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Cosmology- the Study of the Universe Newton opens the door to the universe The same laws of force that apply to the earth also apply to the entire universe. Problem with Gravity If the universe was not infinite, then gravity would pull it back together. If the universe was infinite, then gravity would cause clumping. Newton’s solution was to postulate that the universe was infinite, and also perfectly uniform. The flaw in this solution was that a comet or any other change would break the perfect symmetry and start to clump matter. Problem with infinitely large universe An infinite number of stars results in an infinite amount of light and heat, yet our night sky is dark and cold. Dust can not explain the dark sky, as infinite age and infinite heating would cause it to glow. Current solution The universe is very large, although finite in size. The universe has not been here forever. The universe is expanding. The sky is dark because some light has not had time to reach us, and some light never will. The Einsteinium View – the Growing Universe Before the 1920s, it was believed that the universe consisted of only the Milky Way galaxy. Hubble proved that the “spiral nebulae” were beyond the Milky Way galaxy using the brightness of a Cepheid star to determine distance. The Expanding Universe In 1912, Vestro Slipher used the redshift of light to conclude that all of the objects in the universe were moving away from us. Later in 1929, Hubble demonstrated that at one time, all matter was in one location. This is the start of the big bang theory. Age of universe Speed/distance = Hubble’s constant 1/Hubble’s constant = Age of universe The first calculated age was 1.8 billion years, but we know now that this was way off- 13.7 billion years is the accepted value. Relativity Equation and Universe Expansion During the 1920s, Alexander Friedmann and Georges Lemaitre independently concluded that the universe had to be either expanding or contracting. Einstein built in a fudge factor to prevent expansion called the cosmological constant, though he would later call this his biggest blunder. It is space itself that is expanding. The balloon analogy for expansion The galaxies separate from each other just as dots on a balloon separate as the balloon is inflated. Gravity keeps the galaxies from expanding as they separate. The furthest galaxies are speeding away from us faster than the speed of light. Space expanding does not violate the speed of light speed limit. Evidence of Big Bang Velocity and distance calculations of any galaxy results in the fact that each one started off at the same location. Microwave (heat) radiation left over from the big bang (2.7 K)– as space expanded, radiation was stretched out from short wavelengths to longer waves. Big Bang Theory fate of universe If there is enough mass in the universe, gravity will stop expansion and pull the universe back into another big bang. If there is not enough mass, gravity cannot stop the expansion. The Modern View (quantum mechanical) There had to be some asymmetry at the big bang, or the universe would have canceled out, and we would not be here. This asymmetry shows up in the WMAP satellite map of the 2.7 K heat radiation left over from the big bang. What we know Looking back in time, we know how the universe has shaped and evolved up to the very instant of the big bang. Read Phases of the Universe, pages 104 to 107, of Parallel Worlds. What we don’t know The source of the big bang. What the mysterious “dark matter” that actually makes up the majority of the matter of the universe is. What “dark energy” is. Dark Matter In the 1930s, Fritz Zwicky noticed that the Coma cluster of galaxies were rotating so fast that they should fly apart. In 1962, astronomer Vera Rubin studied the rotation of the Milky Way galaxy and found the same problem. In 1978, Rubin and her colleagues had examined eleven spiral galaxies, all of which were spinning too fast to stay together. Dark Matter It bends light, like anything with mass. About 25% of the universe is dark matter, whereas only 5% is our known matter. There is no agreement as to what dark matter is. Dark Energy Dark energy is a theoretical construct to help explain the observed expansion of the universe, so it may or may not be real. To understand dark energy, you need to understand Friedmann’s simplification of Einstein’s equation. Friedmann’s Simplification of Einstein’s equation Friedmann assumed that the universe was isotropic, or the same from all directions. He also assumed that the universe was homogeneous, or totally uniform. Three input numbers for description and fate of universe H- the expansion number, Hubble’s constant. Omega- the average density of matter in the universe . Lambda - the amount of dark energy in the universe. Omega and Critical Density at zero Lambda The critical density is 10 H atoms/m3. If the omega value is greater than the critical density, the universe will be positively curved, like a sphere, and come back together. If omega is less than the critical density, the universe will be negatively curved, like a saddle, and expand forever. If omega is equal to the critical density, the universe will be flat and expand forever. Surprising Result Scientists found the universe to be flat, and yet omega, the mass density, was only found to be 30% of the value it needed to be for a flat universe. The mass used in the calculation included dark matter. Conclusion: there must be even much more “stuff” in the universe than the known matter (5% of universe) and dark matter (25% of the universe). This mysterious “other stuff” must make up 70% of the universe. More Surprises Close examination of red-shift data from distant galaxies showed that the rate of universe expansion was actually increasing. This was an impossible result- gravity should be slowing the expansion down, not speeding it up. It was now impossible to fit the data with any value of Omega. The solution Scientists had to reintroduce Lambda as a repulsive, antigravity type of energy (dark energy). When Lambda was adjusted to fit the known expansion acceleration it accounted for about 70% of the “stuff” in the universe. This was also the value required for the known flatness of the universe What could dark matter be? Hydrogen, helium, lithium, and other atoms are unlikely, because observed matter matches calculated matter. Neutrinos are all around us, and yet undetectable, like dark matter- however, this is unlikely because their mass is too low. Supersymmetry particles (sparticles), although undetected, are candidates. Dark Energy Homogeneous. The mass equivalent of its energy density is 10-29 g/cm3. It is very difficult to detect directly. When the volume of the universe doubles, the density of matter is cut in half, but the dark energy density is nearly unchanged. The Universe as a Free Lunch 0 = 1 + (-1). Mathematically, something from nothing seems possible with opposites. This seems to violate the first law of thermodynamics (which states that energy cannot be created or destroyed). Can we find an example of nothing to something or something to nothing in nature? Cancellation of light Light is its own opposite, and will cancel if it is exactly out of phase. Let’s explore, and see what happens to the energy upon cancellation. Examples of light cancellation Thin film interference – The light does not exist where waves “cancel”; however, energy is not lost, because light transmits 100% instead. Using out of phase, superimposed radio transmitters, waves cancel; however, energy is not lost, because transmitters stop drawing energy at all. These examples are not something from nothing. Negative – Positive energy concept seems to work Negative energy comes from the Heisenberg uncertainty principle. Quantum jitters fluctuate above and below the zero energy line of a vacuum. Virtual particle pairs of positive and negative energy pop in and out of existence. The Casimir Effect is evidence of this. Evidence of a something-fromnothing universe “Nothing” has zero spin– the spin of everything in the universe adds up to zero. Similarly, “nothing” has zero charge– all the charge in the universe adds up to zero. The Big Bang Process A broader understanding of “Condensation” Use the term to apply to almost any change that happens as a result of cooling temperatures Condensation example – First look at reverse process As heat is added ice melts to water As heat is added water vaporizes to gas Water vapor breaks into O2 and H2 O2 and H2 separate into O and H atoms The electrons are driven off of O and H (plasma) The O and H nuclei start to break down The reverse (cooling) process results in condensations Plasma of electrons and H and O nuclei “condense” into H and O atoms H and O atoms “condense” into H2O gas H2O gas condenses into liquid water Liquid water “condenses” into solid water Before 10-43 seconds (Planck Era) Almost nothing is known considered a “singularity” (the math breaks down such as infinities at a point) four forces were all unified into one “superforce Planck Length of 10-33 centimeters 10-43 to 10-35 seconds, (Inflation era) gravity split off of the superforce 10-35 sec, Strong force splits off – starts inflation supper cooled Higgs field results in inflation Tremendous amounts of potential energy liberated potential energy into heat and particles almost identical number of particles and antiparticles Inflation continued extremely high energy gamma rays Matter and energy interchangeable and in equilibrium quarks, gluons, leptons, antiparticles super heated plasma “soup” Inflation provided “bang” for expansion Inflation insured that universe will be “flat” 10-34 seconds to 1 second (end of inflation) Start - universe size of our solar system Antimatter combines with matter = light Friedmann expansion – gravity slows expansion Dark energy not yet a factor quarks “condensed” into groups of 3 (baryons) Proton, neutron, neutrino, electron plasma 1 second to 4 minutes protons and neutrons were almost equal at the start With cooling temps neutrons broke down to form protons and electrons 86% proton, 14% neutron Universe cools and protons and neutrons form helium nuclei After a few minutes mostly hydrogen nuclei, helium nuclei, and electrons universe is still a high temperature plasma The only element nuclei that existed at that time was hydrogen and helium in a 3:1 ratio and trace lithium No larger elements at this time 4 minutes to 380,000 years Universe continues to cool as it expands Friedmann expansion – gravity slowing it down a bit Radiation wavelength expands with space (gamma > x-ray > UV) Radiation interacted with electrons Universe was opaque to “light” 380,000 years - 3,000 K (The dawn of light) Light weakens to less than the ionization energies of hydrogen and helium (the UV range) electrons and nuclei condense to form hydrogen and helium atoms The universe becomes transparent to light Wavelengths increase to visible range Back Into darkness As the universe continues to cool the wavelength continues to lengthen until it completely enters the IR range. The universe went from white to red to darkness The hydrogen and helium gasses continue to be bathed in heat radiation One billion years, 18 K universe is now extremely cold (18 K) as a result on a very slight asymmetry at the very start of the universe giant H and He clouds form The first stars ignite - there are now points of light in the universe Universe about 1/5 of its current size 6.5 billion years (de Sitter expansion) The space between galaxies continues to expand dark energy becomes a significant factor As dark energy increases the expansion of the universe accelerates de Sitter expansion Stars evolve, galaxies and planets form Life and death of star creates more elements Protons and electrons are compressed and heated to create neutrons Hydrogen combines to make helium Hydrogen is used up and star shrinks, heats up more and burns helium to form element up to the size of iron Once helium is used up star collapses and forms larger elements in a super nova 13.7 billion years (now) Dark energy continues to speed up expansion of the universe In view of the fact that we still know little about 96% of the universe, we will end this course with Newton’s quote. “I do not know what I may appear to the world; but to myself I seem to have been only like a boy, playing on the sea shore, and diverting myself, in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me.”