

We only know about a small fraction of the matter in the Universe - kostyk
http://www.bbc.com/earth/story/20150824-what-is-the-universe-made-of

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kordless
> Zwicky's work was largely forgotten until the 1970s, when astronomer Vera
> Rubin discovered that nearby galaxies were not spinning in the right way.

What Vera observed was that the stars in distant galaxies were all spinning
"together". One would expect some stars in the galaxy to spin at a faster
speed than others at varying distances from the center. What she observed is
akin to a single "galaxy" bitmap rotating all at once, where the relative
positions of the stars in the galaxy "image" being in lockstep with each
other.

Dark matter. Hehe.

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willezgo
What I have always found mesmerizing about dark matter, is whether it forms
deeply complex and interesting structures like ordinary matter (like galaxies,
planetary systems, or "dark life", or even radically different structures that
we have no concept of). But we just don't know because it's so hard to detect.

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rocky1138
Why is dark matter only found away from Earth?

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antognini
As the other answers have said, there is dark matter expected near the Earth,
it's just at a very low density. There have been a number of experiments
looking for some signature of weak dark matter interactions near the Earth.
One of these, DAMA, has claimed a detection of an annually varying signal
which would be consistent with the Earth moving with and against an ambient
medium of dark matter over the course of a year. However, no other experiments
have been able to verify this detection.

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cLeEOGPw
That fraction is the most interesting fraction though.

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zamalek
Depending on who you ask :).

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cLeEOGPw
It's not really subjective. Since dark matter has so little interaction, it
probably has just few basic properties like mass and some other. Regular
matter has complex things going on for it. That's why there is life, stars,
etc. composed of regular matter and not dark matter.

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ars
The NASA image of the bullet cluster shows that light bends not exactly where
the two galaxies are colliding.

This is taken as evidence for dark matter (because gravity is not where the
visible matter is).

But I would not expect the light to bend where the galaxies are. I would
expect light to bend where they _were_.

That light has been traveling for millennia, and has been bending the entire
time, so of course it bends at a distant location from where the galaxies are
"now".

So I don't understand how that photo is evidence of dark matter.

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merpnderp
That photo shows where the galaxies were then, not now.

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ars
Are you talking about the speed of light, that everything we see is in the
past?

Because I am not talking about that. So if you mean something else please
clarify.

