WEBVTT 00:00:24.040 --> 00:00:31.520 Near a black hole space and time do some very strange things because the black holes are probably the most 00:00:31.520 --> 00:00:39.680 violent places we know of in the universe. This river provides a beautiful analogy of what happens 00:00:39.680 --> 00:00:43.080 to space and time as you get closer and closer to the black hole. 00:00:47.326 --> 00:00:51.692 Now upstream the water is flowing pretty slowly. 00:00:51.692 --> 00:00:55.040 Let's imagine it is flowing at three kilometers per hour 00:00:55.040 --> 00:01:01.483 and I can swim at 4, so I can swim faster than the flow and can easily escape 00:01:16.160 --> 00:01:19.360 But as you go further, further down the stream towards 00:01:19.360 --> 00:01:24.600 the waterfall in the distance, the river flows faster and faster. 00:01:43.178 --> 00:01:49.640 Imagine that I decided to jump in the river just there at the edge of the falls 00:01:49.640 --> 00:01:52.803 The water is flowing far faster than I could swim. 00:01:52.803 --> 00:01:57.055 So, no matter what I did, no matter how hard I tried 00:01:57.055 --> 00:01:59.788 I would not be able to swim back upstream 00:01:59.788 --> 00:02:05.360 I would be carried inextrably towards the edge and I would vanish over the falls 00:02:20.920 --> 00:02:24.228 Well, it's the same close to the black hole, 00:02:24.228 --> 00:02:28.646 because the space flows faster, faster and faster 00:02:28.646 --> 00:02:30.320 towards the black hole. 00:02:30.320 --> 00:02:36.280 Literally, this stuff, my space that I am in, flowing over the edge into the black hole. 00:02:36.280 --> 00:02:42.600 And then, a very special point, called an event horizon, the space is flowing 00:02:42.600 --> 00:02:46.240 at the speed of light into the black hole. 00:02:50.378 --> 00:02:57.637 Light itself, travelling at 3000km per second is not going fast enough to escape the flow 00:02:57.637 --> 00:03:01.280 and light itself will plunge into the black hole. 00:03:16.268 --> 00:03:23.080 Well, as you fall into the black hole, across the event horizon, then if you were going feet first, your feet will be 00:03:23.080 --> 00:03:27.840 accelerating faster than your head, so you'll be stretched 00:03:27.840 --> 00:03:31.209 and you'll be quite literally spaghettified 00:03:37.840 --> 00:03:40.972 Now as you get right into the center, 00:03:40.972 --> 00:03:43.920 Then our understanding of physics breaks down. 00:03:43.920 --> 00:03:47.760 Our best theory of space and time, Einstein's theory of general relativity 00:03:47.760 --> 00:03:51.720 says that space and time become infinitely curved, that 00:03:51.720 --> 00:03:56.440 the center of the hole becomes infinitely dense 00:03:56.440 --> 00:04:00.320 That place is called the singularity and it is the place 00:04:00.320 --> 00:04:06.123 where our understanding of the Universe stops.