•Thermal history of pregalactic gas can be worked out in detail (and we will do so!).
•
•Density fluctuations tied to temperature fluctuations, revealed finally by COBE, but
small. Lots more details to go into here later in
course.
•
•Two main ideas: top-down vs. bottom-up.
•
•Need for dark
matter (hot or cold) became apparent – normal matter needs help to collapse into
galaxies.