About 'GPS Relativity'
'GPS Relativity' began with a discussion about whether relativistic time dilation has practical consequences on Earth. The conversation eventually turned to navigation satellites, where relativity is not merely an abstract correction: weaker gravity makes their clocks run faster, while their orbital motion makes them run slower.
That suggested a web app connecting those effects to satellites that are visible from the town of Bladel in the Netherlands. The discussion then moved from concept to hardware: an inexpensive VK-162 USB GNSS receiver with a clear view of the sky could supply live information about GPS or GLONASS satellites, one receiver mode at a time. 'GPS Relativity' combines those observations with representative orbit models to show the gravitational effect, the motion effect, their combined clock difference, and information about the selected spacecraft. The sky and receiver data are live; the relativistic values are calculated.
The app was built through an incremental, three-party vibe-coding effort. Kees van Zon conceived the project, made the design decisions, selected and tested the hardware, provided the web app template, and reviewed every change. ChatGPT helped refine the concept and provided calculations, scientific presentation, interface design, and implementation prompts. Codex inspected and modified the codebase one carefully scoped step at a time.
The result is a small public scientific instrument: part live sky display, part relativity demonstration, and part experiment in collaborative software development.
Implementation summary
- OpenAI ChatGPT: GPT-5.5 High
- OpenAI Codex: GPT-5.5 High
- GNSS receiver: Ulegqin VK-162 USB GNSS receiver, mounted outdoors
- USB-to-Ethernet: Silex DS-700 USB device server
- Web-server hardware: MinisForum GD70
- Web-server software: Microsoft Internet Information Services 10.0 on Windows 11
- Website technology: C# ASP.NET Core Razor Pages
Image credits
Spacecraft images are representative of a satellite generation or family and do not necessarily depict the exact selected spacecraft.
- GPS Block IIR satellite rendering. United States Government, GPS.gov image library, source page and image file, public domain as stated by GPS.gov. Local file matches the source image; otherwise unmodified.
- GPS Block IIR-M satellite rendering. United States Government, GPS.gov image library, source page and image file, public domain as stated by GPS.gov. Local file matches the source image; otherwise unmodified.
- GPS Block IIF satellite rendering. United States Government, GPS.gov image library, source page and image file, public domain as stated by GPS.gov. Local file matches the source image; otherwise unmodified.
- GPS III satellite rendering. United States Government, GPS.gov image library, source page and image file, public domain as stated by GPS.gov. Local file matches the source image; otherwise unmodified.
- GLONASS-M satellite photograph. Vitaly V. Kuzmin, Wikimedia Commons, source page, under the Creative Commons Attribution-Share Alike 4.0 International licence. Local file matches the Commons original file; otherwise unmodified.
- GLONASS-K spacecraft model photograph. MKonair, Wikimedia Commons, source page, under the Creative Commons Attribution-Share Alike 2.0 Generic licence. Local file matches the Commons original file; otherwise unmodified.
