1. THE BIG BANG THEORY The Expanding Universe

2. Review Human demonstration

4. Doppler Shift The apparent change in frequency and wavelength as a light or sound wave moves toward or away from an observer Can be used to determine how fast stars or galaxies are approaching or moving away from the Earth If an object is moving TOWARDS Earth, the electromagnetic waves shift towards shorter wavelengths (blue) If an object is moving AWAY from Earth, the electromagnetic waves shift towards longer wavelengths (red)

5. Hubble Edwin Hubble, an American astronomer who studied galaxies at different distances from Earth In 1929, he revealed that he collected evidence that most galaxies undergo a red shift What does this mean?

6. Hubble’s Law The speed at which a galaxy is moving away is proportional to its distance from us Based on evidence that more distant galaxies are moving away from Earth faster than closer galaxies This observed red shift of most galaxies gives evidence that the universe is expanding!

7. The Big Bang Hubble observed that in every direction you look, galaxies at a given distance are moving away at the same rate The universe came into being at a single moment in an event called the Big Bang

9. Evidence for the Theory Cosmic Background Radiation A faint energy echo of the Big Bang After the Big Bang, the universe expanded and cooled off rapidly to about 3000 K Before this, it was too hot for atoms to form, free electrons were everywhere and light (or electromagnetic radiation) could travel only very small distances before interacting with electrons When the universe cooled down, atoms formed and now light energy could travel great distances We can see this light as background radiation or energy and its coming at us from every direction! The temperature of this radiation is very low because of the rapid expansion of the universe, but still detectable

10. Age of the Universe Because astronomers know how fast the universe is expanding, they can infer how long it has been expanding The current estimate for the age of the universe is 13.7 billion years old