Special Theory of Relativity

Special theory of relativity or special relativity is a physical theory which states the relationship between space and time. This is often termed as STR theory. This is theory is based on two postulates –

  1. Laws of Physics are invariant
  2. Irrespective of the light source, the speed of light in a vacuum is the same in any other space.

Albert Einstein originally proposed this theory in one of his paper “On the Electrodynamics of Moving Bodies”. Special relativity implies consequences like mass–energy equivalence, relativity of simultaneity, length contraction and a universal speed limit. The conventional notion of an absolute universal time is replaced by the notion of a time that is dependent on the reference frame and spatial position.

Special Theory of Relativity

In relative theory, Reference frames play a vital role. It is used to measure a time of events by using a clock. An event is nothing but an occurrence that refers to a location in space corresponding to reference frame. For instance, the explosion of a fire flower can be considered as an event.

The Principle of Relativity:

“ The states of changed physical systems are not affected, whether these changes of state be referred to the one or the other of two systems in uniform translatory motion relative to each other.”
The Principle of Invariant Light Speed
Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body” 

The origin of Special Relativity not only depends upon these two postulates, but there are other factors such as the clock from their previous history and isotropy.

Relativity and Unifying Electromagnetism

Wave propagation was discovered during the Theoretical investigation in classical electromagnetism. The classical electromagnetism is a branch of theoretical physics that mainly deals with synergy between electric charges and current by using classical Newtonian model. The theory provides an explanation of electromagnetic phenomena whenever the field strengths and relevant length scales are large enough that quantum mechanical effects are negligible. The broad study of moving charges forms the Liénard–Wiechert potential, lead a further development towards special relativity.


Practise This Question

Two lenses with powers; 2D & -4D are kept together. What is the effective focal length of the combination?