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ASTR 113 – 003 Lecture 13 April 26, 2006 Spring 2006 Introduction To Modern Astronomy II Review (Ch4-5): the Foundation 1. 2. 3. 4. 5. 6. 7. Sun, Our star (Ch18) Nature of Stars (Ch19) Birth of Stars (Ch20) After Main Sequence (Ch21) Death of Stars (Ch22) Neutron Stars (Ch23) Black Holes (Ch24) Star (Ch18-24) 1. 2. 3. Our Galaxy (Ch25) Galaxies (Ch26) Active Galaxies (Ch27) Galaxy (Ch 25-27) 1. Evolution of Universe (Ch28) Cosmology (Ch28-29) Extraterrestrial Life (Ch30) 2. Early Universe (Ch29) 1. Extraterrestrial Life (Ch 30) A Short Movie Universe Note: this movie can only run in-class ASTR 113 – 003 Lecture 13 April 26, 2006 Exploring the Early Universe Chapter Twenty-Nine Spring 2006 Guiding Questions 1. Has the universe always expanded as it does today, or might it have suddenly “inflated”? 2. How did the fundamental forces of nature and the properties of empty space change during the first second after the Big Bang? 3. What is antimatter? How can it be created, and how is it destroyed? 4. Why is antimatter so rare today? 5. What materials in today’s universe are remnants of nuclear reactions in the hot early universe? 6. How did the first galaxies form? 7. Are scientists close to developing an all-encompassing “theory of everything”? Inflation Theory: the Isotropy Problem •The temperature of microwave background radiation from all parts of the sky is incredibly uniform, the same to an accuracy of 1 part in 10000 •Point A and B, in the opposite parts of the cosmic light horizon, can not communicate with each other. •Isotropy problem: how is it possible that the unrelated parts of the universe have almost the same temperature? Inflation Theory: the flatness problem •In order for space to be flat as it is today, the mass density must have been exactly equal to critical density right after the Big Bang •If mass density were slightly smaller than the critical density, the universe would have expanded so rapidly that matter could have never clumped together to form galaxies. •If mass density were slightly larger than the critical density, the gravitational attraction would long ago have collapsed the entire universe in a reversed Big Bang or “Big Crunch” Inflation Theory • Because of the isotropy problem and flatness problem, the universe may not expand at the same rate as we see today • Inflation theory: the universe experienced an extremely rapid expansion shortly after the Big Bang • An initially small universe (comparatively, much smaller than the size of the cosmic light horizon) becomes much larger after the inflation Inflation Theory • Inflationary epoch: a short period of 10-32 second, during which the universe expanded by a factor of about 1050 Inflation explains the isotropy •During the inflationary epoch, the parts of the universe, which were originally in intimate contact and thus had the same temperature, were moved out to tremendous distance (larger than the cosmic light horizon) Inflation explain flatness • The observable universe was a tiny fraction of the entire inflated universe that any overall curvature in it is virtually undetectable Trigger of Inflation Four basic forces in nature 1. Gravity, e.g., holding the Earth to the Sun 2. Electromagnetic force, e.g., holding electrons to nuclei 3. Strong force, e.g., holding protons, neutrons together to form nuclei 4. Weak force, e.g., cause neutron decay into proton Trigger of Inflation • • • Studies of particle physics show that the forces may be identical if the energy of particles involved in the interaction is high enough E.g., electromagnetic force and weak force is identical if particle energy is greater than 100 Gev, or equivalently, temperature greater than 1015 K If the temperature of universe became lower as it expanses, the forces will separate, which is called “Spontaneous Symmetry Breaking” Trigger of Inflation • Inflation occurs at 10-35 second after the Big Bang when temperature of universe dropped to 1027 K; at this temperature, strong force became distinct from the electromagnetic-weak force ASTR 113 – 003 Lecture 14 May 3, 2006 Spring 2006 Introduction To Modern Astronomy II Review (Ch4-5): the Foundation 1. 2. 3. 4. 5. 6. 7. Sun, Our star (Ch18) Nature of Stars (Ch19) Birth of Stars (Ch20) After Main Sequence (Ch21) Death of Stars (Ch22) Neutron Stars (Ch23) Black Holes (Ch24) Star (Ch18-24) 1. 2. 3. Our Galaxy (Ch25) Galaxies (Ch26) Active Galaxies (Ch27) Galaxy (Ch 25-27) 1. Evolution of Universe (Ch28) Cosmology (Ch28-29) Extraterrestrial Life (Ch30) 2. Early Universe (Ch29) 1. Extraterrestrial Life (Ch 30) Trigger of Inflation • Inflation occurs at 10-35 second after the Big Bang when temperature of universe dropped to 1027 K; at this temperature, strong force became distinct from the electromagnetic-weak force Create Matter from “Empty” Space • Matter and energy of the universe is created during the inflation • Before the inflation, the space is “empty”, filled with only virtual particles dictated by quantum mechanics Create Matter from “Empty” Space • In quantum mechanics, Heisenberg’s uncertainty principle states that there is a reciprocal uncertainty between position and momentum • Heisenberg uncertainty principle for energy and time: the shorter the time interval, the greater the energy uncertainty, or the greater the mass uncertainty • In “empty space”, pairs of particles and antiparticles can spontaneously appear and then disappear anywhere in space provided that each exists only for a very short time interval • Antiparticle, or antimatter, is the same as the normal particle, but with opposite electric change • The spontaneously created pair of particles from empty space is called virtual pair, since they can not be directly observed Create Matter from “Empty” Space • For instance, the pair of electron and anti-electron (called position) can last for 6.4 X 10-22 s • During the inflation, the universe expanded so fast that particles were rapidly separated and were deprived the opportunity of spontaneous recombination. As a result, virtual particles became real particles in the real world • After the inflation, the universe was flooded with particles and antiparticles Create Matter from “Empty” Space • Annihilation: when a real particle collides with a real antiparticle, they are converted into high energy gamma ray ---the creation of energy • Pair production: inversely, when two gamma-ray photons collide, a pair of particle-antiparticle is created. But the photon energy must be equal or larger than particle energy (E=MC2) Create radiation or photons • Just after the inflationary epoch, the universe was filled with particles, antiparticles and energetic gamma-ray photons • At t=10-6 second, the temperature in the universe dropped to the threshold temperature of 1013 K, at which the photons can not produce proton and anti-proton pairs (and neutron and anti-neutron pairs) • As a result, matter and anti-matter content decreased, and radiation content increased • At about t = 1 second, temperature fell below 6 X 109 K, electrons and positions annihilated to form low energy gamma-ray photons that can not reverse the process, which further raising the radiation content in the universe • From 1 second to 380,000 years, the universe is dominated by the radiation (so called primordial fireball) derived from the annihilation of particles and antiparticles created early by the inflation Create ordinary matter: asymmetry • If there had been perfect symmetry between particles and antiparticles, every particles would have been annihilated, leaving no matter at all in the universe • The stars, galaxies in the Universe are made of matter, not antimatter • There are 109 photons in the microwave background for each proton/neutron in the universe • Therefore, there is a slight but important asymmetry between matter and antimatter • Right after the inflation, for every 109 antiprotons, there must have been 109 plus one ordinary protons, leaving one surviving after annihilation Hydrogen and Helium: relics of primordial fireball • When the universe was 3 minutes older, the temperature was low enough to pass the deuterium (2H, one proton + one neutron) bottleneck to further produce helium • At 15 minutes, the temperature of the universe is too low for any further nucleosynthesis • Therefore, the relics of primordial fireball are hydrogen, helium (1 helium out of every 10 protons), and photons (1 billion photons for every proton) • Heavier elements are formed later in the stars, not in the early universe Density fluctuations in the Early universe • Jeans length: the scale size of density distribution determined by temperature and density • At the era of recombination, temperature was 3000 K, density was 10-18 km/m3, then the Jean length was 100 light years • An object can grow if it exceeds the Jean’s length. Otherwise, it will be dispersed. “Bottom-up” galaxy formation • Galaxies were formed from smaller “galaxy building blocks”, which were later coalesced along filaments Universe may have 11 dimensions • The physical forces are equivalently to the curvature of space, e.g, gravity from mass resembles the curvature of 3 dimension space • The search for a theory that unifies gravity with the other physical forces suggests that the universe actually has 11 dimensions (ten of space and one of time), seven of which are folded on themselves so that we cannot see them