Is it possible to create a "Time Capsule" using encryption?

I want to create a digital time capsule which will remain unreadable for some period of time and then become readable. I do not want to rely on any outside service to, for instance, keep the key secret and then reveal it at the required time. Is this possible? If not, is some kind of proof possible that it is not?

One strategy would be based on projections of future computing capabilities, but that is unreliable and makes assumptions about how many resources would be applied to the task.

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)

StackExchange Computer Science Q#1514, answer score: 5