A stork brings them... or...
One of the basic principles on a dist. system is lack of a global clock.
So how are the timestamps assigned to blocks, by the machine that mines it? Couldn't it just insert a fake one?
On page 7 of the Ethereum whitepaper Vitalik says that the algorithm for checking that a block is valid contains the following check:
Check that the timestamp of the block is greater than that of the [median of the 11 previous blocks] and less than 2 hours into the future
So then this notion of time in BTC is quite fuzzy isn't it?
Is there anything I can read that will tell me the exact time bounds of the BTC system?