Transcript Unit 1
EXAMS: Group Lec 002 May 15, 2:45-4:45pm Van Vleck B102 Group Lec 001 May 16, 12:25-2:25pm Camberlin 2103 A Timeline of the Universe The Origin of Helium • • • • • Immediately after the Big Bang, only protons and electrons existed Shortly after the BB, temperature and density was high enough for deuterium to form by fusion After 100 seconds or so, temperature cooled enough so that deuterium could fuse into helium nuclei The temperature continued to cool, and fusion stopped after a few minutes. Big Bang theory predicts that around 24% of the matter in the early universe was helium, which matches what we see. The Epoch of Inflation • Modern technology allows us to test theories back to a time 10-33 seconds after the Universe Birth (UB). • Physics as we know it ceases to function at 10-43 seconds after the UB, called the Plank Time • Using particle colliders, scientists have uncovered a number of clues about what happened in the early universe, after the Plank time • The early universe underwent a period of very rapid expansion • By 10-33 seconds, the universe expanded from the size of a proton to the size of a basketball • This expansion is called inflation Expansion Forever? Or Collapse? • The fate of the universe is ultimately controlled by its total amount of energy – Energy of expansion (positive) – Gravitational energy that can slow the expansion (negative) – Binding energy • If the total energy is positive or zero, the expansion continues forever • If the total energy is negative, the expansion will halt, and the universe will contract and eventually collapse. Dark Energy • Dark energy may provide the solution to the mystery • Dark energy remains constant everywhere, regardless of the universe’s expansion • Provides an outward push to accelerate expansion • Dark energy must make up around 70% of all of the energy in the universe • Much work remains to be done on this frontier… Life on Earth • Life formed on Earth relatively soon after the planet’s formation – For ¾ of the Earth’s history, only algae and single-celled life forms existed – Slowly, more complex lifeforms developed • By 250 million years before the present, dinosaurs and early mammals had evolved. • Hominids, our distant ancestors, developed 5.5 million years ago • Homo Sapiens evolved only 500,000 years ago! Figure 83.04 • Life tends to draw on the substances that are most plentiful: Carbon, Nitrogen, Oxygen and Hydrogen • Amino acids are organic molecules containing these substances • Amino acids form proteins, which provide structure and energy to cells • All life contains DNA – this instruction packet contains all the information needed to build an organism The Origin of Life • So how did amino acids form out of the substances available on the early Earth? • Probably started thanks to complex chemical reactions in the atmosphere and surfaces of Earth • The Miller-Urey experiment attempted to duplicate the environment of the early Earth • A variety of complex organic molecules formed in their “atmosphere” Fossil Eukaryote Algae The Search for Life on Mars • It appears that Mars at some point in its history was very much wetter and warmer than it is today • Scientists have been looking for life there • The Viking landers (1970’s) tested for the presence of microbes, but returned inconclusive results • We are still looking! Fossils of Ancient Martian Life? SETI • SETI: Search for Extra-Terrestrial Intelligence • Listens for electromagnetic evidence of intelligence elsewhere in the universe • To date, evidence has been sparse.