All of this occurred within the first minute of the expansion. After the universe had grown by another factor of 1,000, protons and neutrons combined to form atomic nuclei, including most of the helium and deuterium present today. ![]() When the universe had expanded an additional 1,000 times, all the matter we can measure filled a region the size of the solar system.Īt that time, the free quarks became confined in neutrons and protons. By the time the temperature had dropped to 100 million times that of the sun’s core, the forces of nature assumed their present properties, and the elementary particles known as quarks roamed freely in a sea of energy. He describes these ideas in this article, which he co-wrote for Scientific American in 1994.Īt a particular instant roughly 15 billion years ago, all the matter and energy we can observe, concentrated in a region smaller than a dime, began to expand and cool at an incredibly rapid rate. ![]() Editor’s Note (10/8/19): Cosmologist James Peebles won a 2019 Nobel Prize in Physics for his contributions to theories of how our universe began and evolved.
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