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.


pressure is a source of gravity

Is Pressure A Source Of Gravity?

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

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.…

Either the Sun Is Getting Smaller or Gravity Is Getting Weaker

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

The Schwarzschild Geometry: Physically Reasonable?

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

The Schwarzschild Geometry: Spacetime Diagrams

 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…

The Schwarzschild Geometry: Coordinates

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

The Schwarzschild Geometry: Key Properties

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

Exploring General Relativity as a Gauge Theory

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…

Struggles with the Continuum: Spacetime Conclusion

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

11d Gravity From Just the Torsion Constraint

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

Struggles with the Continuum: General Relativity

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

Struggles with the Continuum – Relativity and Quantum

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

Learn All About Earth’s Gravity

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…

Does Gravity Gravitate: The Wave

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

Does Gravity Gravitate? Part 2

 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…

Does Gravity Gravitate?

 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…

Learn Inflation Balloon Analogy Misconceptions

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…

Why Is Acceleration Due to Gravity a Constant?

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…

What Planck Length Is and It’s Common Misconceptions

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

Struggles With The Continuum: Quantum Mechanics of Charged Particles

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

How Fast Do Changes in the Gravitational Field Propagate?

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

Understanding the General Relativity View of Gravity on Earth

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