epsc midterm.docx - Question 1 1 The\"Big Bang is our current best model for the origin and evolution of the Universe Sequentially starting with the

epsc midterm.docx - Question 1 1 The"Big Bang is our...

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Question 1 1. The "Big Bang" is our current best model for the origin and evolution of the Universe. Sequentially, starting with the moment of the "Big Bang" very briefly explain the evolution of the Universe. Address the formation of matter, expansion, cooling and the first cycle of stellar formation. __________________________________________________________________________________ All matter was created the first instant, modified to produce the first atoms, H and H+=deuterium Singularity Epoch Earliest period Matter condensed on a single point of infinite density and extreme heat From point 0 to approximately 10-43 second Due to the extreme heat and density of matter, the state of the universe was highly unstable. It thus began to expand and cool An expanding Universe? “When did it all begin?” The Big Bang: all mass and energy in a single point It exploded ~13.8 Ga and has been expanding ever since. Cosmologists have developed models of the Big Bang: During the first instant, only energy—no matter—was present. Then, started a rapid cascade of events…. Inflation Epoch A period where the universe grew exponentially The incredibly high temperatures and pressure gave rise to rapid expansion and cooling. Where the phase transition that caused for the separation of forces also led to a period where the universe grew exponentially. Temperatures were so high that the random motions of particles occurred at relativistic speeds. After inflation stopped, the Universe began to cool and matter coalesced and formed.
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Cooling Epoch Few seconds after the Big Bang, energies dropped considerably. A few minutes into the expansion, the period known as Big Bang nucleosynthesis also began. Thanks to temperatures dropping to 1 billion kelvin and the energy densities dropping, o Hydrogen nuclei (protons) within a few seconds o At 3 minutes, protons are fused to form helium nuclei. o Light nuclei (atomic no. < 5) by Big Bang nucleosynthesis The Universe expanded and cooled. After about 380,000 years, electrons combined with these nuclei to form atoms (again, mostly hydrogen) The radiation decoupled from matter and continued to expand through space (Cosmic Microwave Background, CMB), which today is the oldest light in the Universe. The CMB can be seen in all directions at a distance of roughly 13.8 billion light years, but estimates of its actual distance place it at about 46 billion light years from the center of the Universe. After about 380 000 years of expansion and cooling, atoms began to bond; electrons attached to the nuclei. o Hydrogen formed H2 molecules—the fuel of stars. o Atoms and molecules coalesced into gaseous nebulae. Structure Epoch Over the course of the several billion years that followed, the slightly denser regions of the almost uniformly distributed matter of the Universe began to become gravitationally attracted to each other.
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