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Comment by solardev | Hacker News Reader

Not being a graphics person, is this what hardware ray tracing is, or is that something different?

Rayteacing doesn't simulate light, it simulates a very primitive idea of light. There's no diffraction, no interference patterns. You can't simulate the double-slit experiment in a game engine, unless you explicitly program it.

Our universe has a surprising amount of detail. We can't even simulate the simplest molecular interactions fully. Even a collision of two hydrogen atoms is too hard - time resolution and space resolution is insanely high, if not infinite.

And what’s more, it simulates a very primitive idea of matter! All geometry is mathematically precise, still made of flat triangles that only approximate curved surfaces, every edge and corner is infinitely sharp, and everything related to materials and interaction with light (diffuse shading, specular highlights, surface roughness, bumpiness, transparency/translucency, snd so on) are still the simplest possible models that five a somewhat plausible look, raytraced or not.

I wanted to make a dry joke about renderers supporting the double slit experiment, but in a sense you beat me to it.

There sure has been a lot of slits simulated in Blender.

> You can't simulate the double-slit experiment in a game engine, unless you explicitly program it.

Afaik you can't even simulate double-slit in high-end offline VFX renderers without custom programming

Btw there is some movement towards including wave-optics into graphics instead of traditional ray-optics: https://ssteinberg.xyz/2023/03/27/rtplt/

This is very cool. Thx for sharing

Raytracing simulates geometrical optics. That it doesn't take interference pattern into account is therefore a mathematical limitation and of course true, but irrelevant for most applications.

There are other effects (most notable volume scattering), which could be significant for the rendered image and which are simulatable with raytracing, but are usually neglected for various reasons, often because they are computationally expensive.

Even the ray tracing / path tracing is half-fake these days cause it's faster to upscale and interpolate frames with neural nets. But yeah in theory you can simulate light realistically

It’s still a model at the end of the day. Material properties like roughness are approximated with numerical values instead of being physical features.

Also light is REALLY complicated when you get close to a surface. A light simulation that properly handles refraction, diffraction, elastic and inelastic scattering, and anisotropic material properties would be very difficult to build and run. It’s much easier to use material values found from experimental results.

If I understood Feynman’s QED at all, light gets quite simple once you get close enough to the surface. ;) Isn’t the idea was that everything’s a mirror? It sounds like all the complexity comes entirely from all the surface variation - a cracked or ground up mirror is still a mirror at a smaller scale but has a complex aggregate behavior at a larger scale. Brian Green’s string theory talks also send the same message, more or less.

Sure, light gets quite simple as long as you can evaluate path integrals that integrate over the literally infinite possible paths that each contributing photon could possibly take!

Also, light may be simple but light interaction with electrons (ie. matter) is a very different story!

Don't the different phases from all the random path more or less cancel out , and significant additions of phases only come from paths near the "classical" path? I wonder if this reduction would still be tractable on gpus to simulate diffraction

That’s what I remember from QED, the integrals all collapse to something that looks like a small finite-width Dirac impulse around the mirror direction. So the derivation is interesting and would be hard to simulate, but we can approximate the outcome computationally with extremely simple shortcuts. (Of course, with a long list of simplifying assumptions… some materials, some of the known effects, visible light, reasonable image resolutions, usually 3-channel colors, etc. etc.)

I just googled and there’s a ton of different papers on doing diffraction in the last 20 years, more that I expected. I watched a talk on this particular one last year: https://ssteinberg.xyz/2023/03/27/rtplt/

Orbital shapes and energies influence how light interacts with a material. Yes, once you get to QED, it’s simple. Before that is a whole bunch of layers of QFT to determine where the electrons are, and their energy. From that, there are many emergent behaviors.

Also QED is still a model. If you want to simulate every photon action, might as well build a universe.

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