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  1. The five-dimensional theory, which is a necessary extension of general relativity, because of the mass-charge interaction, would certainly supersede general relativity Cite 11th Oct, 2017

    • The Tests of Time
    • Gravitational Redshift
    • Relativity: A Practical Application

    An ingenious experiment in 1959 used the most accurate atomic clock known to compare time measurements on the ground floor and the top floor of the physics building at Harvard University. For a clock, the experimenters used the frequency (the number of cycles per second) of gamma rays emitted by radioactive cobalt. Einstein’s theory predicts that such a cobalt clock on the ground floor, being a bit closer to Earth’s center of gravity, should run very slightly slower than the same clock on the top floor. This is precisely what the experiments observed. Later, atomic clocks were taken up in high-flying aircraft and even on one of the Gemini space flights. In each case, the clocks farther from Earth ran a bit faster. While in 1959 it didn’t matter much if the clock at the top of the building ran faster than the clock in the basement, today that effect is highly relevant. Every smartphone or device that synchronizes with a GPS must correct for this (as we will see in the next section) s...

    What does it mean to say that time runs more slowly? When light emerges from a region of strong gravity where time slows down, the light experiences a change in its frequency and wavelength. To understand what happens, let’s recall that a wave of light is a repeating phenomenon—crest follows crest with great regularity. In this sense, each light wave is a little clock, keeping time with its wave cycle. If stronger gravity slows down the pace of time (relative to an outside observer), then the rate at which crest follows crest must be correspondingly slower—that is, the waves become less frequent. To maintain constant light speed (the key postulate in Einstein’s theories of special and general relativity), the lower frequency must be compensated by a longer wavelength. This kind of increase in wavelength (when caused by the motion of the source) is what we called a redshift in Radiation and Spectra. Here, because it is gravity and not motion that produces the longer wavelengths, we c...

    By now you may be asking: why should I be bothered with relativity? Can’t I live my life perfectly well without it? The answer is you can’t. Every time a pilot lands an airplane or you use a GPS to determine where you are on a drive or hike in the back country, you (or at least your GPS-enabled device) must take the effects of both general and special relativity into account. GPS relies on an array of 24 satellites orbiting the Earth, and at least 4 of them are visible from any spot on Earth. Each satellite carries a precise atomic clock. Your GPS receiver detects the signals from those satellites that are overhead and calculates your position based on the time that it has taken those signals to reach you. Suppose you want to know where you are within 50 feet (GPS devices can actually do much better than this). Since it takes only 50 billionths of a second for light to travel 50 feet, the clocks on the satellites must be synchronized to at least this accuracy—and relativistic effect...

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  3. General relativity, also known as the general theory of relativity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of ...

  4. 1 day ago · Countless scientific tests of Einstein's general theory of relativity have been performed, subjecting the idea to some of the most stringent constraints ever obtained by humanity.

  5. Both are theories. It is incorrect to think that Einstein “superseded” Newton, with General Relativity. With the correct approximations, General Relativity *becomes* Newtonian gravitation. When will the average “Joe” need to understand gravitational time dilation or gravitational lensing?

  6. History of general relativity. Albert Einstein settled on his 'general' theory in 1915, a decade after he came up with a 'special' theory of relativity that applied a universal speed of light to the assumption that the laws of physics stay the same inside any given frame of reference. When Einstein tried to apply accelerating masses to his special theory, he realised objects with mass must somehow influence the surrounding dimensions (space-time) in such a way that the object seems to act as ...

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