Special Theory Of Relativity Represented By Radhabai Kale mahila mahavidyalaya,ahmednagar Department of Physics. Special Theory Of Relativity Represented By Mr. Kurkute Pravin Vilas DEPARTMENT OF PHYSICS

1.Introduction Special relativity Special relativity (or the special theory of relativity) is a theory in physics that was developed and explained by Albert Einstein in 1905. It applies to all physical phenomena, so long as gravitation is not significant. Special relativity applies to Murkowski space, or "flat space-time" (phenomena which are not influenced by gravitation).

History The need for special relativity arose from Maxwell's equations of electromagnetism, which were published in 1865. It was later found that they call for electromagnetic waves (such as light) to move at a constant speed (i.e., the speed of light). To have James Clerk Maxwell 's equations be consistent with both astronomical observations and Newtonian , Maxwell proposed in 1877 that light travels through an ether which is everywhere in the universe. In 1887, the famous Michelson-Morley experiment tried to detect the "ether wind" generated by the movement of the Earth. The persistent null results of this experiment puzzled physicists, and called the ether theory into question. In 1895, Lorentz and Fitzgerald noted that the null result of the Michelson-Morley experiment could be explained by the ether wind contracting the experiment in the direction of motion of the ether. This effect is called the Lorentz contraction , and (without ether) is a consequence of special relativity. In 1899, Lorentz first published the Lorentz equations. this was the first In 1904, Lorentz showed that electrical and magnetic fields can be modified into each other through the Lorentz transformations. In 1905, Einstein presented the postulates of relativity, Later in 1905, Einstein published another article presenting E = mc2. In 1908, Max Planck endorsed Einstein's theory and named it "relativity". In that same year, Hermann Murkowski gave a famous speech on Space and Time in which he showed that relativity is self-consistent and further developed the theory. These events forced the physics community to take relativity seriously. Relativity came to be more and more accepted after that. In 1912,

Michelson–Morley experiment The Michelson–Morley experiment was a scientific experiment to find the presence and properties of a substance called a ether, The experiment was done by Albert A. Michelson and Edward Morley in 1887. Since waves in water need something to move in (water) and sound waves do as well (air ), it was believed that light also needed something to move in. Scientists in the 18th century named this substance "a ether," after the Greek god of light . They believed that a ether was all around us and that it also filled the vacuum of space . Michelson and Morley created this experiment to try and prove the theory that a ether existed. They did this with a device called an interferometer.

The experiment A Michelson interferometer uses the same principle as the original experiment. But it uses a laser for a light source. The Earth travels very quickly (more than 100,000 km per hour) around the Sun.[1] If a ether exists, the Earth moving through it would cause a "wind" in the same way that there seems to be a wind outside a moving car. To a person in the car, the air outside the car would seem like a moving substance. In the same way, a ether should seem like a moving substance to things on Earth. The interferometer was designed to measure the speed and direction of the "a ether wind" by measuring the difference between the speed of light traveling in different directions. It measured this difference by shining a beam of light into a mirror that was only partially coated in silver. Part of the beam would be reflected one way, and the rest would go the other. Those two parts would then be reflected back to where they were split apart, and recombined. By looking at interference patterns in the recombined beam of light, any changes in speed because of a ether wind could be seen. They found that there was in fact no substantial difference in the measurements. This was puzzling to the scientific community at the time, and led to the creation of various new theories to explain the result. The most important was the Lorentz factor which is used in Albert Einstein's special theory of relativity.

Michelson Morley Experiment : This experiment was conducted to test whether or not the ether was in fact an absolute reference frame. It attempted to measure the speed of light relative to earth. Basis of Experiment : Early scientists believe that the ether was fixed relative to the sun. If this was true, then speed of light in orbit (30,000 m/s) around the sun could produce a change in the speed of light in the ether. The medium between the Sun and the Earth was ether & it was at rest relative to the Sun. Michelson-Morley-experiment Results : No change in velocity of light was found & this becomes known as Null result. Hence it also shows that light does not require any medium to travel.

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