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Lecture 3

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Ryerson University
PCS 181
Margaret Buckby

PCS 181 – CLASS 5 Future of an open or flat universe Time after Big Bang Situation 12 1. 1 x 10 years - Hydrogen and helium are depleted -> no new stars can form (hydrogen and helium clouds have been used up for 2. 1 x 10 years formation of stars so new stars can’t born ) - Existing stars run out of fuel 3. 1 x 10 years - All stars will have experienced ~10 disruptive encounters, flinging their planets into space 4. 1 x 10 years - Evaporation of stars and collapse of galaxies into the central Black Holes 30 5. 1 x 10 years - Protons decay (???) - P -> e + v(a positron and neutrino) - e + e ->Y (a photon= a burst of radiative 100 6. 1 x 10 years energy) - Hawking-> Black Holes decay (research report) 7. Far future - The big fizzle = an ever-expanding gas of electrons, protons, neutrons, photons Black hole – a lot of matter in small volume space. Collapse of material into small volume space Super massive black holes – one in Milky Way. Millions of times a black hole Einstein-Rosen (research topic) Future of a closed or oscillating universe 1. The expansion phase = statements 1. Through 5. Above 2. At some unknown future time, re-contraction begins. The density of the universe increases, the number of Black Holes increases. They feast on everything within reach. 3. Black holes will meet and coalesce (merge) into ONE Black Hole=the universe=the new singularity = THE BIG CRUNCH How to decide among these futures - Is there sufficient matter to exert a strong gravitational force? 3 > 5 protons per m of space  gravity will dominate and re-contract the universe  a closed or oscillating universe < 5 protons per m of space  gravitational attraction among all particles is insufficient to “close” the Universe  an open Universe that expands forever Density measurement of universe The sum of all observed, luminous matter-> NOT enough matter to re-collapse the Universe. What about non-luminous matter? Clouds of dark gas, planets, dead stars, Black Holes, neutrinos….DARK MATTER (Vera Rubin) DARK MATTER - A Galaxy Rotation Curve - Plots star velocities vs. their distance from the center of the galaxy. - Vera Rubin -> star velocities measured at the edge of a galaxy violates Newtonian and Keplerian laws. E.g. speed of star a=speed of star b - KEPLER AND Newton - A galaxy’s rotation curve compares the disk stars’ velocities with their distances from the galaxy’s center - Invisible material called DARK MATTER permeates the galaxies - It exerts a gravitational influence on the stars causing them to deviate from Newton’s and Kepler’s laws - DARK MATTER also affects me
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