Complex sentence: Within the books, Dust is equated with Dark matter (although as a "life force") in the real world, these particles make up most of the mass of the universe, but cannot be directly observed.
Split into simpler sentences: Within the books, Dust is equated with Dark matter, although as a "life force". In the real world, dark matter is believed to make up most of the mass of the universe, but cannot be directly observed.