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

If you could spin a carousel fast enough, would time stand still for the people on the carousel? Theoretically, it's a reasonable assumption. Join Marshall Brain as he breaks down the speed of light and time in this podcast from HowStuffWorks.com.

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Episode Transcript

Speaker 1 (00:00):
Welcome to brain Stuff from how Stuff Works dot com
where smart happens. Join Josh and Chuck, the guys who
bring you stuff and should know, as they take a
trip around the world to help you get smarter in
a topsy turv economy. Check out the all new super
Stuff Guide to the Economy from house stuff Works dot com,
available now exclusively on iTunes. Hi Am Marshall Brain was

(00:25):
today's question. If you could spin a carousel fast enough
to get its rim moving at nearly the speed of light,
would time stand still for people on the carousel. At
least in the theoretical sense, this idea is reasonable. If
the carousel were spinning so that the outer edge of
the carousel moved at nearly the speed of light, then

(00:46):
time would appear to slow down for people on the carousel.
When the carousel writers looked out at the world spinning by,
the days would pass very quickly, so the people on
the carousel would age very slowly relative to people not
on the carousel. This would create essentially a time machine
that lets the passengers on the carousel travel into the future.

(01:09):
In a practical sense, this idea has problems because of
the centripetal force that the carousel would generate. Some of
the fastest rotating objects in existence today are high speed flywheels.
High speed flywheels float on magnetic bearings in a vacuum chamber,
so there's very nearly zero friction on them. These flywheels

(01:31):
are able to achieve speeds up to about two hundred
thousand rotations per minute. The main problem with flywheels running
this quickly comes in the form of rotor disintegration. The
outward forces on the rotor are huge. Even if you
assume that the flywheel has a twelve inch diameter running
at a million rpm, the outer edge of the flywheel

(01:52):
would be traveling at only about thirty four thousand miles
per hour, nowhere even close to the speed of light
at a hundred eighty six thousand mile per second. The
other option would be to create an extremely large carousel.
Say you built a ring as big as Earth's orbit,
or about a hundred eighties six million miles in diameter.

(02:14):
This ring would only have to spend at a rate
of about one revolution per hour compared to the Earth's
one revolution per year to achieve something near the speed
of light. Building this ring and then accelerating the entire thing,
of course, would be a big project. Do you have
any ideas or suggestions for this podcast? If so, please

(02:35):
send me an email at podcast at how stuff works
dot com. For more on this and thousands of other topics,
go to how stuff works dot com.