What causes the red-shift of light from distant galaxies?

The red-shift of light from distant galaxies is caused by the expansion of the universe.

When we observe light from distant galaxies, we notice that the light appears to be shifted towards the red end of the spectrum. This phenomenon is known as red-shift. The primary reason for this red-shift is the expansion of the universe. As the universe expands, it stretches the light waves travelling through it, increasing their wavelength. Since red light has a longer wavelength than blue light, this stretching causes the light to shift towards the red part of the spectrum.

To understand this better, imagine the universe as a balloon with galaxies on its surface. As the balloon inflates, the surface stretches, and the galaxies move further apart. Similarly, the space between galaxies is expanding, causing the light waves to stretch as they travel through this expanding space. This stretching of light waves is what we observe as red-shift.

Red-shift is a crucial piece of evidence supporting the Big Bang theory, which suggests that the universe began from a very hot and dense state and has been expanding ever since. By measuring the red-shift of light from various galaxies, astronomers can determine how fast these galaxies are moving away from us. This information helps scientists understand the rate of expansion of the universe and provides insights into its age and future.

In summary, the red-shift of light from distant galaxies is a direct consequence of the universe's expansion, stretching the light waves and shifting them towards the red end of the spectrum. This phenomenon is a key observation that supports our current understanding of cosmology and the history of the universe.