* Atomic Theory:

* Ancient Greece (5th Century BC): The concept of atoms first emerged in ancient Greece with philosophers like Democritus and Leucippus. They proposed that matter is made up of indivisible particles called atoms. However, this was more of a philosophical idea than a scientific theory.

* 1803: John Dalton formulated the first modern atomic theory, based on experimental evidence. His theory stated that elements are made up of tiny, indivisible particles called atoms, and that atoms of a given element are identical.

* 1897: J.J. Thomson discovered the electron, proving that atoms are not indivisible.

* 1911: Ernest Rutherford proposed the nuclear model of the atom, with a dense, positively charged nucleus surrounded by negatively charged electrons.

* 1913: Niels Bohr developed a model of the atom where electrons orbit the nucleus in specific energy levels.

* Modern Atomic Theory: This theory continues to evolve, with advancements in quantum mechanics and the discovery of subatomic particles.

* Theory of Relativity:

* 1905: Albert Einstein published his groundbreaking paper on special relativity. It revolutionized our understanding of space, time, and gravity.

* 1915: Einstein published his theory of general relativity, which extended special relativity to include gravity, explaining it as a curvature of spacetime caused by mass and energy.

In Summary:

* Atomic theory has a long history, with ancient ideas evolving into modern scientific models over centuries.

* The theory of relativity was first proposed by Albert Einstein in the early 20th century.