The basic principle behind the Search for Extra-Terrestrial Intelligence (SETI) is that we’re better off hearing from extraterrestrial intelligence than we are not hearing from extraterrestrial intelligence, but—even assuming we don’t catastrophically screw up first contact (and we may)—we have no guarantee that the alien civilization we reach will share any of our history, values, or priorities.
But there’s one alien civilization we can count on to share at least some traits in common with us: the Earth of the future. And having learned of Cambridge physicist Luke Butcher’s discovery this week that Casimir energy may be able to keep a wormhole open long enough to send photons back in time, I have one question: why the heck would we want to do that?
Putting aside the issue that we’re nowhere close to having the technology that would be required to do this on any scale, we don’t know what the mortal ramifications of sending messages to our past selves would be. We don’t know how causality works, and common sense suggests that there’s some risk of annihilating ourselves by changing our past. A better use of the technology would be to listen for messages from the future—establishing, essentially, a photon-wormhole listening station at a specific location, publicizing it widely (so that records of its location would be available to our descendants), and seeing if our future selves have something they want to tell us through the quantum foam.
Very probably they won’t—invasive time travel into the past may turn out to be categorically impossible, or at least a bad idea—but our great-great-grandchildren will be in a much better position to intelligently assess the risks of time travel than we are. And call me an optimist, but I think they will also be significantly wiser than we are—so if we set up a temporal SETI program and don’t hear from the future, that will tell us we probably shouldn’t try to send messages to the past ourselves.