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Question
If the size of the universe is infinite and the speed of light is constant, are there places light has not reached?
Asked by: Enzo
Answer
Despite a century of hard work by many great geniuses, the large-scale structure of the
universe is still not completely understood. Nevertheless, we can try to speculate
intelligently on the nature of the entire universe.
There are important observational facts which are not in dispute. When we look out as
far as possible with our best telescopes, we observe a universe which is homogeneous,
expanding according to Hubble's Law, and filled with cosmic microwave background
radiation. It is not known if the homogeneity we observe within about 12 billion
light-years of the earth extends all the way to infinity. If it does, then there is no
part of the universe which lacks light, matter, or galaxies. This means that the hot,
dense, big-bang beginning of our universe occurred everywhere throughout all of infinite
space. There was no empty place for light to travel to.
The universe has a finite age, so it is certainly true light has traveled only a finite
distance since the big-bang. Undoubtedly there are remote objects in the universe which
have sent light in our direction and that light has not yet arrived. Indeed, that light
may never arrive if the expansion rate of the universe does not slow down. Recent
evidence indicates the expansion rate of the universe is actually accelerating. This has
an army of cosmologists working overtime, trying to understand it. If the universe is
accelerating, then we will never get to see most of it. Even objects that we can now see
will disappear as they recede beyond the speed of light.
Answered by: Hugh Mongus, M.S., Retired teacher
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