Despite its 10,000-million-mile diameter, the solar system is dwarfed by the
Milky Way galaxy to which it belongs. But the Milky Way, containing 100,000 million
stars, is only a mote in the universe.
There are thousands of millions of such galaxies, most with their own myriad stars
having their own planetary systems. If only 1/10,000 of 1 per cent of these planets
harbour a civilization - and this is a very conservative estimate - the universe must teem with more than 100 million million civilizations.