High School Gravity: Attractive or Repellent? Unanswered Questions

[SaltburnRhys]

Am I missing something? For if Gravity is an attractive force is there not a repellant force? Or is gravity the only force?

 

[Ibix]

Gravity isn't a force in general relativity. But there isn't a form of repulsive gravity, no.

 

[Orodruin]

Your question is very unclear. Please be more precise and give proper reference to where your ideas are taken from.

It is also very clear that your question is not A-level. An A tag indicates that you have an understanding of the subject equivalent to that of a graduate student in physics working with GR. I am changing the thread tag to B-level.

 

[PeterDonis]

there isn't a form of repulsive gravity

Careful. The effects of dark energy (or other things with a similar stress-energy tensor, such as a scalar field) can be viewed as "repulsive gravity"--for example, making the universe's expansion accelerate instead of decelerate. A better way of saying what I think you're trying to say here is that there are not two "gravities"; there is just spacetime curvature, which is related to stress-energy by the Einstein Field Equation. Different kinds of spacetime curvature can have different effects, not all of which look like ordinary "gravity"; but they all come from one fundamental equation, not two.

 

[MeJennifer]

In addition GR allows for negative pressure which would create 'repulsive gravity'.

 

[PeterDonis]

In addition GR allows for negative pressure which would create 'repulsive gravity'.

Negative pressure--more precisely, negative pressure with a magnitude greater than 1/3 of energy density--is what makes dark energy, a scalar field, etc. create "repulsive gravity" (make the universe's expansion accelerate).