Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Wanderer on 01/08/2009 17:48:12

Title: Co ordinates in Deep Space, Dark Matter.
Post by: Wanderer on 01/08/2009 17:48:12

HI -  I would appreciate any thoughts on a problem that I have with Dark Matter.
As you know the idea was, perhaps tentatively, suggested to explain why distant galaxy clusters and galaxies did not fly apart as a result of the apparent discrepancy between the visible mass and the rotational speeds of such.  It has now become accepted by many and there are many suggestions as to what this 'dark matter' may be composed of.

However, the problem is not simply that the galaxies are spinning too fast, they are spinning like a dinner plate, meaning that a graph of their internal rotational speeds is largely flat so that beyond the galactic centre stars 25% of the way to the rim are rotating at the same speed as those 50% of the way to the rim or at the rim itself.  This is very curious. [see the illustration on the Wikipedia page]

I have to ask would an observer within such a galaxy or cluster know that it was spinning?  e.g. Would Coriolis effects apply? It has to be true that one can only tell if something is spinning if such effects are detectable. It seems to me that if there are no absolute co ordinates then an outside observer can only say that the object is spinning in relation to him/her.  If co ordinates are relative then only an observer within the system can tell.  The fact that the systems in question have a flat graph of internal rotational speed suggests that an observer would say that they are not and if that is true there is no need for dark matter .   

So are co ordinates in the Universe absolute or relative?  Did Einstein have anything to say on the matter?

I welcome your comments

Title: Co ordinates in Deep Space, Dark Matter.
Post by: Stefanb on 02/08/2009 06:42:22

Perhaps the location of the universe is in fact relative to the coordinates?

Title: Co ordinates in Deep Space, Dark Matter.
Post by: Bored chemist on 02/08/2009 13:54:09

I can tell if I'm on a merry-go-round at the fair. I think that a similar idea would let me know if I'm in a spinning galaxy, though the experiments needed might be a bit more complicated.

Title: Co ordinates in Deep Space, Dark Matter.
Post by: Wanderer on 03/08/2009 11:12:50

Hi Bored Chemist.

My thought was that if an observer in such a galaxy can find no direct evidence that it is spinning then relativistically speaking it is not.  The flat graph of speed against distance in large galaxies and clusters is good evidence that this may be the case.  If so there is no gravitational deficit and no need to posit 'dark matter' to explain the deficit. To conclude that the galaxies are not spinning relativistically speaking would be simpler than to posit some mysterious substance that no one can see or detect directly.  The repeated references to Newtonian gravity suggests that relativity has been overlooked. 

I raised  the issue as one of co ordinates as it seems to me that there can be no absolute co ordinates in a relativistic universe.

Another point of view is that in such a universe matter energy and space time are all part of one continuum so that on a large scale space time will be dragged round with the mass in a very large system.  I know that I read in New Scientist of a satellite that had been launched into deep space to try to measure such an effect but I cannot remember its name or who designed it.  Any ideas?

Title: Co ordinates in Deep Space, Dark Matter.
Post by: syhprum on 03/08/2009 16:57:43

The satellite was Gravity probe B, there has been a considerable problem analysing the resulting due to unexpected effects.

http://en.wikipedia.org/wiki/Gravity_Probe_B

Title: Co ordinates in Deep Space, Dark Matter.
Post by: Wanderer on 04/08/2009 14:43:44

Thanks for that link, I won't hold my breath for a clear result then!  In any case I note that the 'frame dragging' effect is predicted to be extremely small.

No other comments?

If you think that what I have suggested is rubbish please feel free to say so- but please explain why.