What do you think of dark matter?

Question

What do you think of dark matter?

Answer 1

I'll believe it when I see it.

ROFLMAO

Sorry, I couldn't help myself.

Answer 2

Well... go back to what you know before.  We have a very very limited scope of the Universe.  We have little to no idea about what space is actually made of.  We assume that whatever particles are found on Earth, and the atmosphere, are present in the Universe.  But there could be particles we don't know about.  By definition, the dark matter must interact only gravitationally.  Due to that, any experiment relying on electrical, or magnetic fields won't detect the particles.  Anything that expects a decay and wants to record tracks will not work.  And since on Earth we have a gravitational field, it will not behave differently than other particles.  It's difficult to impossible to detect in a lab.

However, look at why we think there is dark matter.  Zwicky discovered an anomaly.  At the time, it was standard practice to look at the luminous output of a galaxy to infer its mass.  The ratio between the two is fairly consistent throughout the Universe (sort of like saying 4% of the Universe is baryonic).  And, we also know that F = ma, or rather the rotational equivelant with torques.  So, suppose you have some galaxy that you can measure the luminous output of.  Then, you infer a mass.  Now, you observe that it is a spiral galaxy and it is rotating about its center.  You can estimate the distance of an observed arm and its center, as well as the time it takes to move through some measured angle.  You then have all the information needed to see whether the mass inside the galaxy that you infered from the luminous output is the same as what is required to make the galaxy spin.  After a little time, you find that your infered mass is off by a factor of about 400.  Hmm... not enough mass from the luminous matter.  Perhaps... if there were some matter I could not see, as though it were dark, that would be pulling the galaxy together and making it spin as quickly as I have seen, this would all make sense.

So, there, that's the motivation behind an idea like dark matter.  Of course, we've progressed since Zwicky's first suggestion.  In fact, I just did a project loosely related to dark matter -- it was to calculate various observable figures related to the bending of light from a dark matter distribution.  The true test, for my work anyways, would be to find a physical case and see if the math matches up with what we see.

Answer 3

Mysterious substance, many people have different opionions on the matter, none are 100% absolute facts.  All hypothesises.

Answer 4

i think it sucks.

Answer 5

Dark matter has been theoretically posited as the main 'matter' gravitational 'element' within galaxies. If dark matter emitted any form of EM radiation, or interacted with it, we would be able to detect its presence due to its dominant presence. However, dark matter may not be an exotic form of matter at all!

Some theorists have speculated that dark matter could be neutrinos. Neutrinos have a very small nuclear weak force cross-section (probability of interaction) and it would take a light-year of lead to block half of the neutrinos produced by the sun. Thus, neutrinos become possible candidates for dark matter due to their low interaction rate with matter. Furthermore, neutrinos travel at either, the speed of light or close to it. In the later speed case, they may have a very small mass of less than 2.2 electron-volts (ev for short. To convert to a mass - multiply by the charge on an electron (e) and divide by c² (from E = mc²)). Hence, with this tiny mass, neutrinos may interact gravitationally with the universe. Evidence from solar neutrino experiments suggests that neutrinos exhibit flavour oscillations during their passage. The flavour oscillations result in an electron neutrino transforming into the muon and then the tau neutrino and then back again. The muon neutrino has a mass of less than 170 kev and the tau neutrino has a mass of less than 15.5 Mev. Thus, flavour oscillations could result in neutrinos having a greater gravitational influence. There is, however, one drawback to this theory - neutrinos move at close to the speed of light and so localised gravitational condensation into proto-galaxies is difficult to account for!