
Diffusion models are generative methods that progressively add and remove noise to create high-quality synthetic data.Diffusion models are a generative approach that transforms Gaussian noise into ordered data, such as a photo of a cat. The process resembles restoring a mosaic from memory: you have only a rough sketch, but you remember what similar works looked like, and you gradually recreate the pattern—from fuzzy patches to fine lines. The model contains a 'representation' of the world, learned from millions of examples, and thus can generate plausible new images. The key difference from other generative networks is iterativity: the picture is born not instantly but through a chain of small improvements.
The method's roots go back to works on thermodynamics and statistical physics (e.g., the works of Langevin), but the modern embodiment was proposed in 2015 by Jascha Sohl-Dickstein as a stochastic generative model based on non-equilibrium thermodynamics. The breakthrough came after the 2020 publication of the paper 'Denoising Diffusion Probabilistic Models,' which demonstrated outstanding results on image synthesis tasks. Further improvements (accelerated sampling, conditional guidance) led to the creation of systems like DALL-E 2, Imagen, Stable Diffusion, which revolutionized the field of AI creativity.
Forward process: to the original image x0, small amounts of Gaussian noise are added over T steps, obtaining a sequence x1, x2, ..., xT, where xT is practically indistinguishable from white noise. The transition at each step: q(xt|xt-1) = N(xt; sqrt(1-βt)·xt-1, βtI), where βt is the variance schedule. Reverse process: a neural network εθ(xt, t) learns to predict the noise added at step t, minimizing E[||ε - εθ(xt, t)||²]. During generation, one starts from xT ~ N(0, I) and iteratively applies xt-1 = (1/√(αt))·(xt - (1-αt)/√(1-ᾱt)·εθ(xt, t)) + σt·z, where z is noise. To speed up sampling, DDIM (Denoising Diffusion Implicit Models) with step skipping is used. Conditional models augment the input with information about text, class, etc., guiding the reverse process.
Generating photographs from text descriptions, improving telescope images, designing new materials.
Although diffusion seems slow, modern versions create an image in just half a second on a powerful graphics chip.
| D | variable | Diffusion coefficient — diffusion coefficient metre squared per second |
| E | variable | Particle energy — energy joule |
| B | variable | Magnetic field strength — magnetic field strength tesla |
| R_inj | variable | Injection scale (turbulence outer scale) — length metre |
| ε'' | variable | Imaginary part of the dielectric function (dielectric loss) — dielectric function |
| ω | variable | Angular frequency of the applied electromagnetic field — angular frequency radian per second |
| ω_0 | variable | Resonance angular frequency of the oscillator — angular frequency radian per second |
| γ | variable | Damping rate of the oscillator — angular frequency radian per second |
| ω_p | variable | Plasma frequency, related to the density of oscillators — angular frequency radian per second |




















