If the Milky Way were the size of a penny, how big would the rest of the universe be?

A penny is about 1 inch across. If this equals 100,000 light years as the diameter of the Milky Way, the Andromeda Galaxy is about 23 inches away, the Virgo Cluster of Galaxies is about 60 million light years or 50 feet away, and the nearest quasar, 3C273 is about 1.5 billion light years or a bit over 2 miles away.

The visible universe has a horizon at about 14 billion light years and the most distant galaxies seen by the Hubble Space Telescope are nearly at this limit at about 12-13 billion light years. This is about 15 - 20 miles away from the Milky Way 'penny' and is the farthest we can ever see. Because our best model for the universe consistent with data is that it is infinite, then of course there is much more space even at the scale of our penny! In our scale model, though our horizon is at 20 miles from us, the rest of the currently unobservable universe stretches thousands or even millions of miles beyond the last 'penny' we can see. As the universe gets older, these more distant pennies will come into view, but of course we will see them as they were when they were much younger that the actually are.

Return to Dr. Odenwald's FAQ page at the Astronomy Cafe Blog.