[dogbyte12]

Any science wizbangs here? How does diffraction from dust alter light? If light had to go through semi transparent objects, wouldn't the light bouncing through them before passing, minutely slow it down? If our universe is more filled with junk than in it's infancy, couldn't that explain the discrepancy?

[JoeSixPack1]

The light didn't pass through it, it bounced around in it before it came out thus the speed was still constant

[Navy Patriot]

No whizbang here, but your thought that light slows down when it contacts transparent-translucent matter is correct. It also speeds back up when it exits same. Fastest in perfect vacuum.