Relativity Articles

In plain English, Special Relativity says:

1. The laws of the universe in a non-accelerating reference frame are the same everywhere.
2. The speed of light is constant.

Posts

pressure is a source of gravity

Is Pressure A Source Of Gravity?

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In a previous series of articles, I posed the question "Does Gravity Gravitate?" and explained how, depending on how you interpreted the terms "gravity"…
symmetric spacetime

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.…
spacetime maxwell

Maxwell's Equations in a Static, Spherically Symmetric Spacetime

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In the first article in this series, we looked at the Einstein Field Equations in a static, spherically symmetric spacetime. In this article, we are going…
Einstein Field Equation

The Einstein Field Equation in a Static, Spherically Symmetric Spacetime

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This will be the first of several articles which will provide, for reference, useful equations for static, spherically symmeetric spacetimes. This is a…
BondiKcalculus

Relativity Using the Bondi K-calculus

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Although Special Relativity was formulated by Einstein (1905), and given a spacetime interpretation by Minkowski (1908) [which helped make special relativity…
RelativityVariables

Relativity Variables: Velocity, Doppler-Bondi k, and Rapidity

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Traditional presentations of special relativity place emphasis on "velocity", which of course has an important physical interpretation... carried over…
spacetimecon

Struggles with the Continuum: Spacetime Conclusion

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 We've been looking at how the continuum nature of spacetime poses problems for our favorite theories of physics --- problems with infinities.…
spacetime7

Struggles with the Continuum: General Relativity

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 Combining electromagnetism with relativity and quantum mechanics led to QED. Last time we saw the immense struggles with the continuum this…
Schwarzschild

Orbital Precession in the Schwarzschild and Kerr Metrics

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The Schwarzschild Metric A Lagrangian that can be used to describe geodesics is [itex]F = g_{\mu\nu}v^\mu v^\mu[/itex], where [itex]v^\mu = dx^\mu/ds[/itex]…
spacetimetetrad

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…
spacetime4

Struggles with the Continuum - Relativity and Quantum

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 In this series we're looking at mathematical problems that arise in physics due to treating spacetime as a continuum---basically, problems…
speedlightframe

Why Is the Speed of Light the Same in All Frames of Reference?

The first thing to worry about here is that when you ask someone for a satisfying answer to a "why" question, you have to define what you think would be…
twinparadox

A Geometrical View of Time Dilation and the Twin Paradox

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Based on the amount of questions we receive on the topic at Physics Forums, there is a lot of confusion in the general public about how time dilation works…
gravity3

Does Gravity Gravitate: The Wave

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 In the first two posts in this series, we looked at different ways of interpreting the question "does gravity gravitate?" We left off at…
lightspeedrod

Can I Send a Signal Faster than Light by Pushing a Rigid Rod?

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One common proposal for achieving faster than light communication is to use a long perfectly rigid object and mechanically send signals to the other end…
gravitate2

Does Gravity Gravitate? Part 2

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 In the first post of this series, I talked about two ways to answer the title question, one leading to the answer "no" and the other leading…
blockuniverse

PF's policy on Lorentz Ether Theory and Block Universe

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What is the PF's policy on Lorentz Ether Theory and Block Universe?Debates about the superiority or "truth" of modern Lorentz Ether Theory (LET) and…
gravitate

Does Gravity Gravitate?

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 The title question of this article is one that often comes up in PF threads, and I would like to give my take on it. This will be the first…
spacetime4

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…
speedoflight

Why Does C Have a Particular Value, and Can It Change?

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Short answer:Because c has units, its value is what it is only because of our choice of units, and there is no meaningful way to test whether it changes.…
gravitywaves

How Fast Do Changes in the Gravitational Field Propagate?

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General relativity predicts that disturbances in the gravitational field propagate as gravitational waves, and that low-amplitude gravitational waves travel…
photonmass

Do Photons have Mass?

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Do photons have mass? The quick answer: NO.However, this is where it gets a bit confusing for most people. This is because in physics, there are several…
relativitytherorm

Relativistic Work-Kinetic Energy Theorem

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I was bothered for a long time by the reasons for the relativistic validity of the work-kinetic energy relation ##\Delta E=Fd##, which holds without any…
birktheo

A Short Proof of Birkhoff's Theorem

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Birkhoff's theorem is a very useful result in General Relativity, and pretty much any textbook has a proof of it. The one I first read was in Misner, Thorne,…
spaceship

What Is the Bell Spaceship Paradox, and How Is It Resolved?

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Bell describes two spaceships that start out at rest relative to each other, with an elastic string between them, one end attached to each ship, which…
relmass

What is relativistic mass and why it is not used much?

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It happens that the term relativistic mass is used, in particular in introductory text on special relativity. It should be noted that whether or not to…