[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.54,0:00:09.96,Default,,0000,0000,0000,,Space: it's where things happen.
Dialogue: 0,0:00:09.96,0:00:12.58,Default,,0000,0000,0000,,Time: it's when things happen.
Dialogue: 0,0:00:12.58,0:00:14.32,Default,,0000,0000,0000,,We can measure where things are
Dialogue: 0,0:00:14.32,0:00:15.66,Default,,0000,0000,0000,,and when things take place,
Dialogue: 0,0:00:15.66,0:00:17.16,Default,,0000,0000,0000,,but in modern physics,
Dialogue: 0,0:00:17.16,0:00:18.99,Default,,0000,0000,0000,,we realize when and where
Dialogue: 0,0:00:18.99,0:00:22.47,Default,,0000,0000,0000,,are actually part of the same question.
Dialogue: 0,0:00:22.47,0:00:24.68,Default,,0000,0000,0000,,Because when it comes to understanding the universe,
Dialogue: 0,0:00:24.68,0:00:28.06,Default,,0000,0000,0000,,we need to replace three-dimensional space plus time
Dialogue: 0,0:00:28.06,0:00:29.85,Default,,0000,0000,0000,,with a single concept:
Dialogue: 0,0:00:29.85,0:00:33.64,Default,,0000,0000,0000,,four-dimensional space-time.
Dialogue: 0,0:00:33.64,0:00:35.77,Default,,0000,0000,0000,,We'll explore and explain space-time
Dialogue: 0,0:00:35.77,0:00:38.27,Default,,0000,0000,0000,,in this series of animations.
Dialogue: 0,0:00:38.27,0:00:39.23,Default,,0000,0000,0000,,Animations?
Dialogue: 0,0:00:39.23,0:00:40.32,Default,,0000,0000,0000,,Yeah.
Dialogue: 0,0:00:40.32,0:00:42.52,Default,,0000,0000,0000,,Well, we're not very animated are we?
Dialogue: 0,0:00:42.52,0:00:46.86,Default,,0000,0000,0000,,Sure we are! Look, I can go from here to here.
Dialogue: 0,0:00:46.86,0:00:48.66,Default,,0000,0000,0000,,Whoa! How'd you get from here to there?
Dialogue: 0,0:00:48.66,0:00:50.02,Default,,0000,0000,0000,,How fast did you go?
Dialogue: 0,0:00:50.02,0:00:51.69,Default,,0000,0000,0000,,Did you run? Walk?
Dialogue: 0,0:00:51.69,0:00:53.36,Default,,0000,0000,0000,,Did you even go in a straight line?
Dialogue: 0,0:00:53.36,0:00:57.11,Default,,0000,0000,0000,,Ah! To answer that, you'll need to make our cartoon physics
Dialogue: 0,0:00:57.11,0:00:59.54,Default,,0000,0000,0000,,look more like physics physics.
Dialogue: 0,0:00:59.54,0:01:02.11,Default,,0000,0000,0000,,You'll need more panels.
Dialogue: 0,0:01:02.11,0:01:05.30,Default,,0000,0000,0000,,More panels, please!
Dialogue: 0,0:01:05.30,0:01:10.10,Default,,0000,0000,0000,,Okay, in each panel, Andrew's in a slightly different place.
Dialogue: 0,0:01:10.10,0:01:11.98,Default,,0000,0000,0000,,So I can see each one records
Dialogue: 0,0:01:11.98,0:01:14.89,Default,,0000,0000,0000,,where Andrew is at a different time.
Dialogue: 0,0:01:14.89,0:01:18.98,Default,,0000,0000,0000,,That's great. But it would be easier to see
Dialogue: 0,0:01:18.98,0:01:20.44,Default,,0000,0000,0000,,what's going on if we could cut out
Dialogue: 0,0:01:20.44,0:01:22.77,Default,,0000,0000,0000,,all the hundreds of panels and stack them up
Dialogue: 0,0:01:22.77,0:01:26.07,Default,,0000,0000,0000,,like a flip book.
Dialogue: 0,0:01:26.07,0:01:28.16,Default,,0000,0000,0000,,Right, now let's flip through the book
Dialogue: 0,0:01:28.16,0:01:30.61,Default,,0000,0000,0000,,so that we can see one panel after another
Dialogue: 0,0:01:30.61,0:01:34.36,Default,,0000,0000,0000,,getting through 24 in every second.
Dialogue: 0,0:01:34.36,0:01:36.44,Default,,0000,0000,0000,,See! I told you it was an animation.
Dialogue: 0,0:01:36.44,0:01:39.38,Default,,0000,0000,0000,,Now you can see me walking along.
Dialogue: 0,0:01:39.38,0:01:42.05,Default,,0000,0000,0000,,Drawing all those panels and putting them into a flip book
Dialogue: 0,0:01:42.05,0:01:45.76,Default,,0000,0000,0000,,is just one way of recording the way I'm moving.
Dialogue: 0,0:01:45.76,0:01:49.77,Default,,0000,0000,0000,,It's how animation, or even movies, work.
Dialogue: 0,0:01:49.77,0:01:52.35,Default,,0000,0000,0000,,As it turns out, at my walking speed,
Dialogue: 0,0:01:52.35,0:01:55.69,Default,,0000,0000,0000,,it takes two seconds to get past each fence post,
Dialogue: 0,0:01:55.69,0:01:58.52,Default,,0000,0000,0000,,and they're spaced four meters apart.
Dialogue: 0,0:01:58.52,0:02:00.48,Default,,0000,0000,0000,,So we can calculate my velocity --
Dialogue: 0,0:02:00.48,0:02:02.48,Default,,0000,0000,0000,,how fast I'm moving through space - -
Dialogue: 0,0:02:02.48,0:02:05.48,Default,,0000,0000,0000,,is two meters per second.
Dialogue: 0,0:02:05.48,0:02:08.24,Default,,0000,0000,0000,,But I could've worked that out from the panels
Dialogue: 0,0:02:08.24,0:02:11.16,Default,,0000,0000,0000,,without flipping through them.
Dialogue: 0,0:02:11.16,0:02:12.49,Default,,0000,0000,0000,,From the edge of the flip book,
Dialogue: 0,0:02:12.49,0:02:14.61,Default,,0000,0000,0000,,you can see all of the copies of the fence posts
Dialogue: 0,0:02:14.61,0:02:16.44,Default,,0000,0000,0000,,and all of the copies of Andrew
Dialogue: 0,0:02:16.44,0:02:20.12,Default,,0000,0000,0000,,and he's in a slightly different place in each one.
Dialogue: 0,0:02:20.12,0:02:23.23,Default,,0000,0000,0000,,Now we can predict everything that will happen to Andrew
Dialogue: 0,0:02:23.23,0:02:26.78,Default,,0000,0000,0000,,when we flip through 24 pages every second,
Dialogue: 0,0:02:26.78,0:02:28.13,Default,,0000,0000,0000,,including his speed of motion,
Dialogue: 0,0:02:28.13,0:02:30.34,Default,,0000,0000,0000,,just by looking.
Dialogue: 0,0:02:30.34,0:02:33.39,Default,,0000,0000,0000,,No need to flip through at all.
Dialogue: 0,0:02:33.39,0:02:34.64,Default,,0000,0000,0000,,The edge of this flip book
Dialogue: 0,0:02:34.64,0:02:37.70,Default,,0000,0000,0000,,is known as a space-time diagram
Dialogue: 0,0:02:37.70,0:02:40.07,Default,,0000,0000,0000,,of Andrew's journey through, you guessed it,
Dialogue: 0,0:02:40.07,0:02:42.07,Default,,0000,0000,0000,,space and time.
Dialogue: 0,0:02:42.07,0:02:45.15,Default,,0000,0000,0000,,We call the line that represents Andrew's journey
Dialogue: 0,0:02:45.15,0:02:47.51,Default,,0000,0000,0000,,his world line.
Dialogue: 0,0:02:47.51,0:02:49.86,Default,,0000,0000,0000,,If i jog instead of walking,
Dialogue: 0,0:02:49.86,0:02:54.45,Default,,0000,0000,0000,,I might be able to get past a fence post every second.
Dialogue: 0,0:02:54.45,0:02:56.04,Default,,0000,0000,0000,,He's not very athletic.
Dialogue: 0,0:02:56.04,0:02:59.21,Default,,0000,0000,0000,,Anyway, when we look at this new flip book from the edge,
Dialogue: 0,0:02:59.21,0:03:02.26,Default,,0000,0000,0000,,we can do the same analysis as before.
Dialogue: 0,0:03:02.26,0:03:03.84,Default,,0000,0000,0000,,The world line for Andrew jogging
Dialogue: 0,0:03:03.84,0:03:05.30,Default,,0000,0000,0000,,is more tilted over
Dialogue: 0,0:03:05.30,0:03:07.76,Default,,0000,0000,0000,,than the world line for Andrew walking.
Dialogue: 0,0:03:07.76,0:03:10.93,Default,,0000,0000,0000,,We can tell he's going twice as fast as before
Dialogue: 0,0:03:10.93,0:03:14.40,Default,,0000,0000,0000,,without flipping the panels.
Dialogue: 0,0:03:14.40,0:03:16.64,Default,,0000,0000,0000,,But here's the clever bit.
Dialogue: 0,0:03:16.64,0:03:20.36,Default,,0000,0000,0000,,In physics, it's always good to view things from other perspectives.
Dialogue: 0,0:03:20.36,0:03:22.23,Default,,0000,0000,0000,,After all, the laws of physics
Dialogue: 0,0:03:22.23,0:03:23.86,Default,,0000,0000,0000,,should be the same for everyone
Dialogue: 0,0:03:23.86,0:03:26.28,Default,,0000,0000,0000,,or no one will obey them.
Dialogue: 0,0:03:26.28,0:03:29.07,Default,,0000,0000,0000,,So let's rethink our cartoon
Dialogue: 0,0:03:29.07,0:03:31.65,Default,,0000,0000,0000,,and have the camera follow Andrew jogging along
Dialogue: 0,0:03:31.65,0:03:35.24,Default,,0000,0000,0000,,as the fence posts approach and pass behind him.
Dialogue: 0,0:03:35.24,0:03:37.78,Default,,0000,0000,0000,,Still viewing it as a flip book of panels,
Dialogue: 0,0:03:37.78,0:03:39.78,Default,,0000,0000,0000,,we don't need to redraw anything.
Dialogue: 0,0:03:39.78,0:03:42.83,Default,,0000,0000,0000,,We simply move all of the cutout frames slightly
Dialogue: 0,0:03:42.83,0:03:45.11,Default,,0000,0000,0000,,until Andrew's tilted world line
Dialogue: 0,0:03:45.11,0:03:48.00,Default,,0000,0000,0000,,becomes completely vertical.
Dialogue: 0,0:03:48.00,0:03:50.70,Default,,0000,0000,0000,,To see why, let's flip it.
Dialogue: 0,0:03:50.70,0:03:54.42,Default,,0000,0000,0000,,Yes, now I'm stationery, just jogging on the spot,
Dialogue: 0,0:03:54.42,0:03:56.05,Default,,0000,0000,0000,,in the center of the panel.
Dialogue: 0,0:03:56.05,0:03:57.55,Default,,0000,0000,0000,,On the edge of the flip book,
Dialogue: 0,0:03:57.55,0:04:00.36,Default,,0000,0000,0000,,my world line was going straight upwards.
Dialogue: 0,0:04:00.36,0:04:03.03,Default,,0000,0000,0000,,The fence posts are coming past me.
Dialogue: 0,0:04:03.03,0:04:06.31,Default,,0000,0000,0000,,It's now their world lines that are tilted.
Dialogue: 0,0:04:06.31,0:04:09.44,Default,,0000,0000,0000,,This rearrangement of the panels is known as a
Dialogue: 0,0:04:09.44,0:04:11.65,Default,,0000,0000,0000,,Galilean transformation,
Dialogue: 0,0:04:11.65,0:04:16.24,Default,,0000,0000,0000,,and it lets us analyze physics from someeone else's perspective.
Dialogue: 0,0:04:16.24,0:04:18.57,Default,,0000,0000,0000,,In this case, mine.
Dialogue: 0,0:04:18.57,0:04:21.94,Default,,0000,0000,0000,,After all, it's always good to see things from other points of view,
Dialogue: 0,0:04:21.94,0:04:24.69,Default,,0000,0000,0000,,especially when the viewers are moving
Dialogue: 0,0:04:24.69,0:04:26.69,Default,,0000,0000,0000,,at different speeds.
Dialogue: 0,0:04:26.69,0:04:30.53,Default,,0000,0000,0000,,So long as the speeds aren't too high.
Dialogue: 0,0:04:30.53,0:04:33.28,Default,,0000,0000,0000,,If you're a cosmic ray moving at the speed of light,
Dialogue: 0,0:04:33.28,0:04:38.03,Default,,0000,0000,0000,,our flip book of your point of view falls apart.
Dialogue: 0,0:04:38.03,0:04:39.80,Default,,0000,0000,0000,,To stop that from happening,
Dialogue: 0,0:04:39.80,0:04:42.14,Default,,0000,0000,0000,,we'll have to glue panels together.
Dialogue: 0,0:04:42.14,0:04:44.61,Default,,0000,0000,0000,,Instead of a stack of separate panels,
Dialogue: 0,0:04:44.61,0:04:47.98,Default,,0000,0000,0000,,we'll need a solid block of space-time,
Dialogue: 0,0:04:47.98,0:04:50.69,Default,,0000,0000,0000,,which we'll come to in the next animation.