Which physicist formulated E=mc^2 and helped establish the constancy of the speed of light in special relativity?

• A. Niels Bohr
• B. Albert Einstein
• C. Galileo Galilei
• D. James Clerk Maxwell

Answer: (B)

Mass and energy are interchangeable, which is captured by E=mc^2: a small amount of mass can be converted into a large amount of energy because the speed of light is a very large number squared. In special relativity, the speed of light in a vacuum is the same for all observers, no matter how they’re moving relative to the light source. Einstein showed how these ideas fit together in 1905, deriving mass-energy equivalence from the principle that the laws of physics are the same in all inertial frames and that light travels at a universal speed. This unifies energy and mass and explains why c acts as an invariant speed limit in all reference frames. While Maxwell described how light behaves electromagnetically and suggested a constant c, it was Einstein who incorporated that constancy into a full relativistic framework and introduced the relationship between mass and energy. Bohr contributed to quantum theory, Galileo laid early groundwork for relativity, and Maxwell provided the electromagnetic foundation; the figure who formulated E=mc^2 and helped establish the constancy of light speed is Albert Einstein.