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Is there anything like a cosmic mirror?

  1. Feb 8, 2015 #1
    I was wondering if there are objects near our galaxy that can reflect light from the Milky Way back to us for observation. If so, maybe they can provide information about the shape of the galaxy, for example. I'm sure there would be other interesting applications.

    I was thinking about it after learning of http://en.wikipedia.org/wiki/Salar_de_Uyuni, which is a reflective salt flat on earth that can be used to calibrate satellites.
  2. jcsd
  3. Feb 8, 2015 #2


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    Not really. Objects in space are simply too far apart to form a mirror, even for very large wavelength EM waves such as radio waves.
  4. Feb 9, 2015 #3
    Is it even possible to detect reflected radiation from our galaxy?
  5. Feb 9, 2015 #4

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    No, because there is no mirror to reflect it.
  6. Feb 9, 2015 #5
    Thanks for the comments. I'm still a bit curious about the theoretical possibilities, but have dropped plans to find a cosmic mirror.

    Let's say a single photon left our galaxy a long time ago, hit a dust particle at some point, and reflected back instead of being absorbed. By good luck, it happens to land in a telescope on earth and we record the energy & polarization of a single photon (or whatever we can record - I don't know how that works). Can we rule out the possibility of identifying the source of that photon as our galaxy?

    The idea seems to be that without a large set of these observations from a certain area of sky (i.e. the mirror doesn't exist), we would have no way to know where one came from..
  7. Feb 9, 2015 #6


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    No. We have no way of knowing where a single photon came from. It is only when we see large numbers of photons that we can get reliable pictures.
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