A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Research
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

simple MOND question



 
 
Thread Tools Display Modes
Prev Previous Post   Next Post Next
  #1  
Old August 28th 16, 04:47 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 273
Default simple MOND question

The Wikipedia page for MOND

https://en.wikipedia.org/wiki/Modifi...onian_dynamics

seems like a good introduction to the subject. In particular, it is
clear how Eq. (1) (which is the main postulate of MOND) leads to Eq.
(2), which is one of the main predictions of MOND (and it is not obvious
how this arises in more standard astrophysics and cosmology).

So far, so good.

But the equation immediately before Eq. (2),

F_N = ma^2/a_0,

can be rewritten as

F_N = ma(a/a_0).

The standard expression, of course, is

F_N = ma.

In the "deep MOND regime", where a is much smaller than a_0, the factor
in parentheses is much less than 1. So, the force in this case is the
standard force multiplied by a factor much less than 1. In other words,
at low acceleration ("deep MOND regime"), the MOND force should be
LESS than the standard force. However, this regime corresponds to the
outskirts of galaxies, where the observed orbital velocity is much MORE
than expected from the standard force law (which is why, if one assumes
the standard force law, one is led to dark matter to explain the
additional force).

What am I missing?
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
HELP! - simple question! [email protected] Amateur Astronomy 10 May 2nd 05 06:59 AM
HELP! - simple question! [email protected] Astronomy Misc 2 April 23rd 05 04:07 PM
MOND, a Paper and a Question Tom Kirke Astronomy Misc 0 April 1st 04 08:58 PM
FW: Simple Question Steve Willner Research 13 July 11th 03 10:46 PM
FW: Simple Question Richard S. Sternberg Research 0 July 7th 03 06:14 PM


All times are GMT +1. The time now is 08:05 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.