History of the Universe 19.6

The Beginning of the Universe Evidence suggests that the universe is expanding. The Big Bang Theory – an enormous explosion 13.7 billion years ago that caused the expansion and cooling of everything in the universe. This cooling started the formation of atoms, stars, and eventually galaxies. 2

2 3

How do we know the universe is expanding? The Doppler Effect As objects move toward the observer the sound waves and lights waves compress creating shorter wavelengths Shorter wavelengths of light appear blue As objects more away from the observer the sound waves and light waves decompress creating longer wavelengths Longer wavelengths of light appear red

Hubble’s Law In the 1920’s, Edwin Hubble discovered that the light coming from most galaxies was undergoing a red shift indicating that most were moving away from earth. The farther away the galaxy the greater the red shift. Hubble’s Law states that the speed at which a galaxy is moving away is proportional to its distance from us.

Hubble’s Conclusion Most observed galaxies appear for show red shift, therefore the universe is expanding.

Technology that Aids Space Exploration Telescopes Visual – use visible light Radio – use radio waves to retrieve information from space probes. X-Ray – use shorter wavelength than visible light Computers managing data. Space Probes collect information and materials.

Hubble Telescope - 1990