THE BIG BANG THEORY

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.

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 Edwin Hubble wanted to explain why the galaxies appeared to be moving away from us. Hubble realized that dimmer galaxies were most likely farther away from us than were brighter galaxies. 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

HUBBLE’S LAW Galaxies are retreating from us at a speed that is proportional to their distance i.e. the farther away galaxies are, the faster they are moving away from us

THIS MEANS THE UNIVERSE IS EXPANDING!

THE BIG BANG THEORY?

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 Everything in our universe came from that ball

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)

MORE EVIDENCE FOR THE BIG BANG 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).

COSMIC RADIATION BACKGROUND Stephen Hawkins - Cosmic Background Radiation

WHAT HAPPENS AT THE END? Idea One: Universe expands forever Stars burn out, leaving many black holes and other matter Idea Two: 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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