---
title: 'The Algorithm That Made Me Cry'
source: 'https://youtube.com/watch?v=XL5bq8DRn64'
video_id: 'XL5bq8DRn64'
date: 2026-07-24
duration_sec: 470
channel: 'Two Minute Papers'
---

# The Algorithm That Made Me Cry

> Source: [The Algorithm That Made Me Cry](https://youtube.com/watch?v=XL5bq8DRn64)

## Summary

The speaker shares a personal and emotional journey with ray tracing, a light transport simulation technique that can produce photorealistic images. He explains that even with a perfect system, the initial results are noisy and require many samples to converge to a clear image, teaching a valuable life lesson about persistence.

### Key Points

- **Ray Tracing Superpower** [00:00] — Ray tracing can simulate reality by tracing light paths, producing realistic images without AI.
- **Initial Failure** [00:43] — With only one sample per pixel, the image is extremely noisy and looks terrible.
- **Convergence to Beauty** [01:09] — After many samples (e.g., 10,000), the image becomes clean and photorealistic.
- **Life Lesson** [01:24] — Even with a perfect system, initial results may seem broken, but persistence pays off.
- **Free Course** [06:48] — The speaker offers a free master-level course on ray tracing from scratch, including physics and coding.

### Conclusion

Ray tracing demonstrates that perfection requires patience and many iterations. The speaker provides a free course to help others experience the joy of creating such simulations.

## Transcript

I learned a really important life lesson  during my research. You see, I do this kind of   thing. This is ray tracing, or a light transport  simulation as we call it. And it has a superpower:  
what is that? Well, it can simulate reality! Yes.  This is really possible - no AI needed at all. You can give it a scene, and it will simulate  the path of light rays bouncing around,  
and give you an image of what that  scene would look like in reality.  It is absolutely insane that  we can do that. I love it. But wait, not so fast. Even if you do it  perfectly, at first, this is what it looks like. 
Oh my, this is terrible. What is going  on? Well, that is the life lesson.   This was just simulating one ray going  through each of these pixels. That is what  
we call one sample. One sample is not enough. If you do two samples, you get something like   this. Better? Maybe a bit. A hundred samples?  Getting better, but still, a long way off. 
we get the beautiful final image. When you  first do it, it is a very emotional moment.  When we started, I thought this would  be impossible, and yet here it is.
So here is two things I’d like to share with you:  one is a life lesson that I learned. Even if you   have the perfect system, at first, it might  seem that it does not work at all. But you  
have to keep at it. And it may take a long time. And two, I’d love to share this feeling with you,   but it’s impossible, because when you  first succeed, it is beyond words.
But wait, I think I found a way to actually share  this feeling with you. Through a song. A popular   request from you Fellow Scholars, so here it  is. And if you watch until the end of the video,  
I’ll give you something so you can also create  a simulation like this yourself for free. Alright, with that said, this  is Károly and The Papers.
That was so much fun, I hope you enjoyed  it as much as we did. I am not sure if I   ever heard a song written about ray tracing.  Alright, I promised you something. And it is  
for free. I taught this master level course  at the Technical University of Vienna, and I   think knowledge should be for free for everyone.  So it’s not like the courses you see elsewhere,  
it is completely free, in fact you can’t even pay  for it even if you wanted. Although this Fellow   Scholar was hilarious. Alright, so in this one,  I try my best to teach you the physics of light,  
and then we code up a simulation  program together, from scratch. Enjoy!