# GCSE PHYSICS ASTRONOMY

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```					GCSE PHYSICS : ASTRONOMY : THE BIG BANG AND OUR UNIVERSE
EVIDENCE
1. RED SHIFT OF LIGHT FROM DISTANT STARS AND GALAXIES

Red shift

Our Sun contains helium. We know this because there are black lines in the spectrum of the light from
the Sun. These lines are the signature for helium.

(The pattern is actually called an emission spectrum :as level physics)

When we look at the spectrum of a star the same signature is there, but the pattern of lines has moved
towards the red end of the spectrum. We call this red shift.

What causes red shift?

Sound and light are emitted as waves. Think about a duck bobbing up and down on the water. The
ripples spread out evenly in all directions. As the duck swims towards you, the waves get squashed so
the wavelength decreases (blue light). If the duck is swimming away from you, the waves will get
stretched out and the wavelength increases (red light).

Go to the BBC bitesize site for a demo.

So if a star is moving away from you at high speed, the wavelength of the light appears to get longer.
The pattern of lines moves towards the red end of the spectrum - this is red shift.

Approaching Object
 This has shown us that the galaxies containing these stars are also moving away from us at a very high speed.
 This supports the idea that the universe began with something like an explosion which threw things outward in
the same way that debris flies outward from the centre of a bomb explosion.
 What is astounding is that when light is observed from galaxies that are further and further away, the light
signatures (spectra) are shifted more and more to the red wavelengths!
 This means that the further the galaxy is, the faster it is traveling!
 So not only is the Universe expanding, but as galaxies move away from each other they are accelerating.

2. THE TEMPERATURE OF SPACE
The temperature of space was calculated long before the evidence of the correct temperature was found. The
time for which the Universe should have been cooling (from the time that the Big Bang occurred) was calculated,
and it was predicted that the leftover radiation should have a certain temperature. Scientists all over the world
began looking for it.

Two scientists, Penzias and Wilson, involved in very different research found some very annoying “interference”
was being picked up by their newly developed equipment. They tried everything to get rid of it, from pointing their
equipment in different directions, to scraping pigeon droppings off every morning. Nothing worked, everywhere
that they looked, this background radiation was present.

When they finally realised what they had found, they
became famous for finding the remnants of the Big
Bang! The radiation that they found had a very long
wavelength that corresponded to a background
temperature (that had been predicted many years
before) to which the Universe has cooled, 2.7K or
-270.3oC. It is one of the strongest pieces of
experimental evidence of the hot big bang model.

Very precise measurements have been made with the COBE satellite, see Fig. 3 and 4. At present, the
temperature corresponding to the cosmic background radiation equals 2.728 (4) K.

SO WHAT’S NEXT?

The Nobel Prize winning scientist Arno Penzias wonders if physics has anything left to offer after the Big Bang theory. Dr.
Penzias is famous for his discovery in 1965 of the Cosmic Microwave Background, the only real evidence that this ancient
explosion ever happened. It's a kind of "faint echo" heard in every corner of the cosmos and has helped the Big Bang theory
become the most widely accepted, most credible explanation of the origin of the universe.

The theory gives us effect but scientists are still looking for the cause with ideas like Dark Matter, String Theory, Quantum
Gravity, They're looking inside billion-dollar particle accelerators for the creation artist formerly known as god. The Big Bang
model is indeed a triumph of modern science that perhaps asks more questions than it answers, but Arno Penzias thinks
maybe modern cosmology is over-analyzing the evidence.

Try this web-site for information on the future of the universe :
http://www.gcse.com/eb/universe9.htm

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Jun Wang Dr
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