A memory layer for humanity. Time Capsule lets anyone make a promise to the future that can't be lost, edited or quietly deleted, and when it opens, it brings back not just your words but the whole world you wrote them in.
2. Why people can't resist it
Love with a deadline. Writing to your child at 18, or your team at year 10, is one of the most meaningful things a person can do. The app gives it a ritual.
The countdown. A shelf of sealed capsules ticking toward dates makes you come back, add a voice note, invite a cousin.
The reveal is cinema. "What bread cost the week you were born" is irresistible to watch and to share.
3. How it works for real
Login: email or phone, a passkey smart wallet is created silently (Coinbase Smart Wallet or Privy). Gas sponsored by a paymaster on Base, so nobody sees crypto.
Encrypt: letters, voice notes and photos are encrypted on the phone (AES-256). The key is split with Shamir secret sharing between the owner, the guardians, and a time-lock service (drand timelock encryption for date unlocks).
Store: ciphertext goes to Arweave for one-time-paid permanent storage, mirrored on IPFS via Filecoin.
Prove: a SHA-256 content hash, unlock rule and guardian set are written to a small capsule contract on Base. Anyone can later verify nothing was altered.
World snapshot at sealing: a fast cheap model (Gemini Flash or DeepSeek via OpenRouter) summarises licensed news headline feeds of the week, a price API gives local bread and petrol, a weather API gives the day, all frozen into the capsule as text.
Film at unlock: a frontier LLM (Claude or GPT) writes the script from the frozen snapshot; an image model draws stills of the city skyline; a video model (Veo 3.1 Lite, Seedance or Wan) animates 3 to 5 key shots; TTS (ElevenLabs or an open model) reads the letter in a chosen voice.
Pay: USDC on Base for storage and the film credit, with x402 so partner apps (wedding sites, schools) can mint capsules per request.
4. Cost per use
Encryption and the hash on Base: under $0.01. Permanent storage on Arweave: roughly $5 to $10 per GB once, so a letter plus photos (50 MB) is about $0.40. Snapshot text: about $0.01. Unlock film: still panels with Ken Burns motion plus TTS cost about $0.05; 15 seconds of real video at $0.10 to $0.50 per second is $1.50 to $7.50.
Free: 1 capsule, 100 MB, still-panel film. Keeper ($24 one time per capsule): 2 GB permanent storage, guardians, a 60-second video film, and printed keepsake QR card. Teams and schools pay per seat.
5. Growth loop
Every capsule invites contributors and 3 guardians, each of whom sees the shelf and makes their own. Every unlock is a shareable film with "Seal one for someone you love". Capsules for weddings and graduations spread through whole guest lists. Each birthday the family gets a prompt to seal one more letter and photo into the same capsule, so the shelf grows every year and grandparents keep coming back to add theirs.
6. Risks and guardrails
Encryption: content is encrypted on the device. Time Capsule staff and storage hosts can't read it.
Lost keys: guardian recovery. Any 2 of 3 guardians can restore access or confirm an event. Guardians can be swapped while the owner is alive.
Permanence: storage is paid once upfront for 200+ years on Arweave; we also export a portable copy yearly. Be honest in the UI that "forever" relies on that network surviving.
Consent and privacy: contributors approve their own items. Photos of other people need their OK. A recipient can decline a capsule.
Abuse: no capsules that threaten or harass. Unlock can be paused if guardians report coercion. Illegal content is screened on device before sealing.
Death and estates: capsules can be named in a will; guardians handle event-based unlocks.
7. MVP build order
Email login, letter editor, client-side encryption, upload to Arweave (test bundler).
Write the content hash and unlock date to a contract on Base Sepolia; show the proof card.
Capsule shelf with countdowns and contributor invites by link.
World snapshot generator (headlines, prices, weather) frozen at sealing.
Unlock film as still panels with TTS, then upgrade to video shots.