If we pick up a stone and then let it go, why does it fall to the ground?” (Albert Einstein, Relativity: The Special and the General Theory, Ch. XIX).
Gravity, of course. But why gravity? One might say it is simply a law of nature, as Isaac Newton discovered. But, even Newton admitted he did not know why there was such a thing:
But hitherto I have not been able to discover the cause of those properties of gravity from phenomena…(De Principia, Bk. III, General Scholium).
Albert Einstein will seek to explain gravity by positing warped space-time. He writes:
…our universe behaves analogously to a surface which is irregularly curved in its individual parts…something like the rippled surface of a lake…the four-dimensional mode of consideration of the “world” is natural on the theory of relativity, since according to this theory time is robbed of its independence…(Einstein, Ibid, Ch. XXXII).
However, Einstein’s theory, by coupling space with time (if true) would seem to implicate a “frozen” or static universe (see footnote for more on this).1 In his own words:
For people like us who believe in physics, the separation between past, present and future has only the importance of an admittedly tenacious illusion (Einstein, Letter to Vero and Brice Rusconi, 1955).
Instead of Einstein, we could take Newton’s all-pervading “Spirit” as the cause of gravity. Newton wrote:
And now we might add something concerning a certain most subtle Spirit which pervades and lies hid in all gross bodies; by the force and action of which Spirit the particles of bodies mutually attract one another at near distances (Newton, Ibid.).
However, this seems dangerously close to pantheism or occasionalism.2
Therefore, in this post, we will relate another theory on gravity, which is of late making a resurgence in contemporary discussions on the topic, namely, Aristotle’s.
Aristotle is also, quite surprisingly, making a resurgence within other areas of physics as well, such as in quantum mechanics. To this point, Werner Heisenberg, Nobel Prize holder in Physics, wrote:
All the elementary particles are made of the same substance, which we may call energy or universal matter…If we compare this situation with the Aristotelian concepts of matter and form, we can say that the matter of Aristotle, which is mere “potentia,” should be compared to our concept of energy, which gets into “actuality” by means of the form, when the elementary particle is created (Physics and Philosophy, Quantum Theory and the Structure of Matter).
And if Aristotle’s thought, albeit 2,400 years old, can have something to say about quantum theory, it may have something to say about gravity as well.
Therefore, let us turn back the clock and ask from an Aristotelian perspective that timeless question: “If we pick up a stone and then let it go, why does it fall to the ground?”
There is an old saying, that “if you fall, fall forward,” which means that if you fall, make sure it is to your advantage. Curiously enough, the expression is not so far from what Aristotle thought about gravity.
Now, it goes without saying that much of Aristotle’s cosmology is outdated, but his core notions, namely finality and potency, need not be thrown out along with them.
Beginning with finality, here is Aristotle’s thought, as summarized by St. Thomas:
…every agent acts for an end…Now that to which an agent tends definitely must be befitting to that agent, since the latter would not tend to it save on account of some fittingness to it. But that which is befitting to a thing is good for it. Therefore, every agent acts for a good (St. Thomas Aquinas, SCG, C. 3).
Simply put, the only good reason (according to Aristotle) for a thing’s movement towards something, is if that something is, in fact, good for the thing in question.
If true, this would be the reason behind our movement towards rest at night, dandelion’s movement towards the sunlight, and why stones fall towards the center of the Earth.
Now, of course, stones do not think or knowingly move in one direction or another, as Aristotle will state multiple times—they do so due on account of their nature (we can add: specifically, qua mass)—although, this is a question of how the stone falls, which will be treated later.
The present question is why the stone falls, which, according to Aristotle, is because it is good for the stone to do so.
But why would someone think this to be the case?
Here are a couple reasons:
Unity is a perfection.
This is because of the relationship between unity and being. For a thing to be a “thing” (at all) it must be one “thing.” It must have a kind of unity within itself. Without the unity which distinguishes this thing from the various other things around it, it could not be called something, a thing, at all.
Take oxygen for example. Without the unity making it one out of its constitutive parts (protons, neutrons, and electrons) oxygen would not be a thing—a whole, over and above its parts—but rather various things: merely its various constitutive parts.
So for oxygen to be a thing, in its own right, there is required an essential unity over and above its parts: a unity making it one thing.
Thus, oneness and being are really the same as St. Thomas explains:
One does not add any reality to being; but is only a negation of division; for one means undivided being. This is the very reason why one is the same as being (ST, I, Q. 11 A.1).
Therefore in moving towards the center of the earth, the stone moves towards a greater unity, than it would have if it were only suspended in the air (a place with much lower density); and because of the aforesaid relationship between unity and being, by moving towards greater unity the stone also moves toward greater being or perfection.
It is good for a thing to utilize or actualize its potentials. In this way, it is good for a man to actualize his potential to learn theology or even his potential to carry out charitable works.
The stone has potentials as well, such as the potential to gravitate. Yet, without the stone actually gravitating toward some place, its potential to do so would remain merely potential. Dr. Mclaughlin makes the point, this way:
Consequently, since what preserves and fulfills a body’s potencies is good for it, gravitation is a good for the individual body considered as having mass and in relation to a place…In isolation and without a gravitational relationship to a place, this capacity would go unfulfilled (A Defense of Natural Place in a Contemporary Scientific Context, pg. 7).
And since being and being actual are essentially synonymous (potential things don’t have actual existence) then to the degree that a stone actualizes its potentials it also acquires greater being.
In this way, it is better for the stone to gravitate towards the center of the Earth, rather then remain suspended in the air, because by doing so it becomes more actual.
The Common Good
To achieve the common good is good for a thing.
Take a house, for example. Within a typical house, there are various things: walls/floors, furniture, appliances, etc., and all for the sake of the one living within it.
Each of these items has its own particular purpose, but for the sake of the common purpose: accommodating the resident. And just as each thing’s purpose is subordinated to the common purpose, so too each thing’s good is subordinated to the common good.
Therefore, although it may be better for the decorative bamboo plant (in the living room, let’s say) to remain alive, if it’s necessary for the resident that it be thrown into the stove (in order to provide warmth) then it’s good to do so.
And it would be good not only for the resident but also for the plant itself, for by being consumed in the stove, the plant fulfills the ultimate purpose of its existence in the home: again, accommodating the resident.
This is also why it is good for a man to die, as a martyr, for Christ; for a soldier to lay down his life for his country; and for all created things to readily sacrifice their individual good for the common good and purpose of all: namely, the glory of God.
Thus, by gravitating into the Sun, a comet (for example) although it lose its individual good and being, yet fulfills the ultimate purpose of its being; for in adding to the Sun’s mass, the comet adds to the Sun’s potential energy, which adds to the Sun’s longevity, which adds to the continued existence of life on Earth, which all contribute to the greater glory of God.3
Thus, we have three ways of understanding why one might be led to think it good for a stone to fall towards the Earth, but how, according to Aristotle, does it fall?
The answer is to be found in the second of Aristotle’s fundamental notions on the topic: potency
Change, for Aristotle, is always the actualization of some potential (see Fate & Free Will), and comes in four different varieties: substantial, quantitative, qualitative, and local change (cf. Edward Feser, Aristotle’s Revenge, 4.2.1).
Taking Aristotle’s concept of change for granted,4 and bringing it in line with contemporary physics, here is a brief word on how the stone falls.
The stone falls to the Earth because its potential (qua mass) for a “lower” place is actualized by the Earth’s mass. The mass of the Earth actualizes the stone’s potential for this lower place through a medium between them: a field we can call the “gravitational field.”
The stone then passes from one lower location to another, via the actualization of its potential for these lower locations, by the mass of the Earth, and through means of a gravitational field, until it reaches its lowest possible place.
Simple but not Easy
This pseudo-Aristotelian account for gravity seems perhaps too simple; however, it does escape both the occasionalist and pantheistic implications of Newton as well as the abolition of distinctively past, present, and future time alluded to by Einstein.
However, the court isn’t out on the question.
Let us, then, hope that time and research will provide us with a final theory. Also, let us not be surprised if (like in quantum mechanics) the last word goes not so entirely against Aristotle’s.
1. To take the space-time view seriously is indeed to regard everything that ever exists, or ever happens, at any time or place, as being just as real as the contents of the here and now…Contrary to this common-sense conception, the world according to Minkowski is, at all times and places, actuality through and through: a four-dimensional block universe. (Lockwood 2005, pp. 68-69)
The idea is that the block universe concept rules out the reality of temporal passage. But temporal passage follows upon change, so that if there is no temporal passage there can be no change either (Aristotle’s Revenge, 126.96.36.199).
2. If physical objects themselves don’t really do anything, then there is no point in trying to study what they do or how they do it. God, who alone ever really does anything in the natural world, becomes the sole worthwhile object of scientific study, and natural science gives way to theology. But the situation is even stranger than that, at least if we factor in the Thomistic principle that agere sequitur esse (or “action follows being”) – that is to say, that the way a thing behaves reflects what it is. If physical objects do nothing and only God acts, then it would follow that physical things don’t have any existence distinct from God’s existence. Occasionalism would collapse into pantheism, and the Cartesian philosophy of nature would thereby abolish nature altogether (Aristotle’s Revenge, 2.3).
3. However, the gravitation of an object (qua mass) is blind and therefore may not always be good a thing in all respects. For example, it may be good for a man, qua mass, to fall down the stairs, it is certainly bad for him qua rational animal (cf. Thomas Mclaughlin, A Defense of Natural Place in Contemporary Scientific Context).
4. For a thorough defense of the Aristotelian worldview in light of contemporary science, see Ed Feser’s book cited above.