Scientists know of four fundamental forces that shape the world around us: gravity, the weak force, the strong force, and the electromagnetic force.
The electromagnetic force is often linked with light. Light and gravity have been known for a very long time.
In astronomy, light helps us measure most of what we observe. Gravity also shapes how objects move in the Universe.
People have long known that objects fall when dropped. This effect is caused by gravity. Learning how gravity works took much longer. In the 7th century, the Indian astronomer Brahmagupta described gravity as a force that pulls objects together.
In the late 1500s, Galileo showed that, without air or water, objects fall at the same speed.
In 1687, Isaac Newton used mathematics to describe gravity. His work linked gravity with astronomy.
Newton showed that gravity acts across the whole Universe. Although gravity is weak, its effects act over great distances. Newton’s theory worked well in many cases. However, it could not fully explain the orbit of Mercury.
In 1915, Albert Einstein introduced general relativity, which links gravity with space and time.
In 1919, Arthur Eddington tested this theory during a solar eclipse. He showed that the Sun’s gravity bends light from distant stars.
These results supported Einstein’s theory. Today, general relativity remains our best model of gravity. Einstein’s work also predicted the existence of black holes and gravitational waves. Both were later discovered. The first black hole was identified in 1964 in the Milky Way.
In 2015, LIGO and Virgo detected gravitational waves for the first time.
Much about gravity is still unknown. Scientists are exploring whether a particle carries the force of gravity, as with the other forces.
Linking gravity with the other forces is often called the Theory of Everything. This remains a major challenge in physics.
