Terms of use

1. What this site is

Spacetime, by Hand is free educational content about special relativity. It is provided "as is", without warranties of any kind: we check the physics carefully, but we can't promise the site is free of errors or always available, and we aren't liable for losses arising from its use, as far as the law allows. It's meant to help you learn, and it is not a substitute for a teacher, a textbook course or professional advice. If you spot a mistake, please tell us.

Your progress is stored only in your own browser. Browsers sometimes clear storage, so if your progress matters to you, download a copy now and then from the privacy page.

2. Licenses

• Text and figures are licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0. You may copy, share and adapt them for non-commercial purposes, such as teaching a class, as long as you credit Spacetime, by Hand, link to the license, and share your adaptations under the same license.
• The site's code is licensed under the MIT License.
• Your own code, the functions you write in the course, belongs to you. We never receive it.
• Third-party components, such as the KaTeX math typesetting library, keep their own licenses, listed on the About page.

3. Acceptable use

Please use the site the way it's meant to be used: to learn. In particular, don't:

• attack the site, probe it for weaknesses without permission, or try to disrupt it for others (if you find a security problem, please report it to feedback@indicogni.com);
• scrape or copy the site in bulk to resell it or to republish it commercially;
• present the course as the official coursework, product or endorsement of any school, university, exam board or other institution.

4. Third-party content and ads

If ads are shown, they come from Google AdSense, and only after you allow them. We choose where ads may appear and block sensitive categories, but we don't write the ads and aren't responsible for what advertisers say or sell. If you see an ad that seems inappropriate, especially for younger learners, please tell us at feedback@indicogni.com with a description or screenshot, and we'll have it blocked.

Links to other websites are provided for your interest. We don't control those sites and aren't responsible for their content.

5. Inspirations and trademarks

We gratefully credit Edwin F. Taylor and John Archibald Wheeler's Spacetime Physics and The Feynman Lectures on Physics as inspirations. This site is not affiliated with, or endorsed by, their authors, their estates or their publishers. All names and trademarks belong to their owners. Everything on this site is our own original work; see What's ours.

6. Changes and contact

We may update these terms; the date at the top tells you when they last changed, and continuing to use the site after a change means you accept the new version. Questions? Write to feedback@indicogni.com.