[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.63,0:00:10.95,Default,,0000,0000,0000,,In 1977, the physicist Edward Purcell
Dialogue: 0,0:00:10.95,0:00:12.90,Default,,0000,0000,0000,,calculated that if you push a bacteria
Dialogue: 0,0:00:12.90,0:00:14.20,Default,,0000,0000,0000,,and then let go,
Dialogue: 0,0:00:14.20,0:00:16.95,Default,,0000,0000,0000,,it will stop in about a millionth of a second.
Dialogue: 0,0:00:16.95,0:00:18.99,Default,,0000,0000,0000,,In that time, it will have traveled less
Dialogue: 0,0:00:18.99,0:00:21.17,Default,,0000,0000,0000,,than the width of a single atom.
Dialogue: 0,0:00:21.17,0:00:23.20,Default,,0000,0000,0000,,The same holds true for a sperm
Dialogue: 0,0:00:23.20,0:00:24.66,Default,,0000,0000,0000,,and many other microbes.
Dialogue: 0,0:00:24.66,0:00:27.62,Default,,0000,0000,0000,,It all has to do with being really small.
Dialogue: 0,0:00:27.62,0:00:31.34,Default,,0000,0000,0000,,Microscopic creatures inhabit a world alien to us,
Dialogue: 0,0:00:31.34,0:00:32.70,Default,,0000,0000,0000,,where making it through an inch of water
Dialogue: 0,0:00:32.70,0:00:34.72,Default,,0000,0000,0000,,is an incredible endeavor.
Dialogue: 0,0:00:34.72,0:00:37.74,Default,,0000,0000,0000,,But why does size matter so much for a swimmer?
Dialogue: 0,0:00:37.74,0:00:39.36,Default,,0000,0000,0000,,What makes the world of a sperm
Dialogue: 0,0:00:39.36,0:00:40.76,Default,,0000,0000,0000,,so fundamentally different
Dialogue: 0,0:00:40.76,0:00:42.62,Default,,0000,0000,0000,,from that of a sperm whale?
Dialogue: 0,0:00:42.62,0:00:44.06,Default,,0000,0000,0000,,To find out, we need to dive in
Dialogue: 0,0:00:44.06,0:00:46.20,Default,,0000,0000,0000,,to the physics of fluids.
Dialogue: 0,0:00:46.20,0:00:47.96,Default,,0000,0000,0000,,Here's a way to think about it.
Dialogue: 0,0:00:47.96,0:00:49.86,Default,,0000,0000,0000,,Imagine you are swimming in a pool.
Dialogue: 0,0:00:49.86,0:00:52.62,Default,,0000,0000,0000,,It's you and a whole bunch of water molecules.
Dialogue: 0,0:00:52.62,0:00:54.36,Default,,0000,0000,0000,,Water molecules outnumber you
Dialogue: 0,0:00:54.36,0:00:57.15,Default,,0000,0000,0000,,a thousand trillion trillion to one.
Dialogue: 0,0:00:57.15,0:00:58.44,Default,,0000,0000,0000,,So, pushing past them
Dialogue: 0,0:00:58.44,0:01:00.53,Default,,0000,0000,0000,,with your gigantic body is easy,
Dialogue: 0,0:01:00.53,0:01:02.91,Default,,0000,0000,0000,,but if you were really small,
Dialogue: 0,0:01:02.91,0:01:04.63,Default,,0000,0000,0000,,say you were about the size of a water molecule,
Dialogue: 0,0:01:04.63,0:01:06.38,Default,,0000,0000,0000,,all of a sudden, it's like you're swimming
Dialogue: 0,0:01:06.38,0:01:07.96,Default,,0000,0000,0000,,in a pool of people.
Dialogue: 0,0:01:07.96,0:01:09.79,Default,,0000,0000,0000,,Rather than simply swishing by
Dialogue: 0,0:01:09.79,0:01:11.60,Default,,0000,0000,0000,,all the teeny, tiny molecules,
Dialogue: 0,0:01:11.60,0:01:13.56,Default,,0000,0000,0000,,now every single water molecule
Dialogue: 0,0:01:13.56,0:01:16.07,Default,,0000,0000,0000,,is like another person you have to push past
Dialogue: 0,0:01:16.07,0:01:17.74,Default,,0000,0000,0000,,to get anywhere.
Dialogue: 0,0:01:17.74,0:01:20.98,Default,,0000,0000,0000,,In 1883, the physicist Osborne Reynolds
Dialogue: 0,0:01:20.98,0:01:23.10,Default,,0000,0000,0000,,figured out that there is one simple number
Dialogue: 0,0:01:23.10,0:01:26.02,Default,,0000,0000,0000,,that can predict how a fluid will behave.
Dialogue: 0,0:01:26.02,0:01:27.48,Default,,0000,0000,0000,,It's called the Reynolds number,
Dialogue: 0,0:01:27.48,0:01:29.50,Default,,0000,0000,0000,,and it depends on simple properties
Dialogue: 0,0:01:29.50,0:01:31.24,Default,,0000,0000,0000,,like the size of the swimmer,
Dialogue: 0,0:01:31.24,0:01:32.53,Default,,0000,0000,0000,,its speed,
Dialogue: 0,0:01:32.53,0:01:33.60,Default,,0000,0000,0000,,the density of the fluid,
Dialogue: 0,0:01:33.60,0:01:35.65,Default,,0000,0000,0000,,and the stickiness, or the viscosity,
Dialogue: 0,0:01:35.65,0:01:36.90,Default,,0000,0000,0000,,of the fluid.
Dialogue: 0,0:01:36.90,0:01:38.74,Default,,0000,0000,0000,,What this means is that creatures
Dialogue: 0,0:01:38.74,0:01:40.74,Default,,0000,0000,0000,,of very different sizes inhabit
Dialogue: 0,0:01:40.74,0:01:42.74,Default,,0000,0000,0000,,vastly different worlds.
Dialogue: 0,0:01:42.74,0:01:44.71,Default,,0000,0000,0000,,For example, because of its huge size,
Dialogue: 0,0:01:44.71,0:01:46.11,Default,,0000,0000,0000,,a sperm whale inhabits
Dialogue: 0,0:01:46.11,0:01:48.38,Default,,0000,0000,0000,,the large Reynolds number world.
Dialogue: 0,0:01:48.38,0:01:50.13,Default,,0000,0000,0000,,If it flaps its tail once,
Dialogue: 0,0:01:50.13,0:01:52.51,Default,,0000,0000,0000,,it can coast ahead for an incredible distance.
Dialogue: 0,0:01:52.51,0:01:54.25,Default,,0000,0000,0000,,Meanwhile, sperm live
Dialogue: 0,0:01:54.25,0:01:56.21,Default,,0000,0000,0000,,in a low Reynolds number world.
Dialogue: 0,0:01:56.21,0:01:58.38,Default,,0000,0000,0000,,If a sperm were to stop flapping its tail,
Dialogue: 0,0:01:58.38,0:02:00.94,Default,,0000,0000,0000,,it wouldn't even coast past a single atom.
Dialogue: 0,0:02:00.94,0:02:03.10,Default,,0000,0000,0000,,To imagine what it would feel like to be a sperm,
Dialogue: 0,0:02:03.10,0:02:04.56,Default,,0000,0000,0000,,you need to bring yourself down
Dialogue: 0,0:02:04.56,0:02:06.01,Default,,0000,0000,0000,,to its Reynolds number.
Dialogue: 0,0:02:06.01,0:02:08.15,Default,,0000,0000,0000,,Picture yourself in a tub of molasses
Dialogue: 0,0:02:08.15,0:02:09.18,Default,,0000,0000,0000,,with your arms moving
Dialogue: 0,0:02:09.18,0:02:12.14,Default,,0000,0000,0000,,about as slow as the minute hand of a clock,
Dialogue: 0,0:02:12.14,0:02:13.60,Default,,0000,0000,0000,,and you'd have a pretty good idea
Dialogue: 0,0:02:13.60,0:02:15.61,Default,,0000,0000,0000,,of what a sperm is up against.
Dialogue: 0,0:02:15.61,0:02:17.85,Default,,0000,0000,0000,,So, how do microbes manage to get anywhere?
Dialogue: 0,0:02:17.85,0:02:20.19,Default,,0000,0000,0000,,Well, many don't bother swimming at all.
Dialogue: 0,0:02:20.19,0:02:22.80,Default,,0000,0000,0000,,They just let the food drift to them.
Dialogue: 0,0:02:22.80,0:02:24.02,Default,,0000,0000,0000,,This is somewhat like a lazy cow
Dialogue: 0,0:02:24.02,0:02:27.07,Default,,0000,0000,0000,,that waits for the grass under its mouth to grow back.
Dialogue: 0,0:02:27.07,0:02:29.04,Default,,0000,0000,0000,,But many microbes do swim,
Dialogue: 0,0:02:29.04,0:02:32.01,Default,,0000,0000,0000,,and this is where those incredible adaptations come in.
Dialogue: 0,0:02:32.01,0:02:33.47,Default,,0000,0000,0000,,One trick they can use
Dialogue: 0,0:02:33.47,0:02:35.83,Default,,0000,0000,0000,,is to deform the shape of their paddle.
Dialogue: 0,0:02:35.83,0:02:37.55,Default,,0000,0000,0000,,By cleverly flexing their paddle
Dialogue: 0,0:02:37.55,0:02:39.99,Default,,0000,0000,0000,,to create more drag on the power stroke
Dialogue: 0,0:02:39.99,0:02:41.42,Default,,0000,0000,0000,,than on the recovery stroke,
Dialogue: 0,0:02:41.42,0:02:44.94,Default,,0000,0000,0000,,single-celled organisms like paramecia
Dialogue: 0,0:02:44.94,0:02:45.52,Default,,0000,0000,0000,,manage to inch their way
Dialogue: 0,0:02:45.52,0:02:47.72,Default,,0000,0000,0000,,through the crowd of water molecules.
Dialogue: 0,0:02:47.72,0:02:49.78,Default,,0000,0000,0000,,But there's an even more ingenious solution
Dialogue: 0,0:02:49.78,0:02:52.50,Default,,0000,0000,0000,,arrived at by bacteria and sperm.
Dialogue: 0,0:02:52.50,0:02:54.90,Default,,0000,0000,0000,,Instead of wagging their paddles back and forth,
Dialogue: 0,0:02:54.90,0:02:57.36,Default,,0000,0000,0000,,they wind them like a cork screw.
Dialogue: 0,0:02:57.36,0:02:59.21,Default,,0000,0000,0000,,Just as a cork screw on a wine bottle
Dialogue: 0,0:02:59.21,0:03:01.99,Default,,0000,0000,0000,,converts winding motion into forward motion,
Dialogue: 0,0:03:01.99,0:03:04.83,Default,,0000,0000,0000,,these tiny creatures spin their helical tails
Dialogue: 0,0:03:04.83,0:03:06.63,Default,,0000,0000,0000,,to push themselves forward
Dialogue: 0,0:03:06.63,0:03:10.26,Default,,0000,0000,0000,,in a world where water feels as thick as cork.
Dialogue: 0,0:03:10.26,0:03:12.51,Default,,0000,0000,0000,,Other strategies are even stranger.
Dialogue: 0,0:03:12.51,0:03:14.53,Default,,0000,0000,0000,,Some bacteria take Batman's approach.
Dialogue: 0,0:03:14.53,0:03:17.25,Default,,0000,0000,0000,,They use grappling hooks to pull themselves along.
Dialogue: 0,0:03:17.25,0:03:18.81,Default,,0000,0000,0000,,They can even use this grappling hook
Dialogue: 0,0:03:18.81,0:03:21.77,Default,,0000,0000,0000,,like a sling shot and fling themselves forward.
Dialogue: 0,0:03:21.77,0:03:24.22,Default,,0000,0000,0000,,Others use chemical engineering.
Dialogue: 0,0:03:24.22,0:03:27.51,Default,,0000,0000,0000,,H. pylori lives only in the slimy, acidic mucus
Dialogue: 0,0:03:27.51,0:03:29.99,Default,,0000,0000,0000,,inside our stomachs.
Dialogue: 0,0:03:29.99,0:03:30.40,Default,,0000,0000,0000,,It releases a chemical
Dialogue: 0,0:03:30.40,0:03:32.72,Default,,0000,0000,0000,,that thins out the surrounding mucus,
Dialogue: 0,0:03:32.72,0:03:34.67,Default,,0000,0000,0000,,allowing it to glide through slime.
Dialogue: 0,0:03:34.67,0:03:35.68,Default,,0000,0000,0000,,Maybe it's no surprise
Dialogue: 0,0:03:35.68,0:03:37.15,Default,,0000,0000,0000,,that these guys are also responsible
Dialogue: 0,0:03:37.15,0:03:39.06,Default,,0000,0000,0000,,for stomach ulcers.
Dialogue: 0,0:03:39.06,0:03:41.28,Default,,0000,0000,0000,,So, when you look really, really closely
Dialogue: 0,0:03:41.28,0:03:42.98,Default,,0000,0000,0000,,at our bodies and the world around us,
Dialogue: 0,0:03:42.98,0:03:45.11,Default,,0000,0000,0000,,you can see all sorts of tiny creatures
Dialogue: 0,0:03:45.11,0:03:47.12,Default,,0000,0000,0000,,finding clever ways to get around
Dialogue: 0,0:03:47.12,0:03:48.78,Default,,0000,0000,0000,,in a sticky situation.
Dialogue: 0,0:03:48.78,0:03:50.12,Default,,0000,0000,0000,,Without these adaptations,
Dialogue: 0,0:03:50.12,0:03:52.63,Default,,0000,0000,0000,,bacteria would never find their hosts,
Dialogue: 0,0:03:52.63,0:03:55.38,Default,,0000,0000,0000,,and sperms would never make it to their eggs,
Dialogue: 0,0:03:55.38,0:03:57.55,Default,,0000,0000,0000,,which means you would never get stomach ulcers,
Dialogue: 0,0:03:57.55,0:04:00.71,Default,,0000,0000,0000,,but you would also never be born in the first place.