Re: Is time travel possible
speaking of time travel, i remember an argument given by a philosophy professor at ucsd, prof. craig callender, when i took his metaphysics class once. if i'm not mistaken, i think prof. lane taught at ucsd for quite some time, so i'm wondering if you know him, prof.lane? craig callender, he's written a book called "introduction to time" that's sorta like a picture book that talks about the philosophy of time. if you do know him, i wonder if you two has ever discussed this, because prof. callender seems to be particularly interested in philosophy of time, as he has always brought this up in the two classes i've had with him.
we were discussing the philosophy of time, like what time is and how one defines time and whatnot, and we got to the point about time travel. the ideas i get from TV, is that it's not logically contradictory to go back to the past to change the present, or even the future. we've seen movies like terminator, back to the future, and many others that use time travel as the main idea. now, his argument is one that i find really interesting, although it's still quite hard for me to grasp. he proposes that time travel with the idea "going back to the past to change the present" is logically impossible.
why?
this is what he argues. let's take terminator 2 for example. so the robots send a machine to the past to kill john o'connor, and then the old john o' connor sends arnold schwarznegger back to protect the young john oconnor. well, according to prof. callender, the old john o'connor does not need to send arnold back to protect him, BECAUSE HE ALREADY EXISTS AT HIS PRESENT. the idea is that since he already exists AT THE PRESENT, that means IN THE PAST, that bad robot sent to kill him DID NOT SUCCEED, for if that robot SUCCEEDED, he wouldn't have been there IN THE PRESENT. so in a way, what prof. callender proposes is that no matter what you do, you CANNOT go back to the past to change the present, because the present HAS EXISTED. if you had gone to the past and change it, THIS PARTICULAR present would not have existed, it would have been some OTHER present. and then, if the present is already the OTHER present you want, then you wouldn't have gone back to the past to change it. so the bottomline is, it's ONE BIG MESS OF CONTRADICTION.
another way to think about it is this: say once in the past, you're offered $1 million, but you rejected it because you thought it was a scam. well, now, at the present moment, your life is hellish. you're poor, you have 4 kids, your wife/husband left you. so you want to go back to the PAST and accept that $1 million instead of rejecting it, hoping to change the PRESENT life you dread so much. BUT. if you HAD GONE back to the past and change it, then you wouldn't be living the life you're living right now. if you HAD GONE back to the past and change it, then you'll be rich RIGHT AT THIS MOMENT. and if you're rich, there's no need to go back to the past. it's circular. if this is still confusing, let's say you want to change the past. then you work hard to invent a time machine that will bring you to the past. after years of hardwork, you succeeded. then you go back to the past and accept the money. but then, as your PAST SELF proceeds in time, your past self won't have any need to go back to the past and hence your past self would not have invented the time machine. but your past self is YOU, and if you end up not inventing the time machine, how did you go back to the past and make that change of decision?
a comic strip i've read is about this one guy who's broke on monday and decides to borrow money from his future self, him on friday evening after getting his paycheck. so he borrows the money, goes shopping, and eats at a restaurant. at the end of the week, he's broke again, but the question is: does he get the paycheck that he has already spent since monday? if he doesn't, then he couldn't have borrowed the money on monday because on friday he doesn't get a paycheck. if he does, then he's getting 2 paychecks and that just doesn't make sense since he has already borrowed it on monday. if he keeps doing this over and over, that is, keeps borrowing money from his future self, then what happens if he borrowed money from his friday self but then he died on wednesday? will it be an infinite regress?
we were discussing the philosophy of time, like what time is and how one defines time and whatnot, and we got to the point about time travel. the ideas i get from TV, is that it's not logically contradictory to go back to the past to change the present, or even the future. we've seen movies like terminator, back to the future, and many others that use time travel as the main idea. now, his argument is one that i find really interesting, although it's still quite hard for me to grasp. he proposes that time travel with the idea "going back to the past to change the present" is logically impossible.
why?
this is what he argues. let's take terminator 2 for example. so the robots send a machine to the past to kill john o'connor, and then the old john o' connor sends arnold schwarznegger back to protect the young john oconnor. well, according to prof. callender, the old john o'connor does not need to send arnold back to protect him, BECAUSE HE ALREADY EXISTS AT HIS PRESENT. the idea is that since he already exists AT THE PRESENT, that means IN THE PAST, that bad robot sent to kill him DID NOT SUCCEED, for if that robot SUCCEEDED, he wouldn't have been there IN THE PRESENT. so in a way, what prof. callender proposes is that no matter what you do, you CANNOT go back to the past to change the present, because the present HAS EXISTED. if you had gone to the past and change it, THIS PARTICULAR present would not have existed, it would have been some OTHER present. and then, if the present is already the OTHER present you want, then you wouldn't have gone back to the past to change it. so the bottomline is, it's ONE BIG MESS OF CONTRADICTION.
another way to think about it is this: say once in the past, you're offered $1 million, but you rejected it because you thought it was a scam. well, now, at the present moment, your life is hellish. you're poor, you have 4 kids, your wife/husband left you. so you want to go back to the PAST and accept that $1 million instead of rejecting it, hoping to change the PRESENT life you dread so much. BUT. if you HAD GONE back to the past and change it, then you wouldn't be living the life you're living right now. if you HAD GONE back to the past and change it, then you'll be rich RIGHT AT THIS MOMENT. and if you're rich, there's no need to go back to the past. it's circular. if this is still confusing, let's say you want to change the past. then you work hard to invent a time machine that will bring you to the past. after years of hardwork, you succeeded. then you go back to the past and accept the money. but then, as your PAST SELF proceeds in time, your past self won't have any need to go back to the past and hence your past self would not have invented the time machine. but your past self is YOU, and if you end up not inventing the time machine, how did you go back to the past and make that change of decision?
a comic strip i've read is about this one guy who's broke on monday and decides to borrow money from his future self, him on friday evening after getting his paycheck. so he borrows the money, goes shopping, and eats at a restaurant. at the end of the week, he's broke again, but the question is: does he get the paycheck that he has already spent since monday? if he doesn't, then he couldn't have borrowed the money on monday because on friday he doesn't get a paycheck. if he does, then he's getting 2 paychecks and that just doesn't make sense since he has already borrowed it on monday. if he keeps doing this over and over, that is, keeps borrowing money from his future self, then what happens if he borrowed money from his friday self but then he died on wednesday? will it be an infinite regress?
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