PGP/GPG can used to sign text, others use public key to verify them. So one could say, that these cryptographic algorithms deal with space.
Are there any algorithms that can deal with time? E.g. I sign a document at 2011-10-10 10:10:10, others can verify this document is really, truly signed at 2011-10-10 10-10-10.
I know there are solutions based on a common trusted time source (a notary), but is it possible that a pure algorithm solution exists?
Or perhaps some amazing dedicated piece of hardware can do this? (E.g. half-life of certain well-known material, etc.)
In a simple way: Can we give nature a private key and ask nature to sign our documents using a natural timestamp?