410 
The Solar System [oh. xyi 
per 5000 million years, so that our own system, with an age of the order of 
2000 million years, is probably the youngest system in the whole galactic 
system of stars. 
The contrast between the slowness of cosmogonic events as disclosed by 
the figures just given, and the rapidity with which events move on our earth, 
leads to some interesting reflections. Let us suppose that civilisation on our 
earth is 10,000 years old. If each planetary system in the universe contains 
ten planets, and life and civilisation appear in due course on each, then civilisa 
tions appear in the galactic system at an average rate of one per 500 million 
years. It follows that we should probably have to visit 50,000 galaxies 
before finding a civilisation as 3 7 oung as our own. And as we have only 
studied cosmogony for some 200 years, we should have to search through 
about 25 million galaxies, if they exist, before encountering cosmogonists as 
primitive as ourselves. We may well be the most ignorant cosmogonists in 
the whole of space.