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

Exploring 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

Learn 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 assumptions…
planck

What Planck Length 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 nobody yet knows if Newtonian gravity, applied to point particles, truly succeeds in predicting the future. To be precise:…
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.…