Here* he is presuming Geocentrics are Relativists (or that Relativism is a necessary truth):
Geocentrism, as advocated by creationists or other religiously fundamental people, is certainly wrong.
How, you may ask? What is going on is that you can do a change of reference frame to a geocentric one, and by Einstein's mathematics of relativity the math must still work out. I readily admit that. This means that, physically, geocentrism is just as valid as, say, heliocentrism.
But note the words "just as valid". Also, by relativity, it cannot be any more valid; geocentrism is just another change of frame (although to a non-inertial one).
What Geocentrists are saying is that geocentrism is the one, true frame. They must say that because that is what is says in the bible. Now pay attention here, because this is the important bit: to say Geocentrism isn't wrong, you have to accept the premise that any frame of reference is just as valid as any other. But to claim that Geocentrism is correct, you have to ignore that very same premise.
Geocentrism as the One True Way is therefore self-contradictory. It doesn't work.
Here** he has linked to an explanation of non-inertial frames of reference:
A non-inertial frame of reference does not have a constant velocity. It is accelerating. There are several ways to imagine this motion:
- The frame could be traveling in a straight line, but be speeding up or slowing down.
- The frame could be traveling along a curved path at a steady speed.
- The frame could be traveling along a curved path and also speeding up or slowing down.
Use these links or identical ones at the end of this explanation to see some non-inertial frame animations:
- Elevator Example of a Non-inertial Frame
- Rotating Example of a Non-inertial Frame
Such an accelerating frame of reference is called a non-inertial frame because the law of inertia does not hold in it. That is, an object whose position is judged from this frame will seem to spontaneously change its velocity with no apparent non-zero net force acting upon it. This completely violates the law of inertia and Newton's laws of motion, since these laws claim that the only way an object can change its velocity is if an actual non-zero net force is applied to the object. Objects just do not start to move about here and there all on their own.
From this I will single out the most salient point:
an object whose position is judged from this frame will seem to spontaneously change its velocity with no apparent non-zero net force acting upon it.
OK, the question before us is whether alpha Centauri is moving, despite no apparent net force acting on it, or whether Earth is moving despite no directly apparent net force acting on it.
Whether Earth is an inertial frame of reference and alpha Centauri is moved by an angel back and forth 0.76 arch seconds. Or whether Earth is a non-intertial frame of reference and itself moving 190,000,000 miles distance*** between January 1st and six months later. Whether you consider that movement as by God or as by an angel or as by - classic Newtonian model - equilibrium evading it between its forces of inertial movement at a tangent from its real orbit and on other hand movement radial to its actual orbit, and inward, by attraction from Sun. EITHER WAY - whichever non-zero net force you presume as being at work on whichever body - the net force is not directly apparent.
If Phil Plait wants to exclude from his considerations explanations like "God can turn the Universe around us each day, how do you know He doesn't?" he can of course exclude them from his considerations. But not from mine. And if he wants to exclude from his considerations explanations like "God can have granted an angel to move alpha Centauri 0.76 arch seconds, as seen from earth, back and forth each year", he can exclude those from his considerations too, but not from mine.
One which I am NOT excluding from consideration, but rejecting as provenly unrealistic is his explanation that gravity and inertia can equal out in orbits for thousands° of them. One astronaut has in weightless but not non-friction environment, on Mir I think, tested another attraction than gravitational one, namely electrical charge on water droplets. I am sure Phil Plait knows the footage. I counted first of all any single droplet's successive orbits around charged knitting needle as 10 - 20, medium 15 small orbits. I never counted two droplets as simultaneously in orbit and I counted several water droplets as already glued to knitting needle during each show of a new water droplet.
So, how do we decide whether geocentrism is a non-inertial or Geocentrism an inertial frame of reference?
To Phil it would already be decided - despite the water droplets - by his not being a fan of saying "God did it". Now, this is not a way of deciding questions that a Christian can accept. Not unless they are the Miller type of not-quite-Christian "Christians"°° whose admiration for "God as designer" means they think "He" designed a universe able to work without him and without angels.
This brings us to the question why a designer is better the more self-working his product is. In Commercial conditions he usually wants to sell it, so he must design it so it will work without him. A knife will work without the smith that made it - once he has sold it. In Industrial conditions he is often constructing a labour saving device which will need less attention than that to most of its action from the one using it. A car driver wants the wheels to turn without his interfering directly with that.
But does a Musician want a Music Box more than a Violin? And can no Violin builder also be a great Violin player? The Christian or even just generally theistic take on God (as believed by Christians, Sunni Muslims or Rabbinic Jews - presuming they keep out of Sadducee errors) is that God created a Universe in such a way as Him being the only one who can run it. And that He is indeed running it. It also includes a universe having created spirits above the created bodies.
Summa Theologica, First Part - on God and Creation
Question 110 - How angels act on bodies
Article 3. Whether bodies obey the angels as regards local motion?
Objection 1. It would seem that bodies do not obey the angels in local motion. For the local motion of natural bodies follows on their forms. But the angels do not cause the forms of natural bodies, as stated above (Article 2). Therefore neither can they cause in them local motion.
Objection 2. Further, the Philosopher (Phys. viii, 7) proves that local motion is the first of all movements. But the angels cannot cause other movements by a formal change of the matter. Therefore neither can they cause local motion.
Objection 3. Further, the corporeal members obey the concept of the soul as regards local movement, as having in themselves some principle of life. In natural bodies, however, there is not vital principle. Therefore they do not obey the angels in local motion.
On the contrary, Augustine says (De Trin. iii, 8,9) that the angels use corporeal seed to produce certain effects. But they cannot do this without causing local movement. Therefore bodies obey them in local motion.
I answer that, As Dionysius says (Div. Nom. vii): "Divine wisdom has joined the ends of the first to the principles of the second." Hence it is clear that the inferior nature at its highest point is in conjunction with superior nature. Now corporeal nature is below the spiritual nature. But among all corporeal movements the most perfect is local motion, as the Philosopher proves (Phys. viii, 7). The reason of this is that what is moved locally is not as such in potentiality to anything intrinsic, but only to something extrinsic--that is, to place. Therefore the corporeal nature has a natural aptitude to be moved immediately by the spiritual nature as regards place. Hence also the philosophers asserted that the supreme bodies are moved locally by the spiritual substances; whence we see that the soul moves the body first and chiefly by a local motion.
Reply to Objection 1. There are in bodies other local movements besides those which result from the forms; for instance, the ebb and flow of the sea does not follow from the substantial form of the water, but from the influence of the moon; and much more can local movements result from the power of spiritual substances.
Reply to Objection 2. The angels, by causing local motion, as the first motion, can thereby cause other movements; that is, by employing corporeal agents to produce these effects, as a workman employs fire to soften iron.
Reply to Objection 3. The power of an angel is not so limited as is the power of the soul. Hence the motive power of the soul is limited to the body united to it, which is vivified by it, and by which it can move other things. But an angel's power is not limited to any body; hence it can move locally bodies not joined to it.
If something is moving without an apparent net force affecting it, a Christian may well presume, without absurdity, that the non-apparent net force affecting it is an angel. He is not obliged to think two of his senses, eyes as well as inner ears, are fooling him on the apparent inertiality of our frame of reference. If Phil Plait feels so obliged, I submit that is because he is denying the existence of God and of angels.
Nanterre University Library
*** Cited after a Flat Earth book which misses the point on p. 67, it was printed in 1899:
Zetetic Cosmogony; Or, Conclusive Evidence that the World is Not a Rotating-revolving-globe, But a Stationary-plane-circle
° Or millions of them. Or billions of them. Which he would claim for earth around sun.
°° See my refutation of Miller in four parts, linking here to first part, from then links within series:
Responding to Miller, Staying with Father Murphy's God, part 1