[LINK] Updating Drake’s Equation with values from modern astronomy

A pa­per pub­lished in Astro­biol­ogy: A New Em­piri­cal Con­straint on the Prevalence of Tech­nolog­i­cal Species in the Uni­verse (PDF), A. Frank and W.T. Sul­li­van.

From the ab­stract:

Re­cent ad­vances in ex­o­planet stud­ies provide strong con­straints on all as­tro­phys­i­cal terms in the Drake equa­tion. [...] We find that as long as the prob­a­bil­ity that a hab­it­able zone planet de­vel­ops a tech­nolog­i­cal species is larger than ~ 10-24, hu­man­ity is not the only time tech­nolog­i­cal in­tel­li­gence has evolved.

They say we now know with rea­son­able cer­tainty the to­tal num­ber of stars ever to ex­ist (in the ob­serv­able uni­verse), and the av­er­age num­ber of planets in the hab­it­able zone. But we still don’t know the prob­a­bil­ities of life, in­tel­li­gence, and tech­nol­ogy aris­ing. They call this cu­mu­la­tive un­known fac­tor fbt.

Their re­sult: for tech­nolog­i­cal civ­i­liza­tion to arise no more than once, with prob­a­bil­ity 0.01, in the life­time of the ob­serv­able uni­verse, fbt should be no greater than ~ 2.5 x 10-24.


It’s con­ve­nient that they calcu­late the chance tech­nolog­i­cal civ­i­liza­tion ever arose, rather than the chance one ex­ists now. This is just the num­ber we need to es­ti­mate the like­li­hood of a Great Filter.

They state their re­sult as “[if we set fbt ≤ 2.5 x 10-24, then] at in a statis­ti­cal sense were we to re­run the his­tory of the Uni­verse 100 times, only once would a lone tech­nolog­i­cal species oc­cur”. But I don’t know what re­run­ning the Uni­verse means. I also can’t for­mu­late this as say­ing “if we hadn’t already ob­served the Uni­verse to be ap­par­ently empty of life, we would ex­pect it to con­tain or to have once con­tained life with a prob­a­bil­ity of 1024″, be­cause that would ig­nore the chance that an­other civ­i­liza­tion (if it coun­ter­fac­tu­ally ex­isted) would have af­fected or pre­vented the rise of life on Earth. Can some­one help re­for­mu­late this?

I don’t know if their mod­ern val­ues for star and planet for­ma­tion have been used in pre­vi­ous dis­cus­sions of the Fermi para­dox or the Great Filter. (The pa­pers they cite for their val­ues date from 2012, 2013 and 2015.) I also don’t know if these val­ues should be trusted, or what con­crete val­ues had been used pre­vi­ously. Peo­ple on top of the Great Filter dis­cus­sion prob­a­bly already up­dated when the as­tro­nom­i­cal data came in.