The Big Bang Theory (Oxford AQA IGCSE Physics)
Revision Note
Written by: Dan Mitchell-Garnett
Reviewed by: Caroline Carroll
Cosmic Microwave Background Radiation
Cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the universe
It comes from radiation that was present shortly after the beginning of the universe
It is detected everywhere throughout the Universe
The CMBR map is the closest image that exists to a map of the Universe
It shows that the temperature of the Universe, and therefore the objects in it, are more or less uniformly spread out
CMBR map of the universe
The CMBR comes from high-energy radiation which originated just after the Big Bang
As the Universe expanded, the wavelength of this radiation increased
It therefore lost energy and produced the CMBR which can be observed today
The Big Bang Theory
Scientists believe the universe began with a ‘big bang’, 14 thousand million years ago
The Big Bang theory is currently the only theory that can explain the existence of CMBR
A giant explosion, known as the Big Bang, caused the Universe to expand outwards
As each point moved away from the others, the Universe began to cool
As a result of the initial explosion, the Universe continues to expand
The expansion of the Universe over time
The Big Bang theory is very well supported by two main pieces of evidence:
Cosmological red-shift
This provides strong evidence for the expansion of the UniverseCosmic Microwave Background Radiation (CMBR)
This provides evidence for the expansion of the Universe and that it had a hot beginning
Worked Example
Describe and explain what can be deduced about the history of the Universe from the CMBR.
Answer:
Step 1: Recall the features of the CMBR
Microwave radiation is detected from all directions at a similar intensity
Step 2: State the source of this radiation
This is the radiation produced just after the formation of the Universe
Step 3: Describe how the wavelength has changed and explain why
When the Universe was formed, the radiation was high in energy and short in wavelength
Now the wavelength is longer
This is because the Universe has expanded, causing the wavelength to increase
Step 4: Suggest what this infers about the Universe at its beginning
This suggests the Universe was initially very small and very energetic and has been expanding since
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