Nearly 400 years after Newton’s law of universal gravitation, an “external force transmitted by unknown means,” we are still struggling to understand the nature of gravity — what it is, how it came into being, and how it relates to particle physics.
The problems is most likely conceptual. Consider the following image. This device uses electricity (electromagnetism) to generate a magnetic field that keeps the globe suspended. It illustrates than electromagnetism and gravity exist in the same realm.
Now consider the following image. The Earth rotates around the sun and the moon rotates around the earth. The gravity of the sun keeps the Earth in its orbit and the gravity of the Earth keeps the moon in its orbit. The universe could not have developed the way it did without gravity.
A textbook explanation of gravity: “Newton realized that the reason the planets orbit the Sun is related to why objects fall to Earth when we drop them. The Sun’s gravity pulls on the planets, just as we now understand Earth’s gravity pulls down anything that isn’t held up by some other force.”
In both of the above images, the same “force” is at work. In the former, we call it magnetism, in the latter we call it gravity. If James Clerk Maxwell, the father of electromagnetic theory, had lived before Newton, perhaps we would have called gravity simply planetary magnetism.
China’s natural philosopher never discussed gravity, but they had a word that covers both gravity and (electro) magnetism: qi (or chi). Qi does not differentiate between gravity and magnetism, but it conceptually accommodated both.
The Chinese anticipated other key developments in modern physics. Most notably, they conceptually unified space and time about 1000 years before Einstein did so with his Relativity Theory. The article below includes a brief explanation of the Chinese view of nature.