FTL interstellar travel. STL interstellar travel remains possible, even with 1960s technology (if not 1960s economy.) https://galileo.phys.virginia.edu/class

FTL interstellar travel. STL interstellar travel remains possible, even with 1960s technology (if not 1960s economy.) https://galileo.phys.virginia.edu/classes/321.jvn.fall02/Dyson.pdf https://galileo.phys.virginia.edu/classes/321.jvn.fall02/Dys... And STL travel is sufficient to invoke the Fermi argument.