The Unmoved Mover: Aristotle, Aquinas and Modern Physics

The unmoved mover is Aristotle's name for the first source of all motion: an eternal, wholly actual being that moves everything else without being moved itself, drawing the world as the object of its love and desire. Thomas Aquinas took up the argument as the first of his Five Ways and identified that mover with God. Modern readers bring two hard questions to it. Physics says nothing in the universe is absolutely at rest, and process theists say a God who cannot be moved cannot love. Below we set out Aristotle's argument in his own words, both challenges at full strength, the Thomist, Newtonian and process replies, and where Frame-Indexed Classical Theism stands among the classical attributes of God.

Key takeaways

• The unmoved mover moves without being moved. In Metaphysics XII, Aristotle describes "something which moves without being moved, being eternal, substance, and actuality," and he calls it God.
• The argument turns on borrowed motion. A chain of movers that each borrow their moving from another explains nothing unless something moves without borrowing. Aquinas made this his First Way.
• Two modern challenges press hardest. Physics: bodies keep moving without a mover, and nothing is absolutely at rest. Theology: a God who is never acted upon seems unable to love.
• Frame-Indexed Classical Theism (FICT) reads "unmoved" as a nature. Where Newton and the neo-Lorentzians place the unmoved standard inside physics and process theists give God motion, FICT holds that God is the Rest against which all motion is motion, which physics can neither find nor refute.

What is the unmoved mover?

The unmoved mover is the first source of change that is itself unchanged, and Aristotle reaches it by an argument from borrowed motion. The argument begins with a principle Aristotle states in the Physics: "Everything that is in motion must be moved by something." By motion he means far more than travel from place to place. Motion is any change, the passage of a thing from what it could be to what it actually is, as wood becomes hot or a seed becomes a tree, and it belongs to his larger account of matter and form. A mover that is itself moved must borrow its moving from another, and Aristotle refuses an endless line of borrowers: "it is impossible that there should be an infinite series of movents, each of which is itself moved by something else, since in an infinite series there is no first term." His conclusion is "the first of unmoved things, which being eternal will be the principle of motion to everything else."

In the Metaphysics he says what that first principle is. There is "something which moves without being moved, being eternal, substance, and actuality." It does not push the world. "The final cause, then, produces motion as being loved, but all other things move by being moved." Aristotle then names it: "On such a principle, then, depend the heavens and the world of nature," a living being, "eternal, most good," and, he adds, "for this is God." Its life is pure contemplation, and "its thinking is a thinking on thinking." Aristotle posited a further mover for each heavenly sphere, with one primary mover holding the whole in unity. The same principle is often called the prime mover.

Christian theology received the argument through Aquinas, whose Five Ways open with it and close the first proof with a sentence most students of Thomism know: "Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God." If the unmoved mover stands, the God of the creeds has a philosophical witness as old as Athens. If modern physics or modern theology has retired it, a central support of classical theism has gone with it.

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Does motion need an unmoved mover? The challenge at its strongest

Aristotle's answer is yes, and three modern challenges say no. We should first see the argument at its best, because its critics often meet a weaker version. The series Aristotle has in mind is not a chain stretching back in time, like a line of dominoes. He held that motion is eternal, so his argument never needed a first moment. The series is of movers acting now, each lending what it has only because it is receiving it. His own example is a man moving a stone with a stick: the stick "will not move anything unless it is itself moved by the man." Remove the hand and the stick lies still, however long the stick. An infinite series of such borrowers explains no motion at all, because none of its members has motion of its own to lend.

Three challenges press this argument hardest, and each deserves its full force. The first comes from physics. Newton's First Law states that "every body continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it." Once set moving, a body needs no mover to keep it moving. The philosopher Anthony Kenny drew the conclusion in his study of the Five Ways: "it seems that Newton's law wrecks the argument of the First Way."

The second challenge is relativity. Since Einstein, no experiment conducted inside a sealed laboratory can tell whether the laboratory is moving uniformly or at rest, and the laws of physics take the same form in every such frame. There is no preferred frame and no state of rest simply as such. On the popular reading, as Volume Six reports it, the very idea of an absolute standpoint, "God's included, has been retired by experiment." Such a mover, on this view, is a relic of a cosmos with a fixed centre.

The third challenge is theological, and it comes from people who love God. Aristotle's god thinks only of itself, since anything less would be beneath it, and on the common reading it moves the world without knowing or caring that the world exists. Volume Four puts the problem in one line: the Unmoved Mover is "absolute at the price of isolation, an Absolute who cannot relate." Process theists press the point against Aquinas as well. The Stanford Encyclopedia summarizes their charge: the classical God "is a God who acts but is never acted upon and can therefore never interact. This is summed up in the non-biblical Aristotelian formula of God as the unmoved mover." Fritz Rothschild described the God of Abraham Heschel, who feels and is felt, as "the Most Moved Mover," and Charles Hartshorne adapted the phrase.

So the unmoved mover stands accused twice over: too still for physics, and too still for love.

How do classical theists and their critics answer?

The Thomist reply begins with what Aquinas meant by motion. In the First Way, "motion is nothing else than the reduction of something from potentiality to actuality," and the example is not a coasting body but a living dependence: the staff moves "only because it is put in motion by the hand." The question is what makes a thing actually be what it is at this moment, not what keeps a body sliding across the ice. On that reading inertia is beside the point, a reply Edward Feser and other defenders of Aquinas have pressed. Aquinas also corrected Aristotle. His God is the Creator who gives being, not only the beloved goal that draws the heavens, a doctrine developed under creation out of nothing. Because God has no unrealized potential, He is pure act, and His relations to creatures are real in the creature but not in God. This reply rests on a sound metaphysics of change. Yet it does not say what "rest" can mean once physics has made all rest relative, and its "unmoved" is still heard as indifference.

Isaac Newton gave the most influential modern answer, and he gave it as a physicist. Absolute space and absolute time, for Newton, were a real and immovable backdrop to all motion, and infinite space was, so to speak, the sensorium in which the omnipresent God perceives all things. His instinct was right: something unmoved anchors the moving. But he built that anchor into physics itself. Leibniz objected in Newton's own lifetime that a uniform space no experiment could detect violates the principle of sufficient reason, and that a divine sensorium makes space itself quasi-divine. Einstein finished the matter empirically: no experiment finds the absolute backdrop, and physics runs complete without it. The theology Newton had joined to absolute space seemed to fall with it, and for three centuries its fall has been scored as the fall of the Absolute.

William Lane Craig defends a careful alternative. God is timeless without creation and temporal since creation, and the divine present picks out one privileged way of slicing spacetime, one absolute simultaneity, real though physics cannot detect it. Craig appeals to Hendrik Lorentz, whose theory kept a true rest frame and reproduces every prediction of special relativity. We should grant him the point he sees most clearly: the physics does not settle the metaphysics. But the price is high. Volume Six calls Craig's hidden frame "undetectable in principle and dynamically idle," and it trades God's eternity for a very long duration. Volume Three, Resolving Time and Eternity, takes the Boethian route instead: the eternal One apprehends the whole of time at once, which delivers everything the divine "now" was hired to deliver, without the undetectable physics and without the temporalized God.

Process theism and open theism answer the third challenge by giving up the first word of the phrase. God is the most moved mover, affected by every creature, His experience growing with the world's. This is close kin to what Brian Davies called theistic personalism, a God who is a person much as we are persons. These views rightly insist that love responds. A God moved by His creatures, however, needs them, depends on them for what He is, and can guarantee nothing about how the story ends. Whether God can respond without changing is the subject of the article on whether God can change His mind.

The method behind the answer that follows is set out in Volume One, which you can read free.

How does Frame-Indexed Classical Theism answer?

Frame-Indexed Classical Theism (FICT) is a research program in analytic theology that dissolves classical theological dilemmas by diagnosing them as artifacts of a single error: one term carried across two frames as though it meant the same thing in each. Newton put the unmoved standard inside physics as absolute space, Craig's neo-Lorentzian view puts it inside physics as a hidden frame, and process theism gives God motion so that He can love. FICT keeps God unmoved and keeps Him near, because the error lies in the word "rest" itself.

Within physics, rest is a relation. A passenger is at rest with respect to her seat and hurtling with respect to the ground, and there is no further fact about what she is "really" doing. Said of God, rest means something else entirely. Volume Six defines it: "Rest is immutability: the unmoved steadfastness of the divine nature, the standard against which all change is change, possessed absolutely and relative to nothing." "Unmoved" says what God is, not where He is or how fast He is going. He needs no backdrop to be measured against, because by His aseity He depends on nothing at all.

Once the two senses are held apart, both verdicts stand. In Volume Six's words, "physics is right that no laboratory is privileged, and theology is right that the Ground of all laboratories stands unmoved." Newton's error was an error of address: he looked for the unmoved One among the frames. Lorentz, the book says, built "the right house on the wrong lot," and Craig's hunger for a real divine standpoint is honored when that standpoint is moved from the best seat in the universe to the ground of being beneath every seat. Hence the book's conclusion: "God is the Metaphysical Rest Frame of the cosmos," where "frame" is the creature's word stretched upward by analogy, not a coordinate system God occupies.

Scripture draws the same line between the moving heavens and the God who remains:

"In the beginning you laid the foundations of the earth, and the heavens are the work of your hands. They will perish, but you remain; they will all wear out like a garment. Like clothing you will change them and they will be discarded. But you remain the same, and your years will never end." (Psalm 102:25-27, NIV)

James says the same of the Father: "Every good and perfect gift is from above, coming down from the Father of the heavenly lights, who does not change like shifting shadows" (James 1:17, NIV). When Paul stood before Epicurean and Stoic philosophers in Athens, Aristotle's own city of learning, he did not tell them God was far off. He quoted their poets: "'For in him we live and move and have our being.' As some of your own poets have said, 'We are his offspring.'" (Acts 17:28, NIV). The same distinction answers Newton's first law. Physics describes how bodies keep moving within an ordered world. The unmoved mover answers a different question, why there is a moving order at all, and Hebrews names who holds that order in being: "The Son is the radiance of God's glory and the exact representation of his being, sustaining all things by his powerful word" (Hebrews 1:3, NIV).

The relational charge from process and open theists dissolves the same way. Volume Four argues that a relationship must be genuine for each party in its own mode. For us, relating is unfolding and becoming. For God, it is the whole communion possessed at once. Demand that God change in order to love, and the relationship becomes less real to Him, received in installments instead of held entire. The unchanging God loves without measure, and in the Son He entered His people's suffering. The statement of FICT sets out the position in one place.

Volume Six, Resolving Rest and Relativity, gives the full argument and engages Newton, Lorentz and Craig by name.

Has the unmoved mover survived modern physics? Five simulated attacks

We have run thousands of simulated attacks against Frame-Indexed Classical Theism, drawn from academic and peer-reviewed sources. The five below press hardest on the claim that God is the unmoved standard of all motion, the standard that Newton's absolute space and Craig's neo-Lorentzian frame both place inside physics.

Physics already has a rest frame: the cosmic background

Here's one of those attacks and how the Many Beings framework would address it.

Relativity's "no preferred frame" is a symmetry of the laws, not of the actual universe. The universe's matter and radiation do pick out a frame: the one in which the cosmic microwave background, the afterglow of the early universe, looks the same in every direction. Our motion against it has been measured for decades, and the Planck satellite team reported in 2014 that it has an accepted value of about 369 kilometres per second, confirmed by an independent method. Craig nominates the cosmic time of that frame as the physical counterpart of God's present. Physics, the objection concludes, already has its rest frame, so there is no need to look outside the universe for one.

The defense grants the measurement and denies what it is taken to show. What the dipole measures is our velocity relative to the average motion of the radiation. It shows no law taking a privileged form in that frame. In Volume Six's words, the frame is "emergent and conventional, a matter of the matter's average motion, not dynamical; the laws privilege it in no way, and relativity is untouched by it." Cosmic time is a convenient coordinate fitted to the symmetry of one solution, doing descriptive work and no work as an absolute. And if the frame were dynamical, it would still be "one more citizen of the democracy," a frame inside the system. The unmoved Ground was never going to be found among the citizens.

Physics cannot rule out a hidden absolute rest frame

Here's one of those attacks and how the Many Beings framework would address it.

This attack found a real weakness in an earlier wording. Michel Janssen's 2002 study of Einstein and Lorentz treats their theories as rival interpretations of the same structure and shows that physics chose Einstein for explanatory reasons, not because any experiment refuted Lorentz's rest frame. Craig's Time and the Metaphysics of Relativity (2001) defends exactly such a hidden frame. So if the claim that no absolute rest exists in creation rests on "a century of confirmation," it rests on evidence that fits its denial equally well. Volume Six itself concedes that "the physics underdetermines the interpretation."

The defense is that the claim never needed physics, and Volume Six was corrected to say so. The premise now rests on metaphysics: "location is already relativity, so any rest a created frame possesses is rest relative to something." To be somewhere is to be placed among other somewheres. Physics "supplies its echo, never its ground." Grant Lorentz his hidden ether, then, and nothing changes. A rest relative to a created medium is still a rest relative to something, and the unmoved mover's Rest is relative to nothing. Even an undetectable Lorentzian frame would be one more location within the creation that God sustains.

Rotation and acceleration are absolute, so not all motion is relative

Here's one of those attacks and how the Many Beings framework would address it.

Newton's rotating bucket showed that spinning water climbs the walls whatever the bodies around it are doing, and modern instruments confirm the point. E. J. Post's 1967 review of the Sagnac effect describes ring interferometers that detect rotation from inside a closed apparatus, and an accelerometer reads acceleration with no window to look out of. Relativity kept these absolutes. So the claim that "motion and rest are frame-relative" is false as stated, and the oldest physical case for an absolute, the one Newton used, still stands inside physics.

The defense is that rotation and acceleration are exactly the absolutes relativity keeps, and they single out no frame of rest. Every observer agrees on an accelerometer reading and on a Sagnac phase shift. That agreement is what makes them invariant, like the speed of light. The frames in which the laws take their simplest form are an infinite family, and belonging to a family is not a crown worn by one member. Volume Six restricts its claim to uniform motion and credits Newton with keeping relativity there "despite his absolutes." Nothing in the argument denies that a spinning bucket can tell it is spinning. What no experiment can find is a single frame of absolute rest, and God was never a candidate for one.

Nothing in nature is ever truly still

Here's one of those attacks and how the Many Beings framework would address it.

Volume Six reads each boundary of physics as pointing toward a divine attribute, and it reads absolute zero, the temperature no process can reach, as pointing toward God's changelessness: "the utter stillness of a system with no thermal motion left to lose." Quantum physics replies that the cold limit is not stillness. A ground state still carries zero-point motion, required by the uncertainty principle. The standard laboratory example, explained by Francis Simon in 1934, is that liquid helium never freezes at ordinary pressure, however close to absolute zero it is cooled. Perfect changelessness, the objection concludes, is a physical fiction, and an attribute modeled on it inherits the fiction.

The defense notes the words the objection skips. The stillness in view is thermal: "no thermal motion left to lose." Zero-point motion is not thermal motion. It is what remains when there is no heat left to give up. The quantum ground state is also a stationary state, whose measurable properties do not change with time. And God's changelessness was never physical stillness extended. The same passage calls it the Rest "that is a nature and not a temperature." The divine Rest is reached by denying the creature's restlessness, not by cooling the creature down. The zero-point residue confirms the point: even at its floor, the creature is not the Rest.

Then whether an absolute exists depends on your point of view

Here's one of those attacks and how the Many Beings framework would address it.

Many readers raise this objection first: is frame-indexing relativism? Volume Six concludes that whether "there is an absolute frame" depends "on the operative perceptual frame." That sounds like perspectivalism: an absolute that exists from God's side and not from ours is no absolute at all. A careful reader set this sentence against Volume Three, where the timeless reality is said to be "indexed to no frame," and asked why Volume Six makes the existence of the absolute depend on a standpoint.

The defense is in the same sentence. Volume Six indexes the question to the operative frame "and the definition of 'frame' pertinent to it," and its next words name the two objects: "physics is right that no laboratory is privileged, and theology is right that the Ground of all laboratories stands unmoved." The physical verdict is about laboratories, coordinate vantages within spacetime. The theological verdict is about the Ground of all of them. Nothing is said to exist from one side and not from the other. The book says it flatly: "There is one absolute Rest, and it is God's." What varies with the frame is the meaning of the word, not the reality of the Rest.

The books in the series carry the same method into time, change and infinity.

Frequently asked questions

Is the unmoved mover the same as the prime mover?

Yes. Both names translate Aristotle's description of the first source of motion, "something which moves without being moved." Older English favours the first name, and the second stresses that nothing moves it. In everyday English "prime mover" also names an engine or the main muscle in a movement, so context decides which is meant.

Did Aristotle think the unmoved mover was God?

Yes. In Metaphysics XII he calls it "a living being, eternal, most good," and adds, "for this is God." His God differs sharply from the God of Scripture, however. It did not create the world, which Aristotle held to be eternal. It thinks only of itself, and on the usual reading it moves the heavens as the object of their love without knowing them. Aristotle also posited further movers for the heavenly spheres.

Does Newton's first law disprove the unmoved mover?

No, though Anthony Kenny argued that it seems to wreck the First Way. Inertia describes how a body keeps moving once moving. Aquinas's argument concerns what makes a thing actually be what it is at each moment, so the two answer different questions. Frame-Indexed Classical Theism agrees with that Thomist reply and adds that the unmoved mover is the ground of the whole moving order, not a force that keeps one body in motion or a physical backdrop like Newton's absolute space.

Is the unmoved mover the God of the Bible?

Aquinas identified this mover with God, and Scripture's God does not change: "I the LORD do not change" (Malachi 3:6, NIV). But Scripture's God creates the world from nothing, knows every creature and loves it, which Aristotle's mover does not. The argument shows that a first, unmoved source of change exists. Its neighbour, the argument from contingency, shows why such a source must exist by its own nature.

Can an unmoved God respond to prayer?

Yes. Classical theism holds that God wills our prayer and His answer together in one eternal act, so the prayer is a real cause on our side with no change on His. God's love is full and active, not a mood that rises and falls, as the article on whether God has emotions explains. Volume Four, Resolving Immutability and Interaction, develops the account in full.

Where to go from here

Aristotle said the unmoved mover moves the world "as being loved," and Augustine heard in that a truth about the human heart. He opened his Confessions with a prayer: "You move us to delight in praising You; for You have made us for Yourself, and our hearts are restless until they rest in You." Physics confirms the first half from below. Every frame it can find is in motion, and every rest it can measure is relative. The Rest it cannot find is the One who holds every frame in being and draws every restless creature toward Himself.

Volume One sets out the method behind this reading from first premises, and it is yours free.