The Evidence for the Big Bang Student Resource Sheet 5 Science and Religion in Schools: Unit 4a

Unit 4a Evidence for the Big Bang The Big Bang model is a concise explanation for 3 independent observations: The red shift of light from distant galaxies The presence of large amounts of helium in the universe The cosmic microwave background radiation Each can possibly be explained in other ways, but the Big Bang model draws all of them together into a convincing story

Unit 4a The red shift Spectrum of light from the sun Fraunhoffer lines Light from a cluster of galaxies 10 9 light years away

Unit 4a Hubble’s original data Red shift due to expansion Further away, the longer the light has been traveling Universe has expanded more Red shift is bigger The velocity (speed) is basically how much the distance to the galaxy has changed in the age of the universe

Unit 4a Much improved data Distance scale 250 x bigger Much more convincing! Implication - the universe had a start

Unit 4a Expansion of the universe Expansion of the universe is NOT a rushing to fill empty space The WHOLE universe is expanding - there is no empty space

Unit 4a Helium abundance Universe is 24% He (by mass) Stars fuse hydrogen into helium In 14 billion years, stars have not burned hot enough, or long enough to make this much helium The oldest stars (11 billion years) also have ~ 24% He so this He cannot have been made in stars! Big Bang - in early history the whole universe was the same temp as the inside of a star! Fusion in the first three minutes of history made the helium This shows that the universe was hot in earliest times

Unit 4a Cosmic Microwave Background Arno Penzias Robert W Wilson (Nobel Prize, 1978) Persistent microwave noise independent of time and direction Relic radiation from Big Bang Thermal radiation now redshifted so it is in the microwave part of the spectrum

Unit 4a CMB (Cosmic Microwave Background) for fun and profit Dates to years into history Epoch of recombination (bad name!) Before then, all matter ionized At this time temp of universe down to the point at which atoms could form All free electrons captured Thermal radiation decouples from the matter Imprint of matter density on temperature variations The density fluctuations ‘seed’ galaxy formation WMAP whole sky map ±200  K