General Discussion
In reply to the discussion: The universe is much bigger than big [View all]cthulu2016
(10,960 posts)But even if there is only one tiny bit of something in a thousand of cubic miles of deep space, when we look from earth in any direction we are looking through billions of those units of a thousand cubic miles of space. So there will eventually be a bit a piece of dust in the path of every photon that would have otherwise made it to our eye.
The dust is, for the most part, incredibly thinly spaced. So thin that it doesn't interfere much with nearby stars. But over many, many, many light-years of space it adds up. (Matter in nearly empty space like microscopic water droplets in our air. They don't interfere much with things up close, but things at a distance look hazy. The longer the distance the more water droplets a photon has to miss along the way.)
When the Hubble takes these pictures of distant galaxies it is adding together all the photons over hours of time to put an image together...each photon like a jig-saw puzzle piece. But in real time, these things are invisible to our eyes.