What color is the dark matter

Discussion in 'Astronomy, Exobiology, & Cosmology' started by timojin, Oct 17, 2016.

  1. timojin Valued Senior Member

    Messages:
    3,252
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. DaveC426913 Valued Senior Member

    Messages:
    18,935
    Interesting.

    What the article is saying is that they've found a correlation between the amount of visible matter and the galactic rotational speed. But it is not the typical correlation we would expect (or there would be nothing needing explaining). They don't have any idea why there's a correlation, simply that there is.

    They can use their new formula to predict galactic rotation, based on visible matter present.
    But, to address the rather misleading title: predicting is not the same as explaining.

    They admit, one possibility is simply that the amount of visible matter and the amount of dark matter share a closer link than previously thought. Which would explain the correlation - but without throwing out DM and having to introduce modified gravity.

    The upshot of the article is that they have discovered a law, rather than creating a theory.
     
    Last edited: Oct 17, 2016
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. PhysBang Valued Senior Member

    Messages:
    2,422
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. DaveC426913 Valued Senior Member

    Messages:
    18,935
    By far-flung analogy:

    We observe that the per cent of visible marbles in a jar is strongly correlated with the volume of the jar. The problem is that we know - very accurately - the size of white marbles, and it is not enough to fill the jar they occupy.

    What we have found though, is that, if we count the number of marbles we see, we can predict the size of the jar. (One marble seems to require a one-litre jar. Two marbles = 2 litres.)

    This is not to say that there are no invisible marbles in the jar. There are actually plenty, and they definitely affect the size of the jar. The jar's volume can be predicted by - but not explained by - visible marbles alone.

    Two possibilities:

    1] The ratio of visible to invisible marbles is correlated, meaning we only need to count visible marbles to predict the size of the jar.

    2] We are wrong about the size of marbles and have to change our understanding of how large visible marbles are. (Surely they're not 1 litre!) This would fly in the face of all our marble knowledge.
     
    Last edited: Oct 17, 2016
  8. Ultron Registered Senior Member

    Messages:
    245
    The article is not accesible.
     
  9. Q-reeus Banned Valued Senior Member

    Messages:
    4,695
  10. Magical Realist Valued Senior Member

    Messages:
    16,602
    Dark matter btw is octarine.

    “It was octarine, the colour of magic. It was alive and glowing and vibrant and it was the undisputed pigment of the imagination, because wherever it appeared it was a sign that mere matter was a servant of the powers of the magical mind. It was enchantment itself.
    But Rincewind always thought it looked a sort of greenish-purple.”


    Terry Pratchett, The Color of Magic
     
    Last edited: Oct 20, 2016
  11. paddoboy Valued Senior Member

    Messages:
    27,543

    Please Register or Log in to view the hidden image!

    Whatever colour it is, at this stage it is certainly necessary, to explain effects we see, and evidence to its existence with the "bullet cluster" observation, has now seen it generally accepted within mainstream cosmology.
     
  12. Ultron Registered Senior Member

    Messages:
    245
    I have the arxiv paper already some time, but I wanted to read the article in cosmomagazine posted in OP.
     
  13. Q-reeus Banned Valued Senior Member

    Messages:
    4,695
    You couldn't access that low-grade interpretation of original academic paper? No problem with anyone else it seems. A tip - anything like that happens again, go here:
    http://www.isitdownrightnow.com/
    I have found it pretty reliable.
     
  14. Fraggle Rocker Staff Member

    Messages:
    24,690
    If something has been named "dark matter," isn't that a gigantic clue that it might be impossible to see at all?
     
  15. The God Valued Senior Member

    Messages:
    3,546
    This matter, albeit hypothetical, does not have EM interaction, a primary aspect necessary for associationg anything with color. So DM has no associated color concept.

    PS : DM shows only gravitational effect, it interacts with baryonic matter gravutationally only, gravity transmits at the speed of c, so the gravitational influence of DM must also transmit at c. Now how does 'c' jump in here when DM has no business with EM? This shows either the concept of DM is faulty or light speed is independent aspect, does not originate from EM.
     
  16. Daecon Kiwi fruit Valued Senior Member

    Messages:
    3,133
    Are you trying to say that the gravity of Dark Matter is different to the gravity of every other body in the Universe because Dark Matter doesn't interact with the electromagnetic spectrum?

    I'm pretty sure that all gravity transmits at c, regardless of its source.
     
  17. The God Valued Senior Member

    Messages:
    3,546
    Thats good.

    1. How are you sure that Gravity of Dark Matter would traverse at c?

    2. How are you so sure that a particle which has no Electro Magnetic interaction will have something to do with light speed?

    Well, I am personally saying nothing about properties of DArk Matter, simply because IMO dark matter is just non sense.
     
  18. paddoboy Valued Senior Member

    Messages:
    27,543
    DM is accepted cosmological theory and is necessary to explain the effects we see. This point was made quite streniously with expletive deleted after his continued unsupported nonsense re DM not being needed.
    And just as obviously, as the name DM suggests, DM does not have any colour.
    That is confusing at best, and fabricated nonsense at worst.
    See my previous reply.
     
  19. The God Valued Senior Member

    Messages:
    3,546
    1. What is the color of radiation in ultra violet and Infra red range?

    2. Why the second para is confusing? What is fabricated about that?
     
  20. Yazata Valued Senior Member

    Messages:
    5,902
    What color is dark matter?

    That would depend on what dark matter is, I guess.

    If dark matter is composed of MACHOs, conventional smaller objects not visible to Earth observers like brown dwarfs, stray planets and unconsolidated cosmic debris, all of which would contribute mass, then their color would depend on their composition and on the nature of the light source illuminating them, I guess.

    https://en.wikipedia.org/wiki/Massive_compact_halo_object

    If dark matter is composed of WIMPs, an unknown form of matter that has mass but doesn't interact with other physical forces in the ways that baryonic matter (familiar matter composted of protons and neutrons) does, then it would be invisible, I guess. Light would just pass through a big clump of WIMPy dark matter.

    https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles

    Another question: If there is lots of dark matter out there in the interstellar voids, what would that mean for star-ships travelling at a velocity close to the speed of light? Collisions with consolidated MACHOs would obviously be disastrous. Collision with WIMPs may or may not be. That would depend on whether the WIMP particles clump up into macroscopic bits of matter and whether they would exert any force on bayonic matter hitting them.
     
    Last edited: Oct 22, 2016
    ajanta likes this.
  21. paddoboy Valued Senior Member

    Messages:
    27,543
    They are frequencies of the EMR outside our the viewable range of the human eye, and have no connection with DM.
    Just as I said: DM has nothing to do with the EMS, and obviously has no colour as the name suggests, as is also obvious with the blackness of space...black of course being the absence of colour.
     
  22. paddoboy Valued Senior Member

    Messages:
    27,543
    I'm sure we would be safe in presuming the question was of WIMPS and/or any form of non baryonic matter which does not interact other than gravitationally.
    Great question!
    I believe the following answers it admirably...............
    https://www.quora.com/What-are-the-...if-it-travels-in-a-straight-path-for-10-years
    If the spaceship can start from any point in the observable universe and travel in any direction, then the probability that it will hit anything bigger than the occasional subatomic particle or molecule of interstellar gas (from which it can probably be effectively shielded) within a distance of 10 light-years from its starting points is as near zero as makes no difference.

    Why? Because most of the universe is empty space. Really empty space, and an awful lotof it.

    First of all, there are the immense voids between galaxies. Then there are the even more immense voids between galactic clusters. And, finally, there are the stupendously immense voids between galactic superclusters. These various voids are between millions and hundreds of millions of light-years across, in any direction. And there is nothing in these voids but passing photons of light, neutrinos, an extremely sparse scattering of lone particles and maybe more exotic stuff like dark matter - which is so weakly interacting that it will pass right through the spaceship without a blip. So there is simply nothing in these voids for a spaceship to hit - certainly not within 10 lights years of any typical point, and probably not even within several million light-years of it.
     
  23. Boris2 Valued Senior Member

    Messages:
    1,106
    If it exists, the graviton is expected to be massless (because the gravitational force appears to have unlimited range) and must be a spin-2boson. The spin follows from the fact that the source of gravitation is the stress–energy tensor, a second-order tensor (compared to electromagnetism's spin-1 photon, the source of which is the four-current, a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. As the graviton is hypothetical, its discovery would unite quantum theory with gravity.[4]This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.

    https://en.wikipedia.org/wiki/Graviton

    so being massless it must travel at c.
     

Share This Page