As a person with a general interest in astronomy, can you still make an observation that makes a profound contribution towards understanding the nature of the universe? Yes, absolutely!
All you need to do is to go out at night and look at the stars (and then step inside and decorate your Christmas tree).
What do you notice? The sky is really dark at night, very dark, and is speckled by stars here and there. As an analogy, imagine stringing a Christmas tree with lights, darkening the room, and then turning on those lights. What would you see? Would it not also be a whole lot of darkness punctuated by a few dozen lights seemingly suspended in space?
Filled with holiday spirit, imagine now stringing the tree with lights, followed by the ceiling, the walls, the floor and the furniture as well. Then when you turned on the lights in darkened room what would you see? Of course you would see only piercingly bright lights and no sign of darkness at all.
So, why do we not see piercingly bright lights at night? After all, a fine first assumption to make is that the universe is infinite in size and has existed for all time. If true, then there should be so many stars in the sky all at different distances and of different ages such that in sum total all those stars filling the infinite universe should appear to fill the whole sky up with starlight.
In this case there would be no darkness at all at night, and our sky would be piercingly bright just like the result of the overzealous Christmas decorator. So again, why is it dark at night? This problem has worried people for centuries, and has come to be known as Olber’s Paradox.
In next week’s blog we will see how the simple observational fact that the sky is dark at night will make us test our assumptions that the universe is infinite in extent and age.
