Legal
Privacy and cookies
What this site knows about you: almost nothing, and none of it leaves your browser.
Last updated:
The short version. There are no accounts and no analytics, and we set no cookies. Your progress, answers and code are saved in your own browser so you can pick up where you left off; they are never sent to us. Ads, if they're switched on, load only after you say yes, and are non-personalized unless you opt in further. You can download or erase your data below at any time.
1. Who we are, and how to reach us
Spacetime, by Hand is a free, independent course in special relativity. For anything about privacy, including questions from parents and teachers, write to feedback@indicogni.com. We'll answer in plain language.
2. What we collect
Nothing, on our side. We don't run accounts, sign-ups, analytics, tracking pixels or fingerprinting, and we set no first-party cookies. We have no database of learners. We couldn't tell you who has visited the site even if we wanted to.
Two things are outside that promise, and both are described below: the standard server logs kept by our hosting provider, and ads, which only load if you allow them.
3. What your browser stores for you
To remember your progress, the site saves a few items in your browser's own storage (called localStorage). They stay on your device. They are never sent to us, and the ad code, if you allow ads, cannot read them.
| Key | Purpose | What's in it | Leaves your device? |
|---|---|---|---|
str.v1.progress | Course progress | Chapters visited and passed, exercise results, your predictions, your written answers, the code you wrote | Never |
str.v1.prefs | Preferences | Light, dark or automatic theme; reduced motion | Never |
str.v1.consent | Your ad decision | Whether you allowed ads, whether you allowed personalized ads, whether you confirmed you are 16 or older, and when you decided | Never |
str.v1.trip-board | A scoreboard in the Chapter 11 lab | Your attempts at one challenge. Kept only until you close the tab (sessionStorage) | Never |
Because this is your data, you're in charge of it:
- Download saves a small JSON file you can keep, or load on another device.
- Load accepts a file of up to 1 MB. It is checked carefully before anything is saved, and any code inside it is re-tested before it is allowed to run a lab.
- Erase asks you to confirm, then deletes your progress from this browser for good.
These buttons need JavaScript. You can also remove everything by clearing this site's data in your browser settings.
4. The code you write
Your code stays in your browser. When you press Run, it executes inside a sealed sandbox: a separate, locked-down page that has no access to the rest of the site, to your saved data or to the network. It can only compute and hand back numbers. Your code is never uploaded, shared or shown to anyone.
5. Ads, only if you allow them
Ads help keep the course free (why we have them). Here's exactly how they work:
- Nothing loads before you choose. No ad code, and no request to any ad company, happens until you press "Allow ads". If you choose "No ads", none ever loads. Every lesson stays complete either way.
- The ad provider is Google AdSense. Ads appear in Google's own frames, which cannot read your progress or your code, and we never pass any of your data to them.
- Non-personalized by default. A non-personalized ad is chosen from the page you're reading and rough location (such as your country), not from a profile of you. Google may still use cookies for these ads, to limit how often you see the same ad, to count views in aggregate and to fight fraud.
- Personalized ads are a separate, extra choice. A personalized ad can be based on what Google knows about your browsing on other sites. You can allow them only in the "Choices" panel, and only by confirming that you are 16 or older. If you are under 16, please don't.
Google explains its side in How Google uses information from sites or apps that use its services, and you can control Google's ad personalization in your Google ad settings.
Ads may be switched off entirely on this site, in which case none of this section applies and you'll never be asked.
6. Cookies and similar technologies
A cookie is a small file a website asks your browser to keep. We set none. The browser storage described in section 3 works like a cookie that never leaves your device: it is only there to provide what you asked for, which is remembering your progress.
| Name or pattern | Provider | Purpose | Lifetime | Category |
|---|---|---|---|---|
| Cookies | Spacetime, by Hand | None. We set no cookies at all. | Not applicable | Not applicable |
str.v1.* (browser storage) | Spacetime, by Hand | Remember your progress, preferences and ad decision (details) | Until you erase it | Strictly necessary |
__gads | Google (only if you allow ads) | Ad delivery, limiting repeats, measuring ad views | Up to about 13 months | Advertising |
__gpi | Google (only if you allow ads) | As __gads | Up to about 13 months | Advertising |
IDE | Google, on doubleclick.net (only if you allow ads) | Ad delivery and measurement; personalization only if you allowed personalized ads | Up to about 13 months | Advertising |
The Google entries are typical examples, not a complete list. Google maintains the full, current list of the cookies it uses, their purposes and lifetimes in How Google uses cookies. If you allowed ads and later change your mind, the site stops loading ad code at once; cookies Google already set can be cleared in your browser settings.
7. Your choices
- Privacy choices button. It's at the bottom of every page. Use it to allow or refuse ads, or to change your mind. Withdrawing consent reloads the page so that any ad code already loaded is gone.
- Global Privacy Control. If your browser sends the Global Privacy Control signal, we honor it: the personalized-ads option stays switched off.
- Your browser. You can block cookies, use private browsing, or clear this site's data at any time. The course works fully without ads, and storage failures only mean your progress isn't remembered.
8. Your rights
We hold no personal information about you on our side, so in practice there is little for us to hand over or delete: everything this site stores is already in your hands, and the buttons in section 3 let you see and erase it. Your rights still matter, and we respect them.
- In the EU, EEA and UK (GDPR and UK GDPR), you have the right to access your personal data, to have it erased, to object to its use, and to withdraw consent at any time. You can also complain to your local data protection authority. Saving your progress in your browser is based on providing the service you asked for; ads are based only on your consent.
- In the United States, under state privacy laws such as California's: we do not sell or share your personal information, and we honor Global Privacy Control as a request to opt out.
- For data held by Google because you allowed ads, Google's own tools and policies apply. We're happy to help you find them: write to feedback@indicogni.com.
9. Children and teens
- The course is written for high-school learners and is intended for ages 13 and up. Younger learners are very welcome with a parent or teacher.
- We do not knowingly collect personal information from anyone, of any age.
- Ads, if shown, are non-personalized by default. Personalized ads need a separate opt-in that includes confirming "I am 16 or older". Learners in the EU who are under 16 should not opt in.
- Advertisers in sensitive categories, such as gambling, dating, alcohol, tobacco and vaping, weight loss and get-rich-quick schemes, are blocked.
- Parents and teachers can contact us at any time at feedback@indicogni.com.
10. Hosting
The site is served by Cloudflare. Like nearly every web host, Cloudflare may keep standard server logs, such as IP addresses and browser types, for a limited time to keep the service secure and working. We don't use those logs to track learners. Cloudflare's handling is described in the Cloudflare privacy policy.
11. Changes to this policy
If what we store or how ads work ever changes, we'll update this page and the date at the top, and if the change affects ads we'll ask for your choice again. This version was last updated on .