I find it cool that more and more tv and movie special effects are being doing in game engines like unreal.
There was a recent article on the immersive weather video's the weather channel is doing.
If you want realtime graphics rendering, video game engines are basically the cream of the crop right now.
However, realtime graphics has major downsides. Shadows are often calculated ahead of time and are actually non-interactive (aka "Baked Shadows"). There are a whole bunch of other tricks that reduce the amount of work and processing involved. Even if you turn off all of those shortcuts, rasterization doesn't really follow reflections very well. (Even a normal wall reflects the light: stand with a blue shirt close to a white wall, and the white wall will turn a slight-shade of blue).
Modeling those interactions between objects can only be done with Raytracing. And even with RTX Cards, raytracing is a poor estimation pushed through an absurdly blurry denoising filter. To have any real accuracy, you need ~500+ samples at the minimum (maybe 5000+ samples per pixel for Hollywood level effects). The 1-sample-per-pixel methodology that is pushed by RTX Cards is impressive, but still far behind the movie studios.
Back when "Cars" was the latest thing from Pixar (over a decade ago now), they engineers released a paper
describing their techniques; towards the end (section 8 ) they mention a single ray-traced scene taking 414MB. Techniques have improved, but so has scene complexity and effects.
Thanks for the link, but the 414MB scene wasn't a realistic test. It was 15 clones of the same 1960s-style Cadillac with only 2155 NURBs to model the car with a blank background. In fact, I doubt that most things would be modeled off of NURBs (and expect most modern movies to be "sculpted" into a typical trangle mesh... it uses more RAM but it has benefits to the artist who models)
In any case, a modern scene today would use a 20000x10000 HDRi environment map, which is 800MB alone
(just for the skymap !!). That's just one
element that's part of a modern 3d scene.
In any case, the pdf is a really cool insight into the computational requirements needed for Cars.