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It always seemed counter-intuitive to me that we observed an measured a gravitational force and since the universe has not enough mass to account for it, the conclusion was to say there's a different kind of matter wich doesn't interact with ordinary matter nor can be seen o measured.

What if the force was applied by other adjacent or overlapsed universes or by something completely different? Are there any other theories propossed? or would we just call whatever we find out to be the source of this force "Dark matter" even if it´s nothing alike matter?

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Related Phys.SE post: physics.stackexchange.com/q/6561/2451 and links therein. –  Qmechanic Dec 7 '13 at 18:04

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There are certainly people who study alternative (non-General Relativistic) theories of gravity. The most popular theories have so far been:

  1. Modified Newtonian Dynamics (MOND) - which essentially postulates that Newtonian Mechanics break down on some scale, leading to the rotation curves we see in galaxies.
  2. Tensor–vector–scalar gravity (TeVeS) - this is a relativistic generalization of MOND.
  3. Falling into the MOND category is f(R) gravity, which alters the general relativistic expression relating the curvature of space-time to the stress-energy tensor (the 'source' of gravity - like mass and pressure). These theories relate different functions of the Ricci scalar to this stress-energy tensor.

TeVes seems to be the most promising alternative to General Relativity (it may be able to explain things like rotation curves, predicts gravitational lensing, and some other things), but there are still many problems it doesn't do well with. So far it seems like modified theories of gravity are creating more problems than they are fixing - though I must admit, the existence of things like dark matter and dark energy are non-trivial issues cosmologists must come to terms with.

When it comes to things like alternative universes and the like as the cause of our current mysteries, I'm sure these things have been proposed. The problem here is coming up with an experiment to test them. Dark matter has been named as such because we know that it doesn't emit or absorb any radiation. As far as detecting such a particle, many real experiments have been conducted and will be conducted, and is an exciting field of research.

Below shows a few of these experiments and the range of cross-section/mass parameter space it has/will probe:

dmdetectionexperiments

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I will look into both theories, thanks. I will take this opportunity, since you're working on a Ph.D. about the subject, to ask a follow up question. Reading this article the other day I learned about Axions and Cold Dark Matter, could you point me in the right direction to learn what current science favors more and why? between cold dark matter and hot dark matter that is. –  Eduardo Serra Dec 6 '13 at 19:13
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Sure. I see papers making their way to the arxiv (arxiv.org) every so often on the subject of axions. In short, whatever dark matter happens to be, it must be cold. What this means is that it has a rather low velocity dispersion. However, if it were warm/hot, structures on small scale would simply not be there (and this appears not to be the case). Think of it as increasing the kinetic energies of a system of particles, gravity wins if things can cool off. As far as axions go, they are one of many candidates for what the dark matter particle may be. They were first postulated in ... –  astromax Dec 6 '13 at 21:37
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1977 to resolve Charge-Parity (CP) violation (adsabs.harvard.edu/abs/1977PhRvL..38.1440P)(http://…. Here's at least one experiment I know of which was looking for axions (pvlas.ts.infn.it). Though, most of the experiments being run are looking for what's known as WIMPS (weakly interacting massive particles). Generally speaking, there are three types of experimental signatures people are looking for: 1) Indirect - dark matter/anti-dark matter annihilation or decay products, 2) Direct - nuclear recoil experiments, and –  astromax Dec 6 '13 at 21:41
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3) Creating them in the lab - collider experiments. This is a lot to take in, but there are a number of review articles you can read (though they can still be somewhat technical for the average reader). Here is one that I know of: arxiv.org/abs/hep-ph/0404175 –  astromax Dec 6 '13 at 21:42

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