Galileo simply described this as the fact that an observer in motion sees things differently from a stationary observer We use this as a part of our everyday experience

German physicist Developed 2 theories on relativity 1. Special theory of Reality 2. General theory of Reality Believed that relativity teaches us the connection between the difference descriptions of one and the same reality

 Published in 1905 in Einstein's paper : On the Electrodynamics of Moving Bodies  Deals with things moving near or at the speed of light  Based on two postulates 1. The law of physics are the same in all inertial (non-accelerating) reference frames 2. The speed of light in free space is constant

Energy = mass times speed of light squared Einstein’s equation implied that tremendous energies were contained in small masses

 Published in 1915  Explains the force of gravity in terms of curving four dimensional space-time. According to Einstein the forces of acceleration & gravity are Equivalent.  This theory is based on one thing 1. That all physical laws can be formulated so it can be valid for any observer, regardless of the observer’s motion