Can you explain contrastive learning in machine learning in simple terms for someone new to the field of ML?
Sure! Let's say you want to build a model which can distinguish between images of cats and dogs. You gather your dataset, consisting of many cat and dog pictures. Then you put them through a neural net of your choice, which produces some representation for each image, a sequence of numbers like [0.123, 0.045, 0.334, ...]. The problem is, if your model is unfamiliar with cat and dog images, these representations will be quite random. At one time a cat and a dog picture could have very similar representations (their numbers would be close to each other), while at others two cat images may be represented far apart. In simple terms, the model wouldn't be able to tell cats and dogs apart. This is where contrastive learning comes in.

The point of contrastive learning is to take pairs of samples (in this case images of cats and dogs), then train the model to "pull" representations of similar pairs (cat-cat or dog-dog) closer to each other and "push" representations of different pairs (cat-dog) apart. After doing this for a sufficient number of steps, your model will be able to produce unique, reliable representations for cats and dogs, in essence tell them apart.

This method is not limited to images, you can typically use it with any dataset that has similar and dissimilar data points.