I have always been fascinated by gravity, mainly because I never understood it. Richard Feynman, who gave us the heuristic diagrams of quantum interactions, famously observed that “Nobody understands quantum mechanics”; the same is true of gravity. Like everyone, I know it as a tugging force, dragging you back as you climb a hill, pulling you forward as you descend—a force needing to be fought, to struggle against going up or coming down. Seeing images of astronauts floating in their space capsules was a reconciling factor; at least we were grounded, a relief not to find oneself in a condition of permanent levitation. Yet it remains a mystery defying resolution and comprehension.
It’s common knowledge that gravity is one of the four fundamental forces of nature. The strong force binds the fundamental particles of matter together to form larger particles. The electromagnetic force consists of two parts, electricity and magnetism. The so-called weak force is responsible for particle decay, Schrödinger’s Cat, and radioactivity, and has been descriptively combined with the former as the electroweak force—models predict it can be united with the strong force as the electronuclear force. Gravity is the feeblest of these forces especially at atomic and quantum scales, resisting unification with the other forces into a single equation.
Indeed, gravity remains one of the greatest problems for understanding the nature of the universe. Isaac Newton first proposed the idea of gravity as an attraction between two objects—the apocryphal apple—and developed, or discovered, the inverse square law to describe its operative principle. Albert Einstein in his theory of general relativity posited that gravity is not an attractive force but the effect of massive stellar objects bending space and time—a gravitational field minus gravity, so to speak, as it is generally felt and understood. Given an initial push in the Big Bang, for example, after billions of years planets would simply “follow the curve,” banking hard like race cars in natural orbit around their stars. What is called “gravitational lensing” is the effect of galaxies and clusters of galaxies, busy curving spacetime and bending light rays as they hurtle by.
But now we are given to understand that gravity is also a wave, a ripple in spacetime formed from the collision of massive stars and the merging of black holes—detected for the first time on September 14, 2015 at the Laser Interferometer Gravitational-Wave Observatory at the Hanford site in Washington State and dubbed, obviously, GW150914. As Govert Schilling explains in Ripples in Spacetime, gravitational waves are so extremely low-frequency—they can have, for example, a period of 30 years, which means a single wavelength is an almost ungraspable 30 light years—that it is something of a miracle they were ever detected. But the fact is: they exist. The evidence is clearly laid out in Kip Thorne’s monumental Black Holes & Time Warps. (Thorne was an advising producer for the blockbuster film Interstellar. KIPP, one of the robots, is named after him.)
Bringing gravity into the family of forces in a single theoretical framework would then produce, according to the cosmologists, a theory of everything. So far gravity resists absorption. As Thorne wrote, “The gravitational universe [looks] extremely different from the electromagnetic universe.” Hence, the problem for a layman like me. I simply cannot see how gravity can be simultaneously an attractive force, a curvature in spacetime, and a nanohertz wave propagating at the speed of light. When I trudge up a hill, do I feel an adhesive force emanating from the earth beneath my feet, grappling at my ankles and causing me to labor upward and resist plunging downward, or is spacetime bending under and around me, so that I’m really just orbiting, or is a mysterious wave from the remote corners of an expanding universe somehow applying a ghostly velcro to my heels? When I let my pen drop a quarter inch to the tabletop, does it fall because a force is pulling it down, because the quarter inch of space has looped inward owing to the mass of the table, or because two black holes slammed into one another 1.3 billion light years distant, like the GW150914 discovered at Hanford?
There are other complicating issues warping around the gravity riddle. Quantum mechanics, string theory and the postulate of multiple universes introduce hypothetical explanations for the existence and effects of this enigmatic force. Perhaps quantum particles called gravitons exert a furtive impact on the macroworld—but no one can understand what quantum gravity does at 10-xx second intervals. Perhaps, according to string theory, our universe is a brane or a sheet of spacetime hanging out in a higher dimensional space in close contact with other branes that leak across, producing what we know as gravity. Perhaps gravity is “weak” only in a 3-dimensional world; add a few extra dimensions and presto! gravity flexes its muscles, like the skinny guy in the old Charles Atlas commercial. Perhaps, a parallel universe—according to Richard Panek’s The Trouble with Gravity, merely one of potentially 10-500 such universes—generates perturbations in our home universe, which we recognize as gravity. As Panek writes, “gravity might be something that bleeds into our universe from an adjoining universe, or it’s an artifact from a colliding universe”—which may explain why physicists cannot understand or unify gravity in a single equation with the other three forces of nature. In any event, I find it hard to imagine that universe X has cut a dimensional incision between pen and tabletop such that the pen has nowhere to go but in a direction that we know as “down.”
And so, the layman scratches his head and wonders. Discounting gravitons, branes and parallel universes, which remain unintelligible or, as Neil Turok pronounces in From Quantum to Cosmos: The Universe Within, “empty model universes” that cannot be used “to describe expanding universes full of matter and radiation like ours,” the question persists: Is what we call gravity actually three distinct phenomena—attractive force, curvature of space, pulses of waves—operating at different levels, intervals and regions in the universe? Or is it one inscrutable power that is somehow diffracted, as through a prism, into three observable franchises advertised in three different formulaic ways? Some time ago, I ordered via Amazon’s buying options a rare book by theoretical physicist John Wheeler, which I was told by an equally baffled physicist friend might help me make some sense of the question. Though I ordered the book from three different outlets, it never arrived. Perhaps it was sucked into a black hole.
Here I should add an explanatory remark to the reader. Though in my daily work I continue to focus on politics and social commentary, I am convinced that absolute truth—or at least stable truths—can be found only in the scientific realm, in chemistry, physics and math, founded on fundamental principles of observation, testable theory, experimental confirmation and Karl Popper’s notion of falsifiability, articulated in his The Logic of Scientific Theory. For a theory to be accepted as scientific, it must be able to be proven false. The problem with the discursive fields of commentary, scholarship, the misnamed “social sciences,” and the Humanities in general (with the exception of music, which is built on mathematical ratios) is the inevitability of bias, prior convictions and assumptions, and partisan viewpoints that can never be ruled out.
Expository writers—at any rate, the good ones—are also searching for truth, but in the human sphere of culture, politics, society and history. Here the quest for truth is shadowed by the intrusion of personal values and beliefs whose moral component is never rigorously assured. Quarrels and contestations are part of the game. There are strongly held personal convictions and considerable bickering in science, too, but eventually incontestable fact, if not absolutely unsettled truth, will emerge. 2 plus 2 will always equal 4—but poet e.e. cummings can plausibly title a volume Is 5. The distinction between the two spheres of investigation is commonly construed as the difference between subjective parallax and objective methodology.
Even if ultimate truth continues asymptotically to recede, even if science is never settled, which is as it should be, the quest for reliable knowledge is authentic, impartial, scrupulous, never-ending and honorable, producing disparate but incontrovertible results in various fields of inquiry that can test true, as evidenced by practical applications. That’s why your GPS works. That’s why almost every appliance you take for granted works. Such facts, or designated truths, account for the basic morality of scientific inquiry, its “ethical importance,” as Erwin Schrödinger writes in My View of the World, and which he regards as no less compelling than its “logical force.” It is impossible to lie in science, that is, in real science as opposed to politicized science. Science is as close as we can get to truth, which exerts its own species of intellectual and spiritual gravity. That is why, perhaps, science is as close as we can get to God.
As for the truth of gravity itself, admittedly, it continues to escape me. Perhaps one day Wheeler’s book will arrive.