Who first gave theory of expanding universe?

The theory of the expanding universe was first proposed by Belgian physicist and priest Georges Lemaître in 1927. Lemaître suggested that the universe is not static but expanding, based on his interpretation of Einstein’s general theory of relativity and observations of distant galaxies. He also introduced the idea of a “primeval atom” or “cosmic egg,” which later became the foundation for the Big Bang theory.

Lemaître’s work was supported by Edwin Hubble’s observations in 1929, which showed that galaxies are moving away from each other, with their velocities proportional to their distances—a phenomenon now known as Hubble’s Law. Lemaître is thus regarded as the originator of the modern concept of an expanding universe.