WEBVTT - What would happen on a carousel moving at the speed of light?

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

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<v Speaker 1>Stuff Guide to the Economy from house stuff Works dot com,

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<v Speaker 1>available now exclusively on iTunes. Hi Am Marshall Brain was

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<v Speaker 1>today's question. If you could spin a carousel fast enough

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<v Speaker 1>to get its rim moving at nearly the speed of light,

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<v Speaker 1>would time stand still for people on the carousel. At

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<v Speaker 1>least in the theoretical sense, this idea is reasonable. If

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<v Speaker 1>the carousel were spinning so that the outer edge of

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<v Speaker 1>the carousel moved at nearly the speed of light, then

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<v Speaker 1>time would appear to slow down for people on the carousel.

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<v Speaker 1>When the carousel writers looked out at the world spinning by,

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<v Speaker 1>the days would pass very quickly, so the people on

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<v Speaker 1>the carousel would age very slowly relative to people not

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<v Speaker 1>on the carousel. This would create essentially a time machine

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<v Speaker 1>that lets the passengers on the carousel travel into the future.

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<v Speaker 1>In a practical sense, this idea has problems because of

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<v Speaker 1>the centripetal force that the carousel would generate. Some of

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<v Speaker 1>the fastest rotating objects in existence today are high speed flywheels.

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<v Speaker 1>High speed flywheels float on magnetic bearings in a vacuum chamber,

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<v Speaker 1>so there's very nearly zero friction on them. These flywheels

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<v Speaker 1>are able to achieve speeds up to about two hundred

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<v Speaker 1>thousand rotations per minute. The main problem with flywheels running

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<v Speaker 1>this quickly comes in the form of rotor disintegration. The

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<v Speaker 1>outward forces on the rotor are huge. Even if you

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<v Speaker 1>assume that the flywheel has a twelve inch diameter running

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<v Speaker 1>at a million rpm, the outer edge of the flywheel

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<v Speaker 1>would be traveling at only about thirty four thousand miles

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<v Speaker 1>per hour, nowhere even close to the speed of light

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<v Speaker 1>at a hundred eighty six thousand mile per second. The

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<v Speaker 1>other option would be to create an extremely large carousel.

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<v Speaker 1>Say you built a ring as big as Earth's orbit,

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<v Speaker 1>or about a hundred eighties six million miles in diameter.

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<v Speaker 1>This ring would only have to spend at a rate

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<v Speaker 1>of about one revolution per hour compared to the Earth's

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<v Speaker 1>one revolution per year to achieve something near the speed

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<v Speaker 1>of light. Building this ring and then accelerating the entire thing,

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<v Speaker 1>of course, would be a big project. Do you have

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

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

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<v Speaker 1>dot com. For more on this and thousands of other topics,

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