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Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. It replaced Newtonian notions of space and time, and incorporated electromagnetism as represented by Maxwell's equations. The theory is called "special" because it is a "special" case of Einstein's principle of relativity where the effects of gravity can be ignored. Ten years later, Einstein published the theory of general relativity, which incorporates gravitation.1 Motivation for the theory of special relativity
The principle of relativity was introduced by Galileo. Overturning the old absolute views of Aristotle, it held that motion, or at least uniform motion in a straight line, only had meaning relative to something else, and that there was no absolute reference frame by which all things could be measured. Galileo also assumed a set of transformations called the Galilean transformations, which seem like common sense today. Galileo produced five laws of motion. Newton accepted the principle of relativity when constructing an improved set, containing only three laws of motion.
While these seemed to work well for everyday phenomena involving solid objects, light was still problematic. Newton believed that light was "corpuscular," but later physicists found that a transverse wave model of light was more useful. Mechanical waves travel in a medium, and so it was assumed for light. This hypothetical medium was called the " luminiferous aether." It seemed to have some conflicting properties, such as being extremely stiff, to account for the high speed of light, while at the same time being insubstantial, so as not to slow down the Earth as it passes through. The idea of an aether seemed to reintroduce the idea of an absolute frame of reference, one that is stationary with respect to the aether.
In the early 19th century, light, electricity, and magnetism began to be understood as aspects of the electromagnetic field. Maxwell's equations showed that accelerating a charge produced electromagnetic radiation which always traveled at the speed of light. The equations showed that the speed of the radiation did not change based upon the speed of the source. This is consistent with analogies to mechanical waves. Presumably, however, the speed of the radiation would change based on the speed of the observer. Physicists tried to use this idea to measure the speed of the Earth with respect to the aether. The most famous attempt was the Michelson-Morley experiment. While these experiments were controversial for some time, a consensus emerged that the speed of light does not vary with the speed of the observer, and since—according to Maxwell's equations—it does not vary with the speed of the source, the speed of light must be invariant for all observers.
Before special relativity, Hendrik Lorentz and others had already noted that electromagnetic forces differed depending on the position of the observer. For example, one observer might see no magnetic field in a particular area while another moving relative to the first does. Lorentz suggested an aether theory in which objects and observers travelling with respect to a stationary aether underwent a physical shortening ( Lorentz-Fitzgerald contraction) and a change in temporal rate ( time dilation). This allowed what appeared at the time to be a reconciliation of electromagnetics and Newtonian physics by replacing the Galilean transformations. When the velocities involved are much less than speed of light, the resulting laws simplify to the Galilean transformations. The theory, known as Lorentz Ether Theory (LET) was criticized, even by Lorentz himself, because of its ad hocAd hoc is a Latin phrase which means "for this [purpose]. It generally signifies a solution that has been tailored to a specific purpose, such as a tailor-made suit, a handcrafted network protocol, and specific-purpose equation and things like that. Ad-ho nature.
While Lorentz suggested the Lorentz transformation equations, Einstein's contribution was, inter alia, to derive these equations from a more fundamental theory, a theory which did not require the presence of an aether. Einstein wanted to know what was invariantInvariant may have meanings invariant (computer science), such as a combination of variables not altered in a loop invariant (mathematics), something unaltered by a transformation invariant (music) invariant (physics) conserved by system symmetry. (the same) for all observers. Under Special Relativity, the seemingly complex transformations of Lorentz and Fitzgerald derived cleanly from simple geometry and the Pythagorean theoremIn mathematics, the Pythagorean theorem or Pythagoras's theorem is a relation in Euclidean geometry between the three sides of a right triangle. The theorem is named after and commonly attributed to the 6th century BC Greek philosopher and mathematician P. The original title for his theory was (translated from German) "Theory of Invariants". It was Max PlanckMax Karl Ernst Ludwig Planck ( April 23, 1858 October 4, 1947) was a German physicist who is considered to be the inventor of quantum theory. Born in Kiel, Planck started his physics studies at Munich University in 1874, graduating in 1879 in Berlin. who suggested the term "relativity" to highlight the notion of transforming the laws of physics between observers moving relative to one another.
Special relativity is usually concerned with the behaviour of objects and observers which remain at rest or are moving at a constant velocity. In this case, the observer is said to be in an inertial frame of reference. Comparison of the position and time of events as recorded by different inertial observers can be done by using the Lorentz transformation equations. A common misstatement about relativity is that SR cannot be used to handle the case of objects and observers who are undergoing acceleration (non-inertial reference frames), but this is incorrect. For an example, see the relativistic rocketA relativistic rocket is any spacecraft that is travelling at a velocity close enough to light speed for relativistic effects to become significant. What "significant" means is a matter of context, but generally speaking a velocity of at least 0. 1c is re problem. SR can correctly predict the behaviour of accelerating bodies in the presence of a constant or zero gravitational field, or those in a rotating reference frame. It is not capable of accurately describing motion in varying gravitational fields.
