3 knowns and 3 unknowns about dark matter

June 8, 2016 by Glenn Roberts Jr, University of California - Berkeley
A composite image of the “bullet cluster,” a galaxy cluster formed by a collision of two clusters. The pink clumps show hot gas containing most of the normal matter, while the two blue clumps reveal where most of the mass in the clusters is actually contained. This provides evidence for dark matter since most of the mass was expected to be concentrated around the pink areas. Credit: NASA/CXC/M.Markevitch et al.; optical image by NASA/STScI, Magellan/U.Arizona/D.Clowe et al.; lensing map image by NASA/STScI, ESO WFI, Magellan/U.Arizona/D.Clowe et al.

What's known:

1. We can observe its effects.

While we can't see , we can observe and measure its . Galaxies have been observed to spin much faster than expected based on their , and galaxies move faster in clusters than expected, too, so scientists can calculate the "missing " responsible for this motion.

2. It is abundant.

It makes up about 85 percent of the total mass of the universe, and about 27 percent of the universe's total mass and energy.

3. We know more about what dark matter is not.

Increasingly sensitive detectors are lowering the possible rate at which dark mark matter particles can interact with normal matter.

What's unknown

1. Is it made up of one particle or many particles?

Could dark matter be composed of an entire family of particles, such as a theorized "hidden valley" or "dark sector?"

2. Are there "dark forces" acting on dark matter?

Are there forces beyond gravity and other known forces that act on dark matter but not on , and can dark matter interact with itself?

This chart shows the sensitivity limits (solid-line curves) of various experiments searching for signs of theoretical dark matter particles known as WIMPs (weakly interacting massive particles). The shaded closed contours show hints of WIMP signals. The thin dashed and dotted curves show projections for future U.S.-led dark matter direct-detection experiments expected in the next decade, and the thick dashed curve (orange) shows a so-called “neutrino floor” where neutrino-related signals can obscure the direct detection of dark matter particles. Credit: Snowmass report, 2013
3. Is there dark antimatter?

Could dark matter have an antimatter counterpart, as does normal matter, and is there a similar imbalance that favored dark matter over "dark antimatter" as with normal matter-antimatter?

Credit: University of California - Berkeley

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10 comments

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Seeker2
5 / 5 (2) Jun 09, 2016
I can't understand why all matter has to be quantized and emit or absorb radiation when jumping to different energy levels.
kendejo
5 / 5 (1) Jun 09, 2016
..And that 'jumping to different energy levels' might explain why sub-atomic particles seem to appear and disappear. maybe they still exist but are transitioning to a state that we can't detect
Seeker2
3 / 5 (2) Jun 10, 2016
why sub-atomic particles seem to appear and disappear. maybe they still exist but are transitioning to a state that we can't detect
Virtual particle pairs seem to appear and disappear. I don't think we can observe their individual energies but collectively they would form the vacuum energy. Regions of different vacuum energy would then have either a higher density of particle-antiparticle pairs or higher collective energy of these pairs or probably both. Regions of different vacuum energy which form cause entropic gravity. As a matter of fact all gravity may be entropic. Regions of matter block out the vacuum energy so exert less vacuum pressure. This reduced back pressure then causes other matter to be sucked in. Surprise. The force of gravity comes from regions of higher vacuum pressure such as those without matter.
antialias_physorg
4.3 / 5 (6) Jun 10, 2016
If there were a significant amount of anti-dark matter, then there would necessarily either be one heck of a lot of x-ray radiation (which is not there) or maybe some (magical) new set of massless (non-electromagnetic) particles;

Not necessarily. If dark matter interacts as weakly with itself as it does with ordinary matter then there would be no (or very little) dark matter/ dark antimatter reactions taking place

Neutrinos ARE dark matter,
Doesn't really work because if you look at the calculated maps of dark matter distribution then that doesn't mesh with how neutrinos behave.

I can't understand why all matter has to be quantized and emit or absorb radiation when jumping to different energy levels.

It's a matter of resonance and the Pauli exclusion principle
https://en.wikipe...lanation
https://en.wikipe...rinciple
Seeker2
5 / 5 (1) Jun 10, 2016
It's a matter of resonance and the Pauli exclusion principle
https://en.wikipe...lanation
Certainly for real particle pairs.
Seeker2
5 / 5 (1) Jun 10, 2016
e/m fields may be due to the collective alignment of virtual electron-positron pairs. Other forces such as gravity and the strong force may be due to the collective alignment of other particle-antiparticle pairs. No calls please.
Seeker2
5 / 5 (1) Jun 12, 2016
Per http://phys.org/n...les.html "In 10 quintillion years everything in the Universe will have either fallen into a black hole, or been flung out on an escape trajectory. And then those black holes will slowly evaporate over time, as predicted by Stephen Hawking." My guess is by this time the black hole becomes unstable and splits apart and opens up a new big bang before they ever have time to evaporate.
Chris_Reeve
Jun 13, 2016
This comment has been removed by a moderator.
Chris_Reeve
Jun 13, 2016
This comment has been removed by a moderator.
Seeker2
5 / 5 (1) Jun 13, 2016
Galactic Dynamics Textbook Author Admits No Strong Scientific Reason to Believe that Gravity Dominates at Galactic Scales
Vacuum pressure or dark energy or whatever dominates at galactic scales. As long as the dark energy pushes, the lowest energy state of the U is when all matter is collected into its minimum space. Problem is people don't understand what gravity really is. GR happens to describe this effect correctly from a mathematical viewpoint but no where near a physical description of what's going on.

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