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 labour
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 honourable, 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.
