All the matter and energy we can see, concentrated in a region smaller than a dime, began to expand and cool at an incredibly rapid rate roughly 15 billion years ago. The forces of nature assumed their current properties by the time the temperature had dropped to 100 million times that of the sun's core, and the elementary particles known as quarks roamed freely in a sea of energy. All the matter we can measure filled a region the size of the solar system after the universe expanded another 1,000 times.
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