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How do we know the Universe is not infinite in size or time?
Week of June 22nd Question
I would like to start this week's Stump Me article with a thanks to all who are participating by submitting questions!
I would also like to encourage more people to participate. Although only having a handful of questions to select from
makes my job very easy, I would like to see a higher percentage of visitors participating, 1% is a low participation rate!
Anyway, lets get this thing started, I have avoided being stumped once more and hold a flawless record for two weeks
straight now (wooh).
The Universe is big, so big that trying to describe how big it is would be pointless. But the Universe isn't infinite in
size despite that it might as well be as far as we here on Earth are concerned. Just like we know that the Earth isn't
infinite we know our Universe isn't either. How though can we with authority say the Universe isn't infinite?
We can say Earth isn't infinite because we can travel around the globe and have pretty much mapped out the Earth in its
entiriety. We haven't traveled the whole Universe not even a fraction, so how can we assert such nonsense! The
Universe is also really old, but not infinitely old. The Universe did have a beginning we know this, but how?
The answer is actually sadly pretty simple. The night sky is the answer to the limited size and age of our Universe.
If the Universe were infinite in age then light from every star in the Universe would have had time to reach Earth
no matter what the distance. Also, if the Universe were infinite in size and had infinite stars then the night sky
would be filled with infinite light. Our night sky is dark and that is how we know that limits exist on our
impressive Universe.
More specifically, the brightness of a star decreases with the sqaure of distance from the source. However, if you
take the limit of infinite sources at varying distances you quickly realize the diminishing brightness can't overpower
infinity.
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