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Glossary

Machine learning

Machine learning is a way of getting computers to learn from examples instead of fixed rules. A model finds patterns in lots of data on its own and uses them for new cases.

With machine learning, nobody writes out all the rules of a program. Instead, the computer is given many examples and finds the patterns itself. You can compare it to how a child learns what a dog is: not from a definition, but by seeing a great many dogs.

How does it work?

It starts with training data: a large collection of examples, such as photos with the right name attached, or weather maps from the past. A model, often a neural network, makes a prediction. It checks how far off it was and adjusts small settings within itself, the parameters. This repeats millions of times, until the predictions are good enough. A neural network has many layers of such settings. When a network has many layers, we speak of deep learning.

After training, you use the model on new cases it has never seen. It can do more than just recognise things: language models predict the next piece of text, and other models can design images, proteins or materials.

Why it matters

Almost all the AI that makes the news is machine learning. The idea is older than you might think: as early as 1950, Alan Turing proposed building not an adult mind but a childlike machine that you bring up. In doing so he wanted to replace the question of whether machines can think with a test: can an interrogator, using a teleprinter, tell a machine from a human (link)?

Today AI learns from the most varied kinds of data. Researchers at Microsoft, MIT and the European weather centre ECMWF, among others, taught a computer to recognise and correct the fixed errors of weather models. As a result, forecasts two to six weeks ahead get considerably better (link). Chinese researchers did very different work: they trained a model on nearly four million fossils. That mapped the history of life in unprecedented detail, and it suggests that three of the five great mass extinctions unfolded more gradually than thought. Other palaeontologists are somewhat more cautious (link). In every case the result is only as good as the examples the model learned from.

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