We see the universe around us expanding, which gives distant...

We see the universe around us expanding, which gives distant galaxies an apparent velocity of $70 \mathrm{km} / \mathrm{s} / \mathrm{Mpc}$. If you were an astronomer living today in a galaxy that was located billion light-years away from us, at what rate would you see the galaxies moving away from you?

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Key Concepts

Cosmological Expansion

Cosmological expansion refers to the observation that the universe is growing in scale over time, meaning that space itself is expanding. This expansion explains why galaxies appear to move away from each other, with their recessional velocity increasing with distance. It is a fundamental concept in modern cosmology that describes the dynamic behavior of the universe.

Hubble's Law

Hubble's Law is the principle stating that the velocity at which a galaxy recedes due to the expansion of the universe is directly proportional to its distance from the observer. This linear relationship, expressed as v = H? × d, provides a method for estimating the expansion rate of the universe by correlating redshift measurements with distance.

Hubble Constant

The Hubble Constant is the proportionality constant in Hubble’s Law that quantifies the rate of expansion of the universe. It is typically expressed in units of kilometers per second per megaparsec (km/s/Mpc) and represents the amount by which the recessional velocity of galaxies increases with distance. Its precise value is crucial for understanding the age, size, and evolution of the universe.

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