The Silence Beyond

The Silence Beyond walks the edge of everything we have seen so far. It is farther away than the universe is old, in light-years, and that is not a contradiction.

The universe is about 13.8 billion years old, so you might expect the farthest visible things to be 13.8 billion light-years away. They are not. While their light was travelling, space kept expanding, carrying the sources farther off. The formula on this page adds up the distance light could have covered since the beginning, each stretch scaled up by the growth that has happened since. In today's distances the answer is about 46 billion light-years. That boundary is the particle horizon, and the sphere inside it is the observable universe.

Three different edges get confused, and only this one is the edge of sight. The Hubble sphere, where galaxies recede at exactly the speed of light, is much closer, roughly 14 billion light-years. It is not a limit on vision: we already see galaxies that are receding faster than light today. The cosmological event horizon is a third surface, the limit on which events happening now can ever reach us.

Edwin Hubble did not find any of these horizons. In 1929 he showed that galaxies' redshifts grow with distance, the expansion that the horizons depend on. Wolfgang Rindler laid out the distinction between particle and event horizons in 1956.

Nothing beyond the particle horizon is invisible because it is dark. Its light simply has not had time to arrive. The horizon grows every year, and more of the universe comes into view, slowly, from behind the silence.

The Silence Beyond does not hide. They are only early.