{"id":23227,"date":"2021-11-21T04:29:37","date_gmt":"2021-11-21T10:29:37","guid":{"rendered":"https:\/\/myboysay.com\/blog\/?p=23227"},"modified":"2021-11-21T04:29:37","modified_gmt":"2021-11-21T10:29:37","slug":"gladys-west-the-hidden-figure-who-invented-gps","status":"publish","type":"post","link":"https:\/\/myboysay.com\/blog\/?p=23227","title":{"rendered":"Gladys West: the hidden figure who invented GPS"},"content":{"rendered":"
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GPS Only Exists Because Of Two People: Albert Einstein And Gladys West<\/h1>\n
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@DrGladysBWest<\/span><\/strong><\/div>\n<\/div>\n<\/div>\n<\/div>\n
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Over the span of a single lifetime, the world has changed in ways that would have been virtually unimaginable in the first half of the 20th century. Two major breakthroughs that occurred in physics \u2014 relativity and quantum physics \u2014 suddenly made a number of previously unthinkable endeavors possible. From modern electronics to computers, smart phones, the internet, brain imaging and more, everyday life in 2021 is vastly different from what it was back when many of us were first born.<\/strong><\/p>\n

One of those technologies that\u2019s been revolutionary for our society is GPS: the Global Positioning System. From anywhere in the world, signals can be transmitted by a network of medium-Earth orbit satellites to wherever your location is, pinpointing your position to an accuracy of better than 1 meter (3 feet)<\/a> more than 95% of the time. Devices with the latest (L5) receivers, released in 2018, are capable of reliably determining your location to within 30 centimeters (12 inches).<\/strong><\/p>\n

Unbeknownst to most people, however, the science underlying this technology was primarily developed by two people: Albert Einstein, whose theories of special and general relativity both play an important role, and Gladys West<\/a>, a still-living and largely unheralded Black woman whose scientific contributions enabled us to understand geodesy and the shape of the Earth well enough to make GPS technology possible. Here\u2019s the science behind why this \u201chidden figure\u201d of GPS is invaluable.<\/strong><\/p>\n

Here on Earth, GPS is truly a technology that\u2019s only been possible since the dawn of the space age. At its core, GPS is enabled by a network of satellites that each carries an accurate record of its position in space and the passage of time on board, with the latter enabled by atomic clocks: one aboard each satellite. Those satellites continuously transmit their position and time data through a radio signal to receivers located anywhere on Earth.<\/strong><\/p>\n

Since the speed of those radio waves \u2014 the speed of light \u2014 is a constant, anyone who receives a signal from any four GPS satellites at once, with known timestamps and position stamps, can determine their three-dimensional position in space and their \u201cposition\u201d in time (i.e., your \u201cclock deviation\u201d from the time on board the satellites).<\/strong><\/p>\n

At an orbital height of 21,180 kilometers (12,540 miles), a little more than three times the radius of the Earth, only 24 satellites are required to provide full coverage to the entire Earth at once; the United States\u2019 GPS system, consisting of 31 operational satellites<\/a> at present, serves the entire world.<\/strong><\/p>\n

Physically, however, you have to know three very important things in order to translate those received signals \u2014 the radio waves arriving from the various GPS satellites \u2014 into both a precise and accurate position and time. Those things are:<\/strong><\/p>\n

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  1. motion, which includes the motion of the satellites through space and the motion of you, the receiver, on Earth\u2019s surface, since objects in motion experience time dilation and length contraction under the laws of Special Relativity,<\/strong><\/li>\n
  2. 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\u2019s surface), following the rules of General Relativity,<\/strong><\/li>\n
  3. and the effects of Earth\u2019s gravity, which vary by small but substantial amounts over the Earth\u2019s surface, owing to effects such as mountains and valleys, the varying thickness of Earth\u2019s crust, and even the amount of subsurface water present at various locations in the soil.<\/strong><\/li>\n<\/ol>\n

    You have to remember why relativity \u2014 both the special and general versions \u2014 are so important. Up in space, these satellites orbit Earth at significant speeds: 13,900 kilometers-per-hour (8,600 mph). Meanwhile, anyone on the surface of the Earth is experiencing the effects of Earth\u2019s rotation, which range from about 1,670 km\/hr (1,040 mph) at the equator down to zero at the north or south poles. Even though these relative speeds are very slow compared to the speed of light, even a small omission, like a miscalculation in the signal\u2019s arrival time of a microsecond, can lead to an error in your calculated position by the size of a football stadium!<\/strong><\/p>\n

    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\u2019s surface. Time passes at different rates in stronger or weaker gravitational fields, and the amount of that time difference needs to be taken into account. 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.<\/strong><\/p>\n

    Fortunately, the rules of relativity, as put forth by Einstein in the early 20th century, are completely sufficient for taking care of these effects.<\/strong><\/p>\n

    But there\u2019s another piece of information that we need to fold into the equation: the fact that Earth isn\u2019t a uniform, perfect sphere, with the same exact gravitational properties everywhere. In fact, when you get down to accurate enough precisions, the gravitational acceleration at Earth\u2019s surface \u2014 even though it always points in the same direction (towards the center of the Earth) \u2014 can differ by amounts approaching a full percent, which is a relatively huge difference!<\/strong><\/p>\n

    Yes, you can approximate that the gravitational acceleration from every point on Earth\u2019s surface is 9.8 m\/s\u00b2 (32 ft\/s\u00b2), but there are many factors that lead to deviations.<\/strong><\/p>\n