1 00:00:00,560 --> 00:00:03,600 Speaker 1: Welcome to brain Stuff from how Stuff Works dot com 2 00:00:03,640 --> 00:00:07,800 Speaker 1: where smart happens. Join Josh and Chuck, the guys who 3 00:00:07,840 --> 00:00:09,920 Speaker 1: bring you stuff and should know, as they take a 4 00:00:09,960 --> 00:00:12,240 Speaker 1: trip around the world to help you get smarter in 5 00:00:12,240 --> 00:00:15,280 Speaker 1: a topsy turv economy. Check out the all new super 6 00:00:15,320 --> 00:00:18,560 Speaker 1: Stuff Guide to the Economy from house stuff Works dot com, 7 00:00:18,600 --> 00:00:25,040 Speaker 1: available now exclusively on iTunes. Hi Am Marshall Brain was 8 00:00:25,160 --> 00:00:28,840 Speaker 1: today's question. If you could spin a carousel fast enough 9 00:00:28,880 --> 00:00:31,680 Speaker 1: to get its rim moving at nearly the speed of light, 10 00:00:32,040 --> 00:00:36,239 Speaker 1: would time stand still for people on the carousel. At 11 00:00:36,320 --> 00:00:40,760 Speaker 1: least in the theoretical sense, this idea is reasonable. If 12 00:00:40,800 --> 00:00:43,519 Speaker 1: the carousel were spinning so that the outer edge of 13 00:00:43,520 --> 00:00:46,559 Speaker 1: the carousel moved at nearly the speed of light, then 14 00:00:46,720 --> 00:00:50,080 Speaker 1: time would appear to slow down for people on the carousel. 15 00:00:50,520 --> 00:00:54,000 Speaker 1: When the carousel writers looked out at the world spinning by, 16 00:00:54,080 --> 00:00:57,560 Speaker 1: the days would pass very quickly, so the people on 17 00:00:57,640 --> 00:01:01,160 Speaker 1: the carousel would age very slowly relative to people not 18 00:01:01,320 --> 00:01:05,360 Speaker 1: on the carousel. This would create essentially a time machine 19 00:01:05,400 --> 00:01:08,880 Speaker 1: that lets the passengers on the carousel travel into the future. 20 00:01:09,520 --> 00:01:13,200 Speaker 1: In a practical sense, this idea has problems because of 21 00:01:13,200 --> 00:01:17,200 Speaker 1: the centripetal force that the carousel would generate. Some of 22 00:01:17,200 --> 00:01:22,039 Speaker 1: the fastest rotating objects in existence today are high speed flywheels. 23 00:01:22,440 --> 00:01:26,640 Speaker 1: High speed flywheels float on magnetic bearings in a vacuum chamber, 24 00:01:26,959 --> 00:01:31,120 Speaker 1: so there's very nearly zero friction on them. These flywheels 25 00:01:31,120 --> 00:01:33,839 Speaker 1: are able to achieve speeds up to about two hundred 26 00:01:33,840 --> 00:01:38,160 Speaker 1: thousand rotations per minute. The main problem with flywheels running 27 00:01:38,160 --> 00:01:41,840 Speaker 1: this quickly comes in the form of rotor disintegration. The 28 00:01:41,959 --> 00:01:45,520 Speaker 1: outward forces on the rotor are huge. Even if you 29 00:01:45,560 --> 00:01:48,920 Speaker 1: assume that the flywheel has a twelve inch diameter running 30 00:01:48,960 --> 00:01:52,080 Speaker 1: at a million rpm, the outer edge of the flywheel 31 00:01:52,080 --> 00:01:54,880 Speaker 1: would be traveling at only about thirty four thousand miles 32 00:01:54,920 --> 00:01:58,000 Speaker 1: per hour, nowhere even close to the speed of light 33 00:01:58,080 --> 00:02:01,760 Speaker 1: at a hundred eighty six thousand mile per second. The 34 00:02:01,840 --> 00:02:05,440 Speaker 1: other option would be to create an extremely large carousel. 35 00:02:06,040 --> 00:02:09,400 Speaker 1: Say you built a ring as big as Earth's orbit, 36 00:02:09,880 --> 00:02:13,600 Speaker 1: or about a hundred eighties six million miles in diameter. 37 00:02:14,520 --> 00:02:17,080 Speaker 1: This ring would only have to spend at a rate 38 00:02:17,120 --> 00:02:20,799 Speaker 1: of about one revolution per hour compared to the Earth's 39 00:02:20,919 --> 00:02:24,800 Speaker 1: one revolution per year to achieve something near the speed 40 00:02:24,840 --> 00:02:28,720 Speaker 1: of light. Building this ring and then accelerating the entire thing, 41 00:02:28,760 --> 00:02:31,720 Speaker 1: of course, would be a big project. Do you have 42 00:02:31,760 --> 00:02:35,480 Speaker 1: any ideas or suggestions for this podcast? If so, please 43 00:02:35,480 --> 00:02:38,200 Speaker 1: send me an email at podcast at how stuff works 44 00:02:38,240 --> 00:02:41,320 Speaker 1: dot com. For more on this and thousands of other topics, 45 00:02:41,360 --> 00:02:45,280 Speaker 1: go to how stuff works dot com.