Is there some way to generate a non-predictable random number in a decentralised network?
The classic way to do this is to have all parties commit to individual random values by publishing a secure hash of a suitably random-nonce-padded number. Once the commitments have been distributed, the parties open the commitments by publishing the nonce and the number. The numbers are combined in some previously agreed suitable fashion such as adding them modulo some number or xoring them together. As long as your value was included then you are confident that the result is random. If the numbers used are large enough, the nonce is not required.