Prediction from Big Bang Model: Abundance of the light elements
	• Big Bang Nucleosynthesis – T,  both high enough at start to fuse protons into heavier elements – T,   both dropping quickly so only have time enough to fuse a certain amount. – Simple models of expansion predict 24% abundance He • 24% is the amount of He observed* – Abundance of 2H, 3He, 7Li depends on normal matter • Suggests normal matter is only 5% of critical • But we need to also consider “dark matter” and its gravity