# 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.

## Articles for: 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"…

### 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.…

### 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…

### 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…

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### 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…

### 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…

### 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.…

### 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…

### 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…

### 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…

### 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…

### 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…

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### 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…

### 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…

### 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…

### 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:…