Perspectives on Gravity
“The universe is shaped exactly like the Earth,
If you go straight long enough you’ll end up where you were.” – Modest Mouse
Newton conceived of universal gravitation as a ratio of mass to distance.
“…every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.”
Einstein revolutionized classical gravity with General Relativity, merging space with time and formulating the equivalence of mass and energy. Rather than a rigid Cartesian plenum of 3-D space and a one dimensional timeline, Einstein saw a flexible, four dimensional ‘mollusk’ of spacetime contoured by the relations of matter and energy. GR, along with Special Relativity, made the universe a much stranger place, with time dilation, black holes, the relativity of simultaneity, and the constancy of the speed of light as a universal absolute.
Since quantum theory begins at the other end of the cosmological continuum of size, there has been a continuity problem between sub-nuclear physics and astrophysics. Quantum doesn’t match up with relativity very well, so the quest to find a bridge between the two has been a prominent open question for contemporary physics.
Here are a some brief signposts along that highway between QM and GR:
In most, though not all, theories of quantum gravity, the gravitational field itself is also quantized. Since the contemporary theory of gravity, general relativity, describes gravitation as the curvature of spacetime by matter and energy, a quantization of gravity seemingly implies some sort of quantization of spacetime geometry. Insofar as all extant physical theories rely on a classical spacetime background, this presents not only extreme technical difficulties, but also profound methodological and ontological challenges for the philosopher and the physicist. Though quantum gravity has been the subject of investigation by physicists for over eighty years, philosophers have only just begun to investigate its philosophical implications.
Weak gravitational waves that fill the Universe are enough to disturb quantum superpositions and ensure that large objects behave according to classical physics. […] Many theorists now believe that macroscopic superpositions, in which numerous quantum components must maintain a precise relationship with each other, are disrupted by continual environmental influences. Such disturbances, acting differently on each component of a superposition, “decohere” it into a classical state that is, say, dead or alive, but not both. Even a system as small as an atom requires extraordinary protection from stray electromagnetic fields in the lab to remain in a superposition. Since gravitational fields are both pervasive and inescapable, researchers have proposed that they play a fundamental role in ensuring that macroscopic systems behave in a classical way.
We confirm, in this context, that the dynamics of a Brownian particle driven by space-time dependent fluctuations evolves towards Hamiltonian chaos and fractional diffusion. The corresponding motion of the particle has a time-dependent and nowhere vanishing acceleration. Invoking the equivalence principle of general relativity leads to the conclusion that fractional diffusion is locally equivalent to a transient gravitational field. It is shown that gravity becomes renormalizable as Newton’s constant converges towards a dimensionless quantity.
Modified Newtonian Dynamics (MOND) were proposed to explain the galaxy rotation problem. Unexpectedly, when it was first observed, the velocity of rotation of galaxies appeared to be uniform: Newton’s theory of gravity predicts that the farther away an object is from the center of the galaxy it belongs to, the lower its velocity will be (for example, the velocity of a planet orbiting a star decreases as the distance between them increases). These observations gave birth to the idea that a halo of invisible stuff was surrounding each galaxy: dark matter.
In this new model, the gravitational field still increases as you near the black hole’s core. But unlike previous models, this doesn’t end in a singularity. Instead gravity eventually reduces, as if you’ve come out the other end of the black hole and landed either in another region of our universe, or another universe altogether. Despite only holding for a simple model of a black hole, the researchers – and Ashtekar – believe the theory may banish singularities from real black holes too.
Metaphors and Symmetries
Switching gears from the scientific sense of gravity to the personal sense, there are some worthwhile themes to explore. The etymology of gravity links heaviness with seriousness. Gravity relates to grave, and groove. Digging ditches and engraving (scratching). The association with burial and death probably accounts for the connection from grave to words like serious, severe, and swear. The idea of a sworn oath or an engraved ring relates to a sense of a permanent pledge. There is an intent to hold on steadily against all odds, or all distraction. The root of swear crosses over to answer also – a hint that ‘saying’ something out loud can have serious or permanent consequences.
Serious or grave subjects are often called ‘heavy’ or ‘dense’ while frivolous topics are ‘light’ or refer to things which are airy (fluff, puff pieces). Insubstantial or insincere talk is ‘blowing smoke’. Both the literal and figurative meanings of heavy (literal = heavy weight; figurative = heavy important) have light as an antonym, but it is light in two different figurative senses. The antonym of the literal sense of light is dark, which comes back around to gravity in the form of black holes, where the intensity of gravity does not allow light to escape. It could be said that a black hole is a star’s grave.
Under the influence of gravity, weight, density, and pressure increase. Movement becomes more difficult and slow. More power is required to exert the same force. Metaphorically there is a lot of crossover – feelings of stress are compared to being ‘under a lot of pressure’ is associated with risk or powerlessness. Resistance and inertia figure in, as does entropy. Under pressure, time becomes more valuable, and the tolerance for distractions (nonsense), is lowered. Ideally, the significance of the goal should be worth the effort. Monumental investments expect monumental results.
If electromagnetism is the ‘Spring ‘ of matter’s energy, then gravity is its Fall. If energy is a fountain which lights the matter into significance, then gravity is the drain which flattens entropy and reverses its disposition into a one dimensional, time slowing presence – mass. Said another way, gravity is the metabolism of spacetime, and the embodied force of entropy.
Dr. Thanu Padmanabhan of the Inter-University Center for Astronomy and Astrophysics in Pune, India said Gravity “is the thermodynamic limit of the statistical mechanics of “atoms of space-time.”
Erik Verlinde, 48, a respected string theorist and professor of physics at the University of Amsterdam, is quoted as saying that gravity is “entropic force.”
Gravity’s symmetry with electromagnetism extends to the metaphysical. The etymology of the words burden and bear go back to the word for ‘birth’. Themes of give and take, and birth and death, wrap around each other. The idea of curvature, of entropy statistically evening out odd statistics and jagged exceptions is an expression of magnitude and relativity. The pull of gravity doesn’t make things spin or orbit, but since the number of velocities that a body can have is so much greater than the number of ways a body can be stationary, entropy ensures that most everything is moving somewhere, and gravity pulls light things close to heavy things faster than heavy things are pulled to light things, causing the lighter moving thing to wrap its path around the heavier mass in an ellipse.
With a black hole, and on Earth, gravity and entropy suggests a connection to loss and absence. Ultimately, gravity shows that even absence turns back on itself, since it can only ever be the sense of its own absence – the presence of the absence of presence. Sense can only diminish relative to itself, it can only appear to be slow or missing by comparison. Gravity is about falling, collapsing, and squeezing the space and time out of incidents to make them co-incidents with shared inertia. Gravity is the force of pseudointentionality, the entropy of entropy. If perception elides its blindness and entropy to concentrate significance, gravity elides in the opposite way, through quantitative density. Anomalies are crushed and drowned into smooth curves until they explode. Stars explode into clouds which collect into other stars, scars of stars, and galactic spiral clouds of stars.
Are teleonomy, evolution, entropy, and gravity the same thing? If electromagnetism and energy represent uniqueness and creativity on every level, gravity and entropy are a statistical rounding off of all of that uniqueness across all the inertial frames. It settles everything into hierarchies of magnitude on the outside and figurative scales of greatness (importance) on the inside.
Gravity isn’t directly related to time. Although much our timekeeping is modeled after astronomical cycles, neither the rotation of the Earth nor its heliocentric orbit are caused by gravity alone. It seems easy to mistakenly guess that planets have gravity because they spin, as if it were some kind of centripetal force, but the gravity would be almost the same if Earth were not spinning, and gravity itself is not causing the spin in the first place. What we think is that planets condensed from moving clouds of cosmic debris, and when they become smaller, the motion becomes faster (conservation of angular momentum, like a figure skater pulling their arms in for the faster spin).
As far as gravity is concerned, the Earth and Sun only need be drawn together, all orbits, spins, and tilts in the solar system are the residual effects of the events which initially accelerated the cloud of matter into motion or changed its direction. The tilt of the Earth is thought to be the result of collisions with other massive objects during its early history. Without the tilt, you would have no seasons as every position of the Earth’s orbit would produce no noticeable difference. Same with the spin. Gravity doesn’t care if the Earth spins or not.
What gravity does do for time is provide conditions of relative permanence that would not exist otherwise. Without gravity we could still keep track of cycles of time, but they would be forever be changing completely as our view of the universe changes permanently from a non-orbiting planet hurtling aimlessly through space. Gravity provides a frame of circularity which allows greater degrees of order in our perception. Gravity doesn’t make time, but it makes it more relevant.