Big Bang Theory vs Steady State Theory
Red Shift and the Doppler Effect
Red Shift and the Doppler Effect
The Doppler Effect is the observed change in wavelength of a wave due to the motion of the source relative to the observer.
When the object is moving:
This is how the waves from the object would be observed:
With sound this means that when a source is moving towards you, a higher pitch sound will be heard because the wavelength is shortened and when a source is moving away from you, a lower pitch sound will be heard because the wavelength is longer. You can hear this effect in the DOPPLER BALL DEMONSTRATION. With light we call this effect red shift and we can observe redshift by looking at the spectrum of light given off by astronomical objects.
Red Shift
The spectrum from stars for example will have dark line appearing in them. These dark lines indicate what elements the star is composed of e.g. Hydrogen. So, since the Sun is so close to use we can consider it to be stationary. So we can compare the dark lines from other objects to the sun’s spectrum. If these dark lines are more towards the red end of the spectrum, then we say that the light has been red shifted and the object is moving away from us. If the line is towards the violet end then we say the light has been blue shifted and the object is moving towards us.
In astronomy the Doppler Effect is used to measure the motion of the galaxies. The faster a galaxy moves the greater the red shift will be.
The Big Bang Theory
To explain Hubble’s extraordinary discoveries about our expanding universe, astronomers came up with the Big Bang Theory. The Big Bang theory states that the whole universe started from a single tiny point that expanded rapidly in an explosion about 13 Billion years ago and is still expanding today (like the surface of a balloon, all galaxies are moving apart from each other, there is no centre!). Matter was thrown out in all directions forming stars and galaxies. Both Space and time were created in the Big Bang.
However the Big Bang theory had some competition…
There are 2 main theories about the Universe.
The Big Bang Theory - All matter and energy in the entire universe and the four dimensions of time and space, were created in an explosion from a single tiny point about 14 billion years ago.
The Steady State Theory - The universe on a large scale does not change with time (evolve). It has always existed and will always continue to exist looking much as it does now. The density of the universe remains the same because as the universe expands matter is continuously being created to fill the gap.
Questions
1. What is the main difference between the Big Bang Theory and the Steady State Theory?
Complete the table on the following page
2. Which theory are Scientists more likely to believe?
3. Why?
Evidence / How does this support the Big Bang Theory? / How does this support Steady State theory?Red Shift
Cosmic Microwave Background Radiation
Some challenging extension ideas…
Olbers
Paradox
The Hubble
Deep Field
Abundance of Elements
Evidence for the Big Ban