Frame from But what is a neural network? | Deep learning chapter 1 Plays with YouTube's privacy-enhanced embed

But what is a neural network? | Deep learning chapter 1

Open on YouTube First HN thread

16 HN users recommended this explainer in 14 different months between 2017 and 2025.

2007–2026
5 strong recommendations 11 recommendations 3 citations HackerTube score 16.5

HN treats it as the standard first stop for learning neural networks, praised for making the math intuitive.

3Blue1Brown's first chapter on deep learning explains what neurons and layers are and the math underlying a basic neural network, using handwritten digit recognition with visual animations.

Pull quote: “the visualisations and explanations of the math/concepts are so amazing” (HN, 2017)

Also tagged: neural networks, deep learning, 3blue1brown, gradient descent, visualization, machine learning basics

What Hacker News said

19 labeled comments from the HN archive; up to 20 are kept per video, favoring different commenters. Each one links back to the original thread.

Strongly recommends hal9000xp November 2017 under Ask HN: Best way to get started with AI?
Accessible math explanations that removed fear of ML
Read the full comment
I'm in the same boat. For long time, I was interested in AI but at the same time intimidated by math. I'm relatively comfortable with discrete mathematics and classical algorithms and at the same time calculus and linear algebra is completely foreign to me. Also, I do not accept way to learn ML without good understanding of core principles behind it. So math is a must. A few months ago, I stumbled upon very amazing YouTube Channel 3Blue1Brown which explains math in very accessible way and at the same time I got feeling that I finally started understanding core ideas behind linear algebra and calculus. Just recently he published 4 videos about deep neural networks: [this video] [link] [link] [link] So my fear of ML was gone away and I'm very excited to explore whole new world for neural networks and other things like support vector machines etc
Strongly recommends mandliya December 2017 under What was the best CS, SE or Math video you watched in 2017?
Amazing visualisations give intuition for neural networks
[this video] 3Blue1Brown’s playlist on neural networks. Like other 3Blue1Brown videos, the visualisations and explanations of the math/concepts are so amazing, they give you the intuition behind the neural networks naturally.
Ties together neural nets, gradient descent and dot products
Read the full comment
Essentially a computer neural network is just a lot of addition (and matrix multiplication) of floating point numbers. The parameters are the "strength" or "weights" of the connections between neurons on different layers and the "bias" of each neuron. If neuron Alice is connected to neuron Bob and Alice has a value of 0.7, and the weight of Alice's connection to bob is 0.5, then the value sent from Alice to Bob is 0.35. This value (and the values from all the other incoming connections) are summed at added to the neuron's negative bias. I highly recommend checking out 3blue1brown series on how neural nets, gradient descent, and the dot product (implemented as a matrix multiplication) all tie together: [this video]
Strongly recommends 6mian April 2024 under But what is a GPT? Visual intro to Transformers [video]
Excellent introduction that made Karpathy's videos understandable
For me 3brown1blue series: [this video] was an excellent introduction that made Andrej's videos understandable. Then I did 3 first chapters of fastai book, but found it too high level, while I was interested in how things works under the hood. Going through Andrej's makemore tutorials required quite a lot of time but it's definitely worth it. I used free tier of Google Colab until the last one. Pausing the video a lot after he explains what he plans to do and trying to do it by myself was a very rewarding way to learn, with a lot of "aha" moments.
Recommends miklosme May 2020 under Humans Not Invited
Extensive explanation of neural networks in a playlist
If you want an extensive answer, I recommend the neural network playlist on 3Blue1Brown: [this video] For a quick answer, watch this segment: [link]
Recommends ianbutler February 2023 under GPT in 60 Lines of NumPy
Great mathematical series on gradient descent and loss
I think FastAI lesson 3 in "Practical Deep Learning for Coders", has one of the most intuitive buildups of gradient descent and loss that I've seen. * Lecture [1] Book Chapter [2] It doesn't go into the math but I don't think that's a bad thing for beginners. If you want mathematical, 3blue1brown has a great series of videos [3] on the topic. [1] [link] [2] [link] [3] [this video] * I've been messing around with this stuff since 2016 and have done a few different courses like the original Andrew Ng course and more.
Recommends circuit10 April 2023 under The future of generative AI is niche, not generalized
Technical look at how modern AI training works
Read the full comment
If a human brain doesn’t use maths, what does it use? It’s Magic? > "training", more accurately described as references Uh, no, that's not at all how the training process works. The training process very roughly mirrors evolution/natural selection except more more direct and faster. This is a good introduction to the concept of how a computer could learn: [link] This is a more technical look at how exactly it works in more modern AIs: [this video] (it's a series) > If it encounters a problem it hasn't been programmed for, it cannot reason a new solution. But an LLM can? It's not as good at it as a human but it can Relevant: [link] (if you don’t want to click it it says “referring to AI models as "just math" or "matrix multiplication" is as uselessly reductive as referring to tigers as "just biology" or "biochemical reactions"”) > By your logic, video game characters must use reasoning, when no, they don't. It's maths. “By your logic, if tigers are dangerous, then bananas must be too, when no, they aren’t. It’s biology.”
Recommends segmondy June 2023 under Getting into AI This Summer
Starting point for studying AI
Studying C or Python is studying C or Python. Rather, study AI. Pick up python along the way, skip C. [this video] [link] There's tons of book, but I recommend this since it's hands on "Hands-On Machine Learning with Scikit-Learn, Keras, and TensorFlow" [link] [link] download some local LLMs and play with them along the way. Good luck.
Visual, approachable explanation of neural networks and AI from 3blue1brown
>> YouTube has always been a mixed bag As an outsider but avid reader of this stuff linked from HN, I would recommend the channel 3blue1brown. He's got several NN and AI related videos, and the couple I've seen were pretty good. [this video]
Recommends rottc0dd March 2025 under Deep Learning Is Not So Mysterious or Different
Visual introduction to deep learning
If anyone wants to delve into machine learning, one of the superb resources I have found is, Stanfords "Probability for computer scientists"( [link] ). It delves into theoretical underpinnings of probability theory and ML, IMO better than any other course I have seen. (Yeah, Andrew Ng is legendary, but his course demands some mathematical familarity with linear algebra topics) And of course, for deep learning, 3b1b is great for getting some visual introduction ( [this video] ).
Recommends Razengan September 2025 under Qwen3-Next
Catch up on neural network basics via a legendary playlist
A while ago I had caught up with the basics thanks to the legendary 3blue1brown and his playlist on Neural Networks: [this video] and other helpers like Artem Kirsanov: [link]

Citations, criticism and jokes

Cites it vanderZwan March 2018 under HALP: High-Accuracy Low-Precision Training
Yes, while I haven't done anything with ML myself, I heard via the 3Blue1Brown video on Deep Learning[0] that the sigmoid function isn't really that used anymore. But I figured allowing that being able to tweak the dynamic range could make it a good fit for the rescaling and recentering approach. You know what, I'll just go ahead and post a link to this article on the Unum google group, perhaps someone there can add some thoughts[1]. [0] [this video] [1] [link]
Cites it afarrell February 2020 under Dopamine and Temporal Difference Learning
Intro to neural nets used as background
I can partly understand some this based on an EE101-level control theory, a High School level model of how neurons work, and 3blue1brown's intro to neural nets[1]. However, I have a strong personal interest in developing a much deeper understanding of dopamine neurons and their role in Executive Function. Can anyone recommend a good curriculum which can take a random web developer from "Knows what a myelinated axon, a sigmoid function, and a feedback loop are" to having a solid enough background to dive into the research on this? [1] [this video]
Cites it dpoloncsak November 2025 under I hate screenshots of text
Digit recognition as the Hello World of ML
They can , sure...that's really just LLMs though. ML models to recognize handwriting have existed way before LLMs could call tools, though Identifying digits is like the "Hello World!" of ML [this video]

Keyboard shortcuts

/
Search
j k
Next / previous video in a list
Enter
Open the focused video
l
Like (on a video page)
w
Watch later (on a video page)
?
This help
Esc
Close