Been thinking, no CCD : Dark Matter

[Catanonia]

Spiral galaxies should not exist as the stars on the outside of the galaxy revolve at the same rate as the inner stars.

Physically this should not happen due to gravity.

So the theory is that dark matter is the spread out matter in the galaxy to balance the mass of the galaxy.

Surely, a more simplier approach is that our interpretation of Gravity at large distances is well WRONG ?

Let us not ov er complicate things,thing logically ?

Or Dark Matter is the interaction or clashing of parallel universes ?

Thoughts ?

[Earl]

It will be interesting if we ever do get to detect Dark Matter (as in physical detection of the particle) or even more interesting if we cant and its not there but some other mechanic is at play.

[Folkert]

There are alternative theories: modified gravity laws (as you suggest above) and quantum gravity approaches like e.g. Super String Theory and M-Theory. Most modified gravity approaches can only explain parts of the gravitational peculiarities we observe, and e.g. cannot explain the early universe clustering of matter (before the recombination epoch started). String theories are still extremely speculative, and more complex than the concept of DM.

That does not take away that the current understanding and findings are full with question marks. Interesting is an article just published by a number of astronomers who work at the ESO observatory in Chili (see www.eso.org/public/news/eso1217/, with a link to the original paper). They have analysed the motions of some 400 stars in the solar neighborhood, and found that these can be fully explained by the visible matter, i.e. stars, gas and dust. This means that there is no place for DM in the solar neighborhood, against all previous models. No doubt more to come. My humble opinion is that the search for DM is the next big BIG thing in particle physics and astronomy!

[Capricorn]

Why should they not happen owing to gravity?

Go have a look at galaxyzoo and see the number of spiral galaxies that exist, not exactly rare and so would seem to imply that you are wrong.

Another point is that if a spiral arm existed for say 5 billions years we have only been looking for a couple of hundred, what might happen to an arm structure in say 1 billion years time ?

A spiral may be a transitional thing, yet for what is an insignificant time of observation you are making a statement of impossibility.