OK, so the universe is probably infinite, there’s stars in every direction, and stars are super bright!
So, why isn’t it basically daylight all the time? I mean, there must only be brightness not black.
It’s an interesting question, “why is space black?” Well fortunately, the question was first asked by German Astronomer Heinrich Wilhelm Olbers in 1823. It’s known as Olber’s Paradox, and states that if the universe is infinite, static, and timeless, then the night sky should be lousy with stars.
Ergo, the universe isn’t static and there must be stars that are so far away and their light just hasn’t had time to reach us yet. So, if we give it billions more years will we eventually be able to tan at midnight?
Don’t hold out too many hopes, because Hubble’s discovery of universal expansion also means that the farther away something is, the faster the space between it and us is stretching out. After a huge enough distance, space will be stretching out faster than light can close the gap.
There’s another facet to the paradox though. Well, if the universe is all expanding away from everything else. It stands to reason that if you go far back enough, it was all clumped together. This is where the theory of the Big Bang comes in.
However, if there was a bright instantaneous flash of existence that happened literally everywhere, shouldn’t we be able to see that too? Again, the riddle is solved by the expansion of space.
In 1964 Arno Penzias and Robert Wilson were working on a totally unrelated experiment with a radio telescope and they couldn’t shake this weird, unwanted static. After making sure everything was functioning correctly, even cleaning the inside of the antennae for bird droppings for hours. They realized that the signal was coming from everywhere, and you can’t stop the signal. They concluded that the Cosmic Microwave Background Radiation must have been the light from the Big Bang, but had been stretched out after billions of years until it was low-energy microwaves that our eyes can’t see.
Boom, and the universe makes sense again!