5/6/15 WHO REMEMBERS DOPPLER SHIFT?
•  The Doppler Effect is the perceived change in wavelength of a wave that is
emitted from a source that is moving away or toward an object.
THE BIG BANG THEORY
RED SHIFT
•  When objects move away from us, they appear red
•  When objects move toward us they appear blue
•  Observations made in the early 1900’s revealed that most of the galaxies we
can see have Doppler shifts toward the red end of the spectrum
•  The light waves are being stretched
•  The Earth and the source of light are moving away from each other
HUBBLE’S LAW
HUBBLE’S LAW
•  Edwin Hubble wanted to explain why the galaxies appeared to be moving
away from us.
•  Galaxies are retreating from us at a speed that is proportional to their
distance
•  Hubble realized that dimmer galaxies were most likely farther away from us
than were brighter galaxies.
•  i.e. the farther away galaxies are, the faster they are moving away from us
•  He tried to find a relationship between the distance to a galaxy and their red
shift.
•  He found that galaxies exhibiting the greatest red shift are the farthest away
•  Greater red shift = greater speed
1 5/6/15 THE BIG BANG THEORY?
THIS MEANS THE UNIVERSE IS
EXPANDING!
THE BIG BANG THEORY
•  The Big Bang Theory says that once the entire universe was confined
in a hot, dense, supermassive ball
•  Approximately 13.7 billion years ago, a “violent explosion” occurred,
hurling the material in all directions
EVIDENCE OF THE BIG BANG
•  Red Shift – Hubble’s Law
•  Cosmic Background Radiation
•  Radio signals from all over the universe, could be
leftover from Big Bang (H-pg 848)
•  Everything in our universe came from that ball
MORE EVIDENCE FOR THE BIG BANG
COSMIC RADIATION BACKGROUND
•  Cosmic Microwave Background radiation (CMB’s) : the existence of an
isotropic radiation bath that permeates the entirety of the Universe
•  In 1964, two young radioastronomers, Arno Penzias and Robert Wilson,
accidentally discovered the CMB using a well-calibrated horn antenna.
•  They were trying to determine what was causing static in telephone
lines. They worked for Bell Telephone company.
•  It was soon determined that :
•  the radiation was diffuse,
•  emanated uniformly from all directions in the sky,
•  had a temperature of approximately 3 Kelvin (2.73K).
Stephen Hawkins - Cosmic Background Radiation
2 5/6/15 WHAT HAPPENS AT THE END?
SOURCES
•  Idea One:
•  Universe expands forever
•  Stars burn out, leaving many black holes and other matter
•  Idea Two:
• 
http://school.discoveryeducation.com/curriculumcenter/universe/activity2.html
• 
http://aether.lbl.gov/www/science/cmb.html
• 
http://space.about.com/od/astronomybasics/a/Origin-Of-The-Universe.htm
•  Universe eventually starts contracting (coming back
together)
•  Galaxies collapse on each other forming the “Big Crunch”
•  Idea Three:
•  Steady State Theory proposes that the universe looks the
same as it always has.
•  Right now, astronomers believe that Idea One is most
likely…
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