How long can a huge, deadly secret be kept? According to this paper, evidence was accumulating from lung-cancer studies in the 1940's-1950's, but in 1960 only 1/3 of doctors knew. The official warning from the Surgeon General began in 1964.
Start date: big tobacco knows. A single research study isn't enough evidence, and the industry isn't homogeneous. Lets define this date as when half of the leaders of the companies (CEO's, etc) "believe" that smoking causes lung cancer. Here, "believe" includes denial or willful ignorance and indicates the point where an impartial person would be convinced. According the the aforementioned paper, perhaps using the midpoint of 1950 would be a reasonable start date?
End date: Information availability. We define this date when a "preponderance of evidence" was available for a person who had access to major libraries and other public information infrastructure of the time. 1964 is an upper bound here, as the government was a lagging indicator. In 1960, 1/3 of doctors resisted the propaganda machine and found the link; our knowledgeable person also resists most propaganda and digs deeper into the underlying evidence. The significant fraction of doctors in 1960 suggests that the information was initially available a few years earlier (1955?) but was at first downplayed and overlooked.
So we have 1950-1955 under this estimate, with about 5 year error margins, suggesting under a decade of secrecy if we do not count hiding in plainish sight. This suggests that no big secrets will be hidden very long in todays age of online media so long as the fake news is filtered out. Is this 5-10 year time-frame a reasonable conclusion?
