Astronomy: Big Bang EQ: How did the universe begin? ** Copy all pink and yellow words. p. 89

The ‘Big Bang’

What is or was the “Big Bang”? The famous cosmologist P. J. E. Peebles stated this succinctly in the January 2001 edition of Scientific American: "That the universe is expanding and cooling is the essence of the big bang theory. You will notice I have said nothing about an 'explosion' - the big bang theory describes how our universe is evolving, not how it began." (p. 44).

Picture of the night sky from Earth

Hubble Deep Field image

Building a Universe Infinitely dense point not governed by our physical laws or time All matter and energy contained in one point

Building a Universe Instantaneous filling of space with all matter

How do we know the Universe is expanding? We look at the spectra for stars and galaxies

f Don Lincoln, Fermilab f Doppler Effect The Doppler effect says that things moving away from you look redder than they would if they weren’t moving. Things moving towards you look more blue.

Red shift - as light from distant galaxies approaches earth there is an increase of space between earth and the galaxy, which leads to wavelengths being stretched

Redshift Quasars & Cosmology Department of Physics, Applied Physics & Astronomy, RPI In reality the space between the galaxies is expanding.

Hydrogen Iron Sodium Hydrogen Oxygen

Consequences If everything is moving away from us and things farther away are moving faster … Then the Universe is expanding!

Expanding Universe Space itself is expanding, not matter flying apart within space. Examples: – dots – rubber band – raisin bread – ants on a balloon It does not mean we are at the center of the Universe every part of the Universe sees everything moving away from it

Cosmic Microwave Background Radiation If the universe was once very hot and dense and it has been slowly cooling off for ~13.7 billion years then there should be a level of radiation (heat) everywhere we look. In 1964, Arno Penzias and Robert Wilson, discovered a noise of extraterrestrial origin that came from all directions at once - radiation left over from the Big Bang

Formation of Matter In June 1995, scientists detected helium in the far reaches of the universe - consistent with an important aspect of the Big Bang theory that a mixture of hydrogen (75%) and helium (25%) was created at the beginning of the universe. Why these two elements?

History of the Universe Timeline

History of the Universe Timeline

History of the Universe Timeline

Evidence for the Big Bang Expanding Universe – Red Shift Cosmic Microwave Background Radiation – seen throughout the universe Abundance of elements (H & He)