Ring Around the Universe - A Geometric Puzzler

stahrwe · Mon Aug 02, 2010 2:07 pm

It's been a while since I've done a puzzler, but it's hot out and a little light math always refreshes me so here goes.

For the poets here, don't abandon this just because it's math. All you need to know to solve this is the most rudamentary facts about circles and a tiny bit of algebra.

Suppose I was somehow able to wrap a rope around the universe so that it was just lieing on the edge of the universe all the way round. Now suppose I add 1 foot, (12 inches) to the lenghth of the rope and arrange it so that it is equally distant from the edge of the universe all the way round. How much space would there be between the edge of the universe and the rope?

froglipz · Mon Aug 02, 2010 5:50 pm

ummm 1.91 inches?

President Camacho · Tue Aug 03, 2010 5:28 am

hmm..

stahrwe · Tue Aug 03, 2010 7:39 am


	froglipz wrote: ummm 1.91 inches?

That was too easy wasn't it?

I always like this puzzler because it seems intuitively impossible.

BTW; you get the same answer whether you start with the universe or a soda can.

thanks for playing.

The solution is a simple comparison of two circles.

Circle 1 is the circumference of the universe, the forumla for which is 2pi(r)

Circle 2 is the circumference of the universe with an additional 12 inches added: 2pi(R)

But 2pi(R) is just 2pi(r) + 12

divide both sides by 2pi
and you get:

r + ~2inches.

froglipz · Tue Aug 03, 2010 11:29 am

I was stuck for a couple hours on the not knowing the dimensions of the universe part. Once that light dawned on me...

stahrwe · Tue Aug 03, 2010 12:14 pm


	froglipz wrote: I was stuck for a couple hours on the not knowing the dimensions of the universe part. Once that light dawned on me...

It was posed to me by an astronomy grad studment many years ago congrats on your solution!

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