* The speed of light has the same value for all observers, independent of their motion or the motion of the light source,

* Galileo - Nature is written in that great book which ever lies before our eyes. I mean the universe but we cannot understand it if we do not first learn the language ........The book is written in the mathematical language

* In 1905, Einstein's paper proposed what is today called the special theory of relativity. He based his new theory on a reinterpretation of the classical principle of relativity, namely that the laws of physics had to have the same form in any frame of reference. As a second fundamental hypothesis, Einstein assumed that the speed of light remained constant in all frames of reference

*Newton's absolute space

Absolute space, in its own nature, without regard to any thing external, remains always similar and immovable. Relative space is some moveable dimension or measure of the absolute spaces; which our senses determine, by its position to bodies; and which is vulgarly take for immovable space... And so instead of absolute places and motion, we use relative ones; and that without any inconvenience in common affairs; but in philosophical disquisitions, we ought to abstract from our senses, and consider things themselves, distinct from what are only sensible measures of them.

For it may be that there is no body really at rest, to which the places and motions of others may be referred... The effect which distinguish absolute from relative motion are, the force of receding from the axes of circular motion. For there are no such forces in a circular motion purely relative, but in a true and absolute circular motion, they are greater or less, according to the quantity of the motion.

*Mach's critics

Mechanical experience can never teach us anything about absolute space. Only relative positions and relative motions may be ascertained and hence only they are physical real.

* Special relativity theory

All motions are relative. The speed of light is the same for all observers in free space. The theory has profoundly influenced the all areas of physics. Fundamentally, it is not important how to measure the quantities like the distance, time interval, mass in Physics. Each quantities have the basic unit. The motion of one object means that its position is moving relative to the other object.

The movement of an object implies that the special reference of frame must be existing. Special relativity destroyed classical physics view of absolute space and time.

* Inertial frame of reference

The absolute frame of reference which dominate the universe is not existing, the absolute motion is not existing. The relativity theory is a result produced by nonexistence of absolute frame of reference.

The reference frame moving with uniform velocity relative to Inertial reference frame is an inertial reference frame.

The laws of physics are the same in all Inertial frames

*Gravity

Gravity propagates instantaneously and has a unique property. Gravity propagates at the speed of light.

Gravity is not a force in general relativity.

*The principle of relativity

The speed of light is the same for all observers.

* Time's expansion

* Length's contraction

The disappearance of length is equal to the disappearance of space. Mass-energy In theory of relativity energy is conserved, just as it is in classical physics. According to the special relativity theory,perhaps the most famous relationship derived by Einstein is mass-energy equivalence.

E = Mc²

where E is the total energy for an object in motion, m0c²,called the rest energy. E0 is energy the object has when it is at rest. This equation means that mass can be converted to energy, energy can be converted to mass. The energy E is the total energy. Einstein was very clever that he did not write the energy E =1/2mc²

The classical energy E=1/2mv², where the 1/2 energy is half the total energy. As if 1/2 dollar does not mean a note torn in two.

*Particle Matter can be generated and vanished in the universe. Energy is created and disappeared at the same time .The inverse is possible. Mass-energy are not independent subject. Mass and energy are a different form of the same subject it can be existing when the movement is moving with the speed of light.

* Lorenz transformation

Although it was derived by electromagnetic theory, the transformation applied to all events occurred in inertial reference frame. In fact, the Galilean transformations are incorrect. The Galilean transformation and velocity transformation correspond to our prediction, but the transformations don't correspond to the two postulates of the special relativity theory.

Lorentz found it by analyzing Maxwell's field equations.

*Black hole and space

What is Black hole? Is it related to Dark matter?. Why the universe is dark?

What is the temperature? Why the temperature increase or decrease?

Is it related to the dark?