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The invisible object.

  1. Oct 31, 2005 #1
    If an object is incapable of reflecting and absorbing light, our eyes wouldn't be able to see it, correct?

    Do you think a solid or liquid mass on Earth is capable of resisting light absorption and reflection to a degree that it's entirely unseen (therefore achieving true invisiblity)? Do you think certain masses have yet to be discovered due to our inability to see them?

    Note: I'm not talking micro-organisms here. I'm talking about things large enough to be seen with the naked eye if they were visible (i.e. things easily seen like rocks/sands, water, and insects).
     
  2. jcsd
  3. Nov 4, 2005 #2
    Dark Matter may fit the bill. This is a form of matter hypothesised to exist in quantities much greater than ordinary matter, but it would be invisible to us. Light would pass right through it and not be reflected by it. The only way we have of detecting its presence is the gravitational force it would exert on ordinary matter (this is how it has been "detected" in cosmology).

    MF
     
  4. Nov 4, 2005 #3
    Interesting. I've heard of dark matter before, but I've never known anything about it. Thanks for the explanation. :)
     
  5. Nov 4, 2005 #4
    Well we discovered the air molecule, which is like you're talking about.
    But that there may exist a rock incapable of absorbing light somewhere down in africa? Sure. Who knows.
    But if this was a widely spread phenomena, we would encounter it when building buildings and stuff like that.
     
  6. Nov 4, 2005 #5
     
    Last edited: Nov 4, 2005
  7. Nov 4, 2005 #6
    I guess, unless it's under water or in some secluded desert somewhere. :tongue2: But good point. If anything of the sort were located in a populated region, I think we would've run into something by now (if it were large enough).
     
  8. Nov 4, 2005 #7
    Well, even in the given scenario above, I still wouldn't be able to "see" the object. At least I don't think so. What you speak of is seeing something relative to the environment, right? And for you to hold the invisible object in front of you, you'd have to find it first...

    I'm not totally sure of the physics of it all, so I can't really pretend I know what I'm talking about. I'm not really sure where the light would go if it couldn't be reflected or absorbed. Wouldn't it technically be trapped by the object, unable to go anywhere (like a person running into a brick wall)?
     
  9. Nov 5, 2005 #8
    You don't ever 'see' anything. All you ever see is how something affects light.

    Trapped is absorbed. Bouncing off a wall is reflected.
     
    Last edited: Nov 5, 2005
  10. Nov 5, 2005 #9
    Incorrect. If the object does not absorb light (like perfect glass) then you would see right through it.
    It is not correct that "everything has to absorb or reflect". It is possible for light to travel straight through objects without being absorbed (glass being an imperfect but good example)

    MF
     
    Last edited: Nov 5, 2005
  11. Nov 5, 2005 #10
    Not if it were Dark Matter.
    The hypothesis is that Dark Matter does NOT interact with ordinary matter either through the strong or weak nuclear forces, or through the electromagnetic force - it interacts only through the gravitational force. Thus the only way you would ever be able to detect the presence of dark matter is through the gravitational field that it produces, and we all know that gravity is an incredibly weak force. So we could all be surrounded by Dark Matter and not know it.

    Unfortunately this subject is really physics - not philosophy - you may get more sensible replies if you post your question in a physics thread

    MF
     
  12. Nov 5, 2005 #11

    Mk

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    I agree finger's response in that your correction is incorrect, nothing says that all light has to be absorbed or reflected when passing through a medium.

    There I would say you are wrong, the hypothesis is that dark matter does not interact with the electromagnetic force. Dark matter may or may not intereact with the strong and weak nuclear forces.
     
    Last edited: Nov 5, 2005
  13. Nov 5, 2005 #12
    depends on whose hypothesis you are referring to

    :smile:

    MF
     
  14. Nov 5, 2005 #13
    I was unclear, I was referring to the original post. I should have said absorbed, reflected or transmitted. But he didn't say transmitted and I mentioned that.
     
  15. Nov 6, 2005 #14
    The thing I find distasteful with dark matter is that it seems like a cop out. It isn't fully defined, and therefore can be used as an answer to all sorts of questions.
     
  16. Nov 6, 2005 #15
    It's an attempt (an hypothesis) to explain the observed dynamics of galaxies and globular clusters (which dynamics are inconsistent with the observed matter). If dark matter does exert gravitational attraction then it should be a testable hypothesis.

    Why is this a cop out?

    What else would you like "defined" about Dark Matter?

    MF
     
  17. Nov 6, 2005 #16

    selfAdjoint

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    Umm, what kind of particles it's made of?

    If the nonlinear Einstein gravity proposal is correct (jury's still out on it) then the original reason for introducing dark matter is gone. Now, they have other reasons for assuming dark matter exists, so it may still be needed, but the galactic profile reason is in trouble.
     
  18. Nov 7, 2005 #17

    Mk

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    I would think equations also predict existence of this mysterious dark matter, not only something made up!
     
  19. Nov 7, 2005 #18
    Dark ones, of course :tongue2:

    The "reason" for introducing any hypothesis is to fit the observed data.
    With respect, in strict scientific terms the "nonlinear Einstein gravity proposal" cannot ever be "proven to be correct", the best we can ever hope is that "it fits the observed data".

    The only way to falsify the hypothesis of Dark Matter is to show the hypothesis does not agree with experiment, not to come up with an alternative hypothesis.

    MF
     
    Last edited: Nov 7, 2005
  20. Nov 7, 2005 #19
    where do you get your detailed equations from in the first place? are these handed down by God? No, they are made up to fit the observed facts (unless you have access to a ToE which contains no a priori assumptions?)

    MF
     
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