The Cosmic Microwave Background (Edexcel GCSE Physics)

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The Cosmic Microwave Background

  • The discovery of the CMB (Cosmic Microwave Background) led to the Big Bang theory becoming the currently accepted model since it is not supported by the Steady State theory
    • The CMB is a type of electromagnetic radiation which is a remnant from the early stages of the Universe
    • It has a wavelength of around 1 mm making it a microwave, hence the name Cosmic Microwave Background

  • In 1964, Astronomers discovered radiation in the microwave region of the electromagnetic spectrum coming from all directions and at a generally uniform temperature of 2.73 K
    • They were unable to do this any earlier since microwaves are absorbed by the atmosphere
    • Around this time, space flight was developed which enabled astronomers to send telescopes into orbit above the atmosphere

  • According to the Big Bang theory, the early Universe was an extremely hot and dense environment
    • As a result of this, it must have emitted thermal radiation

  • The radiation is in the microwave region
    • This is because over the past 14 billion years or so, the radiation initially from the Big Bang has become redshifted as the Universe has expanded
    • Initially, this would have been high energy radiation, towards the gamma end of the spectrum
    • As the Universe expanded, the wavelength of the radiation increased
    • Over time, it has increased so much that it is now in the microwave region of the spectrum

CMB Red Shift, downloadable IGCSE & GCSE Physics revision notes

The CMB is a result of high energy radiation being redshifted over billions of years

  • The CMB radiation is very uniform and has the exact profile expected to be emitted from a hot body that has cooled down over a very long time
    • This phenomenon is something that other theories (such as the Steady State Theory) cannot explain

  • The CMB is represented by the following map:

CMB, downloadable IGCSE & GCSE Physics revision notes

The CMB map with areas of higher and lower temperature. Places with higher temperature have a higher concentration of galaxies, Suns and planets

  • This is the closest image to a map of the Universe
  • The different colours represent different temperatures
    • The red / orange / brown regions represent warmer temperature indicating a higher density of galaxies
    • The blue / green regions represents cooler temperature indicating a lower density of galaxies

  • The temperature of the CMB is mostly uniform, however, there are minuscule temperature fluctuations (on the order of 0.00001 K)
    • This implies that all objects in the Universe are more or less uniformly spread out

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Ashika

Author: Ashika

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.