How do astronomers calculate the expansion of the universe?

When light-emitting galaxies move away from us, their wavelength increases and they are shifted to the red end of the electromagnetic spectrum, which is known as redshift in physics. Astronomers have found galaxies that are approximately 13 billion light years distant, and they know that galaxies were not formed for at least the first 500 million years.

We know that the universe is expanding, though the precise rate is unknown; some theorize that it may be at or greater than the speed of light. They have found that the more distant the galaxy, the faster it is moving away from us. To calculate this, they use Hubble's Constant, or H0 ~ (30 km/s)/Million light years.

The redshift of distant galaxies, which is measured by measuring the Doppler effect on the light emitted by galaxies as they move away from us, is the primary method used by astronomers to calculate the expansion of the universe. The more distant a galaxy is, the faster it appears to be moving away, indicating the expansion of the universe. Cosmic microwave background radiation, on the other hand, provides additional evidence for the universe's expansion through the measurement of its temperature fluctuations, which reflect the expansion's history. These techniques, combined with theoretical models, enable astronomers to determine the rate of universe expansion.