One of the things I always wondered was why Galileo’s Eppur si muove! (And yet, it moves!) was such a big deal. Yes, he was talking about heliocentricity, and the Earth moving around the Sun instead of the other way around.
But I was a little bit puzzled. Why, after all, would the Earth moving be such a revolutionary idea? Every night, if you look up and watch the skies over time, you’ll see something like this:
The sky rotates! Not only do the stars in the night sky rotate, but the Sun’s path through the sky also goes along one of the same paths that the stars do, as does the Moon. (For a spectacular video, go here, or here for my writeup of it.)
So, it always seemed to me that there are two possible explanations for this observed phenomenon. The first one is that the entire sky — everything in the heavens above the clouds — is rotating once a day. The ancients thought of this as a “celestial sphere”, thinking that everything in the heavens was on a huge, fixed sphere that rotated once a day.
But the second possibility is that the Earth is rotating, and we only see the heavens appear to rotate because we, ourselves, are on something that rotates. In fact, if we define our rotation as clockwise, we will see the heavens appear to rotate counterclockwise. (This is a large image, I know.)
So, why was “eppur si muove” such a big deal? Didn’t we know about this second possibility? Didn’t people at least consider it?
The answer, shockingly, is no, not really. Why didn’t we consider it? Because looking up and noticing that the heavens rotate predated our idea that the Earth could be round. If the Earth is flat, then it wouldn’t make sense for it to rotate, would it?
The huge mistake is that once we discovered the Earth was round (in about 300 B.C., by the way), we didn’t reconsider this problem. We didn’t go back and say, “Hey, you know what? Instead of this celestial sphere idea, maybe it’s just us that’s spinning!” And so we held onto the idea of a fixed Earth for nearly 2,000 more years.
I can’t help but wonder, if we went back and critically re-examined our assumptions and conclusions based on what we know now, if we would uncover some fantastic possibilities that could challenge our current scientific views of the Universe? Or, if everything we have concluded to this point really is the scientific best we can do with what we know?