How did Einstein develop General Relativity? What does it mean for different kinds of masses to be equivalent? How does gravity do what it does?

How did Einstein develop General Relativity? What does it mean for different kinds of masses to be equivalent? How does gravity do what it does?
What makes Iceland so warm despite its high latitude? What powers everything from glaciers to geysers?
Why are small stars red? Why are small stars so common? Why are small stars so interesting for the hunt for life?
What did Hubble really discover? Why does redshift imply an expanding universe? Why is the night sky dark? Why is there so much hydrogen, and how is that connected to the Big Bang?
How does gravity bend the path of light? Does it seriously act like a lens or is that just a metaphor?
What strange creatures inhabit the so-called “particle zoo”? Why is it a zoo instead of something simpler?