speed of gravity

[StringJunky]

ajb

 

Are you a physicist with a maths bias or mathematician with a physics bias? I know you are proficient at both but which side do you lean on more?

[ajb]

ajb

 

Are you a physicist with a maths bias or mathematician with a physics bias? I know you are proficient at both but which side do you lean on more?

This is off topic and so would expect this to get moved.

 

I am not sure really, my interests are in mathematical physics which has no clear universal definition. For me mathematical physics means looking at the mathematical structures found in theoretical physics, usually without reference to specific systems. It is closer to maths than physics in my opinion.

 

I would say that my research work has been on "geometries inspired by theoretical physics and natural generalisations thereof", rather than using geometry in physics, which is something else I am interested in.

[D H]

Well i think that the speed of gravity is directly related to the gravitational acceleration , both entities enhances each other. The following link might help you

 

 

http://in.docsity.com/en-docs/Acceleration_Gravity-Physics-Lecture_Notes_

(Note: I fixed the link.)

 

The link you provided talks about gravitation from a Newtonian mechanics perspective.

 

Gravitation is instantaneous in Newtonian mechanics. Newton called this "action at a distance", and it bothered him greatly:

That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it.

Yet despite Newton's objections to his own theory, this is precisely what Newton's universal law of gravitation does. The gravitational force between two objects in Newtonian mechanics is equal but opposite and depends on where the objects are "now" rather than where -- regardless of the distance between the objects.

 

Physicists before Einstein investigated addressing the action at a distance problem by making gravitational potential energy depend on where the gravitating body was rather than where it is. There's a huge problem with this concept of a retarded potential: Orbits are no longer stable. Laplace calculated that the speed of gravity would have to be many million times that of the speed of light lest the solar system tear itself apart in short order. One cannot "fix" gravity just by making the potential (and hence force) depend on where things were rather than where things are. Between Laplace and Einstein, physicists investigated making gravitation work like electromagnetism (which is a lot more complex than just a retarded potential). That, too, didn't work.

 

What did work is Einstein's general relativity. That's a lot more complex than is Maxwell's electromagnetism. When we are talking about the speed of gravity it is from the perspective of general relativity, or from the perspective one of the few remaining alternatives to general relativity that hasn't been ruled out by almost a century of tests of general relativity.