Is there anything like a cosmic mirror?

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Discussion Overview

The discussion revolves around the concept of whether there are cosmic objects that can reflect light from the Milky Way back to Earth, potentially providing insights into the galaxy's shape and other applications. Participants explore theoretical possibilities and the challenges of detecting such reflections in the context of astrophysics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant proposes the idea of cosmic mirrors that could reflect light from the Milky Way, suggesting they might provide information about the galaxy's shape.
  • Another participant argues that objects in space are too far apart to function as mirrors, even for large wavelength electromagnetic waves.
  • A question is raised about the possibility of detecting reflected radiation from our galaxy.
  • It is asserted that without a mirror, there can be no reflection of light back to Earth.
  • A hypothetical scenario is presented where a single photon reflects off a dust particle and returns to Earth, questioning whether it could be identified as originating from the Milky Way.
  • Another participant responds that it is impossible to determine the source of a single photon, emphasizing the need for a large number of observations to draw reliable conclusions.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of cosmic mirrors and the detection of reflected light, with no consensus reached on the theoretical possibilities or implications of such reflections.

Contextual Notes

The discussion highlights limitations in understanding the detection of single photons and the challenges posed by the vast distances in space, which may affect the ability to identify sources of light.

zthompson47
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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.
 
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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.
 
Is it even possible to detect reflected radiation from our galaxy?
 
No, because there is no mirror to reflect it.
 
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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..
 
zthompson47 said:
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?

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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