Complex sentence: He also mused about what is now referred to as the "Fermi Paradox": that with the billions and billions of star systems in the universe, one would think that intelligent life would have contacted our civilisation by now.
Split into simpler sentences: He also mused about a proposition which is now referred to as the "Fermi Paradox". This contradiction or proposition is this: that with the billions and billions of star systems in the universe, one would think that intelligent life would have contacted our civilisation by now.