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Transcript
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:
The waves in front of the
object get ‘squashed together’
so the wavelength decreases.
The waves behind the object
get ‘stretched out’ so the
wavelength increases.
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
Violet
Sun’s
spectrum
Another
star’s
spectrum
Shifted towards the red
end
Red
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.
Everywhere we look galaxies are red shifted!
This was discovered by a good looking, pipe smoking American Astronomer
called Edwin Hubble in 1929 (pictured right).
This tells us that nearly all other galaxies are moving …………… from us!
Hubble also noticed that the further away the galaxy, the greater its red shift and therefore the
……………. it is moving
In fact the speed a galaxy is moving is directly proportional to its distance from us
Speed of
Galaxy
(m/s)
We call the constant that relates the
distance to the speed of a Galaxy
Hubble's constant!
Velocity = Hubble's Constant x Distance
Distance from us, (m)
Extra Info: Just for your enjoyment!
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 for the Big Ban
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
The End of the Universe?
So we now think it all started with a big bang! But how will it all end? There are 2 different ideas and which one
will happen depends on how dense the Universe is. If there is there is over a certSaudis Expand Regional Power
as Others Falterain amount of mass per bit of space then gravity will slow the expansion and slowly drag
everything back together into a “Big Crunch”. If there is not enough mass then the Universe will continue to
expand forever, everything will slowly get spread out and the Universe will die in a “Big Yawn”!
Astronomers are trying to solve how much mass is in the Universe as we speak!