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.

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.

Do NOT take notes on the next few slides! These are just FYI slides….

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!

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.

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.

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.

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.

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.

Okay, now it’s time to start writing again….

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.

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.

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.

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.