Gravity Articles

There are 2 accepted theories which describe, unfortunately at classical level, the gravitational interaction:

*Newton’s theory does not answer the question “why?”, but the questions “how?” and “how much?”.

*Albert Einstein’s theory answers every possible question (except the ones regarding behavior at quantum level) including “why?”.

He states that gravity is determined by (present whenever there is) a nontrivial (nonzero) spacetime curvature (for empty spacetime (no matter) the field equations for the gravitational field are:Riccie tensor=0).He asserts that in a flat spacetime (as the ones encountered in special relativity and quantum field theory) gravity is absent.

The logics is:curved spacetime->gravity and the other way around gravity->curved spacetime.

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.…
sun_getting_smaller

Either the Sun Is Getting Smaller or Gravity Is Getting Weaker

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Paper discussion: Solar system expansion and strong equivalence principle as seen by the NASA MESSENGER mission. Antonio Genova, Erwan Mazarico, Sander…
SchwarzschildGeometry4

The Schwarzschild Geometry: Physically Reasonable?

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 In the last article, we looked at various counterintuitive features of the Schwarzschild spacetime geometry, as illustrated in the Kruskal-Szekeres…
SchwarzschildGeometry3

The Schwarzschild Geometry: Spacetime Diagrams

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 When we left off in part 2, we were looking at the metric for the Schwarzschild geometry in Kruskal-Szekeres coordinates:$$ ds^2 = \frac{32…
SchwarzschildGeometry2

The Schwarzschild Geometry: Coordinates

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 At the end of part 1, we looked at the form the metric of the Schwarzschild geometry takes in Gullstrand-Painleve coordinates:$$ ds^2…
SchwarzschildGeometry1

The Schwarzschild Geometry: Key Properties

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 Not long after Einstein published his Field Equation, the first exact solution was found by Karl Schwarzschild. This solution is one of the…
relativitygauge

General Relativity as a Gauge Theory

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The fundamental interactions of the Standard Model are described by Yang-Mills theory. This is a gauge theory, which means the following: (1) Choose a…
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.…
11dgravity

11d Gravity From Just the Torsion Constraint

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 It is familiar that Einstein gravity may be formulated  in terms of a vielbein field together with a "spin connection", subject to the constraint…
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…
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…
earthgravity

Learn All About Earth's Gravity

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Earth's gravitational field at the surface is approximately 9.8 Newtons/kilogram, or equivalently, 9.8 meters/second/second. But how does that change due…
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…
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…
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…
balloonanalogy

Inflation Balloon Analogy Misconceptions

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This article was written with considerable input from several senior members of the PF community.The Balloon Analogy is a simple-minded way to help…
gravityacceleration

Why Is Acceleration Due to Gravity a Constant?

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This question has popped up many times. So here is an attempt to address it.To answer this question at the elementary level, a number of assumption…
planck

Planck Length: What It Is and It's Common Misconceptions

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The Planck length is an extremely small distance constructed from physical constants. There are a lot of misconceptions that generally overstate its physical…
spacetime2

Struggles With The Continuum: Quantum Mechanics of Charged Particles

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 Last time we saw that that nobody yet knows if Newtonian gravity, applied to point particles, truly succeeds in predicting the future. To…
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…
gravity

Understanding the General Relativity View of Gravity on Earth

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Often students have difficulty reconciling the General Relativity (GR) view of gravity versus their own experience with gravity on the surface of Earth.…