What is the origin of gravity?

Gravity is a property of spacetime.
| Photo Credit: Johnson Martin/Unsplash

A: For a long time, people wondered what makes the planets go around the sun and why anything thrown up comes down. The English scientist Isaac Newton probed the origins of this mysterious force and came up with the laws of gravitation. According to these laws, which we would have learnt in school, the force acting between two objects depends on their masses and the distance between them.

The mathematics of the laws suggested that the origin of gravity was the object itself. That is, by virtue of its own mass any object may have an influence on another (massive) object. But in his final analysis Newton concluded that massive bodies gravitated at all because god had deemed it so. It wasn’t until Albert Einstein published his general theory of relativity that scientists acquired a clearer picture of gravity’s origins.

According to this theory, gravity is a property of space and time taken together (to be exact, of four-dimensional spacetime). It isn’t technically a force that causes objects to move one way or another. Instead, the presence of energy and momentum in a region of spacetime has the effect of deforming spacetime there (like when you lay your head on a pillow). Objects moving there may seem to have been deflected from their straight path by a force. This is gravity.

First published on August 29, 1996; updated today.