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Comment by ReactiveJelly | Hacker News Reader

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

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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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