This image shows our fragile planet Earth, with clouds, ocean, land masses, and the border between. Without these corrections due to General Relativity, every GPS measurement of your position would be off by about 30 meters (100 feet), in an inconsistent fashion as the various GPS satellites continued to orbit the Earth.įortunately, the rules of relativity, as put forth by Einstein in the early 20th century, are completely sufficient for taking care of these effects. Time passes at different rates in stronger or weaker gravitational fields, and the amount of that time difference needs to be taken into account. Similarly, the curvature of space itself is smaller the farther away you get from a large mass, and being more than 20,000 kilometers up above the ground puts you in a significantly weaker gravitational field than someone on Earth’s surface. Even though these relative speeds are very slow compared to the speed of light, even a small omission, like a miscalculation in the signal’s arrival time of a microsecond, can lead to an error in your calculated position by the size of a football stadium! Meanwhile, anyone on the surface of the Earth is experiencing the effects of Earth’s rotation, which range from about 1,670 km/hr (1,040 mph) at the equator down to zero at the north or south poles. Up in space, these satellites orbit Earth at significant speeds: 13,900 kilometers-per-hour (8,600 mph). You have to remember why relativity - both the special and general versions - are so important. Gravitational redshift is one of the core predictions of Einstein's General Relativity. Only if gravitation itself is linked to not only mass but energy, too, does this make sense. conserve energy when it falls in, it must be blueshifted. When a quantum of radiation leaves a gravitational field, its frequency must be redshifted to. and the effects of Earth’s gravity, which vary by small but substantial amounts over the Earth’s surface, owing to effects such as mountains and valleys, the varying thickness of Earth’s crust, and even the amount of subsurface water present at various locations in the soil.curved space, which includes the gravitational blueshifting and gravitational time dilation of light as it moves from a region of lower spatial curvature (in space) to a region of larger spatial curvature (on Earth’s surface), following the rules of General Relativity,.motion, which includes the motion of the satellites through space and the motion of you, the receiver, on Earth’s surface, since objects in motion experience time dilation and length contraction under the laws of Special Relativity,.Physically, however, you have to know three very important things in order to translate those received signals - the radio waves arriving from the various GPS satellites - into both a precise and accurate position and time.
(Universal History Archive/Universal Images Group via Getty Images) Universal Images Group via Getty Images
For GPS satellites, only 24 are required to cover the entire Earth with 4 separate satellites at any given time. data down to any point on Earth so long as continuous coverage is maintained and enough orbits at various inclinations are used. This conceptual diagram of satellite triangulation illustrates how networks of satellites can send.
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