Re: Time Travel Simulation Re solves “Grandfa ther Paradox”

"David Deutsch david.deutsch-LR/[email protected] [Fabric-of-Reality]" <[email protected]> Sun, 15 Feb 2015 12:22:30 +0000
Newsgroups	gmane.science.physics.fabric-of-reality
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On 14 Feb 2015, at 14:12, hibbsa-/[email protected] [Fabric-of-Reality] <[email protected]> wrote: 


> Posting here because Deutsch's 1991 contribution to the Grandfather Paradox matter (he shifted the paradox to one between relativity and QM) has been modelled apparently confirming many attributes of Deutsch's idea. 


That experiment by Ralph and Ringbauer is nice but I don't think it does (or could possibly have done) anything to distinguish between the various approaches to quantum mechanics near closed timeline lines. Their results are just determined by how they set up the 'simulation'. But I now strongly suspect that the approach in that 1991 paper was wrong or deficient. It was the right approach within the Schrödinger Picture, but I have since come to realise that the Schrödinger Picture badly misrepresents information flow (and the issues of 'time travel' are largely about information flow). The Heisenberg Picture is needed. 


A while ago Alan Forrester and I tried hard to re-cast the same analysis in terms of the Heisenberg Picture. Normally (in the absence of closed timeline lines) the two pictures are inter-translatable and their differences in regard to information flow are just a matter of the HP providing a very straightforward representation of information flow and the SP being very opaque. But in the presence of CTCs the two Pictures are physically different and there is no unique HP. In fact Alan and I were unable to find *any* self-consistent HP in the presence of CTCs. 


Currently my guess is that there *is* a self-consistent HP and that it will give the same answer as the SP. But alternatively it could be that quantum theory is simply inconsistent with relativity in the presence of CTCs. In which case existing physical theory won't be able to answer whether time travel is possible until progress is made with quantum gravity. 


> Below is the article, within that there is a link to the abstract. > http://www.scientificamerican.com/article/time-travel-simulation-resolves-grandfather-paradox/ 


-- David Deutsch

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      <p>On 14 Feb 2015, at 14:12, hibbsa-/[email protected] [Fabric-of-Reality] &lt=
;[email protected]&gt; wrote: <br>
<br>
&gt; Posting here because Deutsch&#39;s 1991 contribution to the Grandfathe=
r Paradox matter (he shifted the paradox to one between relativity and QM) =
has been modelled apparently confirming many attributes of Deutsch&#39;s id=
ea. <br>
<br>
That experiment by Ralph and Ringbauer is nice but I don&#39;t think it doe=
s (or could possibly have done) anything to distinguish between the various=
 approaches to quantum mechanics near closed timeline lines. Their results =
are just determined by how they set up the &#39;simulation&#39;. But I now =
strongly suspect that the approach in that 1991 paper was wrong or deficien=
t. It was the right approach within the Schr=C3=B6dinger Picture, but I hav=
e since come to realise that the Schr=C3=B6dinger Picture badly misrepresen=
ts information flow (and the issues of &#39;time travel&#39; are largely ab=
out information flow). The Heisenberg Picture is needed. <br>
<br>
A while ago Alan Forrester and I tried hard to re-cast the same analysis in=
 terms of the Heisenberg Picture. Normally (in the absence of closed timeli=
ne lines) the two pictures are inter-translatable and their differences in =
regard to information flow are just a matter of the HP providing a very str=
aightforward representation of information flow and the SP being very opaqu=
e. But in the presence of CTCs the two Pictures are physically different an=
d there is no unique HP. In fact Alan and I were unable to find *any* self-=
consistent HP in the presence of CTCs. <br>
<br>
Currently my guess is that there *is* a self-consistent HP and that it will=
 give the same answer as the SP. But alternatively it could be that quantum=
 theory is simply inconsistent with relativity in the presence of CTCs. In =
which case existing physical theory won&#39;t be able to answer whether tim=
e travel is possible until progress is made with quantum gravity. <br>
<br>
&gt; Below is the article, within that there is a link to the abstract. &gt=
; http://www.scientificamerican.com/article/time-travel-simulation-resolves=
-grandfather-paradox/ <br>
<br>
-- David Deutsch<br>
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        Posted by: David Deutsch &lt;david.deutsch-LR/[email protected]&gt;        <hr=
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