Gravitational Thoery

The human story of gravity first began more than two millennia ago with Greek philosophy. At the time, it was believed that Earth was the center of the universe. The sun and moon travelled in circles around the earth, while all the other stars rotating around it on a fixed sphere. Unfortunately, this model couldn’t account for the planets which moved unpredictably. In fact, the planets got their name from the Greek term “planan” which means “wander”. Later in the 2^nd century C.E. Claudius Ptolemy created a complex model of the universe using circles and epicycles which could be used to explain most observed phenomena. The book he wrote, The Almagest, would remain as the main astronomy textbook for the next 1400 years, until the arrival of Copernicus.

Nicolas Copernicus was born on February 19, 1473, in Poland. There he would grow up and establish a keen interest in astronomy. He spent a lot of time making detailed observations of the sky and the movement of celestial objects. This hard work and dedication would later lead to the production of his manuscript. What he realized was that, by placing the sun at the center of the universe, Ptolemy’s system could be greatly simplified. This discovery was of astounding significance. Up until then, the world believed the earth to be the center of the universe; a delusional idea on the same scale as believing the earth to be flat. Regrettably, the fear of the consequences of his work forced him to develop the theory in secret. He finally published his work, On the Revolutions of the Celestial Spheres near the end of his life. This book contained what would later be referred to as the heliocentric model of the universe.

In Germany 1571, Johannes Kepler was born. He became a math teacher and grew fascinated in the perfection of nature and the idea of perfect circular motion and the five perfect solids (tetrahedron, cube, octahedron, dodecahedron, icosahedron). After measuring the diameter of two spheres, one formed inside an equilateral triangle and the other on the outside, he found that the ratio of their diameters matched the ratio of Jupiter and Saturn’s orbits. Surprised by this discovery, he then nested the five perfect solids within each other, separating them with spheres. He then noted that the ratios of the diameters of the spheres were almost exactly equal to the ratio of the six planets known at the time. In 1596, he published his findings, attracting the attention of Tycho Brahe. Together, they collaborated to improve the model of the universe until Brahe’s death in 1601. Kepler later ran into difficulties when he tried to model Mars’ orbit as a circle. This brought him to the realization that perhaps the planets don’t orbit in perfect circles after all but rather ellipses. These was a startling discovery, as for the last several thousand years’ scientists tended to treat nature as if it acts in a perfect, symmetrical way. After his realization, he went on to create 3 laws regarding planetary orbits which he released in his books Astronomia Nova and Harmonices Mundi. The work he did along with the data Brahe provided made the study of astronomy 100 times more accurate than it was before. His theory also significantly altered human understanding of the universe; leaving behind the first accurate mathematical model of the universe.

The next contributor Galileo Galilei was born a few years before Kepler, in Italy. Over the course of his life he studied the affect of gravity on earth. To start, he realized there was something very wrong with current theorems. If the Copernican model of the universe was to be accepted, then why wouldn’t its results be noticed on earth. For example, an object dropped from a tower should fall a far distance away because of the earth’s rotation as it travels through the air. In order to fill these gaps in understanding Galileo conducted numerous experiments, and tested them with mathematical theory. One such experiment measured the time it took for balls to roll down inclined planes with different slopes. From this he realized that the distance travelled was independent of the plane’s slope and a ball that rolls for twice the time travels four times as far. He then extrapolated this theory to include free falling objects as well, developing the concept of uniform acceleration. Then he also grasped that the only thing affecting the speed of falling objects was air. Bodies falling in a vacuum would all behave the same way. For his next experiment, he rolled a ball down an angled plane and watched it roll back up a second angled plane. He observed that the height to which it rolled was the same height that it started with, regardless of the angles of the planes. For example, if the ball was rolled down a steep slope and then up a gentle slope it would have to travel much further but, nevertheless, would only stop at the same height that it started with. This concept today is explained by the conservation of energy. Galileo, however, used this idea to hypothesize another theory: if the second angled plane was horizontal, then no matter how far the ball travelled it would never reach the original height and therefore would never come to a stop. His conclusion was that an object moving horizontally will keep moving at the same horizontal speed forever, unless acted upon by other forces. This idea was later incorporated into Newton’s first law: The Law of Inertia. Finally, he could explain the dilemma of the object dropped from the tower falling straight down. As both the earth and the falling object have the same horizontal velocities they don’t move horizontally relative to each other. Lastly, he was able to apply this concept to cannonballs to map their trajectories as parabolas. He published his lifetime work in 1638, in his book Two New Sciences. For an astounding contribution to human understanding and for the development of the scientific method Galileo Galilei is recognized as a Cromulist Notable.

After Galileo came Sir Isaac Newton, born in 1642. He grew up in England and became a fellow at Trinity college in 1667. There, his work was strongly influenced by both his rival Robert Hooke and his friend Edmond Halley. Hooke suggested that gravity depended on the distance of an object from the center of the earth. Halley was then able to prove this by climbing up 2,500 feet and observing that a pendulum swung slower at higher altitudes. At the time, Kepler had already shown that an inverse square law may cause a body to move in an ellipse. In 1684, Halley asked Newton what curve a planet’s path would have with an inverse square law of attraction towards the sun. Newton replied that it would be an ellipse, and worked for months to prove it. Adding to the difficulties was the lack of any vocabulary to use for these kinds of calculations. To get a result, he had to invent various terms including mass (the quantity of matter). He provided Halley with the result as a treatise (on the motion of bodies in orbit), which then prompted Halley to ask for more. Just a few years later in 1686, Newton completed and published the Book I of Philosophie Naturalis Principia Mathematica. Newton’s work was so groundbreaking because it explained the discoveries of Kepler and Galileo by generalizing a single theory to unify gravitational motion on earth as well as in space. This was the first great unification of theories. The work conducted by Newton was so excellent that it earned him a place as one of the greatest scientists ever to walk the earth, and remained unchallenged for the next 200 years. To recognize these amazing achievements, Cromulism awards Newton the position of Notable.

The last individual to have a major impact on gravitational theory was Albert Einstein, born in Germany, 1879. By then, Newton’s theory of gravity dominated physics, being used to explain almost any physical phenomena. However, by this time small discrepancies had been discovered which couldn’t be explained using existing theorem. In 1905, Einstein extended Newton’s theory surrounding the motion of objects with high velocities by stating the speed of light remains constant regardless of how one travels. This allowed him to perform calculations for any speed, whereas Newton’s equations were limited to low velocities. Over the course of the next ten years, Einstein made several more discoveries. The first was that mass and energy must influence gravitational fields. The second was that gravitational fields are not forces as Newton had imagined but rather curvatures in space. Therefore, objects are not affected by gravity because it is exerting a force on them but instead because space is being curved and the objects must follow the path of space. For example, Earth travels in a straight line (not in the Euclidian sense) and the mass of the sun curves space. The result is the elliptical path we observe as it follows the curve in its straight path. The consequences of this discovery were huge. If space could be curved by space, there is no reason why light couldn’t bend as it travels through space. To test this Einstein wanted to observe the curve of light from a distant star bending around the sun. This required a solar eclipse as the sun’s light would otherwise block out the light of distant stars during the day. After being delayed by the first World War, this theory was put to the test in 1919. The results were excellent, with Einstein having predicted the light curvature with astounding accuracy. After this discovery, Einstein surpassed Newton as the most famous scientist in the world and reached the Cromulist status of Notable.

Today, the theory of gravity is still worked on to find a unifying equation that incorporates the three other forces of nature. The recent confirmation of Einstein’s theory of gravitational waves adds yet another milestone to the discoveries in this field - a field which has had a profound impact on human understanding and knowledge. It has been developed over several millenniums, through the hard work of some of history’s brightest minds. Cromulism recognizes these achievements of humanity and the people who made them possible.