Why do people say this? How do we know this?

Such a bizarre thought. The generality is one thing. But the actual happening of it is quite something else. How will it look? How long will it take? What will humans experience and for how long? Who will be the last to die? (Don't worry, all rhetorical - I just wonder about this stuff sometimes)

Fascinating photos (you might want to credit them so Medium doesn't yell at you). Thank you! And congrats on the new pub! Yay!