# Bright Sky Paradox: Darkness as a measurement of expansion

I personally love the images I see from Hubble and other deep viewing space based telescopes.  Looking that deep into space takes my breath away in the beauty of the stars, galaxies, and other cosmic objects that bless those images.  Taking images that deep of objects that are that far away shows one way in which space is strongly connected to time.  When you look at something that is hundreds, thousands, millions, or even billions of light years away you are looking through both the space and time of the universe and seeing it as it was at that time in that space.  The astronomer from the early 1800’s, William Herschel, is credited in the new Cosmos series as noting that the sky is filled with these kinds of ghosts.  Images of objects that once were and in some cases still might be.  With the new views from our modern telescopes this is easier to see than ever.

However, if it is indeed assumed that there are stars and galaxies scattered in an almost random way across the entire night sky and the universe is indeed a finite place then it would be reasonable to assume that the night sky should be filled with lights coming from all sorts of celestial objects coming from all directions!  So why then is it not the case that the night sky is bright?

Even with the spaces and distances we are considering, the accumulation of all of the light from all of the universe seems like it should in some way illuminate our night sky.  However, there is one assumption in my current line of reasoning that has managed to sneak its way in without our noticing.  We have assumed a static and non-expanding universe.

A simple explanation can be shown for yourself through the expansion of a balloon.  Start by placing several dots at random distances and positions around a partially inflated balloon.  You can place them close together, far away from one another, or equidistant from dot to dot.  Next, continue to inflate the balloon.  Notice how the distance changes between objects that are near one another.  At first the distance changes slowly, then as the inflation continues the distance changes at a faster rate.  For dots further apart the initial expansion will be much quicker and continue at an ever increasing rate!  That is until the balloon pops.

So what did we observe?

In an expanding universe some positions in space travel further apart from one another at different rates.  This expansion is related to the lack of our bright sky, although it is important to note that this is not the sole reason for the lack of our bright sky.

Looking to be more illuminated on this topic?  Look for follow up posts coming later in the week as I continue to talk on the implications of an expanding universe and even give a solution for stellar density that would result in a bright sky at all periods of all days!

Best,

Josh