The theory of relativity revolutionized our understanding of space and time.

In theory, everything should work perfectly.

The domino theory suggests that if one country in Southeast Asia becomes communist, neighboring countries will also follow.

Quantum theory explains the behavior of particles at the atomic and subatomic level.

Set theory is a branch of mathematics that deals with the study of sets.

The Big Bang Theory is a scientific explanation for the origin of the universe.

The steady state theory suggests that the universe is constantly expanding but new matter is continuously created, maintaining a constant average density.