The speed of light (c) plays a central role in Einstein’s famous equation:
E = mc²,
which shows the relationship between energy (E) and mass (m).

In this equation, c is the speed of light in a vacuum, approximately 299,792,458 meters per second. The equation reveals that a small amount of mass can be converted into a vast amount of energy because c² is an enormous number.

This principle is the foundation of nuclear energy, where tiny amounts of mass are converted into energy in reactions like nuclear fission and fusion. It also implies that mass and energy are interchangeable—two forms of the same physical quantity. This concept has deep implications in physics, from explaining how the Sun produces energy to the workings of particle accelerators and the structure of the universe itself.