I was having a discussion with my wife. I said that it is a shame that Galileo was persecuted for believing that the earth revolved around the sun rather than vice versa when in fact you could legitimately put your coordinate system anywhere. It might be simpler–but not even that much simpler given all the perturbations to center the solar system on the sun, but from a mathematical point of view it makes no difference.
She then challenged me to admit that it is more real to have the earth orbiting the sun that vice versa and I disagreed. Neither is, in my opinion, more real than the other. Then she asked me if a physicist would agree. I first said “yes”, then modified that to “I think so.” So my question is, what would a physicist say? And would all physicists agree?
I am well aware that there are many views among mathematicians of what the actual subject of our study is. Are mathematical objects real? So it would not at all surprise me to discover that physicists might not agree on this.
I am not a physicist but I can see the important difference between imagining the Earth revolving around the Sun then the other way around.
If you were to have the perspective that the Sun revolves around the Earth then this would mean that the Sun orbits the Earth at the fantastic speed of once every 24 hours. If the Sun were orbiting the Earth then it would be by some law of gravity that we simply do not observe in this universe. You would have to radically change what the mass of the Sun is relative to Earth, the distance from the Sun to Earth as well as the Sun’s energy output and many other points that I am sure I am missing.
I am sure a real physicist will answer your question more completely.
It is just that inertial frames are more convenient descriptions of reality than non-inertial frames, and that between two frames the one that is “more inertial”, in the sense of containing smaller centrifugal and Coriolis forces, is better.
The frame in which the sun is stationary and the Earth goes around it is therefore “better” than the one in which the Earth is stationary and the sun goes around it because the latter contains a much larger centrifugal force (which is what holds the sun aloft in this description).
As for which one is more “real”, you’d have to define “real”.
From time to time I’ve considered this as well. But not only would the sun orbit the earth at an amazing speed, but pretty much the same side of the sun would face us . . . not as consistently as the moon, but still quite impressively.
And what about the other planets? Would they also orbit the earth, with intricately looping orbits?
And even more impressive: Could the entire universe revolve around earth, everything swirling around us every 24 hours?
If it were just the earth and sun, no big deal. But it’s not, and the other planets trace incredibly complex paths if you insist on a Solar System reference frame with the earth at the center.
Newton’s universal law of gravitation only makes sense with the planets orbiting around the sun (ie, the planets constantly falling into the sun). It’s unlikely that would have been discovered if we insisted on a Geocentric view of the solar system.
The Bad Astronomer, Phil Plait, says: “I have two things to say that might surprise you: first, geocentrism is a valid frame of reference, and second, heliocentrism is not any more or less correct.” in a blog post about a geocentrism conference.
I think the OP is suggesting a Tychonic system, in which the other planets still go around the Sun, and only the Earth stays at the center. This gives planetary paths no more complicated then those of Earth’s moon in the heliocentric model.
Agreed. The complication – epicycles, and what-not – are all because of the need to explain the observed motion from the Earth’s point of view. And what rule of physics does it violate to have one body rotating around another at any speed? Does physics only allow slow motion, not fast?
The problem with this is that all too many people won’t click on a link and therefore won’t get the joke.
Here’s how Plait finishes that post:
The other quote is also perfectly accurate. It’s an inevitable result of relativity, which states that there is no privileged reference frame.
But in order for Geocentrism to be the One True Frame, as he is at pains to point out, one must either leave out relativity or get it wrong.
He also covers Candyman’s point:
In short, you can argue for geocentrism if you’re looking up from the surface of the earth. It may even be a better frame to do certain things in. But from any other point or for any other purpose, like sending a space probe out, it creates huge problems. And it absolutely can’t be the only answer.
Surprisingly, this isn’t a problem. Space itself is moving “faster than light,” but no object is moving through space at such a speed. The same is true for the Expansionary Phase refinement of the Big Bang Theory.
What’s really amusing about the geostationary model is how geostationary satellites are “held up” instead of falling straight down to the earth: the vast mass of the whirling cosmos, along with relativistic frame dragging, create an outward pull that holds such satellites in place!
It’s a GROTESQUE mathematical fiction, but it doesn’t actually violate any laws.
(Think of it as an accounting trick. You could balance your checkbook perfectly well, given the assumption that you have a trillion dollars more in the balance than you actually have. You could pay the rent, the utilities, etc., and, so long as you don’t actually dip in to that fictional trillion, the numbers all balance just fine. Alternate cosmic “centers” and fictitious rotations all balance perfectly well. They simply require an assumption that we do not readily see in evidence!)
ETA: Martin Gardner referred to this same issue in an old Mathematical Games column. The earth could be stationary, and the universe whipping around it, and the physics permit this. The calculations simply become incredibly unwieldy!
You appear, from your link, to be referring to the epicycles and other complications of the Ptolemaic geocentric system. However, you do not get rid of the need for epicycles (or eccentric points, another complication of Ptolemaic geocentrism) just by going from a geocentric to a heliocentric system. Copernicus had about as many epicycles in his system as Ptolemy did (and so, implicitly, did Tycho Brahe).* You get rid of epicycles by going from circular orbits to elliptical ones, that follow Kepler’s laws.
*Copernicus did, however, succeed in eliminating yet another, even worse complication of the Ptolemaic system, equants. Tycho’s system is indeed, in most respects (the exception being that he has the sphere of the stars is centered on the Earth rather than the Sun), merely the Copernican system in a different reference frame. In order for it to be predictively useful he would have to have used all the epicycles etc. postulated by Copernicus.
Exactly. If you start with the premise that the Earth is motionless and then observe the visible movement of the planets “around” it, you’ll see them speeding up and slowing down and sometimes even changing direction in a seemingly random pattern.
I know that some cosmological equations work this way… But I don’t know if they all do, or what the currently accepted models say. My old cosmology prof implied (but didn’t make clear) that Einstein and Mach had disagreements, and I don’t know if the dust has settled.
(The thought-experiment he taught – I mentioned this in another thread – is: what if the entire cosmos is absolutely empty…except for the earth. Earth, all alone, no stars, no moon, no galaxies, no dust, nothin’. Can the earth be said to “rotate” in a cosmos where there is no “thing” to rotate with respect to? My prof taught us that some sets of equations said yes, and other sets of equations said no. Can anyone update me? This was a damn long time ago, and entire suites of theories have come and gone since!)
You get rid of all these complications by going from a geocentric to a heliocentric system. “Heliocentric” does not mean “circular orbits around the sun.” You can not “get rid of epicycles by going from circular orbits to elliptical ones” unless you move from a geocentric to a heliocentric system. The key point is that geocentrism requires absurd complications totally at odds with newton’s laws etc, while heliocentrism does not.
IANA physicist but it seems like two different questions are being answered in this thread.
Forces-wise, the sun’s effect on the earth’s velocity is much greater than the other way round.
But in terms of coordinates, you can use any frame of reference you like and no frame is more privileged than any other. It’s as correct as any other coordinate system to consider the earth as static and everything else moving relative to it. We do it every day.