Big Bang Theory
Big Bang Theory Big bang theory suggests that the universe began from a single point about 13.82 billion years ago. What existed before this event is completely unknown to science, but there is evidence that time, space and matter had their beginnings in the big bang event. This is not the only scientific theory that attempts to explain the existence of the universe. Steady state theory suggests that the universe had no beginning but rather has existed forever. From 1920-1960, there was a great deal of debate over which theory better described the universe. Two major pieces of evidence support the big bang theory. How did this theory develop, and what is the evidence for it?
Evidence for the Big Bang Theory There are two major pieces of evidence for the big bang theory: The expansion of the universe The background radiation This you do have to write down.
The Expansion of the Universe Edwin Hubble was the first to take careful measurements showing that all galaxies are moving away from us, and therefore the universe is expanding. This evidence comes from examining the light emitted from galaxies. When seen through a spectroscope, the spectral lines expected for specific elements are all red-shifted (shifted to the red side of the spectrum). Edwin Hubble
The Expansion of the Universe Edwin Hubble was the first to take careful measurements showing that all galaxies are moving away from us, and therefore the universe is expanding. This evidence comes from examining the light emitted from galaxies. When seen through a spectroscope, the spectral lines expected for specific elements are all red-shifted (shifted to the red side of the spectrum). red blue a b c d a b c d Continuous spectrum hydrogen in the sun hydrogen in another galaxy All spectral lines are shifted to the red side of the spectrum.
The Expansion of the Universe This is an example of a doppler shift and is easiest to explain using sound as an example. When a plane flies by, you can hear a change in the frequency of the sound it makes. This is caused because the source of the sound (the plane) is moving. As the plane approaches the sound waves get bunched up. As it moves away from you the sound waves get spread out. The same principle applies to a moving source of light. red blue a b c d Continuous spectrum hydrogen in the sun a b c d hydrogen in another galaxy All spectral lines are shifted to the red side of the spectrum.
The Expansion of the Universe This is an example of a doppler shift and is easiest to explain using sound as an example. When a plane flies by, you can hear a change in the frequency of the sound it makes. This is caused because the source of the sound (the plane) is moving. As the plane approaches the sound waves get bunched up. As it moves away from you the sound waves get spread out. The same principle applies to a moving source of light. A moving source waves are spread out waves are bunched up
The Expansion of the Universe Hubble also found that the farther away a galaxy is from us, the more its light is red-shifted. This is known as Hubble s Law. This means that the universe is expanding (inflating). The expansion creates more space between galaxies. https://www.youtube.com/watch?v=t9lkcgu5iwm
The Background Radiation The temperature at an instant after the big bang was 10 23 ºC, too hot for matter to exist. By an hour after the big bang, the universe had cooled down to only 10 000 000 ºC, allowing the formation of hydrogen and helium. Even though this occurred billions of years ago, some heat should still be detectable by radio telescopes. Arno Penzias Robert Wilson
The Background Radiation In 1963, Penzias and Wilson discovered the cosmic microwave background radiation. The Cobe spacecraft has since mapped the background radiation. The map shows that some places in the universe were hotter than others. It is in the cooler areas that matter came together to form the first stars.