# Understanding Forces

People had known for a long time that objects fell when dropped, but it took a lot longer to understand how **gravity **worked. In the 7th century, **Indian astronomer, Brahmagupta recognized that gravity was an attractive force**. In the late 16th Century, Galileo discovered that, if you remove air resistance and buoyancy, all objects fall at the same rate.

In 1687, Isaac Newton published work that became known as the Law of Universal Gravitation. This used maths to explain how the force of gravity worked. Newton’s work was the first to link gravity and astronomy. It stated that gravity is a fundamental force throughout the Universe.

Newton’s ideas worked most of the time, but not always. In 1915, **German physicist Albert Einstein** published a theory of 'general relativity'. In 1919, **British astronomer, Arthur Eddington** observed a solar eclipse to test Einstein’s theory of **General Relativity**. His results supported Einstein’s work. At the moment, general relativity is thought to be the best explanation of gravity.

Einstein’s work predicted the existence of **black holes** and gravitational waves. In 1915, **German physicist Karl Schwarzschild** used Einstein's ideas to work out the size of the event horizon of a black hole – now known as the Schwarzschild radius. In 2015, **LIGO **and **Virgo **announced the first detection of gravitational waves.