HENNING DALHOFF / SCIENCE PHOTO LIBRARY HENNING DALHOFF / SCIENCE PHOTO LIBRARY
Big Bang. Computer illustration of particles forming from the Big Bang in the early universe. The universe is thought to have formed in this huge explosion between 12-15 billion years ago. Particles are thought to have formed as the universe cooled down: first discrete quarks, which then combined to form protons (brown), neutrons (yellow) and electrons (blue). The first atoms formed when electrons began to orbit groups of protons and neutrons (atomic nuclei, lower right).
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