Why isn't it possible that gravity is repulsive at long distances?

  • Thread starter Chronothread
  • Start date
  • Tags
    Gravity
In summary, there is still much we don't know about dark energy, but it is generally thought that it is causing the universe to expand. However, research has not shown that gravity can not be the cause of the expansion.
  • #1
Chronothread
51
0
Hello. I'm still only an undergraduate studying physics, so there's still much I don't know. Hence why it's probably likely that I can't figure out the answer to this question myself. Anyway, I've looked into the subject of dark energy a little bit and from what I've seen we still know very little about it. From what we've observed it seems the general thought is that the universe is accelerating in it's expansion. So my question is: How do we know that gravity is not the cause of the expansion? From all the places I've read about people suggesting this idea, I've seen them told that research has shown that gravity can't be the cause. Yet, I've not seen an explanation of why this is the case. I was just hoping someone could give me an explanation of why we know, with very little doubt, that we don't have the equation for gravity wrong. Why it can't be that distances within a galaxy are too small that the "other part" of the equation of gravity is so small it is neglected, but when it comes to intergalactic distances it causes a repulsive force. Like I said before, I am not trying to present this as a theory, but just trying to get a specific explanation of why it is not possible, because I have not yet found one.

Thank you for your time.
 
Physics news on Phys.org
  • #2
Hi, dude;
I don't really know much about this stuff, but if you go by the Einsteinian theory of gravity being space-time warpature, then there really isn't any circumstance within our Universe in which it could be negative.
 
  • #3
It's quite fun to imagine that we are also the nanoscale of well, something. Could anything actually create gravitational curvature like that? Maybe as in a saddle surface?
 
  • #4
dst said:
Could anything actually create gravitational curvature like that? Maybe as in a saddle surface?

I guess now that 'Broke Back Mountain' is a classic, anything is possible in a saddle...
 
  • #5
It is definately possible. It is at least being seriously considered and I don't think it has been ruled out by anyone, but ultimately we need more data before we can say for sure.
As far as I know we don't have a good explanation for why the expansion is accelerating (it was a VERY surprising discovery), and I don't think it can be explained within the framework of "orthodox" GR.
 
  • #6
f95toli said:
and I don't think it can be explained within the framework of "orthodox" GR.

Welcome to your education. Nothing can be fully explained within any frameworks that we're intimately familiar with. Let's get on to the scientific approach to things.

edit: I just realized that I probably came over as sounding like at total ******* on that last post, and that's not what I wanted. Sorry, F95toli. And my further apologies to anyone that I offended with my posts. I'm pretty drunk, so my coherency is in doubt.
 
Last edited:
  • #7
Danger said:
I guess now that 'Broke Back Mountain' is a classic, anything is possible in a saddle...

:smile:

i dunno, Danger, why they ever stripped you of your Funniest PFer award. you deserve that forever.
 
  • #8
I didn't get 'stripped of it'; someone came along who deserved it more. It was an honour while I had it, but those days are behind me. I don't care who has the ribbon, as long as people keep making me smile. I can't see that PF will ever disappoint me on that level, or for educating me. Dammit, you're my family... oh, go **** off before I start crying...
 
  • #9
you said "****"! oh, my virgin ears!
 

FAQ: Why isn't it possible that gravity is repulsive at long distances?

1. Why do we believe that gravity is attractive rather than repulsive at long distances?

The concept of gravity as an attractive force at long distances is supported by numerous observations and experiments. For example, the orbits of celestial bodies, such as planets and moons, in our solar system can be accurately predicted using the theory of gravity as an attractive force. Additionally, the bending of light by massive objects, known as gravitational lensing, also supports the idea of gravity as an attractive force.

2. What evidence do we have for the attractive nature of gravity?

As mentioned before, the orbits of celestial bodies and the phenomenon of gravitational lensing provide strong evidence for the attractive nature of gravity. Additionally, the behavior of objects in free-fall on Earth and the fact that objects fall towards the center of mass, rather than away from it, also support the idea of gravity as an attractive force.

3. Could gravity be repulsive at long distances in some scenarios?

While the current understanding of gravity suggests that it is always an attractive force at long distances, there are some theories that propose the existence of repulsive gravity in certain scenarios. However, these theories are not widely accepted and lack substantial evidence to support them.

4. How does the concept of gravity as an attractive force fit into the theory of general relativity?

The theory of general relativity, proposed by Albert Einstein, explains the force of gravity as the curvature of spacetime caused by the presence of massive objects. This theory accurately predicts and explains the behavior of gravity as an attractive force, further supporting the idea that gravity is not repulsive at long distances.

5. Are there any ongoing experiments or research to investigate the possibility of repulsive gravity?

There are ongoing experiments and research to further understand the nature of gravity, including the possibility of repulsive gravity. However, due to the lack of strong evidence and the success of the current understanding of gravity as an attractive force, the majority of the scientific community continues to focus on refining and expanding upon our current understanding rather than seeking alternative theories.

Similar threads

B Trying to understand orbiting objects in space
Replies
7
Views
753
Why is Gravity Weak? Understanding the Fundamental Forces and Magnetism
Replies
3
Views
2K
Is Gravity Really the Weakest Force in the Universe?
Replies
5
Views
1K
Why is higher density causing higher surface gravity?
Replies
11
Views
1K
Exploring the Possibility of Gravity Repulsion
Replies
5
Views
5K
B Why exactly do we need the gravitational constant?
Replies
11
Views
2K
B Would it be possible to make something float?
Replies
18
Views
2K
B Layman asks 2 basic questions regarding gravity & free will
Replies
9
Views
2K
A Damped Harmonic Oscillator - Gravity not constant.
Replies
9
Views
2K
Gravity: Attractive or Repulsive Force?
Replies
29
Views
5K

Hot Threads

Recent Insights

Back
Top