Show HN: Physically accurate black hole simulation using your iPhone camera
A new open-source iOS app, Black Hole Vision, uses general relativity–based lensing equations and the iPhone’s GPU to render physically accurate views of the world as if a Schwarzschild or spinning Kerr black hole were in front of the camera. Commenters explore how the simulation works—precomputed lensing maps, Metal shaders, field‑of‑view choices—and where it departs from full realism, noting that effects like time delays, redshift, accretion disks, and jets are intentionally omitted to keep it practical and interactive. The project is framed as public outreach tied to future black hole imaging missions, with interest in potential AR/VR extensions, desktop or web ports, and appreciation that the app is free, open source, and collects no user data.
App concept and physics approach
- iOS app applies general-relativistic gravitational lensing of a black hole to live iPhone camera feeds (front and rear).
- Two main modes:
- Static black hole: non-rotating (Schwarzschild), with “Realistic FOV” (limited by actual camera view, producing lobed dark regions and blind spots) and “Full FOV” (idealized infinite field of view, giving a single circular shadow).
- Kerr black hole: rotating, with adjustable spin parameter; textures for this mode are precomputed in higher precision and used as a lookup map on the GPU.
- Developers emphasize that this is a visual simulation of lensing, not a full black-hole simulation (no time delays, redshift, jets, accretion disks, etc.).
Visual behavior and realism questions
- Some users expect objects to “disappear” or get much dimmer; others explain that strong lensing lets you see behind the black hole while some light is still absorbed.
- Discussion around shadow shape:
- Non-rotating case with full FOV should produce a circular shadow.
- Rotating (Kerr) case is expected to deviate from a circle; some commenters question whether the preview screenshots match theoretical shapes.
- Redshift is discussed: in the chosen setup (sources effectively at infinity and at rest relative to the camera) gravitational redshift at the camera vanishes, so it is not shown.
AR/VR and feature ideas
- Strong interest in AR features: “pin” a black hole in a fixed spot and walk around it; geoshared singularities in real locations; stats based on mass, Hawking radiation, and local gravity.
- Others note this would require full 3D environment mapping or VR, since a black hole acts like a 360° lens.
- Requested features: capture button for warped images, option to hide multi-camera thumbnails, ability to fix orientation of the black hole.
Platforms, implementation, and performance
- Implemented with Apple’s Metal on iPhone; authors note surprising GPU performance enabling real-time high-res lensing.
- Porting to Android or desktop/WebGPU is seen as possible but nontrivial; a browser-based non-rotating version by another researcher is referenced as an alternative.
- One user reports an initial crash related to camera permissions; minimum iOS version requirement (17.5) is acknowledged as unnecessarily high and slated for correction.
- App can be installed on Apple Silicon Macs and works there for at least one user.
Scope, terminology, and expectations
- Some argue that “simulation” overstates it since it’s essentially an image filter for one effect; developers agree but defend the term for “what your surroundings would look like.”
- Suggestions arise for simulating accretion disks or Kerr–Newman black holes; devs respond that doing so would move toward full GRMHD simulations and obscure the live camera view.
- There is meta-discussion on monetization vs. pure educational/outreach value; several commenters appreciate that it’s free, open source, and collects no data.