WEBVTT - How big is the universe?

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<v Speaker 1>Welcome to brain Stuff from how Stuff works dot com

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<v Speaker 1>com slash brain Stuff today for details. I am Marshall

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<v Speaker 1>brain with today's question. If we were to move all

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<v Speaker 1>of the matter in the universe into one corner, how

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<v Speaker 1>much space would it take up. It's hard to answer

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<v Speaker 1>this question exactly because there are some unknowns, but if

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<v Speaker 1>you're willing to accept three assumptions, we can come up

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<v Speaker 1>with an answer that at least sounds reasonable. The first

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<v Speaker 1>question is how big is the universe. No one knows,

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<v Speaker 1>but based on observations, we might guess that it's a

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<v Speaker 1>sphere that's thirty billion light years across. That means that

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<v Speaker 1>the whole universe contains about ten to the thirty second

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<v Speaker 1>power cubic light years. It's incredibly big. The next question

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<v Speaker 1>is how much matter does the universe contain. The mass

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<v Speaker 1>of the universe is a source of debate right now,

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<v Speaker 1>because there's no easy way to put the universe on

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<v Speaker 1>a scale NASA estimates that it's about ten to the

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<v Speaker 1>sixtims for the whole thing. Other estimates give other numbers,

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<v Speaker 1>but they're all in that same ballpark. The next question

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<v Speaker 1>is what density do you want to assume that the

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<v Speaker 1>mass will have once you push it all into one corner.

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<v Speaker 1>If you were to really do this, if you actually

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<v Speaker 1>didn't move all of the mass of the universe into

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<v Speaker 1>one corner, it would condense into a black hole. But

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<v Speaker 1>let's say that you could keep it from doing that,

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<v Speaker 1>and you were somehow able to keep all the mass

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<v Speaker 1>evenly distributed at a density of the sun. If you

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<v Speaker 1>are willing to accept these three assumptions, then all of

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<v Speaker 1>the matter in the universe would fit into about one

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<v Speaker 1>billion cubic light years, or a cube that's approximately a

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<v Speaker 1>thousand light years on each side. Compared to the size

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<v Speaker 1>of the universe, that's tiny. Imagine a despec Compared to

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<v Speaker 1>Planet Earth. The universe is an incredibly empty place. Do

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<v Speaker 1>you have any ideas or suggestions for this podcast? If so,

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<v Speaker 1>please send me an email at podcast at how stuff

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<v Speaker 1>works dot com. For more on this and thousands of

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<v Speaker 1>other topics, go to how stuff works dot com.