| [00:01.48] |
Lesson 14 |
| [00:03.37] |
The Butterfly Effect |
| [00:12.92] |
Why do small errors make it impossible to predict the weather system with a high degree of accuracy? |
| [00:23.11] |
Beyond two or three days, the world's best weather forecasts are speculative, |
| [00:29.38] |
and beyond six or seven they are worthless. |
| [00:33.23] |
The Butterfly Effect is the reason. |
| [00:36.14] |
For small pieces of weather -- |
| [00:38.31] |
-- and to a global forecaster, small can mean thunderstorms and blizzards -- |
| [00:44.49] |
any prediction deteriorates rapidly. |
| [00:47.67] |
Errors and uncertainties multiply, cascading upward through a chain of turbulent features, |
| [00:54.17] |
from dust devils and squalls up to continent-size eddies that only satellites can see. |
| [01:02.68] |
The modern weather models work with a grid of points of the order of sixty miles apart, |
| [01:08.82] |
and even so, some starting data has to be guessed, |
| [01:13.27] |
since ground stations and satellites cannot see everywhere. |
| [01:18.28] |
But suppose the earth could be covered with sensors spaced one foot apart, |
| [01:23.92] |
rising at one-foot intervals all the way to the top of the atmosphere. |
| [01:29.24] |
Suppose every sensor gives perfectly accurate readings of temperature, |
| [01:34.60] |
pressure, humidity, and any other quantity a meteorologist would want. |
| [01:41.09] |
Precisely at noon an infinitely powerful computer takes all the data and calculates what will happen at each point |
| [01:48.75] |
at 12.01, then 12.02, then 12.03... |
| [01:56.86] |
The computer will still be unable to predict whether Princeton, New Jersey, will have sun or rain on a day one month away. |
| [02:06.64] |
At noon the spaces between the sensors will hide fluctuations that the computer will not know about, |
| [02:13.59] |
tiny deviations from the average. |
| [02:16.66] |
By 12.01, those fluctuations will already have created small errors one foot away. |
| [02:24.03] |
Soon the errors will have multiplied to the ten-foot scale, and so on up to the size of the globe. |
