Gravity

1) Gravity in Ancient Times:

A form of law that maintains the harmony of the cosmos by moving all objects, including the stars, winds, and seas, was described by the Ionian Greek philosopher Heraclitus (c. 535 – c. 475 BC), using the word logos. There is no effect or motion without a cause, according to Greek philosopher Aristotle, who lived in the fourth century BC. A heavy body’s tendency to sink downward toward the centre of the universe, where it belongs by nature, can be attributed to the nature of those bodies, such as the element earth.

On the other hand, bright bodies, such as those of the element fire, naturally travel upward toward the inner surface of the Moon’s sphere. Therefore, in Aristotle’s theory, heavy bodies gravitate toward the centre of the cosmos due to an intrinsic gravitas or weight rather than being drawn to the Earth by an outside force.

The centre of mass of a triangle was identified by the Greek physicist Archimedes in the third century BC. Additionally, he proposed that if two objects of equal weight had different centres of gravity, one of them would be in the middle of the line connecting them. Two centuries later, in his book De architectura, the Roman engineer and architect Vitruvius argued that gravity is determined more by a substance’s “nature” than by its weight. By including a causal force that weakens over time, the idea of impetus, developed in the sixth century CE by the Byzantine Alexandrian scholar John Philoponus, alters Aristotle’s thesis that “continuation of motion depends on continued action of a force.”

Indian scientist Brahmagupta described gravity as an attractive force in the seventh century. Impetus was connected to acceleration and mass of objects in the 14th century by the European philosophers Jean Buridan and Albert of Saxony, who were influenced by some Islamic academics. Albert also created a law of proportion relating the speed of an object in free fall with the amount of time that has passed.

Galileo Galilei discovered that all objects had a tendency to accelerate equally in free fall at the beginning of the 17th century. He proposed the fundamental idea of relativity in 1632. Since the middle of the 17th century, a number of researchers have studied the gravitational constant, which has contributed to the development of Isaac Newton’s law of universal gravitation. Early in the 20th century, when Einstein created the special and general theories of relativity, Newton’s classical mechanics was replaced. In the hunt for a theory of everything, different models of quantum gravity are contenders, but gravity remains an outlier.

2) Gravity in Newton’s time:

Between 1640 and 1650, Francesco Maria Grimaldi and Giovanni Battista Riccioli confirmed the relationship between the distance of objects in free fall and the square of the time taken. By observing a pendulum’s oscillations, they were able to calculate the Gravity of Earth constant.

Descartes stated in 1644 that there can be no such thing as empty space and that all motions are curvilinear because of a continuum of matter. As a result, centrifugal force reduces local density and generates centripetal pressure by pushing comparatively light matter away from celestial bodies’ centre vortices. Christiaan Huygens created a mathematical vortex model between 1669 and 1690 using elements of this idea. In one of his demonstrations, he demonstrates how an object dropped from a rotating wheel will travel a distance that increases proportionately to the square of the rotation period.

Robert Hooke proposed in 1671 that gravitation is caused by objects sending waves into the aether. A corpuscular model involving a screening or shadowing mechanism was proposed by Nicolas Fatio de Duillier (1690) and Georges-Louis Le Sage (1748). Le Sage proposed in 1784 that gravity might come from atoms colliding, and in the early 19th century, he extended Daniel Bernoulli’s idea of corpuscular pressure to encompass the entire universe. Hendrik Lorentz (1853–1928) later developed a similar theory using electromagnetic radiation rather than corpuscles.

Descartes’ claim that inertia is constrained by curvilinear motion was used by English mathematician Isaac Newton to support his claim that all bodies are drawn to one another by aether streams in 1675. Aether loses density near mass in a concept put forth by Newton and Leonhard Euler in 1760, which results in a net force acting on objects. Between 1650 and 1900, additional mechanical explanations of gravitation (including Le Sage’s theory) were developed to support Newton’s theory. However, mechanistic models eventually lost popularity because the majority of them produced unacceptably high levels of drag (air resistance), which were not observed. Others are inconsistent with contemporary thermodynamics and break the law of energy conservation.

Robert Hooke proposed an inverse-square force-based theory of orbital motion in a letter to Isaac Newton in 1679. Both Hooke and Newton informed Edmond Halley in 1684 that they had, in January and August of that year, respectively, shown the inverse-square rule of planetary motion. Newton was forced to write De motu corporum in gyrum (‘On the Motion of Bodies in an Orbit’), in which he mathematically derived Kepler’s laws of planetary motion, because Hooke refused to provide his proofs. Newton published Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), which postulates the inverse-square rule of universal gravity, in 1687 with Halley’s backing (and to Hooke’s dismay). In Newton’s theory the density of mass ρ generates a scalar field, the gravitational potential φ in joules per kilogram.

Newton immediately ran out of copies of the Principia, which led him to release a second edition in 1713. The book, which helped make Newton’s theory more well-known, was inspired by the dissertation and was written by French philosopher Voltaire in 1738. Immanuel Kant, a philosopher from Prussia, developed the nebular hypothesis in a cosmological paper he released in 1755 that was founded on Newtonian ideas. Joseph-Louis Lagrange introduced a more refined version of classical mechanics in 1788. Since relativistic effects were not yet known, they are not included in any version. Nevertheless, it is believed that Newton’s theory is remarkably accurate up to a point where weak gravitational fields and low speeds exist.

3) Gravity after Einstein:

After eight years of organising his ideas, Einstein came up with a gravitational agent in 1915. Furthermore, it wasn’t just a force. His theory of general relativity states that gravity is a much stranger phenomenon that results from a mass’s effect on space. The three dimensions of width, length, and height were acknowledged by both Newton and Einstein. It’s possible that matter doesn’t exist in space. Newton, however, didn’t think that objects in space had any impact on it. It was Einstein who considered that impact.

He proposed the idea that a mass could rapidly prod space. It has the ability to push, pull, bend, and distort. The fact that a mass exists in space naturally results in gravity. In his Special Theory of Relativity, published in 1905, Einstein introduced time as a fourth dimension to space, creating space-time. Large masses can also warp time by accelerating or decelerating it.

By stepping on a trampoline, you can picture Einstein’s theory of the warp of gravity. The elastic fabric of space deforms under the weight of your mass. A ball will curve toward your mass if you roll it past the warp at your feet. The more weight you have, the more space is bent. Look at the trampoline’s boundaries; the warp is lessening as you move further away from your mass. As a result, the same Newtonian relationships are clarified, and theoretically predicted with more accuracy, but via a distinct perspective of distorted space.

Newton’s logic was also victoriously shattered by Einstein’s hypothesis. A quick change in mass would need to be reported to the entire cosmos at once if, as Newton believed, gravity were an instantaneous, constant force. Einstein didn’t quite get this. He believed that if the Sun suddenly vanished, it would take some time for the planets to receive the signal to stop revolving. Furthermore, getting to Pluto would take far longer than getting to Mars. There is absolutely nothing instantaneous about that.

What was Einstein’s suggestion for the missing communication agent? Re-enter his really helpful space warp. A change in mass will result in a ripple in space that spreads out from its source in all directions at the speed of light, much like a stone thrown into a pond. The ripple extends and compresses space as it moves. We refer to such an anomaly as a gravitational wave. Finally, General Relativity by Einstein described everything Newton’s theory accomplished (and some things it didn’t), and did it more effectively.

Although Einstein anticipated gravitational waves, he did not have much confidence that they would ever be discovered. Space is just slightly compressed and stretched by gravitational waves. In fact, it is hundreds of millions of times smaller than the size of an atom— ridiculously, terribly, almost impossibly small.

Einstein has so far been correct. Since he first proposed General Relativity eight decades ago, no gravitational wave has been discovered. The first time that scientists even came close was in 1974. In that year, Russell Hulse and Joseph Taylor, two radio astronomers, were studying a pair of neutron stars that orbited one another. Neutron stars are superdense collapsed stars. Hulse and Taylor noticed that, if gravitational waves were truly being produced by the system, the orbits were accelerating at the rate Einstein predicted would take place. Although gravitational waves were first indirectly detected, they were not directly measured. Even while each object has the potential to emit gravitational waves, only enormously huge objects can distort space in a way that can be detected. Only in space can one observe such enormous changes in mass, such as those caused by supernovas, colliding black holes, or neutron stars in orbit.

With one of the most precise scientific devices ever created, LIGO, the Laser Interferometer Gravitational-wave Observatory, scientists are currently looking for waves coming from these sources. It cost more than 365 million dollars and 30 years to develop LIGO, which is a huge, intelligent, and peculiar-looking device. The “discovery” of gravitational waves might be made the front page of every newspaper at any time thanks to its capacity to measure minuscule distances, ushering in the next significant development in our understanding of gravity.