Oliver James, Eugenie von Tunzelmann, Paul Franklin, Kip S. Thorne
2015 · arXiv
Interstellar is the first Hollywood movie to attempt depicting a black hole as it would actually be seen by somebody nearby. For this we developed a code called DNGR (Double Negative Gravitational Renderer) to solve the equations for ray-bundle (light-beam) propagation through the curved spacetime of a spinning (Kerr) black hole, and to render IMAX-quality, rapidly changing images. Our ray-bundle techniques were crucial for achieving IMAX-quality smoothness without flickering. This paper has four purposes: (i) To describe DNGR for physicists and CGI practitioners . (ii) To present the equations we use, when the camera is in arbitrary motion at an arbitrary location near a Kerr black hole, for mapping light sources to camera images via elliptical ray bundles. (iii) To describe new insights, from DNGR, into gravitational lensing when the camera is near the spinning black hole, rather than far away as in almost all prior studies. (iv) To describe how the images of the black hole Gargantua and its accretion disk, in the movie \emph{Interstellar}, were generated with DNGR. There are no new astrophysical insights in this accretion-disk section of the paper, but disk novices may find it pedagogically interesting, and movie buffs may find its discussions of Interstellar interesting.
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Well, interstellar has also some nerd stuff in it. If I remember correctly Kip Thorne did physics consulting on the movie and they even use a simulation running on a cluster to visualize the black hole physically correct. They could have used some arbitrary CGI…but no, they wanted it accurate according to science. https://arxiv.org/abs/1502.03808
The black hole simulation that was shown in the movie Interstellar is explained in detail in this paper, freely available on the arXiv: https://arxiv.org/abs/1502.03808 As a physicist with a modest background in computing, I was also surprised by how powerful the iPhone GPU is. It can indeed lens the input from the camera at high resolution and in real time with high FPS.
If you want to avoid opening Twitter (now known as X), here is the link to the paper: https://arxiv.org/pdf/1502.03808 TLDR “A typical IMAX image has 23 million pixels, and for Interstellar we had to generate many thousand images, so DNGR had to be very efficient. It has 40,000 lines of C++ code and runs across Double Negative’s Linux-based render-farm. Depending on the degree of gravitational lensing in an image, it typically takes from 30 minutes to several hours running on 10 CPU cores to create a single IMAX image. Our London render-farm comprises 1633 Dell-M620 blade servers; each blade has two 10-core E5-2680 Intel Xeon CPUs with 156GB RAM. During production of Interstellar, several hundred of these were typically being used by our DNGR code.“
Previous work on this was done for the movie Interstellar. The resolution of the rendering software was so high that team members were able to examine the black hole very closely - Because Gargantua was spinning at almost the speed of light, the rendering showed that spacetime warped into shapes never seen before. This led to the publication of —> https://arxiv.org/abs/1502.03808 Kip Thorne describes his work not this in a book called the science of interstellar. Kip’s description of black holes here is also fascinating: https://youtu.be/oj1AfkPQa6M — first time I learnt what “warped” space-time means :)
> I'll use Isaac Arthur dismissal of FTL travel as to why what credentials does he have? > Put me firmly in the camp that believes the speed of light is a hard limit on the universe the speed of light isn't a limit in the sense that nothing can be greater than it. it is a crossover point that can't be crossed over for things above or below it to the other side. > I'm not sure why it matters that a black hole would be spinning. black holes that spin are much different than non-spinning holes and have more complicated dynamics. if they are spinning, they are dragging space-time along with them. see this paper that shows some actual visuals of what a spinning black hole might look like and what it does to the light around it. https://arxiv.org/abs/1502.03808
On a related note, there's a paper by the Interstellar special effects team and Nobel laureate Kip Thorne describing how they rendered the black hole in the film and the tradeoffs they made: https://arxiv.org/abs/1502.03808
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