Time travel is a subject that Luky and I both love. He doesn't even fight for the remote when a movie like
Twelve Monkeys is showing. However, he thinks too much about the implications.
Everyone is pretty familiar with the clichéd scenario often referred to as the "grandfather paradox," by which some theorists purport to prove the impossibility of time travel because it allows for the absurd circumstance whereby a time traveler goes back in time and gets into a battle with (or by other less intentionally hostile means, kills) his own youthful grandfather (great grandfather, etc.). By so doing the time traveler thus prevents the birth of his father, and thus prevents his own birth - which then means he is not around to go back in time and kill his grandfather in the first place - which then means his father (and subsequently the father's time traveling son) are, in fact, born - which THEN means he is back and able to go back in time and, once again, undo his lineage. (Luky says the grandfather paradox was "invented" by a French Sci-Fi writer, René Barjavel, in a story called, "Le Voyageur Imprudent." He later told me he got this on a tip from Wikipedia -
http://en.wikipedia.org/wiki/Grandfather_paradox. I think he has
tip connections.)
I used to think the absurdity rested in the original problem of a time travler's going back to create events which prevent his ever being born, but it was Luky who alerted me to the somewhat more detailed (and even weirder) idea that it actually creates a ridiculous loop of being and not-being.
Anyway, none of that matters according to Luky. He figures that the question of time travel will eventually get dealt with mathematically, and then (as always happens) in the lab. His big question is this - if our own future entails time travel, then why aren't we being visited by travelers from the future?
I told him this sounded to me like a sort of variation on Fermi's paradox, which is credited to a Los Alamos Lab lunchroom insight by physicist Enrico Fermi during a discussion about alien life (according to the "Cosmic Shooting Gallery" article in the November, 2005, issue of
Astronomy Magazine -
http://www.astronomy.com/ - requires registration to access online). Basically, Fermi and friends (including Edward Teller, among the more hawkish of the A-Bomb-development-era nuclear scientists), were talking about the plethora of stars and likely planetary systems in our galaxy, let alone the entire universe. And they were talking about the likelihood of other intelligent beings - and as their conversation continued to list the preponderance of favorable statistical data, Fermi just blurts out the quite natural observation - "Where is everybody?"
Luky demands that I insert here a reference to one of his personal heroes, UC Berkeley Professor of Astronomy, Geoffrey Marcy, who, along with partner, Paul Butler, is the most prolific discoverer of exoplanets (i.e., planets orbiting other stars) today. Luky says that Geoff and Paul, and other planet finders, have certainly reinforced the significance and logic of Fermi's question by establishing at least the premise that there are lots and lots of planets out there. (I hope Geoff doesn't mind, but Luky insists I include a link to his personal website -
http://astron.berkeley.edu/~gmarcy/.)
Anyway, I told Luky Fermi was basically saying that life ought to be so plentiful, and intelligent life ought to be statistically likely enough, that we have reason to expect them to show up! Luky also says this is just another reason why he never believed in alien visitors - yet - because you've got Fermi, Teller and the brightest minds in science sitting in a lunchroom surrounded by the most expensive and most advanced tools and equipment available, and they are eager to actually meet intelligent travelers from other worlds, but they are disappointed that none have bothered to say "hello." I guess he has a point there.
But back to the time issue. Luky's point kind of works on the same logic. He's suggesting that if we will eventually learn to travel time, and if the scapes exist to permit us to do so, then (barring some unforeseen, ridiculous premise, like we happen to be living in the very first scape) we ought to be meeting a lot of travelers from future scapes already!
I said, "Wait a minute. Aren't you presupposing that we have anything going on now that is interesting enough to motivate someone to come back and visit it, real-time?"
"You might be correct," he said, "but I don't think so. I think this sort of time travel is much more likely than planetary alien visitation. I can understand the argument that aliens who are able to travel the lightyears of space may be too advanced to find us of interest, but if time travel becomes a readily viable technology, then I would think many humans - at least your future historians - would want to visit lots of different eras, just for fact-checking, etc. After all, they know they can predict the necessary tools of culture, fashion, language, etc., which they might need - and it's not like they are visiting a wholly different biochemical creature. They're connected. They have history - it is their history."
"Yeah, I guess you're right."
"Yes, and so I think there can be only a few reasons for not visiting."
"And those would be . . . ?" I asked.
"Well, there's the obvious point that something about the physics of time travel - something we do not yet understand - prevents it. And then there's the possibility that those future travelers - be they vacationers or historians - are already here, and for whatever reasons we cannot see them . . . like maybe they have developed some technology which permits them to visit without having any impact at all (and thus, can visit free of the grandfather paradox). Or, it might be more likely that the sorts of humans you have elected to run your countries have made sure there's no need to worry about the grandfather paradox - before we get to the point of inventing time travel you have uninvented mankind."
"Oh!?!? Well, isn't THAT a cheery thought!?!"
Luky got that distant look - like he was trying to smell the ionosphere. "Yeah, I think you've got it in you - but then again, I would expect some very smart dogs from the future to be showing up now to warn the world's canine population to keep our distance . . . so, maybe you DO survive after all."
