**There is a force on Earth called gravity.**

Gravity is one of the most important natural phenomena in human history, and our understanding of it has developed gradually over thousands of years.

Newton’s law of universal gravitation: “The force of gravitation between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them.” This mathematically describes the magnitude of gravity and can explain phenomena ranging from the gravitational pull of the Earth to the orbital motion of the planets in the solar system.

Einstein’s general theory of relativity: “Gravitation is the bending of spacetime by mass.” This definition describes the nature of gravity more fundamentally, and plays an important role in high-energy astrophysics and cosmology. In particular, Einstein’s theory predicted that the path of light can be bent by gravity, a phenomenon known as gravitational lensing.

The mathematical definition and calculations for gravity are as follows

There is a force acting on all objects and between objects that pulls them together.

This force is called the universal force of attraction (gravity), and its magnitude is proportional to the masses m1 and m2 of the two objects and inversely proportional to the square of the distance R between them.

Newton’s law of gravitation expresses this relationship as a formula

Fg = Gm1m2/r2

Let G be the constant of proportionality, m1 and m2 be the (gravitational) masses of each object.

Near the surface of the Earth with a mass Me and a radius Re (r ~ Re), the gravitational force exerted by the Earth on an object of mass m is

F = GMem/Re2 = mg,

where g is the gravitational acceleration due to the Earth received by an object on the surface of the Earth

g = GMe/Re2 = 9.8 m/s2.

**A historical breakdown of the relevant figures is as follows**

**Ancient and medieval: Early concepts of gravityAncient Greek and Roman philosophy**

Aristotle (Aristotle, 384-322 BC)

Aristotle was an ancient Greek philosopher who sought to philosophically explain the motion of objects and natural phenomena. He described gravity as the tendency of objects to return to their “natural position”. According to Aristotle, heavy objects naturally move downward and light objects upward, which can be seen as an early concept of gravity. However, Aristotle’s theory was based on qualitative descriptions rather than quantitative analysis, and was far removed from later scientific research.

Contributions of medieval Islamic scholars

**Alhazen (965-1040)**

Alhazen was an Islamic scholar who did important work in optics and physics, and sought to explore physical phenomena experimentally. He studied the reflection and refraction of light, and developed his concepts of physical laws. His work had a major impact on medieval Europe, and led to a critical re-examination of Aristotle’s theories.

**Avicenna (980-1037)**

Avicenna was a great philosopher and physician in the Islamic world who discussed the motion and force of objects. He developed the concept of force, presenting the view that the motion of objects is maintained by an external force. This helped to advance the understanding of gravity, and later had a significant impact on scientific inquiry in Europe.

Renaissance and Modernity: Scientific Revolution and the Quantification of Gravity

**Galileo Galilei (1564-1642)**

Galileo was an important scientist during the Renaissance who refuted Aristotle’s theories through experimental research on gravity. He experimented with simultaneously dropping heavy and light objects from a tilted tower in Pisa Cathedral and found that all objects fell with the same acceleration, an important discovery that laid the groundwork for a quantitative understanding of gravity.

**Isaac Newton (1642-1727)**

In Philosophiæ Naturalis Principia Mathematica, published in 1687, Newton proposed the law of universal gravitation. Newton explained that all objects attract each other, and that the magnitude of this force is proportional to the masses of the two objects and inversely proportional to the square of the distance between them. Newton’s theory of gravity was a powerful tool for explaining a wide range of phenomena, including the motion of planets in space, elliptical orbits, and falling objects. His theory has been at the center of science for more than 200 years and laid the foundation for modern physics.

**Modern: Relativity and quantum gravityAlbert Einstein (1879-1955)**

In 1915, Einstein published the General Theory of Relativity, which explains gravity as a phenomenon in which mass causes space-time to bend. According to Einstein, objects with mass distort the fabric of spacetime, and the motion of other objects along this distorted spacetime is the essence of gravity. It replaces Newton’s concepts of absolute space and absolute time, and is used to explain complex astronomical phenomena such as the bending of light, gravitational lensing, and black holes. Einstein’s theory revolutionized our understanding of gravity, replacing Newton’s laws, especially in high-gravity environments.

Modern physics and quantum gravity

**Stephen Hawking (1942-2018)**

From the late 20th century to modern times, attempts have been made to unify gravity with quantum mechanics, particularly by physicists like Stephen Hawking, who studied the properties of black holes. Quantum gravity is an attempt to explain gravity within the framework of quantum physics, and while it is not yet fully established, it is becoming an important area of research to further our understanding of gravity. Research like this is essential to understanding the origin of the universe, the internal structure of black holes, and the laws of physics on a cosmological scale.

**The understanding of gravity has evolved from its origins in ancient Greek philosophy, through the Renaissance and Scientific Revolution, to become an important pillar of modern physics. This process is a great example of the evolution of scientific thought, and the study of gravity is still ongoing today.**