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Chapter 23

Chapter 23 Summary Cosmic Perspective

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Western University
Astronomy 1021
Chris Racknor

CHAPTER TWENTY THREE The Beginning of Time Predicting the conditions of the early universe is straightforward as long as we know how matter and energy behave under such extreme conditions Our current understanding of physics allows us to reconstruct the conditions that prevailed in the universe all the 103843way back to the first 10 second our understanding is less certain back to the 10 second beyond 10 second we run up against the present limits of human knowledge Although it may sound strange to talk about the universe during its first fraction of a second our ideas about the Big Bang rest on a solid foundation of observational experimental and theoretical evidence we cannot say with absolute certainty that the Big Bang really happened but no other model has so successfully explained how our universe came to be as it is Conditions of the Early Universe The early universe was filled with radiation and elementary particles it was so hot and dense that the energy of radiation could turn particles of matter and antimatter which then collided and turned back into radiation History of the Universe According to the Big Bang Theory The universe has progressed through a series of eras each marked by unique physical conditions we know little about the Planck era when the four forces may have all behaved as one gravity became distinct at the beginning of the GUT era which may have ended with the rapid expansion called inflation electromagnetism and the weak force became distinct at the end of the electroweak era matter particles annihilated all the antimatter particles at the end of the particle era fusion of protons and neutrons into helium ceased at the end of the era of nucleosynthesis hydrogen nuclei captured all free electrons forming hydrogen atoms at the end of the era of nuclei galaxies began to form at the end of the era of atoms and the era of galaxies continues to this day Observing Radiation Left Over from the Big Bang Telescopes that can detect microwaves allow us to observe the cosmic microwave background which is radiation leftover from the Big Bang its spectrum matches the characteristi
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