Gravity is the oldest known force; yet gravity is the least understood force–in spite of the efforts of Messieurs Newton and Einstein. Gravity has been with us since time immemorial; the other forces have been known for less than 200 years. Newton and Einstein gave us equations that permit us to calculate gravity. But its essence–the means by which it works–remains controversial. The controversy centers mostly around the fact that theorists have been unable to include gravity in Quantum Mechanics. So they have developed String Theory as a means of defining quantum gravity and hypothesized
as the force carrier of gravity. The logic being that, since the other forces have messenger particles (force carriers), then so should gravity.
We exist in a four-dimensional space-time continuum (hereinafter
STC). There are 3 space dimensions and 1 time dimension. (The reason there are 3 space dimensions is that three numbers are required to locate a point in space. This is true for orthogonal Cartesian coordinates or polar-spherical coordinates.) The 3 space dimensions can be mapped into each other and exchanged among themselves. You can move forward and backward in space. Time is fundamentally different. You can only move forward in time. There is no conversion from or into the space dimensions. So, there is no reason why gravity must be the same as the other three forces, even if the other three are actually different manifestations of the same force. Gravity can be unique, just as time is unique.
Gravity has been an enigma that has puzzled Newton, Einstein, and many others. Newton conceived of gravity as action at a distance–although he was never satisfied with that characterization. Einstein established equivalence between gravity and acceleration–gravity is acceleration caused by mass. I will now attempt to explain gravity–I know I'm in over my head.
[Did I ever tell you how I passed my swimming test in the Navy? I was just tall enough to tippy-toe across the bottom of the shallow end of the pool.]
Gravity is a property of most physical things to congregate together. Pick up a 25 pound rock and hold it over your head. It takes a lot of energy and work to separate the baby rock from mother Earth. Now drop the rock. (Watch your toes!) See how the baby wants to snuggle up next to its mother. [I have deliberately avoided using the word
entropy. It is widely misunderstood and often applied locally when entropy has not been changed but just rearranged among localities.]
The strength of gravity between objects is dependent on their mass–which is sometimes confused with weight. (Think of weight as the measure of gravity between two objects.) In general mass is additive. Two golf balls have twice the mass of one. But this is not true in all cases–the exception being sub-atomic
particles. Here is a list of common subatomic particles and their rest mass, in million electron volts divided by the speed of light squared (Rest mass = MeV / c²). You will recognize this as a re-arrangement of Einstein's famous equation: E = m × c². Gluons are the force carrier for the Strong Force. They are the
glue which binds the quarks and hold neutrons and protons together. Like photons (the force carrier for the Electromagnetic Force), they have no rest mass.
A proton consists of 3 quarks (1
down + 2
up + gluon cloud); while a neutron is composed of 3 quarks (1
up + 2
down + gluon cloud). It does not take a rocket scientist to realize that the numbers above do not seem to add up. Not even close.
So, what's going on? Although gluons are massless, they possess energy; and it is the mass equivalent of this energy which provides the missing mass to protons and neutrons. In fact, the gluon cloud contributes almost all the mass. This means that 99% of the mass in protons and neutrons is not really matter, but rather a sort of
congealed form of energy.
Neutrons, protons, and electrons are the main ingredients of atoms. Naturally occurring atoms have from 1 to 92 electrons, an equal number of protons, and about 25% more neutrons. Here is a breakdown of the mass (MeV / c²) of
average atoms per atomic number.
These are the atoms of hydrogen, oxygen, carbon, iron, etc. which comprise the Universe that we observe. In other words, all of the physical matter in the universe (including ourselves) is really no more than countless little blobs of congealed gluons. We and every other physical thing are almost all energy. Although we like to think gravity is a force that acts on mass, it is actually a force that acts on energy.
So mass is not a physical thing–it is a quality, characteristic, or property of matter that defines how matter interacts with the STC. Mass distorts the STC–it causes the STC to curve. You can think of this interaction as matter forming a kind of 4-dimensional depression or
dent in the STC. Every mass tries to pull all other masses into the depression with it. But it is not a stationary dent. It and the mass in it are moving.
Everything in the universe is in constant motion. If you sit perfectly still in a chair, the Earth spins around its axis and revolves around the Sun. The Sun rotates around the Milky Way galaxy, and the Galaxy circles around the Local Group, which moves within a cluster of galaxies. Even if you could travel into deep intergalactic space, you would not be able to define a non-moving rest frame because the galaxies and clusters are moving in different directions and at different speeds relative to your location. But if you could find a stationary location in space, you would still be moving–through time. All matter travels through time, with the exception of objects traveling at the speed of light.
Einstein saw gravity as a warping of the STC caused by mass. The best 2-dimensional analogy of his concept is two bowling balls on a trampoline. The two balls will roll toward each other. The farther apart the two are, the slower they move. The closer together the two are, the faster they roll. If the balls differ in weight (mass), the heavier one moves less and the lighter one rolls more. Thus we speak of the Earth revolving around the Sun; when, in fact, they both revolve around their common center of mass. But the disparity of size is so great that we can just about ignore the movement of the Sun. The close distance of Mercury from the Sun causes it to revolve around the Sun at a relatively fast velocity of 30 mi/sec; while the far-out distance of Neptune from the Sun causes it to revolve around the Sun at a relatively slow velocity of 3 mi/sec.
The strength of gravity diminishes with the square of the distance–just like light. This is probably why light (electromagnetic energy transmitted by massless photons) has been used as a model for gravity transmitted by hypothetical
gravitons–massless force carriers traveling at the speed of light. (Since a finite number of photons disperse in all directions from a source, the density of photons hitting a target decreases as the surface of the light sphere increases. Surface = 4 pi radius², where radius is the distance between source and target.)
If my words are weighty and my logic attractive, I may be able to convince you that the conventional wisdom about gravity is wrong and that once again Einstein was right. [I have put the word
in italics to emphasize that they are ethereal and do not really exit.]
Conventional model–All forces are mediated by an exchange of messenger particles. The
graviton is the force carrier for gravity. Gravitons shuttle back and forth between all objects in the Universe. They are limited in number (huge but not infinite). This is why gravity diminishes with the square of the distance. There is an equal number of gravitons arriving and departing; there must be a balanced flow or else strange things will happen. Gravitons deliver a
message and return or are absorbed and replacements are generated to return. (This mechanism does not seem to be well articulated.)
Most physicists seem to have bought into the
graviton model, especially those who favor Quantum Mechanics. However, there is a sizable minority who reject the graviton model as unproven, especially those who favor Relativity Theory. It's the short-range guys vs. the long-range guys. I'm a long-range guy and I see a number of issues with gravitons:
Operating level–Large bodies like the Sun, Earth, or Moon consist of many smaller objects which have gravitational interactions among themselves. At what level do
gravitons operate–molecular, atomic, subatomic, neutron, proton, lepton, quark. We know that gravity bends light; so photons must emit their own gravitons. Since gravitons convey energy, then they also must have a mass equivalent and generate their own gravitons, which in turn ....
Direction–The message delivered by
gravitons has two components: strength and direction. Strength is easy to handle–it is conveyed by the frequency of graviton arrival per time period. There is a lower frequency the longer the distance because gravitons become more spread out with the radius of the sphere. Direction is the problem. There is no memory mechanism built into whatever particle receives and transmits gravitons, so how does it know where the graviton came from and which direction to move? Gravity is a long range force–it operates over billions of light-years. This is quite different than atomic and subatomic scales where there is a cloud of electrons swarming around the nucleus or a sea of gluons engulfing two or three quarks.
Balance–Since a particle does not know the direction and distance to all other objects in universe, it must radiate in all directions at same rate. This could be at a constant rate or at the rate incoming
gravitons are received. Particles at the center of the Earth or Sun receive many more gravitons than a spec of dust in intergalactic space. (Gravity diminishes with the square of distance.)
gravitation-less–it would appear to have no mass.)
So some matter would convert mass to energy to produce
gravitons and lose mass in the process; while other matter would convert the surplus gravitons to mass and gain mass in the process. How would this work? Would protons and neutrons give up some of their mass? Would they take in more mass? Would they convert into one another? Would electrons or quarks do this? They all have rest mass and gravitation. Would gluons convert to gravitons and vice-versa? How about other messenger
particles such as the photon? How many
gravitons would a photon of star-light traveling through inter-galactic space generate before it is no longer a photon? And what is it then?
Let's conduct a thought experiment you can do at home. Get seven round things the same size–quarter coins, poker chips, checker pieces, large buttons, or beer bottle caps. (I use tokens from the game Othello.) Put one in the center and arrange the other six around it. They will just fit. Your objects can represent stars, planets, moon, asteroids, basket balls, golf balls, etc.–all with the same mass. (They can't be anything as small as molecules, atoms, or sub-atomic particles, because at that level, electrical and other forces overwhelm gravity.) This is a two-dimensional model, but it also works for three dimensions. It's just a little cumbersome to describe and think about.
Assume your seven objects are located in a huge inter-galactic void, so far from all other objects that we can ignore their gravitational pull. We will concentrate on the central object and its
gravitonflows. As your system exists, the central object emits 1/6th of its gravitonsin the direction of each of the six ring objects. At the same time it receives 1/6th of the gravitonsfrom each of the six ring objects. Everything is in balance and harmony.
Let's remove one of the ring objects. Now the central object is receiving 1/6 of the
gravitonsfrom only five objects. Questions: Does the central object know which one of the six ring objects is gone? Does it know which one? Does it continue to emit gravitonsin all directions? How many gravitonsdoes it emit: same as before or just 5/6ths? If same as before, where does it get the additional gravitons? Does it have a gravitonwarehouse? If it receives and transmits 5/6ths of the original gravitons, has its mass decreased to 5/6ths of its original mass. If it receives 5/6ths and transmits 6/6ths of the gravitons, what is its mass? How long can it continue to transmit more gravitonsthan it receives.
Next, remove another ring object, and repeat the questions. Continue removing ring objects until there are none left. I know you will see that this is an impossible situation–
gravitonsare impossible. End of thought experiment.
Penetration and transparency–
Gravitons are in violation of Newton's 3rd Law of Gravitation and should be arrested [pun intended]. The 3rd law states:
Every action has an equal and opposite reaction.
Gravitons are the only things in nature that have an effect without being affected. For gravitons to work, they must interact with every particle of every object–penetration must be complete. For gravitons to work, all matter must be transparent to them–they cannot be stopped by anything. These last two statements cannot possibly both be true.
Penetration–Massless particles vary in their ability to penetrate bodies:
massless, since the definition of mass is being affected by gravity.
mass–a contradiction of terms. Shape and position would also affect gravitation. A pencil's gravity would be more if it were sideways (lateral) than if it were
point-firstto another object. A sheet of paper would have less gravity rolled up in a ball than flattened out and fully exposed to another object.
Crazy! The obvious answer is that gravity
connects with every spec of every object. But how? Not with
Transparency–Gravitational shielding would be a violation of the Equivalence Principle of General Relativity, which states there is no difference between gravity and acceleration. Also the non-existence of shielding has been demonstrated experimentally a number of times–to the extent that a negative can be proved. Let's see if I can illustrate this point:
frontpart of the body shielded the
rearpart of the body from gravity.
gravitons are the Man of La Mancha of physics–they have an impossible task. They must pass through all matter as if it is not there and at the same time they must attract it to go where they came from. Gravitons must interact without interacting. On the other hand, nothing has an effect on gravity, yet it affects everything. Gravity is the Houdini of physics. Houdini was real; the Man of La Mancha is fictional.
General Relativity predicts something called
gravitational radiation. It is a form of energy created by the acceleration of mass. It is analogous to electro-magnetic radiation, which is created by the acceleration of electrons. Gravitational radiation has never been detected. Because gravity is such a weak force, efforts to detect gravitational radiation have focused on the acceleration of massive bodies, such as white dwarfs, neutron stars, and black holes.
An orbiting body is continuously changing course–momentum propels the body straight ahead, while gravity tries to pull it straight down. Thus an orbiting body is continuously accelerated. So the search for gravitational radiation is concentrated on massive orbiting bodies–in particular the Hulse-Taylor binary star system, which consists of two neutron stars orbiting their common center of gravity very rapidly (7.75 hours). The orbit is decaying in precise agreement with the loss of energy due to gravitational radiation as predicted by General Relativity. [Way to go, Einstein!]
Without further ado, let me introduce my newly-minted model of gravity. Mass A compresses the STC and puts a dent in it. (The depth of the dent is proportional to the mass.) This is analogous to pushing a glass or cup into a sink filled with water, which is displaced and overflows the sink in all directions. In this case the dent sends out gravity radiation in all directions. Mass A does not transfer any momentum (energy) to the gravity radiation–mass A is stationary in the dent. The energy comes from the force that created the dent.
The out-flowing gravity radiation causes the STC to curve
down hill toward the dent and parallel to its direction of flow. When the gravity radiation encounters another mass, B, it does not interact with it–no absorption, no transfer of energy or momentum. It just passes by, leaving a curved path to mass A and its dent. (Newton's 3rd law is preserved.) Mass B then slides
down hill toward A's dent. Meanwhile mass B creates its own dent in the STC, which sends out gravity radiation and curves the STC toward itself. Mass A then slides
down hill toward Mass B. And eventually the two collide.
What is the nature of gravity radiation? It can be thought of as waves or particles, or just warped space-time. Picture tension between the mass and the dent, which causes the dent to vibrate and send out the curved paths. [Am I mixing metaphors?] The tension comes about because the mass wants to increase the dent and the STC wants to
flatten it out. (The vibration could be on the order of trillions or quadrillions of Hertz, and therefore undetectable with today's technology.) And of course, gravity radiation also applies to the mass equivalent of energy.
As the gravity radiation advances and spreads out, it diminishes in strength proportional to the square of the distance.
In any case, the strength of the gravity radiation eventually becomes insignificant and then non-existent, so that the Universe does not fill with infinite gravity radiation,
à la Olbers’ paradox.
All the masses and dents in the four-dimensional STC simultaneously create curved paths to themselves. The curved paths overlap and combine into deeper curved paths. The masses follow the deepest curved paths, usually orbits of smaller masses around larger masses, but sometimes a direct, head-on collision course.
The curved gravity paths in the STC are not discrete, one-time events, like a rock dropped in a pond which creates ripples on the pond's surface, or like a photon striking an electron and kicking it up to a higher atomic energy level. Rather the curved gravity paths are on-going artifacts of the STC caused just by the mass sitting in the dent. If the mass moves (is accelerated relative to its rest frame), then additional gravity radiation is created.
This behavior of gravitational radiation is much like the behavior of electro-magnetic radiation when it operates as a long-range force. There is no exchange of messenger particles. Nuclear reactions in a far-off star produce photons, which streak to Earth and strike someone in the eye, sending a message to the brain:
Twinkle, twinkle, little star. The eye does not send photons back to the star.
The basic concept is that gravity is not interaction between masses, rather it is interaction between mass and the STC. [This means some of my introductory paragraphs are not technically correct.] And this begs the question: what is mass? According to theory: mass is a latent property of the STC which is filled with a
Higgs field, a superfluid superconductor of charged, massless bosons, which become massive when the electric and magnetic fields become short-ranged. However, the Higgs boson has not yet been detected in any particle accelerator.
Mass is also the property of matter that projects force in the direction of motion. I am reminded of the often stated principle of General Relativity–Matter tells space-time how to curve, and space-time tells matter how to move. Gravity comes about through the interaction of matter and space. This is a basic fact of life–just like the four dimensions of the STC, the speed of light, the masses of quarks, and atoms consisting of neutrons, protons, and electrons. Why is any of this true? It is the nature of the Universe–it is an incomprehensible mystery as unfathomable as the Christian Trinity.
Ultimately mass, matter, and gravity are all functions of the STC. The essential feature is that the STC is the force carrier of gravity, not some mythical
graviton. I think this model of gravity satisfies the geometrical framework of General Relativity and the discrete quanta of Quantum Mechanics. Someone else will have to do the math–I'm strictly a big-picture guy.