Physicist Rob Sheldon writes: A correspondent asked me recently how we know the age of the universe. The answer is calculated from the inverse of the Hubble constant. That is, if the galaxies are moving away from us at 72 km/s /Mpc, that has units of 1/time, the inverse is the age of the universe (more or less) because it locates the time since everything was at a point. For the universe to be younger, the Hubble constant has to be bigger. In fact, when Hubble first proposed his constant, it gave an age of the universe of about 4 billion years, which is the age of the oldest rocks in the Earth. However every decade saw a decrease in the Hubble Read More ›