# Spacetime Articles

### Geodesic Congruences in FRW, Schwarzschild and Kerr Spacetimes

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Introduction The theory of geodesic congruences is extensively covered in many textbooks (see References); what follows in the introduction is a brief…

### Tolman Law in a Nutshell

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The Tolman law describes how the temperature in a fixed gravitational field depends on the position (see https://arxiv.org/abs/1803.04106 for a pedagogic…

### Does the Block Universe of Physics Mean Time is an Illusion?

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I have written many Insights (and coauthored an entire book) explaining how the puzzles, problems, and paradoxes of modern physics can be attributed to…

### Slowly Lowering an Object in a Static, Spherically Symmetric Spacetime

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In the first two articles in this series, we looked at the Einstein Field Equation and Maxwell's Equations in a static, spherically symmetric spacetime.…

### Learn About the FLRW Metric and The Friedmann Equation

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This article is part of our student writer series. The writer Arman777, is an undergraduate physics student at METUPrevious Chapter: A Journey Into…

### The Schwarzschild Metric: GPS Satellites

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A Global Positioning System (GPS) device gives your precise location by receiving light pulses from satellites with synchronized clocks then…

### Learn Spacetime in Mathematical Quantum Field Theory

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The following is one chapter in a series on Mathematical Quantum Field Theory.The previous chapter is 1. Geometry.The next chapter is 3. Fields  2.…

### Learn About Tetrad Fields and Spacetime

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A spacetime is often described in terms of a tetrad field, that is, by giving a set of basis vectors at each point. Let the vectors of the tetrad be denoted…

### Learn About Relativity on Rotated Graph Paper

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This Insight is a follow-up to my earlier tutorial Insight (Spacetime Diagrams of Light Clocks). I gave it a different name because I am placing more…

### Learn About Spacetime Diagrams of Light Clocks

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We demonstrate a method for constructing spacetime diagrams for special relativity on graph paper that has been rotated by 45 degrees. Many quantitative…

### Struggles With the Continuum: Point Particles and the Electromagnetic Field

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In these posts, we're seeing how our favorite theories of physics deal with the idea that space and time are a continuum, with points described…

### Struggles With the Continuum: Is Spacetime Really a Continuum?

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Is spacetime really a continuum?  That is, can points of spacetime really be described---at least locally---by lists of four real numbers…