"Dark Matter" shouldn't be "Transparent Matter"???

Discussion in 'Physics & Math' started by martillo, Jul 22, 2020.

  1. martillo Registered Senior Member

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    It s said "Dark Matter" occupies about 90% of the Universe. If it was dark we would see quite nothing from the Universe in telescopes. We wouldn't see stars nor galaxies.
    Actually it should be "Transparent Matter"!
     
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  3. paddoboy Valued Senior Member

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    Observational data tells us that the universe is made up of Baryonic matter at around 5%, DM at around 25% and DE at 70%
    DM [Dark Matter] is so called because it only interacts and reveals its apparent existence via gravity.
     
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  5. mathman Valued Senior Member

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    The reason we can see through is because it is made up of (unknown) microscopic particles which don't clump.
     
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  7. exchemist Valued Senior Member

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    I don't think we know that they don't clump. In fact, all we know is that there is more gravitation than can be accounted for by the visible "normal" matter. So if they experience gravitation, they should clump, just like "normal" matter, I should have thought.

    If dark matter does not interact with EM radiation, which is what "dark" signifies, it does not seem to matter whether it clumps or not. It is, as Martillo says, transparent to EM radiation.

    I presume the reason it is called "dark" is because astronomers estimate the masses of galaxies from the stars, which are "bright" and so whatever is behind the discrepancy in gravitation is called "dark", to distinguish it.
     
  8. AlphaNumeric Fully ionized Registered Senior Member

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    Dark matter is proposed not to couple to electromagnetic radiation - this is the reason we "see" things, not because of size. Z bosons are 160,000 times more massive than electrons but they do not interact with photons, unlike electrons, so would be "dark" (if they didn't decay into other particles almost immediately).

    Dark Matter is the name of the cause of the galactic-level (and above) phenomena of there seeming to be gravitational effects far in excess of the matter we can see in galaxies - the primary example being galaxies are spinning too quickly. It's considered 'matter' because if it works on the level of a single galaxy it probably isn't something related to the fabric of space-time alone. This is in contrast to Dark Energy, which is called "dark" to fit the naming convention. In its case it is more "Dark = poorly understood", since we have only speculative ideas about what the underlying cause of the increasing expansion rate of the universe - if it were matter it'd have clumped via gravity and it seems too smooth for that and the only other known 'thing' that affects space-time is energy. "Dark Energy" is better viewed as a place holder for some phenomena we can only vaguely detect. Whether it'll be any more than that is currently unknown.
     
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  9. DaveC426913 Valued Senior Member

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    As far as we can tell, DM doesn't interact elecromagnetically even with itself.

    That means no collisions.

    DM particles will happily orbit a centre of mass (whether DM or normal matter) indefinitely without any collisions to cause it to clump.
     
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  10. exchemist Valued Senior Member

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    Excellent point! I stand corrected.
     
  11. Janus58 Valued Senior Member

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    No. "Dark matter" refers to anything that interacts gravitationally, but is not detectable via normal electromagnetic inspection.
    There are two possible types of dark matter:
    MAssive Compact HAlo Objects ( MACHOs),which would be things like Black holes. They do interact with light in that they will absorb light crossing their event horizons. They individually have a lot of mass, but are so compact, that they are for all practical purposes invisible.
    Weakly Interacting Massive Particles (WIMPS). These are sub-atomic particles that have mass, but don't participate in the Electromagnetic interaction.

    While WIMPs are what most people are thinking about when they use the term "dark matter", strictly speaking, the term applies to either.

    How much of the total Dark matter is made up of each isn't precisely known. The best we can say is that there is a upper limit on how much of it can be comprised of MACHOs. (Essentially, a universe with a whole lot more black holes in it would not have evolved into the type of universe we see around us today.)
     
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  12. paddoboy Valued Senior Member

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    OK, while your explanation is one that I agree with, I was prompted to google anyhow.
    Before I present that, we do know [at least my thoughts were] that DM congregates into large regions under gravity, but that the lack of electromagnetic attraction [and at the atomic scale strong and weak nuclear forces] prevent it from clumping and forming asteroids, planets etc . My definition of clumping.

    anyway I found this.....
    https://www.nasa.gov/feature/goddard/2020/hubble-detects-smallest-known-dark-matter-clumps

    and this.......................
    https://phys.org/news/2020-01-hubble-smallest-dark-clumps.html
    JANUARY 9, 2020

    Hubble detects smallest known dark matter clumps
    more at link..........
    >>>>>>>>>>>>>>>>>>>
    Perhaps how we define "clumping" is of importance.

    and then we have this........
    https://www.discovermagazine.com/the-sciences/dark-matter-might-clump-to-form-planets



    https://arxiv.org/abs/1707.03829
    The distributions of dark matter and baryons in the Universe are known to be very different: the dark matter resides in extended halos, while a significant fraction of the baryons have radiated away much of their initial energy and fallen deep into the potential wells. This difference in morphology leads to the widely held conclusion that dark matter cannot cool and collapse on any scale. We revisit this assumption, and show that a simple model where dark matter is charged under a "dark electromagnetism" can allow dark matter to form gravitationally collapsed objects with characteristic mass scales much smaller than that of a Milky Way-type galaxy. Though the majority of the dark matter in spiral galaxies would remain in the halo, such a model opens the possibility that galaxies and their associated dark matter play host to a significant number of collapsed substructures. The observational signatures of such structures are not well explored, but potentially interesting.
    :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

    Interesting to say the least, and supports our still near total ignorance of DM.
     
  13. paddoboy Valued Senior Member

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    How would a hypothetical purely quark/gluon star appear?
    Or would this state of matter only be possible deep inside Neutron/Pulsars?
    You may also like to comment on my previous post Janus.
     
  14. paddoboy Valued Senior Member

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    The highlighted bit seems rather contrived to me.
     
  15. exchemist Valued Senior Member

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    I've just been reading a bit about WIMPs. There seems to be also another candidate particle for dark matter, known as the "axion"?
     
  16. exchemist Valued Senior Member

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    9,858
    I've just been reading a bit about WIMPs. There seems to be also another candidate particle for dark matter, known as the "axion"?
     
  17. exchemist Valued Senior Member

    Messages:
    9,858
    I've just been reading a bit about WIMPs. There seems to be also another candidate particle for dark matter, known as the "axion"?
     
  18. Michael 345 New year. PRESENT is 70 years old Valued Senior Member

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    This is about a bit of the missing Universe. Not the Dark Matter missing bit. A bit of Normal Universe 5% Universe missing



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  19. Beaconator Registered Senior Member

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    • Please do not post pseudoscience in our Science sections.
    Dark matter was disproven by the loudest formula

    what we today believe to be dark matter is nothing more than a clerical error between our mathematical ability to understand wave particle theory. The three ideals any (;:LENS);: has is the smallest medium and largest.

    sometimes the smallest is a wave sometimes the largest is a particle.

    sometimes the largest is a wave of particles or a blurry lens.
     
  20. RainbowSingularity Valued Senior Member

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    observable
    detectable
    naked human eye opacity perceptual range

    physics yes ?
     

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