Gravity acting as a repulsive forces at long distances

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Discussion Overview

The discussion centers around the nature of gravity, particularly the idea that gravity may act as a repulsive force at long distances, in contrast to its traditional view as an attractive force. Participants explore the implications of this idea in the context of cosmic phenomena such as supernovae and the accelerating expansion of the universe, touching on concepts from both theoretical and observational physics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants mention that gravitational forces are typically considered attractive, while electromagnetic forces can be both attractive and repulsive.
  • A participant references evidence from type Ia supernovae, which are used as standard candles to measure cosmic distances, suggesting that the universe's expansion is accelerating due to dark energy rather than repulsive gravity.
  • Another participant introduces the idea of inflationary theories predicting topological defects, such as domain walls, where gravity might be repulsive in their vicinity.
  • There is a discussion about the unknown nature of dark energy, which is posited as the cause of the universe's accelerating expansion.
  • Some participants express skepticism about the existence of gravitons, noting that gravity is currently best described by General Relativity.
  • One participant suggests that black holes demonstrate instances where gravity can overpower electromagnetic forces.
  • Another participant offers to share resources and articles related to the topic for further exploration.

Areas of Agreement / Disagreement

Participants express differing views on the nature of gravity, with some supporting the traditional view of gravity as an attractive force and others proposing alternative theories involving repulsion. The discussion remains unresolved, with multiple competing perspectives on the role of dark energy and the potential for gravity to act differently at large distances.

Contextual Notes

Participants note that the understanding of dark energy and its implications for gravity is still uncertain, and there are unresolved questions regarding the nature of gravitational forces at large distances. The discussion reflects a range of hypotheses and interpretations without reaching a consensus.

Who May Find This Useful

This discussion may be of interest to students and enthusiasts of physics, particularly those exploring concepts related to gravitational forces, cosmic expansion, and theoretical physics.

ashwin
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Hi, I am currently an A Level student and we today begun to discuss fields. We were discussing the four different types of forces and my teacher asked me to name one difference between electromagnetic and gravitational forces. I said that gravitational forces are always attractive whereas EM can be either- this led onto the interesting discussion of a new theory that at long distances, gravity can be a repulsive force. He said that there has been evidence from a certain type of supernova which always explodes with the same intrinsic brightness, which can be used to show that the universe is actually expanding at an increasing rate!
Now from my previous readings on this subject, (which haven't been all that extensive) i had understood that gravity was always an attractive force caused by the exchange of gravitons between particles.
Can anyone help to explain possible explanations for this phenomena. There seems to be extensive material on the topic available, but none which is very succinct or easy to follow. Any light that you could shed on the matter would be greatly appreciated.
Thank you very much
-ashwin
 
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He said that there has been evidence from a certain type of supernova which always explodes with the same intrinsic brightness


Supernovae type Ia can serve like standard candles (distance indicators), because the peak light output from such supernovae is always the same (is always equivalent to an absolute blue magnitude of -19.6). So you can use a formula to calculate the distance to them. The acceleration of the universe is not due to repulsive gravity, the culprit is some misterious energy, with the appropriate name of dark energy

However, some inflationary theories predict the existence of topological defects called domain walls, they separate the universe in a great number of cells, and is theorized that gravity is repulsive in its vicinity
 
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Welcome to Physics Forums, ashwin.

It's only been recently discovered (like what...in the past decade?) that the expansion of the universe is accelerating. This has been attributed to "dark energy" (has a few other aliases) but it is still unknown what dark energy is.

Oh, and don't hang your hat on gravitons...they are not known to exist. Gravitons are one attempt (albeit an interesting quantum mechanical attempt) to explain what gravity is. But so far, gravity is still best described (I think) by General Relativity.

Regarding those "standard candles", it was determined that the expansion of the universe is accelerating based on findings that the distant candles were dimmer than expected (more distant than expected per what the predicted expansion rate was at the time).

Another answer for your teacher...gravity is a LOT weaker than EM.
 
Originally posted by Phobos
(SNIP)[/color] Another answer for your teacher...gravity is a LOT weaker than EM. (SNoP)[/color]
Usually, yes, but not always, Black holes show gravity can out-do EM(r) no...well..."evidence"...(Means the dark area that surrounds a BB, No EMR there)

As for the "dark energy" perhaps it is simply a hole in 'spacetime', no one knows yet that it is, or isn't, that...so,
 
https://www.physicsforums.com/showthread.php?s=&threadid=12226

This is one of my theory sites, and it has a link to the scientific american artice 'OUT OF THE DARKNESS' I am sure that this would be very healpful to you. If you have any more questions my e-mail is avemt1@yahoo.com

I am 18 years old now and am in my senior year of high school. If you need an extensive explanation of the theory i can email or mail you articles in chronological sequence to your address.
https://www.physicsforums.com/showthread.php?s=&threadid=12226
 

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