of the Universe :Alexander Friedmann, 1922, made two very simple assumptions about the universe: 1-The universe looks identical in whichever direction we look; 2-This would be true if we were observing the universe from anywhere else. On the basis of general relativity and these two assumptions, he showed that the universe was not static but instead expanding. Edwin Hubble, 1929, observed exactly what Friedmann predicted that all galaxies were moving away from us, the farther the galaxy was, the faster it was moving away. The Expansion of the Universe

The Hot Early Universe :At the big bang the universe had zero size and so must have been infinitely hot but as the universe expanded, the temperature of the radiation would have decreased. George Gamow, 1948 was the first to put forward this picture of a hot early stage of the universe and made a remarkable prediction that radiation from the very hot early stages of the universe should still be around today. This is the cosmic microwave background of radiation that was discovered by Penzias and Wilson in 1965 (approximately 2.7 Kelvin). The Hot Early Universe

Evidence for Early Hot Universe:The Microwave Background Radiation :Evidence for Early Hot Universe:The Microwave Background Radiation

The Birth of the Theory :Roger Penrose, 1965 showed that a star that collapses under its own gravity is trapped in a region whose boundary eventually shrinks to zero size. This means that all the matter in the star will be compressed into a region of zero volume, so the density of matter and the curvature of space time become infinite. In other words, one has a singularity contained within a region of space-time known as a black hole. The Birth of the Theory

The Birth of the Theory :Stephen Hawking (1965) assumed that if the direction of time is reversed in Penrose’s theorem so that the collapse became expansion, the conditions of his theorem would still hold. Penrose’s theorem had shown that any collapsing star must end in a singularity; the time-reversed argument showed that the expanding universe as described by Friedmann’s model must have begun with a singularity. The final result was a joint paper by R. Penrose and S. Hawking (1970) which showed that the universe started from a big bang singularity, the primeval explosion that brought all space and time, all matter and energy, into being. The Birth of the Theory

The Hot Big Bang ModelThe Big Bang Singularity :At some point in the past, between ten and twenty thousand million years ago, the distance between the neighbouring galaxies must have been zero. At this stage which is known as the big bang singularity, the density of the universe and the curvature of space time would have been infinite; therefore, the general relativity and all other physical laws would break down. One cannot predict what would come out of the singularity. The Hot Big Bang ModelThe Big Bang Singularity

One Second Old!Radiation & Sub-atomic Particles :One Second after the big the bang the temperature would have fallen to about ten thousand million degrees. At this time the universe would have contained mostly photons, electrons, and neutrinos and their antiparticles, together with some protons and neutrons. One Second Old!Radiation & Sub-atomic Particles

100 Seconds to 100 hrs Plasma of Light Elements :About one hundred seconds after the big the bang, the temperature would have fallen to one thousand million degrees where protons and neutrons would no longer have sufficient energy to escape the attraction of the strong nuclear force. They would start to combine together to produce the nuclei of atoms of deuterium or heavy hydrogen. The deuterium nuclei would then have combined with more protons and neutrons to make helium nuclei; there would also be small amounts of a couple of heavier elements, lithium and beryllium. Within only a few hours of the big bang, the production of nuclei of helium and other elements would have stopped. 100 Seconds to 100 hrs Plasma of Light Elements

Formation of Atoms :In the next million years or so when the temperature had dropped to a few thousand degrees, the electrons and nuclei would no longer have had enough energy to overcome the electromagnetic attraction between them. They would then have started combining to form atoms. Formation of Atoms

Formation of Galaxies :The universe as a whole would have continued expanding and cooling. In regions that were slightly denser than average, the expansion would have been slowed down by extra gravitational attraction. This would have eventually stop expansion in some regions and cause them to start to collapse. The gravitational pull outside these regions may cause them to rotate slightly and as the collapsing region gets smaller, it spins faster and eventually balances the attraction of gravity. In this way the disk-like rotating galaxies like our own galaxy, The Milky Way, were born. Formation of Galaxies

Formation of Stars :As time went on the gas in the galaxies would break up into smaller clouds that would collapse under their own gravity. As these concentrated, the temperature of the gas would increase until it became hot enough to start nuclear reactions. These would convert the hydrogen into more helium and the heat given off would raise the pressure, and so stop the clouds from contracting any farther. They would remain in this state for a long time as stars like our own sun, burning hydrogen into helium and radiating the energy as heat and light. Formation of Stars

Eagle Nebula: The Pillars of Creation :Eagle Nebula: The Pillars of Creation

Formation of our Solar System :Our own sun contains about 2% of heavier elements like carbon and oxygen because it is a second or third generation star. It was formed some five thousand million years ago out of a cloud of rotating gas containing debris of earlier supernovas. Most of the gas in that cloud went to form the sun or got blown away. However, a small amount of the heavier elements collected together to form the bodies that now orbit the sun as planets like the earth. Formation of our Solar System

Shall we put it this way? :S. Hawking: This picture of a universe that started off very hot and cooled as it expanded is in agreement with all observational evidence that we have today. We are therefore thoroughly confident that we have the right picture, at least back to one second after the big bang. Shall we put it this way?