What is the significance of red-shift in cosmology?

Red-shift is significant in cosmology as it provides evidence for the expansion of the universe.

In more detail, red-shift refers to the phenomenon where light from distant galaxies is shifted towards the red end of the spectrum. This happens because the wavelengths of the light are stretched as the galaxies move away from us. The concept is similar to the Doppler effect, where the pitch of a sound changes if the source is moving relative to the observer. In the case of light, if a galaxy is moving away, its light appears redder; if it were moving towards us, it would appear bluer (blue-shift).

The discovery of red-shift in the light from distant galaxies was a groundbreaking moment in cosmology. In the 1920s, American astronomer Edwin Hubble observed that almost all galaxies are moving away from us, and the further away a galaxy is, the faster it is receding. This relationship is now known as Hubble's Law. The red-shift of galaxies provides strong evidence that the universe is expanding, which supports the Big Bang theory. According to this theory, the universe began as a very hot, dense point approximately 13.8 billion years ago and has been expanding ever since.

Red-shift also helps cosmologists measure the rate of expansion of the universe, known as the Hubble constant. By analysing the red-shift of light from various galaxies, scientists can estimate how fast the universe is expanding. This information is crucial for understanding the past, present, and future of the cosmos.

In summary, red-shift is a key piece of evidence for the expanding universe and helps scientists understand the dynamics and history of the cosmos. It is a fundamental concept in cosmology that has transformed our understanding of the universe.