Astronomers today believe the universe exploded expanded outward

Ø Astronomers today believe the universe exploded (expanded) outward from a single point. Ø This idea is known as the Big Bang Theory.

What evidence supports the Big Bang Theory? Øthe red shift in the spectral lines of distant galaxies Ø the existence of cosmic microwave background radiation

ØEdwin Hubble discovered that the farther away a galaxy was, the faster it was moving away from Earth. Ø This concept came to be known as the expanding universe.

ØTo visualize the movement of galaxies, imagine the dough for a loaf of raisin bread as it rises. ØThe raisins in this rising bread dough are all moving away from one another as the dough expands. ØIn a similar way, galaxies move away from one another as the universe expands.

• In the 1800 s, Christian Doppler discovered that when the source of a sound wave is moving, its frequency changes. • The change in sound you hear is caused by a Doppler shift.

• Doppler shift also occurs with electromagnetic waves, such as visible light, X-rays, and microwaves. • This phenomenon is an important tool used by astronomers to study the motion of objects in space.

• The Doppler effect can be used to determine how fast stars or galaxies are approaching or moving away from Earth. ØWhen a star or galaxy is approaching Earth, the lines in its spectrum are shifted toward the shorter (bluer) wavelengths. ØWhen the star or galaxy is moving away, the lines in its spectrum shift toward the longer (redder) wavelengths. • The larger the shift, the greater is the speed.

What evidence supports the Big Bang Theory? Øthe red shift in the spectral lines of distant galaxies Ø the existence of cosmic microwave background radiation

Cosmic Microwave Background Radiation In 1965, Arno Penzias and Robert Wilson, using a radio telescope, noticed a faint distant glow in every direction. • Today this glow is called the cosmic microwave background radiation. • This glow is energy produced during the big bang, still traveling throughout the universe.

Age of the Universe ØSince astronomers know how fast the universe is expanding now, they can infer how long it has been expanding. ØIf you traveled backward in time, all of the matter in the universe would be at its starting point 13 to 14 billion years ago. ØRecent measurements of the microwave background radiation have led to a more precise age.

Age of the Universe Big bang occurred 13. 7 billion years ago. First stars and galaxies formed 200 million years after big bang. Solar system formed 4. 6 billion years ago. Earth today

BIG BANG THEORY üThe big bang theory describes how the expansion and cooling of the universe over time could have led to the present universe of stars and galaxies. üIt offers the best current scientific explanation of the expansion of the observable universe. üVariations of theory continue to be proposed and are being tested with new observations.