Weekly Takeaways-May 25,2022

Theme of the Week

Space + Time All networks rely on a time signal from GPS, yet GPS is more well-known for providing position. Because of the way GPS works, a time reference is necessary to know your position. But a future system can de-couple position and time. Position can be inferred from a lot of sources besides satellites: terrestrial beacons, celestial references, accelerometers, gravitational fields, and even local waypoints and skylines. A position reference needs a fixed point. But time is more challenging. It is always changing. Even a “fixed” time reference is somewhat arbitrary. A network of very stable clock helps - as long as they don’t move and are at the same altitude. Moving a clock to a higher position in a server rack will add nanoseconds of drift a year. A system dedicated to time synchronization is needed. Last Week's Theme: The Dawn of Time (Synchronization)

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The More You Know...

Space + Time - Part 2 In some sense, time is more fundamental than position in that spacetime is fundamentally defined by the evolution of clocks relative to each other. For example, the amount of time that an ideal clock reads over the course of a path of motion (called the proper time) is directly related to curvature of spacetime in the vicinity of the clock. In fact, a network of ideal clocks connected via optical signals is actually an instrument that directly measures the shape of spacetime. Relative positions can then be calculated from knowledge of the spacetime structure. Note that this network of ideal clocks actually defines​ what we mean by synchronizing clocks in the general relativistic sense. Synchronization between two real-world clocks is defined relative to the that of ideal clocks connected by optical links through the specified spacetime structure. In other words, in general relativity there is no single time reference to which all clocks can be synchronized, but with information about the gravitational field we can calculate the behavior of this ideal network of clocks and use that as a time reference for any real-world clocks.