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How Large is the Earth Compared to the Universe?
or, Using the Earth to build a Road to Pluto.

         Let's start with how big the Earth is. Well, the average diameter of the Earth is 7926 miles, which gives it a radius of 3963 miles and a volume of 261 billion cubic miles of Earth earth (see arithmetic in the last paragraph). Is that a lot of stuff compared to the Universe? You wouldn't think so, but let's take a closer look.

         It's convenient to use light as a measuring stick to consider this question ("consider" comes from con-, with + sidus, sideris, a star; hence consider means "with or of a star"). Light travels 186,000 miles in one second. We can then speak of "light-seconds," "light-minutes," "light-hours," and "light years" as the distance light travels in each of those time intervals. So the Earth is 1/24th of a light-second in diameter, the Moon is just over a light-second away, the Sun 8 light-minutes away, and Pluto, the outermost planet in our solar system, is 4 to 7 light-hours distant depending on what part of its very elliptical orbit it's in.

         The nearest star is 4.2 light years (25 trillion miles) away, the Milky Way galaxy is about 100,000 light years in diameter, and the Universe is currently thought to be 27.4 billion light years across (or 13.7 billion years old, same thing since it started with a Big Bang. So the Universe is immensely vast compared to the size of the Earth: 27.4 billion light years compared to 1/24th of a light-second. That's a ratio of 219 to 1, or twenty million trillion to one! The US national debt as of March22, 2014, was $17.5 trillion. So the diameter of the universe compared to the diameter of the Earth is about the same as comparing more than 1 million times our national debt to $1.

         Suppose you used the Earth's earth to build a road, let's say one foot thick and twelve feet wide. Could you build a road to Pluto using the Earth's earth, or maybe even to the nearest star? Remember that the Earth is 1/24th of a light-second in diameter, compared to the nearest star, which is more than four light years away! Amazingly enough, it turns out that using the Earth's earth you could build a road 12 feet wide and one foot thick across the entire Milky Way galaxy; that's right, that road, built out of all the Earth's earth, would be 100,000 light years long! It's stunning how much stuff there is in our little ol' Earth.

         Now suppose the Earth were composed of ductile steel so that it could be drawn out into a wire. And let's say that the wire we would draw the Earth out into would be about as thick as pencil lead. How long do you think a wire made out of this steel-Earth would be? Believe it or not, such an Earth-wire would stretch across the entire universe AND back again! 261 billion cubic miles of Earth goes a long way. Think of the long-distance call you could make on such a wire: a call to the end of the universe and to the beginning of time!

         For those who want top check the arithmetic (for the wire, anyway): the Earth's volume, by 4/3 x pi x r3 for the volume of a sphere, is 4/3x3.14x(7926/2)3 = 2.61x1011 (or 261 billion) cubic miles = 2.61x1011x(5280x12)3 cubic inches = 6.63x1025 in3 --> the Earth could be drawn out to a 1/16" diameter wire 6.63x1025/[3.1416x(1/32)2] inches long = 2.16x1028 inches at pencil-lead thickness. Since there are 3600x24x365.24 = 31.557 million seconds in a year, and light travels 186,282 miles per second, there are 186,282x31.557x107 = 5.88 trillion miles in a light year. Thus 2.16x1028 inches at pencil-lead thickness = 2.16x1028/(5.88x1012x5280x12) = 5.8x1010 = 58 billion light-years at pencil-lead thickness. And since the universe is only 27.4 billion light years across, this pencil-lead-thick Earth-wire would be more than twice the diameter of the entire universe!


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Carl Woebcke: Compare the Sizes of the Earth and the Universe, 1991-2017. All rights reserved.