Ch 6: The Origin and Fate of the Universe | A Brief History of Time | Summary
What really happened during the very early or late stages of the universe when the gravitational fields are so strong that quantum effects couldn’t be ignored? Does the universe in fact has a beginning or an end? And if so, what could they likely be?
At big bang, the universe is thought to have been infinitely hot but with the expansion, the temperature decreased. Just a second after the big bang temperature might have dropped down by ten thousand million degrees. At the time the universe might just consist of photons, electrons and neutrinos and their anti-particles with some protons and neutrons. About one hundred seconds later after the big bang, the temperature would have fallen to one thousand million degrees. At this high-temperature protons and neutrons would no longer be able to escape the attraction of strong nuclear force but rather begin to combine together to form nuclei of atoms of deuterium which, in turn, would combine to form the nucleus of heavier elements like lithium and beryllium. Within only a few hours of the big bang, the formation of helium and other elements would have stopped and after that, for around a million years the, the universe would just have continued to expand with not much-a-happenings.
When the temperature might have dropped to a few thousand degrees, the electrons and nuclei would not have enough energy to overcome the electromagnetic attraction and would, thus, have started combining to form atoms. The expansion of the slightly denser regions would have been slowed down due to their gravity and would have eventually re-collapsed. The gravitational pull of the surrounding matter caused them to rotate. The smaller regions rotated at a speed to balance off their gravitational force and in this way, the rotating galaxies were formed. With the passage of time, the hydrogen and helium gas in the galaxies would break up into smaller clouds which would collapse under their own gravity. Their inter-atomic collisions lead to the nuclear fusion converting hydrogen to helium and the released heat prevented the cloud from further contracting. The earth was initially very hot without any atmosphere but in the due course of time, the emissions from the rocks and other forms that developed later formed the atmosphere that we have today.
To get a clearer picture of the universe, a principle developed, known as the anthropic principle. There are two versions of this: weak and strong. The weak anthropic principle states that in a universe large and infinite in space and/or time, the conditions necessary for the development of intelligent life will be met only in certain regions that are limited in space and time. The strong principle suggested that there are either many different universes or many different regions of a single universe, each with its own initial configuration and perhaps with its own set of laws of science.
If the universe is really completely self-contained, having no boundary or edge, it would neither have a beginning nor an end; it would just simply be. What place for a creator then?
[ A chapter’s summary from the great book A Brief History of Time -By Stephen Hawkins].
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