Space Physics: Red-shift

Space Physics: Red-shift

Red-Shift and the Doppler Effect

  • When a wave source is moving relative to an observer, there is a change in observed frequency and wavelength, termed the Doppler Effect.
  • This effect can be observed for any type of wave, including light and sound.
  • When a light source is moving away from us, its light appears more red than it would if it was stationary. This is known as red-shift.
  • Similarly, when a light source approaches us, its light is more blue due to the decrease in wavelength. This is referred to as blue-shift.
  • Red-shift is characterised by an increase in wavelength and decrease in frequency and energy. Conversely, blue-shift involves a decrease in wavelength and an increase in frequency and energy.

Red-Shift in Astronomy

  • In the field of astronomy, red-shift is a key piece of evidence supporting the Big Bang Theory.
  • Virtually all distant galaxies are moving away from us, as indicated by the red-shift of light they emit.
  • The larger the observed red-shift, the further away the galaxy is.
  • It has been observed that the further away a galaxy is, the faster it seems to be moving away. This is known as Hubble’s law.
  • These observations support the idea that the universe is expanding, with galaxies moving away from each other in every direction.

Cosmic Microwave Background Radiation (CMBR)

  • Another significant evidence for the Big Bang Theory is the Cosmic Microwave Background Radiation (CMBR).
  • This is the radiation left over from the early universe, shortly after the Big Bang occurred.
  • The CMBR is considered as the ‘afterglow’ of the Big Bang and it has been detected in all directions of the universe.
  • The discovery of the CMBR contributes to the model of an expanding universe from an initial singularity, known as the Big Bang.

The Big Bang Theory

  • According to the Big Bang Theory, the universe began from an extremely hot and dense point around 13.8 billion years ago.
  • The universe has been expanding since then, which is supported by the observed red-shift in distant galaxies and the CMBR.