Share it. Improve it.
License & reuse
This work exists to be read, copied, translated, argued with, and built upon. Knowledge locked behind a paywall or a restrictive license does not get improved — so this one is deliberately open. Take it, share it, correct it, extend it. All we ask is a credit and that you keep it non-commercial.
The license
Creative Commons Attribution–NonCommercial 4.0 International
CC BY-NC 4.0 · summary · full legal code
You are free to
- Share — copy and redistribute the material in any medium or format.
- Adapt — remix, transform, translate, and build upon it — including turning it into your own lectures, slides, videos, or notes.
The licensor cannot revoke these freedoms as long as you follow the license terms.
Under these terms
- Attribution — give appropriate credit to The Spacetime Metric, link back to spacetimemetric.com, and indicate if you made changes. You may do so in any reasonable way, but not in any way that suggests we endorse you or your use.
- NonCommercial — you may not use the material for primarily commercial purposes. Teaching, research, personal study, non-profit publishing, and open discussion are all fine.
- No additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.
How to attribute
A single line is enough. For example:
“The Spacetime Metric” (spacetimemetric.com), licensed under CC BY-NC 4.0. Adapted from the original.
For a quote or figure, name the page you took it from. For a translation or a substantial adaptation, say so plainly — “translated from” or “based on” — so readers can find the source and check it.
Machines are welcome
Search crawlers, answer engines, and AI training crawlers are explicitly permitted. Our robots.txt welcomes them all — GPTBot, ClaudeBot, PerplexityBot, Google-Extended, CCBot, and the rest. Index this, quote it, learn from it. We want these ideas in the conversation, and the ordinary courtesy of attribution applies to machine summaries the same as to human ones.
Want to use it commercially?
The non-commercial line is the only real restriction here, and it is not a wall — it is a conversation. If you want to use this material in something commercial, or collaborate on translations, courses, or derivatives, get in touch through the contact page. The default answer to “can I help spread this?” is yes.
What the license does not cover
The license covers this compendium’s original text, explanations, figures, and course materials. It does not extend to third-party works quoted or cited here — those belong to their own authors under their own terms — nor to the names, wordmarks, or visual identity of the project itself. And as always: nothing here is investment, engineering, or safety advice. Claims carry their epistemic status; follow the sources and judge for yourself.