Monday, July 18, 2011

A Moving Earth?

Inevitably, in origins debates among Christians, the question is raised:
Since the church was wrong about the earth’s motion, and let science modify its interpretation of the Bible on this point, why should we not do the same for matters concerning origins?

For example, Dr R. Scott Clark, in his book Recovering the Reformed Confession (2008), makes much of the fact that before Copernicus (1473-1543) all Christians were all geocentrists. There were staunch, orthodox Reformed defenses of geocentrism in the late 16th century; geocentrism was the dominant view among the Reformed throughout the 17th century (see my post Reformers Contra Copernicus). Yet today hardly anyone is a geocentrist. According to Clark, no one changed their view because of biblical exegesis. Rather, they changed their view because the science changed, forcing a change in our understanding of Scripture.

The lesson Clark draws from this is that we should be wary of using the Bible to settle scientific issues. In particular, we should not be insistent on a literal view of Genesis 1. In such a manner, Clark seeks space within Reformed circles for his own non-literal view of the creation days.

Science and Motion
Historically, the issue was whether or not the earth was at rest in some absolute sense. The traditional, medieval geocentric view was that the earth was at rest at the center of the universe, with the Sun revolving about the earth once a year.
Most geocentrists held also that the fixed earth was non-rotating: the sun and stars revolved about the earth every 24 hours. 

Copernicus, on the other hand, believed that the universe was helio-centric. He contended that it was the sun, rather than the earth, that was at rest, and that a rotating earth revolved about a stationary Sun.

Who was right? Certainly, for the earth-bound observer, it seems that the sun moves about a stationary earth. However, as seen from the sun, it would be the earth that moves. Such relative motion clearly depends on our vantage point. Unhappily, even with a telescope, we can observe only relative motion. We get exactly the same observations whether we assume the sun moves around the earth or vice versa. 

So how can we prove that the earth is really moving in some absolute sense? To determine absolute motion we need an absolute reference point. What point might that be? the sun? distant galaxies? But how do we know that, say, the sun or a distant galaxy is at absolute rest? at absolute rest with respect to whatTo define absolute motion we must somehow go beyond the observations. 

At one time, when Newtonian mechanics still reigned, it was widely believed that the earth had been proven to be moving in an absolute sense, in that the Newtonian laws of motion hold when the earth is in motion, but not when it is at rest. 

However, after Einstein's general relativity dethroned Newtonian mechanics in 1915, such mechanical considerations no longer help, since general relativity uses only relative motion. Whether we consider the earth to be fixed or moving, we end up with exactly the same physical consequences. According to Einstein, writing in 1938, the two sentences “the sun is at rest and the earth moves” or “the earth is at rest and the sun moves” simply reflect two different choices for coordinate systems, both equally valid.

Much the same points have recently been made by George Murphy ("Does the Earth Move?", Perspectives in Science and Christian Faith 63 (June, 2011):109-115. Murphy, however, argues that, although the center of the earth could be fixed, the earth itself must be rotating, otherwise objects further than Neptune would be moving at speeds greater than the speed of light, which relativity prohibits. On this point, Murphy is mistaken. The relativistic constraint that objects can't move faster than light refers only to motion with respect to the local background space--or aether. The aether itself may move at any speed. Thus, if the entire universe--including the aether-- revolved about the earth, this would not violate relativity.

In this regard, it has been shown that, in general relativity, the universe rotating about a fixed earth produces Coriolis and centrifugal forces, the bulge at the earth's equator, and all other phenomena generally adduced to prove that the earth is rotating (see D. Lynden-Bell, J. Katz and J. Bicak, “Mach’s Principle from the Relativistic Constraint Equations”, Monthly Notices of the Royal Astronomical Society 272 (1995), pp. 150-60). The two reference frames--fixed earth or rotating earth--are thus scientifically equivalent.

Consequently, most scientists grant that the earth’s absolute motion cannot be scientifically proven. 

In short, Dr. Clark's reasoning reveals an outdated knowledge of science. Ultimately, one's choice of an absolute standard of rest must be based on extra-scientific considerations, based on philosophical or theological factors. A geocentric biblical frame of reference is thus beyond any scientific disproof.

The Absolute Standard of Rest
You might think it implausible for the immense visible universe to revolve around a tiny fixed earth. This, however, presumes the materialist error that the visible physical world is all that exists. Christians know better. God’s creation is much larger, encompassing also the vast, spatial heaven where God and His angels reside (see my post Cosmology and Heaven). 

The laws of nature that we observe in our physical universe do not necessarily apply to heaven, which seems to have a different nature. Hence, even if there were scientific proof for the earth's absolute motion within the physical universe, this would not prove the earth's motion within the universe as a whole.

The ultimate focal point of the entire creation is God's heavenly Throne. Would it not be most fitting for God to designate this place--the dwelling place of the Absolute--as the ultimate standard of absolute rest?

The link between the earth and God's throne will become even more obvious in the future after the earth is renewed. Then God's dwelling place shall descend from heaven to be with man (Rev.21:1-4), and the throne of God and of the Lamb shall be established on the earth itself (Rev.22:1-5).

The universe in its fullest sense is, therefore, neither helio-centric nor geo-centric but, rather, Christo-centric.

The earth’s rest, defined in terms of God's holy Throne, serves to remind us of the presence of God and of the multi-dimensional richness of His creation. Of course, such geocentricity, correlated as it is to a currently invisible heaven, does not necessarily have any scientific consequences, since scientific observations and laws are limited to merely the visible universe

Geocentricity and Genesis
There are many similarities between the 17th-century Reformed battle against Copernicus and the current debate on origins. In both cases, the main issue was one of Biblical authority versus scientific theorizing. The Reformed theologian Gisbertus Voetius (1589-1676), a major anti-Copernican, believed the Bible to be inerrant and fully authoritative. He held that science should accordingly conform to Scriptural truths; yielding to Copernicanism meant exalting human reason over God's Word.

In both cases, the Bible was challenged by dogmatic scientific claims going well beyond the observational evidence. In both cases, the data can be readily explained by alternative theories more consistent with the biblical givens. In both cases, many theologians surrendered too readily, over-estimating the power of human science and lacking sufficient confidence in God’s word.

The two issues are in fact directly connected. For example, Prof. N.H. Ridderbos [Is There a Conflict Between Genesis 1 and Natural Science,1957, pp. 42-44] was convinced, on purely exegetical grounds, that the Genesis days were literal days. However, this plainly entailed geocentricity since, for example, the earth was created before the Sun and stars. Consequently, Ridderbos, (erroneously) believing geocentricity to have been scientifically falsified, rejected the plain reading of Genesis 1.

The Copernican revolution banned God from the modern universe, which no longer has a place for heaven; the Darwinian revolution banned God from history.

In sum, before we adapt Scripture to accommodate some alleged scientific fact--particularly concerning absolutes or origins--it would be prudent to weigh the cost in terms of Biblical authority and honest exegesis.


 James A. Gibson said...

Dr. Byl,

I read your book, The Divine Challenge, some years ago. It was a pleasant surprise to find that you have a blog. On to the substance...

You said that when an astronomer claims "the earth’s absolute motion cannot be proven," I have to wonder about what notion of proof is in play here. If it is logical certainty, then the claim is right. But it is not substantial, since most (all?) scientific claims have at best inductive/abductive evidence. If something weaker than logical certainty will do, then we why can't we use theoretical virtues to determine which of the two hypotheses - geocentrism vs. heliocentrism - is better?

Let's suppose you are right that the two views are empirically equivalent. I don't know if this is the case (my training is not in astronomy, but in philosophy). Even so, one reason for preferring one hypothesis H1 over H2, where H1 and H2 are empirically equivalent, is that H1 is simpler. Granted, the notion of simplicity requires some cashing out. But once we fix that notion, doesn't the geocentric view come out less simple than the heliocentric view? Galileo, you probably know, gave this argument in his Two Dialogues. And he intended it to work against the Tychonic system. Further, once we add in considerations about elegance, wouldn't that push the probability in favor of a moving earth?

In short, it seems your argument against Clark is problematic for this reason: the central theoretical virtue at which you aim is empirical adequacy, but scientists rely on many other theoretical virtues. Hence, once those virtues are considered, you don't get underdetermination by the relevant scientific considerations.

Mike Tu said...

Professor Byl,

Thanks for this post. I am especially intrigued by your description of the universe as Christocentric. It certainly puts a "new" twist on the truth of Colossians 1:16.

Now, a question that's always been on my mind as I've read your articles/books: In your view of science, how do you distinguish between a scientific *observation* and a scientific *theory*? This is a question that comes in my mind when reading your works in dialogue with Gordon Clark's critiques of empiricism.

For example, I can imagine Hooke's law of F=kx being a theory that is a pragmatically useful (but not absolutely true) predictor of a spring's behavior. But what would the observation be? Seeing something with a spring-like-shape moving? How would I be able to judge what is a spring, apart from judging/theorizing something that I see as a spring? How would I distinguish a true spring from a spring-shaped-brick with metallic spray paint on it?

I hope that question came out clearly. Thanks ahead of time. :)

Bryan Johnson said...

It could also be pointed out that in the context of standard cosmology there are galaxies receding away from us at speeds greater than the speed of light; this is defended on the same grounds (i.e., the Hubble expansion rate can exceed the speed of light because it is space itself that is expanding).

Anonymous said...

Thank you, Dr Byl, for this post.

Great quote of Luther from pagan astronomer:


Greg Welty said...


Something like the following point has been made by J. P. Moreland in a few places (_Christianity and the Nature of Science_, _Three Views on Creation and Evolution_).

Let's concede that heliocentrism (HC) is a simpler scientific theory than geocentrism (GC), because it banishes epicycles upon epicycles and other complicated things.

So, with respect to the theoretical virtue of simplicity, which we concede is relevant to theory-confirmation, HC is simpler than GC, while remaining empirically adequate. Thus, it has a stronger claim to our belief than GC.

But as Christians seeking to formulate an *overall* view of God and the world that would most commend itself to our belief, we have other sources of information besides science, including the Bible (properly interpreted).

In particular, with respect to various 'geocentric-sounding' passages of Scripture, such as Joshua 10:13, there are at least two theories:

(J1) The literal interpretation of Joshua's description of natural phenomena is in general reality-depicting, and Joshua 10:13 is -- naturally -- an instance of this.

(J2) Despite the fact that the literal interpretation of Joshua's description of natural phenomena is *in general* reality-depicting, what is spoken of in Joshua 10:13 is an exception to this rule, and should be understood as phenomenological description only. The sun didn't 'really' stop, even though it looked that way. (Ditto for any other isolated passages of Scripture that seem to conflict with HC above.)

Clearly, as a hermeneutical approach, J1 is far simpler than J2.

And now we come to the main point. Even though HC is clearly simpler than GC, it is not clearly the case that (HC+J2) is simpler than (GC+J1). The overall simplicity gained by HC seems lost by the addition of J2. So if simplicity is a theoretical or epistemic virtue, the fact that HC is not only empirically adequate but also simpler than GC doesn't -- by itself -- tell us whether to accept HC, at least if we are interested in the overall simplicity of points of view.

My sketch is cartoonish, but you get the idea.

John Byl said...


Thanks for your comment, which is quite correct.


Regarding the distinction between observation and theory, I would say that the observations are measurements of the stretching (x) of actual springs under tension due to various weights (F). For a particular spring, this gives a set of data points of x versus F. Over a certain range, the relationship will be roughly linear; the slope gives k, from which we infer the observational law F=kx. Theory comes into play once we try to explain the law in terms of basic physical principles or extend its application to (as yet) unobserved parts of reality.

How do we distinguish springs from non-springs? We could define a spring as an object that obeys Hooke’s law.

Of course, there is a sense in which all observations are theory-dependent (e.g., we presume certain properties of space-time, perception, etc.). Nevertheless, I maintain that there is a significant gap between the actual observational data—where there is usually general agreement concerning observational background theory--and our attempts to explain and extend that data—where worldview differences come more readily to the fore, allowing for a variety theoretical models.

John Byl said...

Hi James

You raise some interesting thoughts about scientific proof. Let me note, first, that Galileo’s heliocentric model was no simpler than the Tychonic system. Second, the main problem concerns how we choose an absolute standard of rest. In Newtonian mechanics absolute motion can be defined with respect to an inertial frame of reference (i.e., where Newton’s laws hold). In terms of this definition, both the Sun and Earth are in absolute motion. Thus, after about 1687, both heliocentricity and geocentricity were widely considered to have been decisively disproven. However, in general relativity there is no preferred frame of reference. Hence the Newtonian dynamical proof is no longer valid.

It might be argued that scientific theories involving a moving earth are more elegant, or fruitful, or ?…... But unless it can be shown that more elegant or fruitful theories are in fact more likely to be true, such considerations carry no epistemic weight. Indeed, a Christian scientist could argue, with better justification, that one should prefer theories that are compatible with Scripture.

I argue, further, that the universe is larger than what is accessible by science. Hence extra-scientific considerations are needed to define the standard of absolute rest.

 James A. Gibson said...


Thanks for your comment! I can't take a stand on the right interpretation of Joshua, though I once read Walton's view on the matter, and it struck me as plausible. Anyway, I think what your comment nicely brings out is that there is a tricky issue in the wing: how much weight should one place on certain kinds of evidence? I take it that the issue is not over the infallibility of Scripture - so the issue is not whether the Bible includes a falsehood. Rather, there are interpretations of a text which are not *required* by the text itself (that is, there is no contradiction between the relevant text and some other passage). And in those cases, how does one weigh hermeneutical evidence with extra-textual evidence? I don't see a hard-and-fast rule here. The best I think we can do is to consider the evidence on a case-by-case basis. It is less than an ideal situation, but this is true of how we evaluate evidence and theories generally.

Dr. Byl,

Thanks for your reply. I tried to steer clear of the issue of absolute and relative motion and focus on a more specific issue, which was your emphasis on empirical equivalence and underdetermination. I have a question about your second paragraph. You said, "It might be argued that scientific theories involving a moving earth are more elegant, or fruitful, or ?…... But unless it can be shown that more elegant or fruitful theories are in fact more likely to be true, such considerations carry no epistemic weight." Question: suppose that one could satisfy that this demand. That is, one could show more elegant, explanatorily powerful, simpler, etc., theories were more likely to be true - or 'P' for short. Then on your view, would the following conditional be true: P-->(the non-textual evidence makes it more probable that the earth moves)?

Bryan Johnson said...


The principle of relativity is that relative motion is the only type of motion that has any empirical meaning - it's the only type of motion that can be measured. That is what is meant by the idea that there is no preferred reference frame. The term 'preferred' can be somewhat misleading since there usually is a 'preferred' frame for doing calculations - preferred in the sense of being simpler. You can still send a man to Mars with Ptolemaic astronomy, but you might have trouble getting NASA funding because of the time it would take you to get the calculations right. A good scientist will choose a simple frame for doing calculations, but he does not thereby falsify all the other choices he could have made. Any choice should match the data or you've done the calculation wrong. The point is that there is nothing scientifically inaccurate about geocentric language, based upon our current understanding of science. The principle of relativity says that science cannot settle the question.

John Byl said...


If you could prove (1) that a theory satisfying property X better is more likely to be true and (2) a moving earth theory (MET) currently best satisfies X, then it does seem logical to conclude, (3) “the non-textual evidence currently makes it more probable that the earth moves”.

One problem: you can’t leave out the possibility that further research will uncover a fixed earth theory (FET) that is better yet, in much the same way that relativity ultimately displaced Newtonian mechanics, which was for 2 years widely accepted as an absolute truth.

Moreover, a Christian scientist could continue: however, (4) the textual evidence does in fact contradict MET and (5) the Bible as the inerrant word of God is more authoritative than a mere probabilistic scientific conclusion based on X. Hence, (6) we should prefer some alternative fixed-earth explanation to MET.

Dean Davis said...

Towards the end of his life, Galileo penned these fascinating and much-neglected remarks to his Copernican friend, Francesco Rinuccini:

"The falsity of the Copernican system should not in any way be called
into question, above all not by Catholics, since we have the unshakeable
authority of the Sacred Scripture, interpreted by the most erudite
theologians, whose consensus gives us certainty regarding the stability
of the Earth, situated in the center, and the motion of the sun around
the Earth.

"The conjectures employed by Copernicus and his followers in
maintaining the contrary thesis are all sufficiently rebutted by that most
solid argument deriving from the omnipotence of God. He is able to
bring about in different ways—indeed, in an infinite number of ways—
things that, according to our opinion and observation, appear to happen
in one particular way. We should not seek to shorten the hand of God
and boldly insist on something beyond the limits of our competence."

Skeptics notwithstanding, there is no good reason to doubt the genuineness of this letter, or Galileo’s sincerity, since over the course of his long life he had wrestled with at least three different models of the universe, all of which were more or less observationally equivalent (Ptolemy, Copernicus, Tycho).

This salient fact apparently brought him face to face with the infinite ingenuity of God, and therefore to the humbling realization that apart from divine revelation finite man can know little or nothing about “how the heavens (actually) go” (Isaiah 55:8-9). And since both God and the Church leadership had clearly spoken up in favor of geocentrism, it was only natural for Galileo to relent in this matter.

The crux, then, as always, is this: What saith the Scriptures? And for my part, the Scriptures saith a whole lot about a geocentric cosmos!

RubeRad said...

It seems to me that there are a number of obvious questions being avoided here. Granted any point can be arbitrarily chosen as the origin of a frame of reference, but is gravity at all real? Sure, the effects of gravity have been tweaked by relativity since Newton originally figured out the broad strokes, but in a geocentric frame of reference, what is keeping the sun from obeying Newton's 1st law and continuing in a straight line away from the earth? Jupiter's moons orbit Jupiter, Saturn's moons orbit Saturn, Earth's moon orbits Earth, all of these relationships obey the principle of smaller bodies orbiting larger bodies in an ellipse that follows from the inverse-square strength of gravitational attraction. Why would Earth be the exception to this rule? Are we to expect that someday scientists will discover some special properties of Earth and Sun that explain why the Sun would orbit the Earth in precisely the same inverse orbit that we would observe if the Earth were to orbit the Sun by our current understanding of physics? (Or is this mechanism hidden in the invisible part of creation?)

"It might be argued that scientific theories involving a moving earth are more elegant, or fruitful, or ?…... But unless it can be shown that more elegant or fruitful theories are in fact more likely to be true, such considerations carry no epistemic weight."

So what does "true" mean to you? It seems that you are operating with a definition of "true" that is completely orthogonal to science. Why do you bother refuting science with pseudo-science, instead of just saying "don't forget, none of it is true anyways"?

Like here: "else objects further than Neptune would be moving at speeds greater than the speed of light, which relativity prohibits. On this point Murphy is mistaken." Why isn't your next sentence "The bible does not tell us that velocity of matter can never exceed the speed of light"?

RubeRad said...

"You can still send a man to Mars with Ptolemaic astronomy"

I seriously doubt that is true. Perhaps you could use Ptolemaic astronomy and a geocentric coordinate system to predict where the various solar-system bodies would be, but that would merely allow you to chart a course to Mars. There are still fundamental issues of gravity to overcome; how is Ptolemaic astronomy going to help you choose a path that requires a feasible amount of fuel to escape the gravitational pull of various bodies in the solar system, or take advantage of solar gravity to "slingshot" past the sun and intersect Mars' orbit precisely when Mars is passing by? (Or how is it even possible with Ptolemaic astronomy to know the distance to Mars?)

And, as I noted above, given an understanding of gravity, how can your model not include the Earth orbiting the Sun due to gravity?

My point is that you are not presenting a full picture when you say "there is nothing scientifically inaccurate about geocentric language, based upon our current understanding of science". Better to say, there is nothing computationally beyond tolerance about geocentric systems in many contexts where heliocentric effects are negligible.

I deal in satellite imagery professionally, and we use geocentric computations all the time (although not exclusively; we have been able to work with some astronomical imagery, such as Lunar and, um, Mars-ian? Martial? You get the point). But that's because we know that if we computed in a more comprehensive heliocentric model, the gravitational effects of the sun, other planets, their moons, asteroids, etc. on a near-earth satellite are negligible compared to the gravitational effects of the earth. The effects are so much smaller than our error budget that we ignore the fact that the Earth orbits the Sun. It's not just that geocentric/heliocentric are potato/potahto, equally "true" (whatever that means around here); heliocentric is "correct", and geocentric is "incorrect", but with a degree of inaccuracy which we can tolerate.

It's the same with Newton and relativity. Newton is "incorrect", but if you're just trying to bomb the neighboring country, the velocities are so small relative to the spped of light that the inaccuracies are within acceptable (and well-understood) tolerances and you don't need to switch to relativistic calculations.

RubeRad said...

"If you could prove (1) that a theory satisfying property X better is more likely to be true"

Given your concept of "true", what does "likely to be true" mean, and what form of proof could be used to prove "likely to be true"?

John Byl said...

Ruberad writes:
So what does "true" mean to you? It seems that you are operating with a definition of "true" that is completely orthogonal to science. Why do you bother refuting science with pseudo-science, instead of just saying "don't forget, none of it is true anyways"? Like here: "else objects further than Neptune would be moving at speeds greater than the speed of light, which relativity prohibits. On this point Murphy is mistaken." Why isn't your next sentence "The bible does not tell us that velocity of matter can never exceed the speed of light"?

1.I take the usual, correspondence view of truth: a proposition is true if and only if it corresponds to what actually is the case. Concerning theories, a theory is true if all it postulates--events, entities, and relations--actually correspond to reality. To the extent that such might not be adequately observable, the truth of a particular theory may be impossible to establish.

2. My point was that Newtonian proofs for the absolute motion of the earth are no longer valid within general relativity, since the latter deals only with relative motion. This is hardly "refuting science with pseudo-science."

3. Your remarks about calculating orbits concern only the usefulness of a theory. Useful theories are not necessarily true. The difficulty here is not just that relativity is more accurate than Newton, but that it operates under an entirely different conception of space-time, force, etc.

Hugh McCann said...

"Science & Truth" by Gordon Clark (+1985) recommended:

Bryan Johnson said...


Ignoring the gravity of the sun and other solar system bodies is a separate issue from which of those bodies is at the center of the solar system. Brahe will get the same answer as Copernicus to as many digits of precision as you like, as long as they both include the gravitational effects of the same bodies. This should be obvious as they are simply different coordinate systems. Things are not so obvious when you consider the entire universe, but Lynden-Bell et. al. have shown that motion is relative in that case as well. The statement that the universe rotates about a fixed earth (or any other point you choose) is no less scientifically precise than the statement that the earth moves in a fixed universe.

RubeRad said...

"The statement that the universe rotates about a fixed earth (or any other point you choose) is no less scientifically precise than the statement that the earth moves in a fixed universe."
How about the statement "the gravitational force between the earth and sun is approximately (within 1%) F=GmM/r, and because the mass of the sun (M) is so much larger than the mass of the earth (m), that force causes a negligible effect on the momentum of the sun, compared to the change of momentum it causes the earth"?

Daniel C said...


as I see it, Dr Byl's point was that, with an absence of an absolute ppint of reference, the idea of being "in a state of absolute rest" is subjective. Therefore, the point is that one could very well embrace geocentrism and also Copernican astronomy.

Bryan Johnson said...


I'm not sure this is what you're getting at, but it's certainly true that all theories are approximate and depend upon neglecting certain effects, and that Newtonian mechanics is quite adequate for velocities that are small compared to the speed of light. The notion of relative motion is quite general, however, and if you do enough scientific calculations it becomes clear that it's the only motion that is meaningful, even in Newtonian physics, and at any level of approximation.

RubeRad said...

Yes, I get that motion can only be considered relative, and any body in the universe can arbitrarily be considered to be absolutely at rest for purposes of computing something or other, and no body in the universe can be considered to be absolutely at rest (that includes the Earth by the way). The earth and sun and entire solar system are in (relative) motion with the rest of the milky way, which is in (relative) motion to all the other galaxies in the universe.

BUT the cause of earth's continuing pattern of relative motion with the sun is gravity continuously warping the earth's momentum into an elliptical orbit around the sun.

In short, an observer on the sun would see the earth going around the sun, because the earth is going around the sun.

And an observer on the earth sees the sun going around the earth, because the earth is going around the sun.

How about this: there are 10 to the I don't know how many atoms in the universe. You could establish a frame of reference centered on any one of them. The only atoms whose frames of reference do NOT yield observations of the earth moving around the sun, are earth-atoms (and I suppose lunar-atoms). Therefore, although none of those atoms is surprised that the earth perceives from its inertial frame of reference that it is fixed, the overwhelming consensus of the universe is that the earth is, really, moving around the sun.

RubeRad said...

Another way to put it, although no body in the universe can be considered absolutely at rest, I think it is quite fair to say that the sun is relatively at rest, compared to the earth.

Bryan Johnson said...


The relativity of motion is easier to grasp if one considers simple linear motion, and all of the objections you raise could be raised in that case as well. There is no physical difference between a rocket colliding into a particle at rest (with respect to the rocket) and a particle colliding into a rocket at rest (with respect to the particle). The only scientifically true statement is that they are moving with respect to each other. You don't get to count the number of atoms in the rocket and the particle and say that the one with more atoms is the one that is 'really' at rest. Issues of causality are a separate discussion and relate to the history of the collision. The collision could have been due to the rocket being launched into orbit and colliding with a particle already orbiting the earth, for example, or it could have been due to a particle in the solar wind colliding with a rocket floating through space. The physics of the collision is exactly the same in either case, however, and only depends upon their relative velocity. If you want to talk about the history giving rise to the relative rotation of the earth and the universe, the Biblical record is obviously relevant (for a young-earth creationist) and would actually favor the universe rotating around the earth (in a causality sense) because the earth was there before the firmament and the stars. The main point, however, is that regardless of the history and causality of the situation, the Bible's language about a fixed earth is not scientifically untrue (based upon current science, which regards all motion as relative), unless one sees that language as a claim that the earth is an absolute reference frame.

RubeRad said...

" the Biblical record...would actually favor the universe rotating around the earth (in a causality sense) because the earth was there before the firmament and the stars"
But I'm not talking about first cause, I'm talking about now. Today, is gravity a secondary cause that God uses to uphold the relative motion of the earth and sun (does gravity cause the earth to orbit around the sun)? When did it start to be that way?

Bryan Johnson said...


I agree that gravity is a secondary cause that God uses to uphold the relative motion of the earth and sun (although I prefer to regard the law of gravity as simply a manifestation of God's upholding rather than something outside of Himself that He 'uses'). From a physical perspective, the earth and the sun would not orbit each other were it not for their mutual gravitational attraction but would simply fly apart due to their inertia. But to say that gravity causes the earth to orbit the sun rather than the other way around is to go beyond what we can know scientifically. The only thing you can say with scientific certainty is that gravity causes them to orbit each other. It really is impossible to tell which one is orbiting which.

RubeRad said...

"The only thing you can say with scientific certainty is that gravity causes them to orbit each other."

How can you say that with scientific certainty? If gravity is real (if the understood law of gravity is accurate to within any reasonable precision) then the radius of the Sun's counter orbit is about 280 miles -- that's not enough space to fit the earth into, by orders of magnitude -- much less the 93 million-mile relationship we observe.

Does gravity cause Hubble to go around Earth, or the Earth around the Hubble? Does gravity also cause the sun to go around Mars?

How about a thought experiment. Imagine you alone in deep space, in a mini-death-star just big enough to hold you and keep you alive (say, 2m). There is no other mass for 100 million miles, except a tiny robot, the same proportional mass to you and your MDS as the earth to the sun, which would make the robot I think about the size of a grape. The robot and MDS both have propulsion systems you can control.

Experiment A: position the robot and the MDS an appropriate distance from each other, and give the robot an appropriate velocity in an appropriate direction (i.e. taking advantage of what we know about keeping satellites in earth-orbit, rather than flying off into space, or crashing back to Earth). Hypothesis: the robot will go around the MDS.

Experiment B: Give the MDS the exactly inverse velocity (i.e. identical relative motion between MDS and robot). Hypothesis: the MDS will go around the robot.

Which hypothesis (hypotheses?) do you think will prove successful?

"a manifestation of God's upholding rather than something outside of Himself that He 'uses'"

What do you think "secondary" means? It seems you see gravity as not created, but straight-up miracle. God's just moving all the particles in the universe "around" (if we can use that word), and they way he likes to move things has a particular mathematical pattern we like to call "the law of gravity". So now it's not just distant starlight exhibiting "apparent age", but the sun's orbit around the earth exhibiting "apparent gravity"?

RubeRad said...

"You don't get to count the number of atoms in the rocket and the particle and say that the one with more atoms is the one that is 'really' at rest."

I'm not talking about the relative number of atoms in the rocket vs. particle, or sun vs. earth; I'm talking about the relative number of atoms in the rest of the universe, from which relative motion can be observed.

There is a fundamental difference between a rocket propelling itself into the ocean (or a puddle), and a rocket on the launch pad being hosed down with water. In both cases water particles and a rocket have relative motion. But in one case, force applied to the rocket causes the rocket to move toward the water, and in the other case force applied to the water causes the water to move toward the rocket. In all frames of reference except for inertial frames of the rocket or the water, it is clear in both cases which is "relatively moving", and which is "relatively still".

Bryan Johnson said...


You have correctly identified the simplest frame for doing calculations, which is the frame in which the center of mass of a system is at rest. For two objects with a large mass ratio between them, the center of mass is nearly at the location of the heavier object, as you also point out. The center of mass of the solar system is sometimes inside the sun, sometimes outside, but more or less near it. And that is why we prefer to think of the planets as orbiting the sun. One could choose a reference frame centered on mars but it's hard to think that way and so we don't. As I said before, however, the model of Tycho Brahe is empirically equivalent to that of Copernicus. There is no observation or experiment that can distinguish between them.

Bryan Johnson said...

In your MDS/robot thought experiment, if you showed up after the experiments had been performed (assuming I hadn't destroyed the robot with my MDS), how would you go about determining which experiment I had performed? Without knowing the history of the experiments it would be impossible for you to tell the difference because there is no difference once they are in orbit about each other.

Bryan Johnson said...

In your rocket/water example, the causality issues relate to the history of the situation - how did the rocket and water get in their state of relative motion? Once they are in a state of relative motion, however, there is no empirical difference between the two states with different causes - there is no signature of the history that gets imprinted on the final state. If you came upon the rocket/water system in relative motion and didn't know anything about how they got in that state, it would be impossible for you to distinguish between the two histories you describe.

Bryan Johnson said...

I do regard gravity as a miracle, in a sense. That is getting off topic from the original post, however, so we could continue that discussion over at my blog if you wish.

RubeRad said...

"In your MDS/robot thought experiment how would you go about determining which experiment I had performed?"

Simple. If you had performed experiment A, the relative motion would be orbital (robot elliptical around MDS). If you had performed experiment B, the relative motion would be linear (MDS away from robot). (i.e. hypothesis B would have failed)

"I do regard gravity as a miracle, in a sense. That is getting off topic from the original post"

It's only off topic if you beg the assertions of the post. If the relative motion of all bodies (in particular the earth and sun) are simply miraculous, then yes, all questions of what orbits what else are sophistry.

But if gravity is a real force (something created, on our side of the Creator/created distinction), then there is a real secondary cause to astronomical relative motion that allows us to objectively say which body is orbiting, and which body is being orbited.

At this point I don't see the benefit of hopping over to your blog; we've already dug a pretty deep rut around this tree.

Bryan Johnson said...

I see that I did not read your thought experiment carefully enough, although now I fail to see its relevance to the discussion. The question is whether you can tell the difference between the sun (MDS) orbiting the earth (robot) and the earth (robot) orbiting the sun (MDS), and your example only includes one of those final states. If I gave the MDS an initial velocity smaller by the square root of the mass ratio, it would orbit the robot and you wouldn't be able to distinguish between the final states. Are you claiming that it would be impossible to get the sun to orbit the earth, or that you know something about their initial velocities? If not, how is your example relevant? The fact that they both have the same initial linear motion is only an "apparent" connection. Relativity is only relevant for uniform linear motion or uniform rotational motion, neither of which apply to the situation you describe (except for the final state in which they orbit each other).

Bryan Johnson said...

I'm happy to discuss the nature of gravity here as long as Prof. Byl allows us to go on. I see physical laws as miraculous in the sense that I regard them as manifestations of the obedience of creation to God's sustaining word ("upholding all things by the word of His power", where power is the same word used on occasion to describe miracles). The view that God created the laws of physics and just set things in motion seems too deistic to me. In any case, I fail to see how this view of things makes gravity any less real. Do you think the laws of physics are more real than God?

RubeRad said...

"Are you claiming that it would be impossible to get the sun to orbit the earth"

Yes. If the sun were tapped with a force of epsilon, then it would move very slowly in whatever direction, and gravitational force would impel the earth to crash into the sun. However, if the sun were given an initial velocity comparable to earth's orbital velocity (~30km/s), then it would continue pretty much in a straight line barely perturbed by the force of gravity with the earth.

I suppose it is possible (likely?) that as the sun speeds away from (or speeds past) the earth, gravity would pull the earth into orbit around it.

But this would only happen if the earth is not fixed in space.

I guess what must have happened is that for Days 1-3 the Earth was NOT fixed; on Day 4, God sent the Sun whizzing by at about 30km/s with a closest approach of 93 million miles, gravity pulled the Earth into orbit "around it", and Ps 104:5 should be translated "After Earth's orbit around the sun stabilized on Day 4, God decreed that an inertial frame of reference with an origin at the center of the Earth is the standard for 'absolute rest'".

You win.

Steve Drake said...

Dr. Byl, Critics claim that you don't mention stellar parallax or the aberration of starlight in any of your posts, (see for example: (comments #117 and following in "The need for an informed worldview") yet I'm thinking you most likely have and I wonder if you might direct me to it? Note that I am being charged with expert-worship for referencing your works. Blessings.

John Byl said...


In my post I did not refer to stellar parallax and aberration of starlight simply because they both concern only relative motion.

Stellar parallax concerns only the relative motion of the earth, sun and stars. You get the same observational results whether
(1) you consider the earth to be moving about a fixed sun, with a fixed stellar background,
(2) you consider the sun, along with the stellar background, to be moving about a fixed earth.

According to the special theory of relativity, the aberration of starlight depends only on the relative velocity between the observer and the light from the star. See, for example,

Thus, as far as relativity is concerned, neither parallax nor aberration demand an absolute frame of reference.

RubeRad said...

Actually, stellar parallax in your scenario (2) is an amazing coincidence (or argument from design), because rather than simply rotating around a fixed earth, the stars' relative orbits are jiggling with exactly the parallax that is consistent with (1)

John Byl said...

In the geocentric model, stellar parallax is not an amazing coincidence. The stars are taken to be fixed relative to the sun--embedded in the background space. This background space shares in the annual motion of the Sun, thus producing the observed parallax.

Anonymous said...

I'm interested to know what you think of RubeRad's gravity objection, Dr. Byl.

John Byl said...

Ruberad treats gravity from an essentially Newtonian perspective (e.g., the Sun will move in a straight line unless perturbed by the earth’s gravity), with relativity adding just a tiny bit of tweaking. In Newtonian mechanics absolute motion can be defined in terms of an inertial frame of reference (i.e., a reference frame in which Newton’s laws of motion hold).

However, although the observational consequences of relativity may be a tweaking of Newtonianism, the theoretical bases of the two theories are entirely different. Certainly, gravity still holds in general relativity. Yet, as I stress in my post, general relativity does not posit any preferred inertial frames—its equations are valid in all reference frames. We get exactly the same observational results whether we consider the earth as rotating in a fixed universe or whether we consider the universe to be rotating about a fixed earth. No gravitational miracles are involved here, only a shift from Newtonian to relativistic dynamics.

Moreover, the universe is much larger than its mere visible physical dimension. Hence, the standard of absolute rest should ultimately be based on God’s (normally invisible to us) heavenly throne, rather than on any fallible scientific considerations.

PeterinScotland said...

Are you really talking about a real rotation of the sun round the earth, or is this some kind of philosophical statement? I have very little scientific knowledge but it seems to me obvious that the sun is a massive object with tremendous gravity and that in terms of reality rather than spiritual significance everything else in the solar system is either rotating around it or rotating around a planet that is rotating around it. For instance you have a big magnet and a small magnet. It's all very well to say they have an equal and opposite pull on each other (I think??) but you try and pick up a truck with the small magnet - you can't - you need the big magnet!

I came to this blog post after skimming your "God and Cosmos". I like the way you present the difficulties of various Creationist viewpoints. I am concerned that certain major creationist organisations present their theories as "truth" as much as the media and schools present evolution and non-theistic theories of the origin of the universe as "truth". (Secularists claim that evolution and theories of origins of the universe are two separate things - but they're both in opposition to Biblical creation and they are taught concurrently and interrelatedly).