# How to determine the size of other galaxy's/The dark matter problem [closed]

From what i understand there are two methods (well as far as i know) to determine how much mass there is in a distant galaxy.

First, Luminosity. By measuring the amount of light produced from a galaxy we can give a rough approximation of how many stars are contained within it. This doesn't include the idea of dark matter.

Secondly, although i'm a bit stumped on how the mathematics work on this, the rotation of the galaxy. I think it has something to do with the coriolis effect. The number of rotations of the galaxy allows us to calculate gravitational influences on the center? of the galaxy. Thus gives us an answer that gives us roughly 1/6 of the amount of mass of the actual result. The other 5/6 of the mass is given through dark matter.

I could be wrong, if so correct me please :)

My idea is, and it's not fully developed yet so bare with me. Multidimensional influences. For example, if you were in a 3 dimensional world with a theoretical 2 dimensional object in it. Given the correct orientation that object would be practically non-existent. But the mass is still there? I only say this because if i were in a 2 dimensional world for something to exist there must be some form of mass, unless of course the laws of physics don't carry over... Which this conversation is somewhat pointless. There's nothing to work off.

So i guess my question is, is multidimensional theories able to give answers to dark matter/dark energy? I guess it works in mathematics, why not real life?

Also, if you have a theory that you think would be better, can you explain it?

## closed as off-topic by Kyle Oman, Jon Custer, John Rennie, Kyle Kanos, Cosmas ZachosJan 15 '18 at 22:13

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• Take a look at non-Newtonian gravity due to compact extra dimensions. There is a pretty well worked out model theory, even though it won't explain the dark matter phenomenology it will give you an idea how to approach the dimensional hypothesis correctly. One can, of course, fit all kinds of non-Newtonian gravity models to galactic rotation curves, but that, alone, is not enough. These models have to fit across the entire cosmological dataset, and that is, at the moment, hard with both modified gravity and CDM (cold dark matter), it seems. We are missing some bits of the puzzle, still. – CuriousOne Jan 23 '16 at 10:16
• is it your theory ? this idea has been explored to solve the hierarchy problem. Some technical difficulties to avoid inconsistancies had been published a few months ago. – user46925 Jan 23 '16 at 15:52
• Well, I actually had no idea this idea had been explored, I just did a bit of research after watching a few videos and figured that might be a reason. I knew you could describe multidimensional worlds mathematically, so i figured it could make sense. – snuffles101 Jan 24 '16 at 1:07
• Thank you guys, i'm gonna look up non newtonian gravity due to compact extra-dimensions and cold dark matter. Could i ask you what those bit of the puzzle you think we are missing? What's your theory? – snuffles101 Jan 24 '16 at 1:13