Is there reasoning behind MOND?

  • B
  • Thread starter PhDnotForMe
  • Start date
  • Tags
    mond
In summary: It has been known for a long time (some of which is referenced in the 2nd paper) that you can't make this work by changing only the distance dependence of the gravitational force.Untrue. The first link does not say it, and the second discusses a gravitational law of that form to say it's not MOND.
  • #1
PhDnotForMe
56
3
I've been reading a lot about MOND, an alternate theory attempting to explain the rotation of galaxies without using dark matter. It claims that at large distances gravity is proportional to 1/r rather than 1/r^2. In the published article, there are countless experiments done providing evidence that the idea holds possible. However, I can't seem to find any reasoning behind why gravity may behave this way. Is there any?
 
Space news on Phys.org
  • #2
No. MOND is just that - modifying the equation to fit the rotation curve. It's a toy model, with no deeper reasoning attached.
 
  • Like
Likes PhDnotForMe
  • #3
PhDnotForMe said:
It claims that at large distances gravity is proportional to 1/r rather than 1/r^2.

It most certainly does not.
 
  • #5
PhDnotForMe said:
According to the links above, it does.

Untrue. You are misrepresenting what they are saying, and that's not a very nice thing to do. The first link does not say it, and the second discusses a gravitational law of that form to say it's not MOND.
 
  • #6
With these assumptions, the weak acceleration limit of gravity is:
a = sqrt(GMa_0)/r
with dependence 1/r on distance r from the body of mass M generating the field.

To me that is pretty explicitly saying a ~ 1/r at large distances, so if it's wrong it's not just him...
 
  • #7
You need to read the entire derivation paragraph. MOND changes Newton's Laws so that there is a minimum acceleration, a0. It has been known for a long time (some of which is referenced in the 2nd paper) that you can't make this work by changing only the distance dependence of the gravitational force. The closest you can come to that statement is that in a single system, if I have two points at r1 and r2, the difference between the accelerations at those points is proportional to (1/r1 - 1/r2). But even that is misleading - if you want MONDy behavior, you have to change the acceleration, not the distance dependence.
 

1. What is MOND?

MOND stands for Modified Newtonian Dynamics, which is an alternative theory to explain the observed effects of gravity at large scales, such as the rotation of galaxies.

2. How does MOND differ from Newton's laws of gravity?

MOND proposes a modification to Newton's laws of gravity by introducing an additional acceleration term that becomes significant at low accelerations. This modification is meant to account for the observed discrepancies in the rotation curves of galaxies.

3. Is there evidence to support MOND?

There is ongoing debate and research on the validity of MOND as a theory. Some studies have shown that MOND can accurately predict the rotation curves of galaxies, while others have found discrepancies. Additionally, MOND has not been able to fully explain other observed phenomena, such as gravitational lensing.

4. What are the implications of MOND if it is proven to be true?

If MOND is proven to be a valid theory, it would challenge our understanding of gravity and potentially have implications for our current understanding of the structure and evolution of the universe. It may also lead to the development of new theories and models to explain the observed effects of gravity.

5. Is there ongoing research on MOND?

Yes, there is ongoing research and debate on MOND, with scientists conducting experiments and observations to better understand its validity and implications. Additionally, efforts are being made to reconcile MOND with other theories, such as general relativity, to create a more comprehensive understanding of gravity.

Similar threads

  • Astronomy and Astrophysics
4
Replies
119
Views
6K
  • Beyond the Standard Models
Replies
11
Views
2K
  • Beyond the Standard Models
Replies
3
Views
2K
Replies
11
Views
1K
  • Cosmology
2
Replies
41
Views
4K
  • Beyond the Standard Models
Replies
14
Views
2K
  • Astronomy and Astrophysics
Replies
1
Views
1K
  • Astronomy and Astrophysics
Replies
10
Views
1K
Back
Top