[ba-unrev-talk] Fwd: [issues] Sci Am : Time Travel piece
>From: Steve Kurtz <kurtzs@freenet.carleton.ca>
>To: ISSS issues <issues@isss.org>
>
>Fun diversion. Multiverses too anthropocentric in conception? Plenty of
>space, but not enough time? :-)
>
>Steve
>
>August 12, 2002
>
>
>The Chronology Protection Conjecture
>
>
>The mind is still the safest way to time travel
>
>
>By Michael Shermer
>
>
>In the original Star Trek series, Dr. McCoy falls through a time portal in
>a city "on the edge of forever," and changes the past in a way that erases
>the Enterprise and her crew, with the exception of Captain Kirk and Mr.
>Spock, who must return to the past to fix what McCoy has undone. Time
>travel is a well-worn staple of science fiction writers, but not only does
>it violate numerous physical laws, there are fundamental problems of
>consistency and causality. The most prominent is the "grandfather
>paradox," in which you travel back in time and kill your grandfather
>before you were born, which means you could not have been born to then
>travel back in time to kill your grandfather. In Back to the Future, Marty
>McFly faces a related but opposite dilemma, in which he must arrange for
>his mother to date his father in order to ensure his conception.
>
>One way around such paradoxes can be found in extremely sophisticated
>virtual-reality machines (think of a holodeck), programmed to replicate a
>past time and place in such detail that it is indistinguishable from a
>real past (which one can never know in full in any case). Another option
>involves a multiple-universes model of cosmology in which you travel back
>in time to a different but closely parallel universe to our own, as
>portrayed in Michael Crichton's novel Timeline, where the characters
>journey to another universe's medieval Europe without worry of mucking up
>our own chronology.
>
>Your Past or Someone Else's?
>
>The fundamental shortcoming for both of these time-travel scenarios is
>that it isn't really your past. A virtual-reality time machine is simply a
>museum writ large, and transporting to some other universe's past would be
>like going back and meeting someone like your mother, who marries someone
>like your father, producing someone like, but not, you--surely a less
>appealing trip than one in your own time-line.
>
>To make that trip you need the time machine of Caltech's Kip Thorne, who
>had his interest piqued in time travel when he received a phone call one
>day from Carl Sagan. Sagan was looking for a way to get the heroine of his
>novel Contact--Eleanor Arroway (played by Jody Foster in the film
>version)--to the star Vega, 26 light-years away. The problem Sagan faced,
>as all science fiction writers do in such situations, is that at the speed
>of, say, the Voyager spacecraft (the fastest human-made object), it would
>take about 490,000 years to get to Vega. That's a long time to sit, even
>if you are in first class with your seat back and tray table down.
>Thorne's solution, adopted by Sagan, was to send Ellie through a
>wormhole--a hypothetical space warp similar to a black hole in which you
>enter the mouth, fall through a short tube in hyperspace that leads to an
>exit hole somewhere else in the universe. (Think of a tube running through
>the middle of a basketball--instead of going all the way around the
>surface of the ball to get to the other side, you tunnel through the
>middle.) Since, as Einstein showed, space and time are intimately
>entangled, Thorne theorized that by warping space one might also be
>warping time, and that by falling through a wormhole in one direction it
>might be possible to travel backward in time.
>
>Thorne's initial calculations showed that it was theoretically possible
>for Ellie to travel just one kilometer down the wormhole tunnel and emerge
>near Vega moments later--not even time for a bag of peanuts. After he
>published his theory in a technical physics journal in 1988, the media got
>a hold of the story and branded Thorne as "The Man Who Invented Time
>Travel." Not one to encourage such sensationalism, Thorne continued his
>research and by the early 1990s began growing skeptical of his own thesis.
>
>Trouble with Time Machines
>
>Whether it is possible to actually travel through a wormhole without being
>crushed out of existence, Thorne reasoned, depends on the laws of quantum
>gravity, which are not fully understood at this point. What he and his
>colleagues ultimately discovered is that, as Kip told me, "all time
>machines are likely to self-destruct the moment they are activated."
>Thorne's colleague Stephen Hawking agreed, only half sardonically calling
>this conclusion the "chronology protection conjecture," in which "the laws
>of physics do not allow time machines," thus keeping "the world safe for
>historians." Besides, Hawking wondered, if time travel were possible,
>where are all the time tourists from the future?
>
>It's a good question and, in conjunction with the paradoxes and physical
>law constraints, makes me skeptical as well. Until much more is known
>about quantum gravity and wormholes, virtual-reality machines and multiple
>universes, I'll do my time traveling through the chronology projector of
>the mind.
>
>------------------------------------------------------------------------
>
>Michael Shermer is publisher of Skeptic magazine (www.skeptic.com) and the
>author of In Darwin's Shadow: The Life and Science of Alfred Russel Wallace.
>
>------------------------------------------------------------------------
>
>
>
>
>
>--
>http://magma.ca/~gpco/ http://www.scientists4pr.org/ Anyone who believes
>exponential growth can go on forever in a finite world is either a madman
>or an economist.--Kenneth Boulding
>
>
>Fun diversion. Multiverses too anthropocentric in conception? Plenty of
>space, but not enough time? :-)
>
>Steve
>
>August 12, 2002
>
>The Chronology Protection Conjecture
>
>The mind is still the safest way to time travel
>
>By Michael Shermer
>
>In the original Star Trek series, Dr. McCoy falls through a time portal in
>a city "on the edge of forever," and changes the past in a way that erases
>the Enterprise and her crew, with the exception of Captain Kirk and Mr.
>Spock, who must return to the past to fix what McCoy has undone. Time
>travel is a well-worn staple of science fiction writers, but not only does
>it violate numerous physical laws, there are fundamental problems of
>consistency and causality. The most prominent is the "grandfather
>paradox," in which you travel back in time and kill your grandfather
>before you were born, which means you could not have been born to then
>travel back in time to kill your grandfather. In Back to the Future, Marty
>McFly faces a related but opposite dilemma, in which he must arrange for
>his mother to date his father in order to ensure his conception.
>
>One way around such paradoxes can be found in extremely sophisticated
>virtual-reality machines (think of a holodeck), programmed to replicate a
>past time and place in such detail that it is indistinguishable from a
>real past (which one can never know in full in any case). Another option
>involves a multiple-universes model of cosmology in which you travel back
>in time to a different but closely parallel universe to our own, as
>portrayed in Michael Crichton's novel Timeline, where the characters
>journey to another universe's medieval Europe without worry of mucking up
>our own chronology.
>
>Your Past or Someone Else's?
>
>The fundamental shortcoming for both of these time-travel scenarios is
>that it isn't really your past. A virtual-reality time machine is simply a
>museum writ large, and transporting to some other universe's past would be
>like going back and meeting someone like your mother, who marries someone
>like your father, producing someone like, but not, you--surely a less
>appealing trip than one in your own time-line.
>
>To make that trip you need the time machine of Caltech's Kip Thorne, who
>had his interest piqued in time travel when he received a phone call one
>day from Carl Sagan. Sagan was looking for a way to get the heroine of his
>novel Contact--Eleanor Arroway (played by Jody Foster in the film
>version)--to the star Vega, 26 light-years away. The problem Sagan faced,
>as all science fiction writers do in such situations, is that at the speed
>of, say, the Voyager spacecraft (the fastest human-made object), it would
>take about 490,000 years to get to Vega. That's a long time to sit, even
>if you are in first class with your seat back and tray table down.
>Thorne's solution, adopted by Sagan, was to send Ellie through a
>wormhole--a hypothetical space warp similar to a black hole in which you
>enter the mouth, fall through a short tube in hyperspace that leads to an
>exit hole somewhere else in the universe. (Think of a tube running through
>the middle of a basketball--instead of going all the way around the
>surface of the ball to get to the other side, you tunnel through the
>middle.) Since, as Einstein showed, space and time are intimately
>entangled, Thorne theorized that by warping space one might also be
>warping time, and that by falling through a wormhole in one direction it
>might be possible to travel backward in time.
>
>Thorne's initial calculations showed that it was theoretically possible
>for Ellie to travel just one kilometer down the wormhole tunnel and emerge
>near Vega moments later--not even time for a bag of peanuts. After he
>published his theory in a technical physics journal in 1988, the media got
>a hold of the story and branded Thorne as "The Man Who Invented Time
>Travel." Not one to encourage such sensationalism, Thorne continued his
>research and by the early 1990s began growing skeptical of his own thesis.
>
>Trouble with Time Machines
>
>Whether it is possible to actually travel through a wormhole without being
>crushed out of existence, Thorne reasoned, depends on the laws of quantum
>gravity, which are not fully understood at this point. What he and his
>colleagues ultimately discovered is that, as Kip told me, "all time
>machines are likely to self-destruct the moment they are activated."
>Thorne's colleague Stephen Hawking agreed, only half sardonically calling
>this conclusion the "chronology protection conjecture," in which "the laws
>of physics do not allow time machines," thus keeping "the world safe for
>historians." Besides, Hawking wondered, if time travel were possible,
>where are all the time tourists from the future?
>
>It's a good question and, in conjunction with the paradoxes and physical
>law constraints, makes me skeptical as well. Until much more is known
>about quantum gravity and wormholes, virtual-reality machines and multiple
>universes, I'll do my time traveling through the chronology projector of
>the mind.
>
>Michael Shermer is publisher of Skeptic magazine
>(<http://www.skeptic.com>www.skeptic.com) and the author of In Darwin's
>Shadow: The Life and Science of Alfred Russel Wallace.
>
>
>
>
>
>
>--
><http://magma.ca/~gpco/>http://magma.ca/~gpco/
>http://www.scientists4pr.org/
>Anyone who believes exponential growth can go on forever in a
>finite world is either a madman or an economist. Kenneth Boulding (01)