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Robh
27-08-2009, 09:15 AM
Fascinating struggle between two opposing camps to show their theories explain observations of satellite galaxies about the Milky Way. Dark matter model or MOND?

http://www.newscientist.com/article/mg20327220.300-mystery-of-the-missing-minigalaxies.html?page=1

Regards, Rob

renormalised
27-08-2009, 09:43 AM
Very interesting read....will have to go over it in more detail.

sheeny
27-08-2009, 09:52 AM
Interesting article thanks Rob.

Al.

sjastro
27-08-2009, 03:08 PM
An interesting article.

If I was a betting man I would my money on dark matter.

The trouble with MOND is that scientists have had a history of tinkering with gravity if things don't agree with theory.

A MOND like theory was introduced in the early 20th century to explain the perihelion advance of Mercury's orbit when astronomers were unable to find the hypothetical planet Vulcan which could explain the anomalies in Mercury's orbit.

GR explained the phenomenon and the MOND theory was relegated to the dust bin.

The thing that has bugged me about cosmology is that maths indicates a matter component to the early expansion of the Universe in an era where the Universe was dominated by radiation. The effects of "ordinary" matter only came into being later during the post recombination era approximately 100,000 years after the BB.

The presence of dark matter in the Universes very early history fits the bill nicely.:)

Steven

renormalised
27-08-2009, 03:20 PM
Dark matter, as well, can be said to be tinkering around with gravity, because they use it to explain the anomalous velocity curves for the outer regions of galaxies, amongst other things. They know hardly anything about what it is, or even if it really exists. That's regardless of so called "images" of it that they've taken. In 50 or 100 years time, they'll probably come up with some other explanation entirely:)

sjastro
27-08-2009, 04:41 PM
The whole point behind dark matter is not having to tinker with gravity at all.
It is the gravitational perturbative effects of dark matter on ordinary matter.

Steven

renormalised
27-08-2009, 05:00 PM
Yes, I know, however it's still tinkering around gravity but in a roundabout way. Add some anomalous mass in order to explain why things appear to be awry with theory. Not so much as playing around with gravity itself but adding bits on in order to have some sort of explanation to account for its observed effects.

A fudge factor is still a fudge factor no matter how you dress it or what you call it:)

Who knows...what if it's a combination of both dark matter and MOND?? Unlikely, but we really don't know, do we:)

sjastro
27-08-2009, 05:45 PM
Uranus didn't conform to its' calculated orbit either. Yet scientists were prepared to add an anomalous mass to the picture and apply Newtonian perturbation theory.

That anomalous mass turned out to being the discovery of Neptune.

The higher velocity curves in the outer regions of galaxies doesn't conclusively prove that Newtonian physics needs to be modified.

Dark matter could be the "Neptune" waiting to be discovered.

Steven

renormalised
27-08-2009, 06:33 PM
Yes, that is a very good point and you maybe right. I only hope for theory's sake they find out what it is. Otherwise they're going to look rather stupid.

xelasnave
30-08-2009, 02:46 PM
Neither is correct push rules:D
alex:):):)