system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the universe being portrayed as dark when during day time (on Earth), everywhere appears bright. There are so many stars in the universe, shouldn't the "dark space" be filled with light?
gpt
This line of thinking is exactly what led to the Big Bang theory of cosmic evolution.  Scientists initially believed the Universe to be infinite and eternal, but if it was so then surely every line of sight in the sky should end on a star, and the night sky should be completely bright.  Therefore, the Universe must either have a boundary or some beginning point, and there can't have been stars forever just as there are now.  Remember that when you look out into space you are also looking back in time, because it takes light time to travel to Earth.  If you look far enough you find no stars or galaxies - the earliest light we see is the cosmic microwave background, emitted roughly 350,000 years after the Big Bang.  

Today, cosmologists think the Universe is infinite (or at least has no boundary) and it is well accepted that the Big Bang which created physics as we know it happened roughly 13.7 billion years ago.