Is it possible to create a "Time Capsule" using encryption?
The problem is known as timed-release cryptography. For some references/introduction look at:


"Time-lock puzzles and timed-release Crypto" by R.R. Rivest, A. Shamir, and D. A. Wagner (1996) 


Our motivation is the notion of "timed-release crypto", where the goal is to encrypt a message so it cannot be decrypted by anyone, not even the sender, until a pre-determined amount of time has passed. The goal is to "send information into the future" ...


or "Provably Secure Timed-Release Public Key Encryption" J.H. Cheon et al. (2008)