1 What is deep learning?
Amid intense media attention and soaring expectations, this chapter separates signal from noise and lays out what deep learning really is. It clarifies the relationship between artificial intelligence, machine learning, and deep learning: AI aims to automate intellectual tasks; machine learning learns rules from data rather than relying on hand-crafted logic; and deep learning focuses on learning successive, increasingly abstract representations. Neural networks implement these layered transformations, and training adjusts their weights to minimize a loss function through backpropagation—an iterative process that turns simple building blocks into powerful, task-relevant representations.
The chapter explains why deep learning has become the dominant approach: it automates feature engineering (simplifying workflows), scales efficiently on modern hardware, and supports continuous learning and reuse through pretraining and adaptation. It highlights the rise of generative AI fueled by self-supervised learning and foundation models, which leverage massive datasets to produce text, code, images, and more—often controllable via prompting rather than task-specific programming. This capability underpins recent breakthroughs, from fluent chatbots and coding assistants to photorealistic image synthesis, human-level perception tasks, improved translation and speech systems, and robust real-world applications like autonomous driving and advanced recommender systems.
At the same time, the chapter urges caution about short-term hype. It distinguishes today’s systems as cognitive automation rather than general intelligence, noting that adaptability to the truly unknown remains a defining gap between automation and human-like intelligence. Drawing on past boom-and-bust cycles (AI winters), it warns that inflated expectations can prompt retrenchment if results don’t match promises—though any future slowdown would likely be mild given demonstrated value. The balanced outlook: deep learning’s core ideas are here to stay, its impact is already meaningful and growing, but progress should be judged by measurable capabilities rather than speculative timelines for AGI.
Artificial intelligence, machine learning, and deep learning

Machine learning: a new programming paradigm

Some sample data

Coordinate change

A deep neural network for digit classification

Deep representations learned by a digit-classification model

A neural network is parameterized by its weights.

A loss function measures the quality of the network’s output.

The loss score is used as a feedback signal to adjust the weights.

The promise of AI
Although we may have unrealistic short-term expectations for AI, the long-term picture is looking bright. We’re only getting started in applying deep learning to many important problems for which it could prove transformative, from medical diagnoses to digital assistants.
In 2017, in this very book, I wrote:
Right now, it may seem hard to believe that AI could have a large impact on our world, because it isn’t yet widely deployed – much as, back in 1995, it would have been difficult to believe in the future impact of the internet. Back then, most people didn’t see how the internet was relevant to them and how it was going to change their lives. The same is true for deep learning and AI today. But make no mistake: AI is coming. In a not-so-distant future, AI will be your assistant, even your friend; it will answer your questions, help educate your kids, and watch over your health. It will deliver your groceries to your door and drive you from point A to point B. It will be your interface to an increasingly complex and information-intensive world. And, even more important, AI will help humanity as a whole move forward, by assisting human scientists in new breakthrough discoveries across all scientific fields, from genomics to mathematics.
Fast-forward to 2025, most of these things have either come true or are on the verge of coming true – and this is just the beginning.
- Tens of millions of people are using AI chatbots like ChatGPT, Gemini, or Claude as assistants on a daily basis. In fact, question-answering and “educating your kids” (homework assistance) have turned out to be the top applications of these chatbots! For many people, AI is already the go-to interface to the world’s information.
- Hundreds of thousands of people interact with AI “friends” in applications such as Character.ai
- Fully autonomous driving is already deployed at scale in cities like Phoenix, San Francisco, Los Angeles, and Austin.
- AI is making major strides towards helping accelerate science. The AlphaFold model from DeepMind is helping biologists predict protein structures with unprecedented accuracy. Renowned mathematician Terence Tao believes that by around 2026, AI could become a reliable co-author in mathematical research and other fields when used appropriately.
The AI revolution, once a distant vision, is now rapidly unfolding before our eyes. On the way, we may face a few setbacks – in much the same way the internet industry was overhyped in 1998–1999 and suffered from a crash that dried up investment throughout the early 2000s. But we’ll get there eventually. AI will end up being applied to nearly every process that makes up our society and our daily lives, much like the internet is today.
Don’t believe the short-term hype, but do believe in the long-term vision. It may take a while for AI to be deployed to its true potential – a potential the full extent of which no one has yet dared to dream – but AI is coming, and it will transform our world in a fantastic way.
[1] A. M. Turing, “Computing Machinery and Intelligence,” Mind 59, no. 236 (1950): 433-460.
[2] Although the Turing test has sometimes been interpreted as a literal test – a goal the field of AI should set out to reach – Turing merely meant it as a conceptual device in a philosophical discussion about the nature of cognition.