Did Newton discover gravity? Nature of scientific discovery
Let me start with a passage from the iconoclastic philosophical fiction Zen and the Art of Motorcycle Maintenance, or ZAMM, by Robert Pirsig to set the tone.
“For example, it seems completely natural to presume that gravitation and the law of gravitation existed before Isaac Newton. It would sound nutty to think that until the seventeenth century there was no gravity.”
“So when did this law start? Has it always existed?”
John is frowning, wondering what I am getting at.
“What I’m driving at,” I say, “is the notion that before the beginning of the earth, before the sun and the stars were formed, before the primal generation of anything, the law of gravity existed.”
“Sitting there, having no mass of its own, no energy of its own, not in anyone’s mind because there wasn’t anyone, not in space because there was no space either, not anywhere…this law of gravity still existed?’”
Now John seems not so sure.
“If that law of gravity existed,” I say, “I honestly don’t know what a thing has to do to be nonexistent. It seems to me that law of gravity has passed every test of nonexistence there is. You cannot think of a single attribute of nonexistence that that law of gravity didn’t have. Or a single scientific attribute of existence it did have. And yet it is still ‘common sense’ to believe that it existed.”
I’m going to be provocative as Pirsig was above and question the premise of whether gravity was indeed discovered. I am sure most people would doubt my sanity for asking this question. But, let’s play this game and see where it leads.
So, did Isaac Newton really discover gravity? Or did he invent it?
Since discovery assumes the phenomenon existed before it was explained, we can say gravity existed long before Newton without anyone rolling their eyes at you, right? Can we, though?
Let’s understand how Newton came upon gravity and see if it was discovered or if he made it up. The story begins with Galileo Galilei, who asked the most obvious of questions that nobody had bothered to wonder about until then: what makes objects, from a small ball to giant stars and planets move?
What he observed was the simple yet remarkable fact that objects moving in a straight line at a uniform speed will keep moving at that speed for eternity if left undisturbed. Now this is what we learn in elementary physics textbooks. But why should objects behave this way? Turns out we have no idea but since Galileo we have accepted this enigma of inertia without question. Here starts the mystery that underlies the most basic thing we know about objects in the world.
Newton, one of mankind’s greatest geniuses, expanded on Galileo’s insight and said the only way to break out of inertia is to apply force, that is, a push or pull to change the speed or the direction of motion of the object. He wondered if the motion of planets followed the same principle. Ancient thinkers, from Aristotle in the West to Brahmagupta in the East, had theorised that objects were attracted to the earth because it was in their nature to do so. Newton ignored this non-explanation, and applied the laws of motion to the motion of planets. So, what are the consequences of applying force to a moving object? If a push is applied in the direction of motion of the object, the object accelerates and vice versa. A sideward application of force changes the direction of motion.
Let’s consider this application of force, as Newton did, in the case of circular motion. Visualise spinning a stone tied to a string. We must apply a constant force towards the centre to keep the stone spinning in a circle. Newton easily explained this by invoking his laws of motion. If left to itself, the stone would keep traveling in a straight line forever, assuming there was no friction or any other force acting on it. However, applying a constant inward or sideward force alters the straight path into a circular one. The natural direction of motion of the stone is apparent when the string is suddenly released. The stone escapes in a tangential direction indicating a constant force that was applied inwards along the radius while it was spinning in a circle.
Coming back to planetary motion, Newton applied the same logic and concluded correctly that planets revolving in circular or elliptical orbits around the sun must always have some kind of force pulling them towards the centre of the sun.
So, what’s the nature of this force and how is it transmitted between, say, the sun and a planet millions of miles away with nothing in between? In the case of the stone, it was the string that acted as the conduit for the force pulling it towards the centre.
This “spooky action at a distance” without anything connecting the two bodies was a far departure from the 17th century physical understanding based on mechanical philosophy as envisaged by the highly influential Descartes.
What’s mechanical philosophy? It’s the commonsensical view that an object cannot be displaced from its position without coming in direct contact with another moving body. Generalising this conclusion, every kind of change in our universe must have a mechanical or material cause. This system or philosophy, also called materialism, has been a dominant paradigm for scientific exploration of our universe, including understanding of the connection between the mind and the brain.
However, this commonsensical worldview of materialism was dealt a body blow (pun intended) by Newton’s discovery that the sun and the planets attract each other without anything connecting them, a sort of “spooky action at a distance”, as the famous phrase attributed to Albert Einstein describes it.
Here, take a moment to absorb and appreciate the rather “occult” nature of this interaction between matter without any contact and the sheer genius of Newton. He conjured up a force, which he called gravity or the force of gravitational attraction, to make sense of how stars, planets and galaxies moved in space.
As Pirsig remarks in ZAMM, “Well, I predict that if you think about it long enough you will find yourself going round and round and round and round until you finally reach only one possible, rational, intelligent conclusion. The law of gravity and gravity itself did not exist before Isaac Newton. No other conclusion makes sense.”
I am sure it feels absurd to say that the law of gravity, indeed gravity itself, didn’t exist before Newton. However, when one sees it as a mystical force acting remotely between objects then the absurdity of the concept of gravity seems inescapable. In fact, Newton himself was embarrassed by his idea as he noted in his correspondence with Richard Bentley: “It is inconceivable that inanimate brute matter should (without the mediation of something else which is not material) operate upon and affect other matter without mutual contact…That gravity should be innate inherent and essential to matter so that one body may act upon another at a distance through a vacuum without the mediation of anything else by and through which their action or force may be conveyed from one to another is to me so great an absurdity that I believe no man who has in philosophical matters any competent faculty of thinking can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws, but whether this agent be material or immaterial is a question I have left to the consideration of my readers.”
To be clear, we are not denying the obvious observation that an apple falls from the tree to the ground or that our planet is revolving around the sun. However, the scientific explanation for these observations or facts – that there’s this attractive force called gravity and it behaves according to the law of gravity – was not around until Newton dreamed it up in the 17th century. Moreover, Newton’s law of gravitation survived not just because it was a fanciful thought from the mind of a genius but because it predicted and explained many of the observations physicists were puzzled by in his time, from the peculiar orbital motions of planets around the sun to why tides occur. In time, though, it was found that observations, like distortions in Mercury’s orbit, were not accurately predicted by Newton’s gravitational law.
When this happens, scientists generally either modify the theory to fit the anomalous observation or reject it completely and devise a new theory. In early 20th century, Einstein took the latter path. He questioned the existence of gravitational force, and revolutionized physics by postulating a universe where such a force is rendered superfluous. In place of Newton’s theory, Einstein came up with an even more bizarre formulation, the General Theory of Relativity. It posits that gravity is not a force but a result of the fabric of space – comprising the three spatial dimensions of length, breadth and height, and the fourth dimension of time – being bent by the presence of massive objects like the sun or a planet.
Let’s go back to our observation that an apple always falls to the ground. The Einsteinian explanation for this would be that space-time between the apple and the earth is “squeezed out” due to the earth’s large mass and this appears to us as if the apple is falling towards the earth. What about the earth then? Why doesn’t it fall into the sun, which is almost 13,00,000 times heavier? Einstein would say the speed with which the earth revolves around the sun (1,10,000 km per hour) keeps it from falling into the sun. The earth is just traversing a “straight line” in a space-time geometry warped by the presence of the sun in the centre.
Notwithstanding the counterintuitive nature of this explanation, Einstein’s theory and its mathematical formulation was not only able to explain more observations than Newton’s did, it also removed the certainty and absoluteness Time and Space enjoyed in our minds. Einstein’s theory even predicted many hitherto unknown phenomena such as gravitational waves (or ripples in the space-time continuum which were indeed recently detected), black holes and the expansion of the universe.
What does all this mean to us, the ordinary folk? First and foremost, it gives us a glimpse into how science proceeds from known to unknown. In Noam Chomsky’s words, “Any scientific theory is based on finite number of observations, and it seeks to relate the observed phenomena and to predict new phenomena by constructing general laws in terms of hypothetical constructs such as ‘mass’ and ‘electron’.”
Thus, scientific theories are mental constructs dealing with concepts invented by the mind and just approximations to what we like to call “reality” or “truth” that is out there.
It would be wrong to conclude from this that if scientific theories are indeed creations of the human mind, then Newton and Einstein are only as “true” as a lay person and, as such, we needn’t bother listening to scientists about climate change, pollution, and vaccinations. That is because assuming such fantastical concepts and pursuing them in a logical manner has not only led to spectacular scientific achievements such as knowledge of the physical and chemical nature of our cosmos, and the anatomy, physiology and biochemistry of processes that sustains life, but also ushered in technological advancements such as antibiotics, vaccinations, computers, mobile phones, internet and GPS without which modern life can’t be imagined. Therefore, the uncertainty in our understanding of the world gained through careful, painstaking scientific research over centuries can’t be replaced by assertions based on superstition and all kinds of quackery as has become commonplace in today’s age of taking random WhatsApp forwards and YouTube videos as gospel. That uncertainty is built into science is proof that unlike religion, nationalism and sociopolitical “isms” with their associated orthodoxies, the scientific method is self-correcting and reinvents itself or perishes in the face of observations not predicted by its framework. Science, unlike these “isms”, is not staking claim to exclusive, privileged and hegemonic access to ultimate “truth”, “reality”, “God”, or whatever one likes to call the Unknown. Science paves a systematic path to get at the best possible approximation of the truth or the unknown.
In the end, our incurable ignorance of the underlying nature of the world we are born in, including our bodies and minds, warrants an ultimate skeptical attitude in general that scientific worldview upholds. This is aptly captured, in the context of the question about the universe’s ultimate origin, in these lines from Nasadiya Sukta in Rig Veda:
“But, after all, who knows, and who can say Whence it all came, and how creation happened?
The gods themselves are later than creation, So who knows truly whence it has arisen?
Whence all creation had its origin, He, whether he fashioned it or whether he did not, He, who surveys it all from highest heaven, He knows, or maybe even he does not know.”
I would like to thank Dr Vinod Kumar Tandon, IIT Roorkee; Dr Shashank Tandon, University of Utah; Praveen Chandilkar, KLES School of Science; and Shobha CK of American Family Insurance for helping prepare this article.