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THE MOTION OF UNIVERSAL EXPANSION
Edwin Hubble's discovery of cosmic expansion proved that motion was truly universal in its scope. Mathematically, that expansion can be expression in an equation known as Hubble's Law: v = Hr (recessional velocity = the Hubble constant * distance) "H" is the constant of proportionality, which astronomers have named the Hubble constant in Edwin's honor. As a simple exercise, if H = 70 km/s per Mpc, and you measured a galaxy moving away from Earth at v = 350 km/s, then the distance to the galaxy would be r, where 350 km/s = (70 km/s/Mpc) * r and thus r = 5 Mpc. Now, if we realize that both km and Mpc are measurements of length, this actually gives us a way to compute the approximate age of the universe! The quantity 1/H - the multiplicative inverse of the Hubble constant - can be expressed in units of time, and is roughly the amount of time the universe has been expanding. |