I made this meme some time ago, and I’m rather fond of it, so I’m putting it here to start with, because it makes the point that this post is about.
Since the time of the Greeks, it was commonly believed that the earth was stationary at the center of the cosmos, with the sun and other planets orbiting the stationary earth. This belief was not insane. There are actually very many good reasons to think it is true, based on experience and phenomenological evidence.
Incidentally, the fact that the earth was “at the center” DID NOT mean that the ancients thought that this made the earth SUPER-IMPORTANT, and that, somehow, Copernicanism wrecked this idea that the earth and humanity was SUPER-IMPORTANT. Did you ever read Dante’s Divine Comedy? Or at least the Inferno? Do you remember where Satan was? That’s right, the bottom of Hell, the lowest, meanest, place in the cosmos was … the center.
Back on point. Copernicus proposed a theory or a model that the earth went around the sun instead of the sun going around the earth. It wasn’t a very good model, since it had at least as many ad hoc adjustments as Ptolemy’s model, and was actually less predictively accurate. Nonetheless, although most astronomers regarded it as a mere curiosity, a small number of persons, most notably Galileo Galilei (whose Latin name was thus Galileus Galileus—which Kepler found endlessly amusing) decided, for reasons that are not clear, that Copernicanism was ABSOLUTE TRUTH, and started insisting it was, even when, like Galileo, they couldn’t come up with any compelling evidence.
But largely thanks to the work of scientists like Tycho Brahe and Johannes Kepler (Galileo actually contributed pretty much NOTHING to the debate, other than to get some people so angry and upset that research was probably retarded in some quarters), the astronomical models were improved. Ironically, by the time of Galileo’s famous trial in 1633, when he was still choosing to die on the hill of an utterly dogmatic Copernicanism, science had already passed him by: serious astronomers were debating between the Tychonic system and the Keplerian system by them. Copernicus was as dead and done as Ptolemy.
Kepler’s elliptical orbits and laws of planetary motion more or less edged out the Tychonic model between 1630 and 1650. If we are really generous and pick the 1630 date, then we can rightly say that people believed that the earth orbited the sun between 1630 and 1687, or 57 years. Not quite as long as the 2000 years of believing the sun went around the earth, nor the 1400 or so years of the Ptolemaic system.
What happened it 1687, you ask? Isaac Newton, natural philosopher, published his Philosophiæ Naturalis Principe Mathematica (the Principia for short), in which he conclusively demonstrated that the earth and the sun orbit ONE ANOTHER, or more specifically, they both orbit their common center of gravity, which is a point actually located inside the sun, given its much greater mass than the earth.
Of course the planetary motions are much more complicated than this, since the other planets also have mass and therefore affect both the sun and the earth, and for that matter, EVERY SINGLE BODY IN THE ENTIRE UNIVERSE WITH MASS affects both the earth and the sun. Nevertheless, THE POINT HERE is that NEITHER “the sun orbits the earth” NOR “the earth orbits the sun” is an entirely accurate statement.
STOP SAYING THIS AS IF IT WERE TRUE. WE’VE KNOWN IT ISN’T SINCE 1687!
You might say, well, Eve, fair enough, it’s not STRICTLY TRUE that the earth orbits the sun, but it’s kind of true, because the effects of the other planets aren’t that great, and the effects of all the other massive bodies are so slight they can be discounted, and the common center of mass of the sun and the earth is inside the sun, which means that the combined effects of everything means that the earth goes around a moving point that is usually or always inside the sun, so isn’t it at least KIND OF TRUE that the earth orbits the sun?
Newtonian motion, complex as it is, requires there be ABSOLUTE MOTION against the background of ABSOLUTE SPACE and ABSOLUTE TIME. This was already being highly questioned in the 19th century, but it wasn’t until Einstein’s theories of special and then general relativity were produced that the notion was throughly killed to death.
Motion always occurs RELATIVE TO a given frame of reference. That is what RELATIVITY means. And there JUST IS NO ABSOLUTE, ONE TRUE FRAME OF REFERENCE. You can use any point you like. The choice of an inertial frame of reference really depends on what you are trying to do, and it will be a choice made, by and large, to make your math easier.
If you want to, you can pick the center of mass of the earth as your frame of reference. In which case, within this frame of reference, all motion in the universe DOES, in fact, move around or is relative to the center of the earth, which is stationary.
If you want to you can pick the center of mass of the sun as your frame of reference. In which case, within that frame of reference, all motion in the universe DOES, in fact, move around or is relative to the center of the sun, which is stationary.
Or you can pick the Omphalos at Delphi, thought to be the center of the world by the ancient Greeks.
Or your belly button.
Or my cat.
Or Alpha Centauri.
Or literally ANYWHERE. ANY POINT IN SPACE ANYWHERE.
So, just to put a fricking stake in the heart of the vampire meme: THE EARTH DOES NOT GO AROUND THE SUN IN ANY ABSOLUTE SENSE. YOU CAN SAY IT DOES, BUT ONLY BY PICKING AN ARBITRARY FRAME OF REFERENCE AND ANYONE ELSE CAN PICK A DIFFERENT FRAME OF REFERENCE AND SAY IT DOESN’T GO AROUND THE SUN AND YOU’LL BOTH BE EQUALLY RIGHT AND WRONG, RELATIVISTICALLY.
To end, here’s a meme, which explains why atheists shouldn’t even be talking about this: