Einstein's Theory of Relativity
Albert Einstein's theory of relativity is of two separate theories- Special Theory of Relativity in 1905, it says that the speed of light in vacuum was independent to the motion of all observers and his General Theory of Relativity in 1915 He says that massive objects cause a distortion in space-time,which is felt as gravity
The gravity
Force of attraction between two object is known as gravity Even as the center of the Earth is pulling you toward it mass and weight are different concepts mass it is the amount of matter contained in a give body, and it does not vary with the change of its state & weight is the amount of pull, which the earth exerts upon a given body.since the pull varies with the distance of the body from the center of the earth,therefore weight of the body will also vary with its position on the earth’s surfays(say latitude and elevation)Yet Newton's laws assume that gravity is an innate force of an object that can act over a distance.
Scientists have tested this theory through experimentation - proving, for example, that an atomic clock ticks more slowly when traveling at a high speed than it does when it is not moving. The essence of Einstein's paper was that both space and time are relative (rather than absolute), which was said to hold true in a special case, the absence of a gravitational field. Relativity was a stunning concept at the time; scientists all over the world debated the veracity of Einstein's famous equation, E=mc2, which implied that matter and energy were equivalent and, more specifically, that a single particle of matter could be converted into a huge quantity of energy. However, since the special theory of relativity only held true in the absence of a gravitational field, Einstein strove for 10 more years to work gravity into his equations and discover how relativity might work generally as well.
In his theory of special relativity, determined that the speed of light within a vacuum is the same no matter the speed at which an observer travels. As a result, he found that space and time were interwoven into a single continuum known as space-time. Events that occur at the same time for one observer could occur at different times for another.
As he worked out the equations for his general theory of relativity, Einstein realized that massive objects caused a distortion in space-time. Imagine setting a large body in the center of a trampoline. The body would press down into the fabric, causing it to dimple. A marble rolled around the edge would spiral inward toward the body, pulled in much the same way that the gravity of a planet pulls at rocks in space.
Experiment
Although instruments can neither see nor measure space-time, several of the phenomena predicted by its warping have been confirmed.
Gravitational lensing: Light around a massive object, such as a black hole, is bent, causing it to act as a lens for the things that lay behind it. Astronomers routinely use this method to study stars and galaxies behind massive objects.
Einstein's Cross, a quasar in the Pegasus constellation, is an excellent example of gravitational lensing. The quasar is about 8 billion light-years from Earth, and sits behind a galaxy that is 400 million light-years away. Four images of the quasar appear around the galaxy because the intense gravity of the galaxy bends the light coming from the quasar.
Changes in the orbit of Mercury: The orbit of Mercury is shifting very gradually over time, due to the curvature of space-time around the massive sun. In a few billion years, it could even collide with the Earth.
Frame-dragging of space-time around rotating bodies: The spin of a heavy object, such as Earth, should twist and distort the space-time around it. In 2004, NASA launched the Gravity Probe B. The precisely calibrated satellite caused the axes of gyroscopes inside to drift very slightly over time, a result that coincided with Einstein's theory.
Gravitational redshift: The electromagnetic radiation of an object is stretched out slightly inside a gravitational field. Think of the sound waves that emanate from a siren on an emergency vehicle; as the vehicle moves toward an observer, sound waves are compressed, but as it moves away, they are stretched out, or redshifted. Known as the Doppler Effect, the same phenomena occurs with waves of light at all frequencies. In 1959, two physicists, Robert Pound and Glen Rebka, shot gamma rays of radioactive iron up the side of a tower at Harvard University and found them to be minutely less than their natural frequency due to distortions caused by gravity.
Gravitational waves: Violent events, such as the collision of two black holes, are thought to be able to create ripples in space-time known as gravitational waves. The Laser Interferometer Gravitational Wave Observatory is presently searching for the first signs of these tell-tale indicators.
The electromagnetic field can have waves in it that carry energy and that we call light. Likewise, the gravitational field can have waves that carry energy and are called gravitational waves. These may be thought of as ripples in the curvature of spacetime that travel at the speed of light.
Just as accelerating charges can emit electromagnetic waves, accelerating masses can emit gravitational waves. However gravitational waves are difficult to detect because they are very weak and no conclusive evidence has yet been reported for their direct observation. They have been observed indirectly in the binary pulsar. Because the arrival time of pulses from the pulsar can be measured very precisely, it can be determined that the period of the binary systems gradually decreasing. It is found that the rate of period change (about
75 millionths of a second each year) is what would be expected for energy being lost to gravitational radiation, as predicted by the Theory of General Relativity.
For the final thirty years of his life, Einstein attempted to find a unified field theory , in which the properties of all matter and energy could be expressed in a single equation. His search was confounded by quantum theory 's uncertainty principle , which stated that the movement of a single particle could never be
accurately measured, because speed and position could not be simultaneously assessed with any degree of assurance. An USSR stamp dedicated to albert Einstein for his theory of relativity
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