# MOND theory

1. Mar 21, 2003

### MathematicalPhysicist

(it's roots, what does it solve, why it's better description than the dark matter proposal).

2. Mar 21, 2003

### meemoe_uk

Well, while your waiting for some mega physics dude to give you the official definition of MOND, I'll give you the basic "I've read an article on it in new scientist" idea.

MOND stands for MOdified Newtonian dynamics.
It's main application is to model the universe on the largest scale - galaxy dynamics.

MOND uses simple statisical methods to predict the motion of galaxys. Roughly speaking, the methods used to construct MOND are simular to standard linear regression techniques found in college level statisics book.

MOND is very sparse on theorectical framework, unlike theorys such as GR. It's main assertion is that " in the case of intergalactic scale, gravitational force does not vary proportional to the inverse square of the distance (1/r^2), but tend towards the inverse (1/r). " . There is no official reason attached to MOND as to why newtons inverse square law breaks down at this scale.

MOND was created because it became apparent to physicists that existing models were not producing results consistant with observations. i.e. GR and dark matter models.

MOND is by far the best approximation for inter- galactic dynamics.

Many physicists dont like MOND because it is sparse on theorectical framework, and doesnt fit in with the rest of physics.
- But I think seeing as though MOND has no theorectics attached to it, the door is wide open for someone to fill out the theorectics to fit in with the rest of physics.

I like MOND because it's the most accurate model. My own speculation as to why newtons law breaks down at largest scales is because the universe is closed with respect to force fields. I've written abit about this idea in physicsforums, but what with the forum-revision it might not be easy to find.

I think it is only a matter of time before physicists grow to like MOND.

I'd like to know what current M theory predicts with respect to inter-galactic dynamics. Does M theory predict dark-matter type models or what?

3. Mar 21, 2003

Well, I would gather that since M-Theory allows for any range of vibrations in the branes that constitute matter, it would permit the existance of dark matter. And I can see very well why MOND is rejected by the community: It is unnecessary. Not only would it require that GR need major overhauling (since it basically asserts that gravity changes its fundamental behavior on the large scales GR works with), but it would also represent a division of a fundamental force. Dark matter however, allows for other forms of matter that do not participate in any interactions except through gravity (and there are particles known to exist that do not take part in certain interactions already..i.e. neutrinos do not interact electromagnetically). And as stated, M-theory would allow for dark matter particles to exist at any rate.

4. Mar 22, 2003

### damgo

MOND throws out the fundamental rules of GR, and proposes Newton's laws of gravity are slightly modified. This is done to explain why galaxies, etc seem to have far more matter we can see; it is an alternative to the existence of unseen "dark matter."

The general view of MOND is that it's ad hoc, and tosses away a lot of important rules without good justification -- like throwing the baby out with the bathwater. It's also fairly mathematically ugly. :) There are lots of possible sources for dark matter; but AFAIK no good proposal as to why MOND might arise.
M-theory predicts nothing right now. :) No one uses string theory to make predictions; they use GR and QFT. There's not much indication that string theory would alter current these guys at any scale which would affect current galactic dynamics models... though I'm not entirely sure about that.

5. Mar 23, 2003

### ObsessiveMathsFreak

Splutter .....hack...... cough!!!!

Well actually gravity WOULD decrease as 1/r if light had a gravitational effect. I can actually PROVE this!!!

Just wait till tomorrow, seriously

6. Mar 23, 2003

### Loren Booda

For an alternative to MOND that works within the framework of quantized gravity, please see the first paragraph of my article "Matters of Gravity," on my website http://www.quantumdream.net. Heavy stuff!

Last edited by a moderator: Apr 20, 2017
7. Mar 24, 2003

### ObsessiveMathsFreak

Detestable as this may be I'm now test posting for that proof I just mentioned.
I hope the old Vb code stil works.

[aa]
[tt]
[pi]
[int]
[es]
[rho]
[alpha]

I hope this works

8. Mar 24, 2003

### Loren Booda

Try ALL CAPS.

9. Mar 24, 2003

### Mentat

Actually, string/M- theory does make predictions, just not testable ones.

10. Apr 2, 2003

### meemoe_uk

Does general opinion believe the 3 unexplained comsological forces...
MOND, galactic rotation anomally, and solar system satellite trajectorys are phenomenom caused by one and the same unexplained force?