what is “the big bang?” model for how our universe began. states that all matter and energy in...
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What is “The Big Bang?”
• Model for how our universe began.
• States that all matter and energy in the universe were once concentrated at a single point, exploding outward in a huge cosmic explosion.
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What does this model predict?
• 1.) That the universe should be moving outward away from a singular point.
• 2.) That there should be a left-over ‘echo’ from or evidence of this explosion.
• 3.) That the universe’s temperature should be above absolute zero.
• 4.) That there should be a precise ratio of Hydrogen to Helium in the universe.
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•Do NOT take notes on the next few slides! These are just FYI slides….
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History of the Big Bang—How science discovered the Universe had a beginning• Prior to the discovery of the Big
Bang, scientists held that the universe was eternal and infinite, without beginning or end.
1915—Einstein’s theory of general relativity didn’t allow for a static universe. Universe would either be expanding or imploding.
Thus, he added a ‘Universal Constant’ to correct what he thought was an error!
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History, continued
• 1920s: Russian mathematician Alexander Friedman and Belgium astronomer George Lemaitre predicted universe was expanding.• Implied that you could therefore trace this
expansion back to a single origin.• Astronomer Fred Hoyle called this the ‘Big Bang’
(he meant it as an insult), and the name stuck.
• 1929: American astronomer Edwin Hubble discovered the ‘red shift’ in light from distant galaxies, indicating galaxies were moving away from each other at incredibly speeds.• First empirical confirmation of Big Bang.
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History, continued
• 1940s: George Gamow predicts that if Big Bang occurred, background temp of universe should be a few degrees above absolute zero.
• In 1965: two scientists accidentally discovered background radiation (temp) was only 3 degrees above absolute zero.• Since 1965, more evidence has been
gathered to support the Big Bang.
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• Quantum physics and particle accelerators have helped scientists predict what may have happened within 1/10 million trillion trillion trillionths of a second after the Big Bang occurred.
• The Big Bang model dispelled the notion that the universe is eternal and infinite, demonstrating instead that the universe had a definite beginning.
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Basic Overview
• All matter and energy concentrated into one point.
• For unknown reasons, point explodes outward.
• Basic particles form, then atoms of hydrogen and helium.
• Over time, through gravity and other physical laws, clouds of hydrogen and helium condense to form stars.
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Overview, continued
• Fusion in stars forms heavier elements.
• Supernova explosions force these elements and debris into space.
• Clouds of dust, gas, and debris accrete to form planets and planetoids.
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• Okay, now it’s time to start writing again….
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Evidences for the Big Bang• The Red Shift
• Light from distant galaxies is shifted toward red end of the visible light spectrum.
• Indicates they are moving away from each other – wavelengths are drawn out/stretched
• Shows our universe is expanding outward, away from an initial starting point.
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Evidences for the Big Bang
• Background Radiation (Cosmic Microwave Radiation)• Left-over, red-shifted radiation from the
Big Bang explosion, found throughout universe.
• Consists of photons (light particles) from time when universe was 300,000 years old.
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Background Radiation, continued
• Background radiation helps us measure the temperature of the universe.• Current temperature: 2.73 Kelvin (-454 °F)• As universe ages it expands and cools,
dropping the background temp. • “Rewind” from the current temperature
and account for rate of expansion, and you will have the initial temp. right after Big Bang.
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Evidences, continued• Hydrogen and Helium Ratios
• Hydrogen and Helium are simplest elements in universe; would have been the first to form
• Prediction: mostly hydrogen (easiest to form), BUT with enough helium to slow rapid decay of neutrons
• Current ratio is 74% Hydrogen to 24% Helium (and 2% heavier elements)—amount of helium is perfect for slowing decay of neutrons.