A friend and I were watching this TED talk given by Brian Greene in which he briefly explained Einstein's revolutionary idea of gravity being the warping of space time:
Seemed pretty straightforward enough for me, but my friend asked me a question that I think I know the answer to, but am not eloquent or knowledgeable enough about astrophysics to answer convincingly.
She asked "If Earth is circling around the Sun's gravity funnel, why doesn't it fall into the funnel, like when you put a penny in one of those donation funnels, and it spins around going deeper and deeper until it falls in?"
Seems to me this analogy is confusing the metaphorical funnel of gravity in Greene's illustration with the actual funnel in real life, in which case there is the real physical funnel AND the gravity that acts on the funnel itself and the penny pulling the penny to the Earth. This wasn't good enough for her because she persisted "Yeah, but if gravity is a like funnel, and it has a pull on the Earth, pulling the Earth towards the Sun, why doesn't it pull the Earth into the Sun? Why doesn't the moon spiral down into the Earth?"
At this point, I'm struggling to avoid circular logic, because the best I can come up with is something Zen like "Everything that would have been pulled into the Sun would have been pulled into the Sun by now. Everything that would have gone floating off would have gone floating off by now. That just leaves the things with just the right amount of mass and distance to be in perfect equilibrium to still be hanging around the way they do." And weakly stating "I'm sure it has something to do with angular momentum."
By the way, I failed physics twice in college and barely passed the third time. Any help yall can lend in explaining this more eloquently would be appreciated. Thanks!