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A few qustions about Dark Matter from a beginner.

  1. Mar 28, 2012 #1


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    As i said in the topic i am still very new in the field, so if my questions are stupid and just a waste of time i apoligize. The stuff i know i've learned by myself so there are gaps.

    Anyway, onto my question:

    Speed of Light(C) travels at 3*108m/s in a vacuum, but when traveling through glas(for example) the speed is only 2*108m/s.

    Then we have Dark Matter, which doesnt emit or absorb light, neither does it interract with matter as far as we know. But it is still all around us, is it possible that the velocity of C changes when travelling through dark matter? As it does when travelling through glas?

    Best regards,
  2. jcsd
  3. Mar 28, 2012 #2


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    A few = One question apparently, my apoligies for the misleading topic.
  4. Mar 28, 2012 #3


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    There is no evidence dark matter interacts with light save for gravitational lensing.
  5. Mar 28, 2012 #4


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    Hi 721, welcome! That's a good question. This place runs on people who want to learn something asking intelligent questions. I agree with what Chronos said about no evidence for speed change.

    Dark matter is a fascinating topic. It is something to keep pursuing and asking about. Do you know about gravitational lensing (Wkpd probably has some informative articles about DM and how clouds of it are mapped by socalled "weak" gravitational lensing.)

    Denser patches of DM distort the background images of more distant galaxies more, that we see thru the "lens" of the clouds of DM. So the clouds can be mapped and their density variations can be mapped. Find out all you can about DM because research on it is progressing, it is a good learning "investment" if you watch science for enjoyment.

    You could also go over into the Physics section and ask WHY glass and water slow down light. It must be because their atoms are interacting with the light as it goes thru. It is standard college physics textbook stuff but nevertheless fascinating. What is the interaction that slows down the light? They'd probably explain it to you over in General Physics forum, or Classical.

    Actually you know maybe Chronos and I didn't tell you everything about your question. My intuition is that a dense enough cloud of DM would slow light a little bit while it was traveling thru the cloud because time passes more slowly deep down in a gravity well. But in realworld cases the effect would be very slight. Probably too small to ever have been observed. It would be associated with "strong" gravitational lensing. Dense concentrations of mass can actually focus plane waves like a magnifying glass. DM is too diffuse to have that effect be measurable. The weak grav lensing that DM does is a more subtle effect of slightly distorting shape.

    Have fun here, keep asking sensible questions like this. Again, welcome.
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