The Expanding Universe  When light or sound moves toward or away from an observer, its frequency/wavelength changes (Known as Doppler effect)  Can be used to see how fast stars/galaxies are moving towards or away from us (when moving towards the lines in the spectrum are shorter/blue wavelengths, when moving away the lines are longer/red wavelengths)

Hubble’s Law  The larger the shift, the greater is the speed of this movement  In 1929 Hubble announced that light from most galaxies is red shifting  Nearly all the galaxies are getting farther away from Earth  Also found that more distant galaxies have greater red shifts (means the distant galaxies are moving away faster than the closer galaxies)

Hubble’s Law  This relationship called Hubble’s Law, says that the speed at which a galaxy is moving away is proportional to its distance from us  The most distant galaxies are moving away at around the speed of light!!!  The observed red shift in the spectra of galaxies shows that the universe is expanding in all directions

The Big Bang Theory  Astronomers theorize that the universe came into being at a single moment, in an event called the big bang  According to this theory all the matter/energy of the universe were at one time concentrated at a single point  It also states that the universe began in an instant, billions of years ago, in an enormous explosion

The Big Bang Theory  After the big bang the universe expanded quickly and cooled down  After a few thousand years of expansion, the universe was cool enough for atoms to form  Gravity pulled atoms together into gas clouds that evolved into stars in young galaxies  Our solar system formed 4.6 billion years ago when the universe was about two thirds its present size

The Big Bang Theory  Evidence for the Theory: -In scientist noticed a signal on their radio telescope, they realized they were detecting a faint distant glow in every direction (called cosmic microwave background radiation)  This radiation was produced during the big bang and is still traveling through space

The Big Bang Theory  The existence of cosmic microwave background radiation and the red shift in the spectra of distant galaxies strongly support the big bang theory  It offers the best current scientific explanation of the expansion of the observable universe  Variations of this theory continue to be proposed

The Big Bang Theory  Age of the Universe: -Since astronomers know how fast the universe is expanding, they can infer how long it has been expanding  If you traveled backward in time, all the matter in the universe would be at a starting point billion years ago  Astronomers estimate that the universe is 13.7 billion years old

Continued Expansion  To have a gravitational force strong enough to reverse the expansion, there must be sufficient mass in the universe  If there is less than this amount of mass, the universe will continue to expand  The mass that glows like stars is easy to measure because it can be seen, however most of the mass in the universe can’t be seen by astronomers

Continued Expansion  Dark matter is matter that does not give off radiation (Light)  Dark matter cannot be seen directly, but its presence can be directed by observing its gravitational effects on visible matter  Galaxies may contain as much as 10 times more dark matter than visible matter

Continued Expansion  Without this much, there would not be enough gravitational force to keep groups of galaxies from flying apart  Astronomers don’t know what it is made out of or how it is distributed through the universe  Most of the mass in the universe is composed of dark matter

Continued Expansion  Astronomers have discovered recently that the universe is expanding at a faster rate  Galaxies are moving apart much faster than expected  A mysterious force called dark energy is theorized to be causing the rate of expansion to increase  It’s likely the universe will expand forever