Can Light Be Multiply Scattered in the Universe?

[oldman]

The phenomenon of gravitational lensing is becoming an important tool for studying objects in the distant universe, according to an article in Time Magazine (September 4 2006).

Lensing is caused by the systematic (angular deviation proportional to the impact parameter?) bending of light from a point source, as the light passes close to a massive object. Lensing can be regarded as one aspect of the small-angle scattering of light by mass --- think of the universe as a (very) large transparent medium in which is embedded a variety of small-angle scattering centres. Light in such a medium will be multiply scattered when it travels over a long enough distance. In a solid this would lead to opalescence.

Is there any evidence for some kind of (red) background radiation which could be caused by such scattering? Or is the universe too small for this to be significant?

 

[marcus]

my understanding of opalescence
http://en.wikipedia.org/wiki/Opalescence
is that there must be some wavelength dependence of the scatteringin usual opalescence the particles are small compared with the relevant wavelengths

an example is that blue is scattered more than red in the atmosphere so the sun looks red if seen thru a long stretch of atmosphere, but the scattered light coming from random directions looks blue (or people put a dribble of milk into clear water and look at a lightbulb through it)

so i don't understand your picture. In the universe the scattering (or lensing) centers are galaxies, which are very big compared with the wavelength of light

all light, out to absurdly long wavelengths (like tens of thousands LY) would be bent by the same angle, so there would be no preferential bending or scattering-----as I understand it----of detectable light.

IOW all detectable light would get bent the same, regardless of wavelength. so don't understand how there could be opalescence.

 

[oldman]

I guess I shouldn't have used the word opalescence without checking its technical meaning, which is what you say it is, Marcus. But the rest of my question about small angle scattering of light by massive objects (like galaxies, stars, black holes still rests. In this case the wavelegth of the light relative to the size of the scattering centre is not relevant.

 

[Nereid]

This is, I think, an area of active investigation - both in terms of working out what the footprint of such weak lensing would be, over very long sight-lines, and observing such footprints.

The longest sightlines - until we can detect relict neutrinos - are to the surface of last scattering; and several papers have been written on lensing footprints in the CMB.

 

[oldman]

This is, I think, an area of active investigation - both in terms of working out what the footprint of such weak lensing would be, over very long sight-lines, and observing such footprints.

The longest sightlines - until we can detect relict neutrinos - are to the surface of last scattering; and several papers have been written on lensing footprints in the CMB.

Thanks, Nereid. This is what I was asking about, in my rather obscure way. If you come across any references that I can access on the web, please let me know.

 

[Nereid]

Thanks, Nereid. This is what I was asking about, in my rather obscure way. If you come across any references that I can access on the web, please let me know.

A random selection (no promises wrt pertinence!):
http://arxiv.org/abs/astro-ph/0605696"
http://arxiv.org/abs/astro-ph/0507301"
http://arxiv.org/abs/astro-ph/0512218"
http://arxiv.org/abs/astro-ph/0511089"
http://arxiv.org/abs/astro-ph/0603019"
http://arxiv.org/abs/astro-ph/0506112"
http://arxiv.org/abs/astro-ph/0512426"
http://arxiv.org/abs/astro-ph/0503276"

In addition, Yousin Park's PhD thesis ("Weak lensing studies with GOODS/ACS fields", June 2006?) looks like it would be a great read, for your purposes, if you could get a copy of it!