A Brief History of Gravity


What is Gravity? HowSaturn Eclipse from Cassini is gravity related to time? Does gravity attract objects? Is the “force” a real  pull, or is it just space-time? No one has ever isolated any gravity - directly measured it apart from assumptions about matter and time. Newton did not claim to know the cause of gravity.  "Hitherto I have not been able to discover the causes of these phenomena, and I frame no hypothesis . . . And to us it is enough that gravity does really exist, and acts according to the laws which we have explained, and abundantly serves to account for all the motions of the celestial bodies, and our sea." Saturn is a good illustration of the mystery of gravity. Why are the rings so thin that we can see through them? Why do they rotate in a plane? Why do the major moons of Saturn rotate synchronously, so the same side always faces the planet? This is a view of Saturn as it eclipsed the sun from the vantage point of the Cassini spacecraft. Photo from NASA.

Archaic thinkers could not imagine time or gravity as we do. Imagine growing up in ancient Babylon. In school you learned about the early kings who had lived for vast ages. The earliest kings reigned for tens of thousands of years. (The longest, according to the record, reigned for 43,200 years - 12 sars). Each generation of kings reigned a shorter time. In school, you studied how the planet gods gave birth to other gods. You learned about how the heavens periodically become unstable when the planet-gods battled each other for supremacy. Every so often, a Great Year occurred, when planet-god battles brought chaos to earth. Cosmos, constants, or orderly laws of nature were not what you learned in school. In the language of Babylon they did not even have words for principle, concept or laws of nature. They studied about catastrophic changes and continuous changes.  According to their traditions, time itself changes, changing speed continually though the seasons. They even used different quantities of water to time the "day watches" and the "night watches" that varied through the seasons. All ancient people believed that their ancestors lived for eons. In fact the Greek word eon (aeon) originally referred to the length of a human lifetime - according to Aristotle.

The archaic people believed everything physical continually changed. They believed that everything was better in the olden days, the golden age.  They longed for the past, when their ancestors had lived immeasurably long lives. In that great long-ago time, people lived for eons. [Indeed, we find that the skulls of the ancients had huge thick brows. The face is the only part of our skeleton that keeps growing as we age. If we lived for geological ages, our brows would grow thick like a Neanderthal's. Neanderthal children did not have the thick brows. The old ones with bad teeth had the extended brows. This suggests that the ancients lived for eons, just as recorded in their genealogies and histories.]  The ancients believed that in that wonderful long-ago time, the earth had produced abundantly. Then the times of chaos came and wrecked the earth. Every ancient society had stories of the battles in the heavens. Even the Bible mentions such a battle in Job and Isaiah. In the Enuma Elis, the younger planet god Marduk (Jupiter) attacks the older planet goddess Tiamut. Marduk sends in the Evil Wind (perhaps a moon) to strike Tiamut and shatter her into pieces. The other gods who marched at her sides fled in terror. But Marduk captured them with his net. Then he assigned stations for the gods, the year and the constellations for each of the 12 months. Notice that it was a result of a great planet slitting war that the orbits of the planets were assigned by the young god Marduk - Jupiter. All archaic peoples had similar stories describing the fearsome battles in the skies. During the times of chaos, they believed some planets would approach Earth and grow into gigantic Titans. As the younger gods fought for supremacy, the older planets who formerly reigned, were pushed back into Tartarus - the cold darkness of the nether gloom.

People who believe that everything is changing cannot imagine unchanging time or its cousin - the force of gravity. Why not? No constants existed in their world view. Everything changed - even the planet orbits.  It was not until the Greek philosophers invented assumptions to limit what can change that they were able to invent logical, mathematical, and natural explanations for the cosmos. The Greek philosophers spent hundreds of years in a long running debate seeking for a first principle on which to found a system of natural science.

Aristotle Aristotle's Gravity, Motion and Time


Aristotle used the word gravity in his Metaphysics. He said, “exhibiting gravity compared with the fiery element, and levity by comparison with the opposites of fire.” 2 Gravity was the opposite of levity. The stars and fire contained levity - not gravity. Aristotle said, “gravity it is a definite weight.” Gravity was the internal property of an object that gave it weight. Different objects had different amounts of gravity. Aristotle believed that a stone fell because it naturally belonged with other stones. If someone threw a stone out over the water, it would fall through the air and water to finally come to rest with the other stones on the bottom of the stream where it belongs by nature. Water by nature seeks other water and so it runs to the sea. Aristotle also believed that heavier objects, those containing more gravity, fall faster than lighter objects.

According to Aristotle, a thrown stone moved because it was being continually pushed along its path.  He believed that behind a moving stone there was a vacuum. The universe abhorred a vacuum, so air rushed in at the back of the flying stone and pushed it along its curved path. Force was something that was transmitted only by physical contact. There was no such thing as “action at a distance”: the idea that far away objects affect things without physical contact.

In Aristotle's cosmos, every place was not the same. Each place contributes to motion. “The typical locomotions of the elementary natural bodies -- namely fire, earth, and the like -- show not only that place is something, but that it exerts a certain influence. Each is carried to its own place, if it is not hindered, the one up, the other down . . . . It is not every chance direction which is ‘up’, but where fire and what is light are carried, similarly, too, ‘down’ is not any chance direction but where what has weight and what is made of earth are carried - the implication being that these places do not differ merely in relative position, but also as possessing distinct potencies.” 3

Aristotle defined time differently from modern people. He wrote, “Not only do we measure the movement by the time, but also the time by the movement, because they define each other. The time marks the movement, since it is its number, and the movement the time.” 4  “... regular circular motion is above all else the measure, because the number of this is the best known. Now neither alteration nor increase nor coming into being can be regular, but locomotion can be. This also is why time is thought to be the movement of the sphere, viz. because the other movements are measured by this, and time by this movement.” 5 In Aristotle's system, time is a mere accident, a numerical accident, as we count the cycles of the heavens and use that count as a time marker. Although Aristotle thought the universe always existed, he did not admit that this was an infinity of time. The infinity is not actual. You cannot add up the bits of past time to arrive at an infinite time - since the past does not exist. Time is an accident, the numbering of the heavenly cycles, not an actuality. Notice that in Aristotle's system time did not have a private existence. It was inseparable from the motion of the heavenly bodies.

Claudius Ptolemy, the Geometrical Astronomer

Almost 500 years after Aristotle, Ptolemy wrote an astronomy book, now called the Almagest. Ptolemy was a Greek living in Roman Egypt. Ptolemy mathematical procedures were based on circular orbits, offset by equants and epicycles. He made no attempt to understand the causes of planetary velocities, retrograde motions and anomalies. He even used different planetary models for calculating a planet’s latitudes than for its longitude. Since the two methods were not physically compatible with each other, there was no attempt to understand physical reality. In fact, Ptolemy thought that physics was nonsense. He wrote,"It is an attribute of all existing things without exception, both mortal and immortal: for those things which are perceptually changing in their inseparable form, it (mathematics) changes with them, . . ." "physics (is guesswork) because of the unstable and unclear nature of matter; hence there is no hope that philosophers will ever be agreed about them." Mathematics, he believed, is unshakable, because when matter itself changes, mathematics changes with it. (Almagest Book One - G. J.Toomer translation), People who think that matter is changing cannot imagine laws of gravity. It was enough that an astronomer could achieve a certain accuracy in measuring angles and calculating orbits. Gravity had no meaning as far as planets were concerned. Planet motions may have involved the gods, since each planet was identified with a celestial divinity.

 GalileoGalileo, The Experimenter.
Galileo watched a pendulum swinging back and forth. He may have timed the swings by feeling his pulse. He noticed that the swings took the same number of pulses, no mater how far the pendulum moved. Later he rolled brass spheres down a grooved inclined plank. He measured the distance they moved relative to a pendulum, musical notes or his pulse (accurate clocks did not exist in his days). He discovered that objects increased their velocity (accelerated) an equal amount during every interval. They also moved a distance that increases with the square of the elapsed time. He compared the speed of large and small objects as they fell, and found them equal. This contradicted Aristotle's opinion that objects with more gravity fall faster. Galileo explained that large rocks fall at the same speed as small rocks because a large rock is just a bunch of small rocks falling together. Galileo also found that all smooth, even motions are relative. He claimed that if you dropped a stone from the mast of a smoothly sailing ship, it would land at the base of the mast. In his day, most professors believed the ship would sail on and the stone would splash astern. Galileo's relativity meant that the stone had the same speed as the ship and would continue that same motion during its fall. A sailor who watched a flying seagull would only notice the relative motion between the ship and the bird. Galileo noticed that how we see the world around us depends on our motion and the motion of the objects we see. Galileo's relativity of motion preceded Einstein's relativity by 300 years. Galileo built a crude telescope that magnified distant objects about 30 times. On January 7, 1610 he turned his telescope to Jupiter, then at opposition. He saw three stars aligned through Jupiter. He recognized that it was unlikely that these were background stars. Subsequent observations revealed that the stars followed Jupiter in it's orbit, a miniature solar system of four moons moving with Jupiter and revolving around it. He also noticed the phases of Venus with his telescope. This was not absolute proof that the earth and the planets orbited the sun, but it suggested that this was a possibility. Galileo, however, did not imagine a force of gravity that affected the Jovian system or the rest of the solar system.

KeplerJohannes Kepler: Laws of Planetary motion without Gravity

Kepler spent ten years trying to find a mathematically precise solution for the Martian orbit. He tested his calculations against Tycho Brahe's observations. Kepler's solution showed that Mars moved in an ellipse, with the sun at one foci. A planet speeds up when it is closest to the sun according to his second law. His third law, ( T1 /T2)2 = ( R1 / R2)3 showed a correlations between orbital period (T in years) and radius (R - distance in AU). Kepler did not imagine that gravity attracted the planets to the sun. Instead he thought there was an "anima motrix" - rays like light - coming from the sun that pushed the planets. Far planets intersected fewer rays and so moved slower. If an invisible string of rays held a planet to the sun, it would have to move in a circle, not an ellipse. Kepler proposed that magnetic fields interacted with the "anima motrix" to modify circular orbits into ellipses. According to his idea, Mars would have a stronger magnetic field than earth because its orbit is more eccentric. Today we know that Mars has no present global magnetic field.

Issac NewtonIsaac Newton  explained that all objects are affected by gravity. He unified astronomy and mechanics by showing that a falling object is reacting to the same force as the orbiting moon. Newton wrote that, “Gravity must be caused by an agent acting constantly according to certain laws.” He arrived at these laws of motion because he took "time" as the independent variable. Newton wrote, “Absolute, true and mathematical time, of itself, and from its own nature, flows equably without relation to anything external.” His absolute space and time successfully predicted planet motions and apples falling from trees. Newton's concept of time, allowed him to invent the force of gravity. Newton studied in Western Europe, the only place on earth where clocks ticked with equally sounding seconds. No other people in history had ever imagined that time always moved at the same speed. Their histories mentioned how the earliest people lived in the great time, the time of Kronos. Everyone observed that daylight was shorter in winter and longer in summer. Ancient people varied the amount of water in a water clock so that the durations of "time" slowed down or sped up to fit the varying length of a day. Claudius Ptolemy sometimes measured astronomical events in “equal hours.” Equal hours were simply angles (time) measured along the equator instead of the ecliptic. He did not imagine that equal hours were really equal chunks of time. Why not? The sun and moon move at different speeds against the background stars at different times of the year. Three thousand years ago every village idiot knew that time ran slower in the past and that it was always speeding up.

Gravity seemed to fit Newton's concept of linear time. However, Newtons gravity uses circular reasoning. Gravity supposedly emanates from all mass. He assumed that mass is unchanging, since matter was not supposed to change its properties as it ages. To measure an unchanging force, one must assume an unchanging time. To measure an unchanging time, one must assume that the properties of matter are not emergent. We cannot in the long term measure a precise velocity or acceleration without a assuming linear time and an unchanging mass. As Einstein pointed out, "The weakness of the principle of inertia lies in this, that it involves an argument in a circle: a mass moves without acceleration if it is sufficiently far from other bodies; we know that it is sufficiently far from other bodies only by the fact that it moves without acceleration." Gravity is the force that comes from mass. It is also the force that moves it. Wait a minute, you say. We measured the mass repeatedly and it always accelerated the same way. How can you say this is circular reasoning? The assumption that time is unchanging is essential to reasoning about gravity and even measuring it. Yet no clock ever isolated any time or precisely compared a past second to a modern one.

Newton's gravity revolutionized science and philosophy. One man's ideas introduced a rigorous mechanical view of the universe.

  EinsteinAlbert Einsteinn: Relative Time and Gravity Fields

At the beginning of the 20th Century, everyone accepted Newton's gravity. However, Einstein questioned the assumptions about absolute space and time. In Einstein's universe, each observer has his own clock and his own ruler, but all observers measure the speed of light equally in every reference frame. Einstein extended Galileo's relativity to include relativity of space and time.

In 1915, Einstein produced his General Theory of Relativity. In Einstein's thinking, gravity is not a force pulling us towards some distant mass but rather the evidence of space-time curvature. All straight lines are bent by the presence of massive objects because space and time are intertwined. Time is slowed down by mass, supposedly because mass warps space-time.

Einstein could explain the acceleration of gravity without the use of an attractive force. Clocks in the vicinity of massive objects slow down. The greater the mass the more all clocks slow down. Apples fall from trees because clocks run a tiny bit faster on the branch than on the ground. Space-time is much harder to visualize than Newton's gravity. The mathematics of gravity is also much simpler than the mathematics of space-time. No one uses complex fields and partial derivatives to compute an orbit when the assumption of gravity is so much simpler.

Experiments, however, showed that clocks really do slow down in the vicinity of massive objects. Einstein, like Newton, used an operational definition of time. He said, “Time is what clocks measure.” An operational definition is not concerned with the actuality of time. Einstein just assumed that time is real because he defined it with clocks.

Einstein's system also depends on assumptions. No one ever directly detected any space-time or even isolated any time. If we deny the existence of time, nothing in the universe would change, therefore we have a right to claim that time is a synthetic idea. Like Newton's gravity, space-time involves perpetual motion without the expenditure of "energy." No one ever detected bends in the vacuum of space as space-time forces the huge earth to continually accelerate into following the bend in the vacuum.

What is gravity? Gravity, like time, is illusive. You think you understand it until you try to explain it. In Einstein's thinking, gravity cannot be divorced from time. Every attempt to isolate any space-time, gravity waves or gravitons has ended in failure. Can we prove Einstein is right? We can prove his theory is more accurate, if we accept the assumptions and operational definitions upon which his gravity theory depends.

Newton and Einstein's concepts of gravity result in different predictions. Einstein's mathematics correlates more accurately with angular changes in Mercury's orbit better than Newton's gravity. The bending of starlight in the vicinity of the Sun is more accurately predicted by space-time than by gravity. Clocks carried in aircraft or rockets compared to identical clocks that remained “stationary” show the blue shift and red shift of clocks as Einstein predicted.

How do we know that gravity does not change throughout history? How do we know that the gravitational constant is really a constant?

Does gravitRobert Dickey change? Robert Dicke.


The physicist, Robert H. Dicke, tried to determine if gravity changes over time. Gravity is the weakest interaction known. Dicke used the effect of the sun on test masses suspended on a quartz fiber in a vacuum chamber. His experiment was designed to test his Scalar-Tensor theory of gravitation. In this theory subatomic mass ratios, electrical charges, and the gravitational constant may all vary togehter. Dicke ran his apparatus for nine months and concluded that there is very little room for a change in electron charge. Dicke's apparatus used a small test mass and a short experiment. It also relied on the basic assumption of science - the scientific first principle.

To test the long term stability of gravity - one could use large objects over long durations. One should not use clocks in such a test, since clocks and gravity seem to be related. Why can't we use radar or laser ranging? If relational change exists, it would affect both clocks and gravity. A test for the stability of gravity could use optical parallax of large bodies over lengthy durations, or the visible way galactic orbits change over cosmic history.

What is gravity?

Is it a real force, or is it the effect of space-time?

The reader may think, we measure the force of gravity with instruments, therefore it must exist in reality. Not necessarily! Pseudo forces exist. Scientists measure Coriolis with precision accelerometers. If you fire a rocket north in the northern hemisphere, Coriolis appears to veer the rocker to the right. The same rocket fired in the same direction in the southern hemisphere appears to veer to the left. Why? We measure a Coriolis force because we are turning, moving as the earth spins. What about plants that wind around a pole in the opposite direction in the northern hemisphere than the southern? Aren't they reacting to the Coriolis force? No! The plant is growing on a moving earth. We invent a Coriolis force to correct for a “rotating earth based co-ordinate system.” We are justified in saying Coriolis is a pseudo force because a co-ordinate system exists in which the Coriolis force disappears.

Centrifugal force is also a pseudo force. If you speed around a corner in your car, you will feel a force pushing you towards the outside of the turning circle. Your body is trying to go straight while the car is veering off. The force is not a real force, even though instruments can measure it. The pseudo force comes from the acceleration of the reference frame that contains the instruments. A reference frame can be imagined where the force vanishes, so it is unlikely to be a fundamental physical force.

Is gravity a pseudo force? Pseudo forces, like centrifugal force, are always proportional to the 'weight' of the object that experienced the 'force' (e.g. the proof-mass in an electromechanical accelerometer). The 'force' of gravity is also proportional to 'mass.' We measure 'mass' circularly with (1) the amount of force needed to accelerate it and (2) the assumption that mass is an intrinsic and unchanging property of matter. If the properties of matter are emerging, changing as matter ages, we would still measure an constant force of gravity and clock-like orbits with clocks. However, using angles, solar system orbits would continue to spiral outwards because angles are not tied to the assumption that the properties of matter are fixed.
   
Sir James Jeans: “The theory of relativity shows that if motions are attributed to forces, these forces will be differently estimated, as regards both quantity and quality, by observers who happen to be moving at different speeds, and furthermore that all their estimates have an equal claim to be considered right. Thus the supposed forces cannot have a real objective existence; they are seen to be mere mental constructs which we make for ourselves in our effort to understand the workings of nature.” 8 “When Newton had found laws of motions of a mechanical system which were true (apart from the minor refinements of the theory of relativity), he put science on a wrong track for two centuries by interpreting them in terms of forces and absolute space and time. It was much the same with the supposed force of gravitation.” 9

Forces and inertia are not necessary to make sense out of the universe. Harvard professor Owen Gingrich derived Kepler's laws without the concept of force for his History of Science class. He uses conservation of momentum and energy as axioms in his formulas. This demonstrates that the concept of force and inertia are not essential to an understanding of the universe. They are simply Newton's way of explaining motion.

Assumptions: the weakest link in the chain of Knowledge


The scientific fundamental assumption affects ideas about space, time and gravity. A fundamental assumption is also known as a first principle. The historical first principle of science is the idea that the properties of matter are not emergent. What would our universe look like if all substance is continually changing itself?

Consider the strange measurements of the ancient astronomers. They are the only measurements that have a long enough base line to test our ideas of space, time, and gravity. The ancient astronomers did not have our assumptions. They made two types of time measurements. Interval measurements are often accurate. The Babylonian planetary synodic periods (in days and fractions of days) are very close to our clock measured units. The ancient space measurements, the angles and distances, radically conflict with our computer models. Eclipses, their dates and locations, are almost always in error when compared to our calculations.  Eclipses are extremely precise events. Three solar system objects precisely align when an eclipse occurs. Why do their eclipse records disagree with our computers? Why did they consistently measure a smaller solar system and larger planets diameters, as Ptolemy did?  How could Ptolemy's errors cancel so that his system worked?  Why did eminent astronomers like Cassini and Flamsteed, using independent parallax methods, arrive at a solar system 7% smaller than we do? What the ancients measured suggests a continually expanding solar system.

HuDF 4491The simplest test of gravity is a visual test.  Primordial galaxies look like tiny seeds, often seen in equally spaced chains. Closer galaxies begin to eject little globs packed with stars. At closer ranges we see how these stars continually accelerate outward as they take up more space. In spiral galaxies we see that the properties of matter change as the stars and gas continually accelerate outward. We see with sight that the atomic frequencies, the inertial properties and the space matter takes up keeps on changing relationally. We see how billions of spiral galaxies grew, spread out, changed into huge growth spirals. What is visible violates every law of science because it violates the scientific creed that the properties of matter are fixed - not emerging. This is a tiny primordial galaxy in the Hubble Ultra Deep Field just beginning to eject a string of equally spaced blue star clumps. Notice that the ancient galactic arm is moving in the opposite direction of all the laws of gravity and that the colors (light frequencies) are different for the core of the galaxy than for the nascent appendage.

What could cause such a universe? The Bible clearly states that the creation is in bondage to phthora - internal change. It even states, in Greek, that gold is presently corrupting itself. Do the properties of matter change as matter ages? We can see the past with our eyes. We can see that the properties of matter always change. Every clock, atomic and orbital, when compared to closer clocks, visibly accelerates. The earliest primordial galaxies shine with atoms that clocked 10% of the frequencies of modern atoms. Why then do we measure clock-like orbits here in the solar system? When matter changes its properties relationally, the atomic clocks, the orbits of the Sun and Moon, the rotations and most of the scientific measuring units are affected in parallel.

The most important assumption you can think about is the modern first principle. It was invented by Aristotle about 2350 years ago. This idea was adjusted by the Catholic scholastic to: the essence of all substance is unchanging. If matter changes AS A RELATIONSHIP, we could not measure it locally since it would affect everything, our measuring units and our instruments.
Yet we can see the evidence with our eyes.

Look at the universe with sight. Observe the history of how galaxies formed and you will get more knowledge about gravity than you will ever find in a physics book. Look! The visible history of the universe violates every idea about gravity. This is because it violates the basic scientific assumption that the properties of matter are not emerging continually.

1. Mathematical Principles of Natural Philosophy by Isaac Newton, Great Books of the Western World Vol 34, page 372.
2. Metaphysics by Aristotle, Library of the Future 3rd Edition, 1994 World Library Inc.
3. The Copernican Revolution by Thomas S. Kuhn, MJF Books 1957, page 98
4. Physics by Aristotle. Book 4, Chapter 13, Library of the Future, 1994 World Library Inc.
5. Physics by Aristotle, Book 4, Chapter 14, Library of the Future, 1994 World Library Inc.
6. Mathematical Principles of Natural Philosophy, Isaac Newton, Great Books of the Western World 1952 Vol 34, page 8.
7. Mathematical Principles of Natural Philosophy, Isaac Newton, Great Books of the Western World, 1952 Vol 34 page 372.
8. Physics and Philosophy by Sir James Jeans, Dover Publications 1981, page 14.
9. Physics and Philosophy by Sir James Jeans, Dover Publications 1981, page 190.


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Last modified on January 8, 2010