mass-energy equivalence

physics

Also known as: mass-energy

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 30, 2026

Quick Summary

The mass-energy equivalence, famously expressed by Albert Einstein's equation E = mc², reveals that mass and energy are fundamentally the same physical entity and can be converted into one another. In this equation, E represents energy, m represents mass, and c is the speed of light.12345

This principle revolutionized the understanding of physics, as mass was previously considered distinct from energy. The equation indicates that even a body at rest possesses "rest energy" equivalent to its mass multiplied by the speed of light squared (mc²). When energy is released, the mass of the body decreases. This conversion is evident in chemical reactions but is far more significant in nuclear reactions, such as those powering stars like the Sun. The speed of light, a fundamental constant, acts as the conversion factor between mass and energy.26758

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

8 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

cosmology
Superunification and the Planck era
…of real pairs with positive mass-energy, a fact first demonstrated in the context of black holes by the English astrophysicist Stephen W. Hawking.
Read More
…of real pairs with positive mass-energy, a fact first demonstrated in the context of black holes by the English astrophysicist Stephen W. Hawking.
Read More

mass
…object was seen to be equivalent to energy, to be interconvertible with energy, and to increase significantly at exceedingly high speeds near that of light (about 3 × 10⁸ metres per second, or 186,000 miles per second). The total energy of an object was understood to comprise its rest mass…
Read More
…object was seen to be equivalent to energy, to be interconvertible with energy, and to increase significantly at exceedingly high speeds near that of light (about 3 × 10⁸ metres per second, or 186,000 miles per second). The total energy of an object was understood to comprise its rest mass…
Read More

matter
…mass) and energy can be converted into each other according to the famous equation E = mc², where E is energy, m is mass, and c is the speed of light. This transformation occurs, for instance, during nuclear fission, in which the nucleus of a heavy element such as uranium…
Read More
…mass) and energy can be converted into each other according to the famous equation E = mc², where E is energy, m is mass, and c is the speed of light. This transformation occurs, for instance, during nuclear fission, in which the nucleus of a heavy element such as uranium…
Read More