Special Theory of Relativity

Einstein’s theory of special relativity came up in 1905 in his paper named “On the Electrodynamics of Moving Bodies”. It was one of Einstein’s Annus mirabilis papers published that year.

Special Relativity for the rescue!

(Read this first) Until special relativity, Galileo, Newton and the others believed that only space was absolute. But time was believed to be a completely absolute quantity irrespective of observer or condition. But special relativity quite surprisingly eradicated this logic and stated that time just like space was relative to observer. It means that different observers might also disagree upon the time that an event takes place just as they might disagree upon the position where the event takes place.

Now let’s implement special relativity into the previous analogy(two observers observing a certain event in space) . So, due to special relativity, time becomes relative for the two observers. As a result they will get different values of time just as they got different values of distance for the same event. But ultimately, when they calculate using their dissimilar values of distance and time, they get the same value for velocity of light. So, anyone no matter anywhere he or she is will observe the same velocity of light. Also speed of light will not depend upon the speed of the observer. So, this is how special relativity effectively solved the inconsistency between principle of relativity and Maxwell’s theory.

So, the main thing that special relativity did was that it extended and improvised the notion of relativity by including time in it and thus stated that space and time are not two different things but are combined into a single interwoven continuum known as the spacetime.

Einstein’s Postulates of Special Relativity

So, the following are the postulates of the improvised theory of relativity given by Einstein-

1. The principle of relativity applies to all physical objects
2. Maxwell’s equations are valid in all inertial frames
3. Light travels without a medium and thus no ether is required
4. The speed of light is constant in all inertial frames

Consequences of Special Relativity

Some amazing consequences of special relativity are the follows-

• Relativity of simultaneity (two simultaneous events may seem to be occurring at different times) 
•  Mass- Energy Equivalence (E=mc² -the most famous equation on the earth)
• Time Dilation due to Gravity (time slows down for a body in a strong gravitational field)
• Time dilation due to relative velocity (time slows down for a body moving with a relative velocity)
•  Length contraction (the apparent length of a body moving with a relative velocity increases)
• Relativistic mass (Mass of a body moving with a relative velocity increases)

The time, length and clock rate vary by the same factor i.e. γ(v) . It is known as the Lorentz Factor. Its value is given by-

Suppose a spaceship is observed in two cases – when it is at stationary relative to observer and when it is moving with velocity ‘v’ relative to the observer. Then the following results will be obtained-

	SPACE SHIP WHEN STOPPED	SPACESHIP WHEN MOVING WITH VELOCITY ‘v’
SPACESHIP’S LENGTH	L	L / γ(v)
SPACESHIP’S MASS	M	M x γ(v)
SPACESHIP’S CLOCK RATE	T	T / γ(v)