Lesson 12, Topic 1
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The Big Bang Theory

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The Big Bang Theory asserts that time and space in our universe began from an incredibly hot point called a singularity about 13.8 billion years ago. The Big Bang is an expansion of space rather than an explosion and the theory assets that the universe has been expanding and cooling for the past 13.8 billion years.

In the first microsecond after the Big Bang, huge numbers of subatomic matter-antimatter pairs (e.g. quarks, neutrinos and electrons) were produced by photons as the universe began to expand and cool. For some unknown reason, the radiation produced one extra matter-particle per billion anti-matter pairs. This small excess of matter accounts for all the matter we see in the universe today.

As the universe expanded and cooled, quarks combined to form hadrons (e.g. protons and neutrons) and, after further cooling, some helium nuclei and a small number of lithium nuclei were formed in a process called nuclear synthesis.

20 minutes after the Big Bang it was too cool for nuclear synthesis to continue and, after 250 000 years, electrons began to combine with nuclei to form atoms.