So does this mean that once you succeed in preventing your birth, you just disintigrate?
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From: "rhinoceros" <
rhinoceros@freemail.gr>
Reply-To:
virus@lucifer.comTo:
virus@lucifer.comSubject: virus: Time travel and free will: A quantum solution?
Date: Thu, 16 Jun 2005 11:31:14 -0600
This was mentioned in New Scientist:
No paradox for time travellers
http://www.newscientist.com/article.ns?id=mg18625044.300THE laws of physics seem to permit time travel, and with it, paradoxical
situations such as the possibility that people could go back in time to
prevent their own birth. But it turns out that such paradoxes may be ruled
out by the weirdness inherent in laws of quantum physics.
<snip>
Because such time travel sets up paradoxes, many researchers suspect that
some physical constraints must make time travel impossible. Now, physicists
Daniel Greenberger of the City University of New York and Karl Svozil of the
Vienna University of Technology in Austria have shown that the most basic
features of quantum theory may ensure that time travellers could never alter
the past, even if they are able to go back in time.
The constraint arises from a quantum object's ability to behave like a wave.
<snip> The object is unlikely to be in places where the components interfere
destructively, and cancel each other out.
<snip>
Waves that travel back in time interfere destructively, thus preventing
anything from happening differently from that which has already taken place
(
www.arxiv.org/quant-ph/0506027). "If you travel into the past quantum
mechanically, you would only see those alternatives consistent with the
world you left behind you," says Greenberger.
[rhinoceros] Here is the paper in a PDF file. I am pasting some of the less
technical parts:
Quantum Theory Looks at Time Travel
http://arxiv.org/PS_cache/quant-ph/pdf/0506/0506027.pdf<snip>
Classically, time travel is inconsistent with free will. If one could visit
the past, then one could change the past, and this would lead to an
alternative present. So there is a paradox here, which is best illustrated
by the famous scenario of a person going back in time to shoot his father
before his father has met his mother, and thus negating the possibility of
his having ever been born. It is for reasons like this that time travel has
been considered impossible in principle.
Of course, one can get around this problem if one considers the universe to
be totally deterministic, and free will to be merely an illusion. Then the
possibility of changing the past (or the future, for that matter) no longer
exists. Since we prefer to think that the writing of this paper was not
preordained at the time of the big bang, we shall reject this solution on
psychological grounds, if not logical ones, and ask whether the paradoxes of
classical physics can be gotten around, quantum mechanically.
<snip lotsa math - As Hawking was told by his publisher, "each formula you
include, you lose half your potential buyers">
According to our model, if you travel into the past quantum mechanically,
you would only see those alternatives consistent with the world you left
behind you. In other words, while you are aware of the past, you cannot
change it. No matter how unlikely the events are that could have led to your
present circumstances, once they have actually occurred, they cannot be
changed. Your trip would set up resonances that are consistent with the
future that has already unfolded.
This also has enormous consequences on the paradoxes of free will. It shows
that it is perfectly logical to assume that one has many choices and that
one is free to take any one of them. Until a choice is taken, the future is
not determined. However, once a choice is taken, and it leads to a
particular future, it was inevitable. It could not have been otherwise. The
boundary conditions that the future events happen as they already have,
guarantees that they must have been prepared for in the past. So, looking
backwards, the world is deterministic. However, looking forwards, the future
is probabilistic. This completely explains the classical paradox. In fact,
it serves as a kind of indirect evidence that such feedback must actually
take place in nature, in the sense that without it, a paradox exists, while
with it, the paradox is resolved. (Of course, there is an equally likely
explanation, namely that going backward in time is impossible. This also
solves the paradox by avoi!
ding it.)
The model also has consequences concerning the many-worlds interpretation of
quantum theory. The world may appear to keep splitting so far as the future
is concerned. However, once a measurement is made, only those histories
consistent with that measurement are possible. In other words, with time
travel, other alternative worlds do not exist, as once a measurement has
been made confirming the world we live in, the other worlds would be
impossible to reach from the original one. This explanation makes the von
Neumann state reduction hypothesis much more reasonable, and in fact acts as
a sort of justification of it.
<snip more maths, sadly making this a non-argument -- take it as a
specialist's opinion>
Thus less ?deterministic? and fuzzier time traveling might be possible, a
possibility we have not yet explored. Neither have we explored the
possibility that feedback should be possible into the future as well as the
past. Of course in this case, it ought to be called ?feedforward? - rather
than feedback.
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------------------------------
Date: Sat, 18 Jun 2005 19:32:45 +0300
From: rhinoceros <
rhinoceros@freemail.gr>
Subject: Re: virus: Time travel and free will: A quantum solution?
Dr Sebby wrote:
>
> ....of course the layman's resolution to this would be, "if time travel
> were possible, wouldnt such a traveler have successfully visited us?"
rhinoceros:
Alas, the party held for time travellers from all times at MIT on May 7
had only limited success...
http://web.mit.edu/adorai/timetraveler/<snip>
Update: The convention was a mixed success. Unfortunately, we had no
confirmed time travelers visit us, yet many time travelers could have
attended incognito to avoid endless questions about the future.
<snip>
More detailed coverage of the event in Wired:
Time Travelers Welcome at MIT
http://www.wired.com/news/technology/0,1282,67451,00.html> ...on another note, one need not kill one's father or anyone for that
> matter. merely being present in the past would create a chain reaction
> of events which would alter the time line of one's mother or father and
> thus result in a different specific sperm impregnating her.. which of
> course would mean a different resultant child.
>
> ...in fact, i would wager(serious money) on the notion that merely
> appearing in the past for a microsecond would result in a chain reaction
> which would entirely alter the present reality...down to every last
> person and all the reactions following. though the altered present
> would likely be rather similar due to large scale nuances in the human
> equation.
All true. Killing your grandpa was only one spectacular scenario. The
idea of that paper was to play with the assumptions that (a) everything
would happen in such a way that you would never find yourself in a
position to kill your grandpa or cause any other change and (b) whatever
you cause by your presence there was bound to happen anyway. This seems
to require that there is a "time loop" already in place for the time
traveller.
According to the author, the man of the present has all the options
open. The man of the future seems to have more limited options; less
places to go, less things to opt for. How much is "less"? A plausible
answer is "none".
The time traveller gag
http://geekpress.com/2005_02_17_daily.htmlYou get some vaguely/slightly futuristic-looking clothes. Make it
plausible, somewhat based on current trends, you're probably aiming for
maybe ten years in the future. You can most likely make do with an
interesting combination of whatever clothes you currently own. Ooh! Or
make a fake tour T-shirt for a band that doesn't exist and mark it "Wild
Tour 2008" or something. whatever. The point is to make it look
plausible that you might come from the future.
Then just run out into the street, select somebody at random and shout
at them, "What's the date today?! Quickly, tell me!"
When they respond, you shout, "What YEAR, man, what YEAR is this?!"
And when they respond again you go, "Noooo! They've sent me back too
far!" or alternatively "I'm too late! It's all going to happen again!"
Then you run away again.
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------------------------------
Date: Sat, 18 Jun 2005 11:10:55 -0600
From: "rhinoceros" <
rhinoceros@freemail.gr>
Subject: virus: Re:Time travel and free will: A quantum solution?
The links in this reply were garbled in the email version, so I am resending it.
[Dr Sebby] ....of course the layman's resolution to this would be, "if time travel
were possible, wouldnt such a traveler have successfully visited us?"
[rhinoceros] Alas, the party held for time travellers from all times at MIT on May 7
had only limited success...
http://web.mit.edu/adorai/timetraveler/<snip>
Update: The convention was a mixed success. Unfortunately, we had no confirmed time
travelers visit us, yet many time travelers could have attended incognito to avoid
endless questions about the future.
<snip>
More detailed coverage of the event in Wired:
Time Travelers Welcome at MIT
http://www.wired.com/news/technology/0,1282,67451,00.html[DrSebby] ...on another note, one need not kill one's father or anyone for that
matter. merely being present in the past would create a chain reaction of events
which would alter the time line of one's mother or father and thus result in a
different specific sperm impregnating her.. which of course would mean a different
resultant child.
>
> ...in fact, i would wager(serious money) on the notion that merely appearing in
the past for a microsecond would result in a chain reaction which would entirely
alter the present reality...down to every last person and all the reactions
following. though the altered present would likely be rather similar due to large
scale nuances in the human equation.
[rhinoceros] All true. Killing your grandpa was only one spectacular scenario. The
idea of that paper was to play with the assumptions that (a) everything would happen
in such a way that you would never find yourself in a position to kill your grandpa
or cause any other change and (b) whatever you cause by your presence there was bound
to happen anyway. This seems to require that there is a "time loop" already in place
for the time traveller.
According to the author, the man of the present has all the options open. The man of
the future seems to have more limited options; less places to go, less things to opt
for. How much is "less"? A plausible answer is "none".
The time traveller gag
http://geekpress.com/2005_02_17_daily.htmlYou get some vaguely/slightly futuristic-looking clothes. Make it plausible, somewhat
based on current trends, you're probably aiming for maybe ten years in the future.
You can most likely make do with an interesting combination of whatever clothes you
currently own. Ooh! Or make a fake tour T-shirt for a band that doesn't exist and
mark it "Wild Tour 2008" or something. whatever. The point is to make it look
plausible that you might come from the future.
Then just run out into the street, select somebody at random and shout at them,
"What's the date today?! Quickly, tell me!"
When they respond, you shout, "What YEAR, man, what YEAR is this?!"
And when they respond again you go, "Noooo! They've sent me back too far!" or
alternatively "I'm too late! It's all going to happen again!"
Then you run away again.
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This message was posted by rhinoceros to the Virus 2005 board on Church of Virus BBS.
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------------------------------
Date: Sat, 18 Jun 2005 18:08:06 +0000 GMT
From: "Erik Aronesty" <
erik@zoneedit.com>
Subject: Re: virus: Re:Time travel and free will: A quantum solution?
> According to the author, the man of
> the present has all the options open.
> The man of the future seems to have
> more limited options; less places to go,
> less things to opt for. How much is
> "less"? A plausible answer is "none".
Althought I agree that "none" is a very reasonable answer, I like the picture of a
haggard time traveler, constantly staring at his PDA and rushing from one appointment
to the next.
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------------------------------
Date: Sat, 18 Jun 2005 20:19:42 +0200
From: "Blunderov" <
squooker@mweb.co.za>
Subject: RE: virus: Time travel and free will: A quantum solution?
[Blunderov] Hmm. Time to reconsider time travel. If it was possible to
only observe the wave displacements that happened x years ago, then one
would have a time machine TV set. Like watching the twinkling of stars
that actually exploded eons ago. All that light and sound from previous
times must have gone somewhere. The trick would be to get it to turn
around and come back here again. Quickly, before it gets any further
away. Oy vei.
Back to the drawing board.
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