Comments on: Does Feynman's approach to QED render the observer problem moot?
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot/
Comments on Ask MetaFilter post Does Feynman's approach to QED render the observer problem moot?Mon, 05 Dec 2005 10:45:44 -0800Mon, 05 Dec 2005 10:45:44 -0800en-ushttp://blogs.law.harvard.edu/tech/rss60Question: Does Feynman's approach to QED render the observer problem moot?
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot
This site:
http://www.skepticreport.com/print/quantum-p.htm
...suggests that Feynman's 'sum over all histories' approach to Quantum Electro-Dynamics has sidestepped the well known 'observer problem' in quantum mechanics (exemplified by the Wigner's Friend paradox). Is this true? <br /><br /> According to some conventional approaches to quantum mechanics, a waveform collapses when a particle is 'observed'. But the meaning of 'observed' is moot. According to the Copenhagen Interpretation is means something along the lines of 'interacts with a classical (as opposed to quantum) system'. But since all systems can be regarded as quantum in some sense, it doesn't really answer the question. In the Schroedinger's cat paradox, a cat whose survival or death depends on the decay of an atom is in a strange alive/dead superimposition-state until an observer opens a box. If you add a human being watching the cat to the room, and close the door ('Wigner's Friend') then the human being is likewise in a superimposition of states ('believing the cat is dead'/'believing the cat is alive') until the observer opens the door and observers him/her. But of course you can keep adding doors forever, until you finally require some ur-observer (God?) to observer the entire universe and force the waveforms to collapse.<br>
<br>
Other explanations include the many-universes theory and the idea that consciousness itself somehow defines an 'observer'. <br>
<br>
The Skeptic site claims that Feynman's approach of summing over all possible histories to arrrive at the probability of a particular event sidesteps the observer problem, but my understanding is that all it does is provide a neat way of calculating the probabilities to an arbitrary accuracy. Can somone help me?post:ask.metafilter.com,2005:site.28474Mon, 05 Dec 2005 10:05:16 -0800unSanephysicsquantummechanicsquantumelectrodynamicsfeynmanBy: sergeant sandwich
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#447845
weird. i was <i>just</i> reading about this last night.<br>
<br>
see if you can find a copy of <a href="http://www.amazon.com/gp/product/1577663217/qid=1133807954/sr=8-6/ref=pd_bbs_6/103-7137949-2307066?n=507846&s=books&v=glance">goswami's <i>quantum mechanics</i></a> and have a look at the last chapter, called something like 'quantum paradoxes: the unfinished chapter'. he spends a good deal of time talking about precisely this issue.<br>
<br>
i think the general conclusion is that there does not exist (yet) a resolution to this paradox of quantum mechanics. goswami's speculation is that consciousness itself might be a quantum mechanical phenomenon, or that the behavior of the observer's mind may ultimately be found to exhibit behavior not yet seen in other quantum mechanical systems.<br>
<br>
nevertheless it's a good read!comment:ask.metafilter.com,2005:site.28474-447845Mon, 05 Dec 2005 10:45:44 -0800sergeant sandwichBy: zanni
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#447948
I don't think the sum over histories approach sidesteps the observer problem. It does sidestep wave-particle duality though, which is related. In some interpretations of QM, the "particle" is actually a wave (wave-function) which collapses to a point-particle after observation. In Fenyman's approach, the particle is always a particle, but it travels over every conceivable path and the totality of the paths make it interfere with itself like a wave. Disclaimer: I am not a quantum mechanic.comment:ask.metafilter.com,2005:site.28474-447948Mon, 05 Dec 2005 11:41:42 -0800zanniBy: Chuckles
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#447962
Have you been following all of <a href="http://www.metafilter.com/mefi/47247#1128348">these</a>, and <a href="http://metachat.org/index.php/2005/12/04/p4230#more4230">this</a>. The issue has been addressed directly and indirectly there. Someone brought up <a href="http://plato.stanford.edu/entries/qm-bohm/">Bohmian mechanics</a>, which is one approach (that <a href="http://www.metafilter.com/mefi/46960#1120001">I</a> looked into), I have no idea how many other approaches there are - many, though.comment:ask.metafilter.com,2005:site.28474-447962Mon, 05 Dec 2005 11:51:30 -0800ChucklesBy: Chuckles
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#447969
Somebody was <a href="http://www.metafilter.com/mefi/46960#1119868">monju_bosatsu</a>, sorry about that...comment:ask.metafilter.com,2005:site.28474-447969Mon, 05 Dec 2005 11:54:09 -0800ChucklesBy: vacapinta
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#447970
zanni is essentially right. The Feynman approach already assumes a "destination" in point B but doesnt have to explain the "collapse" at point B since the particle was always a particle in a sense. The same paradoxes are still there, they've just been reformulated (why is a particle evaluating all possible paths? And why to that destination B?) It is a beautiful approach though, especially since it basically cuts Time out of the picture.comment:ask.metafilter.com,2005:site.28474-447970Mon, 05 Dec 2005 11:55:18 -0800vacapintaBy: delmoi
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#447994
please keep in mind that the cat's alive-or-dead state is <b>A METAPHORE</b>. tia.comment:ask.metafilter.com,2005:site.28474-447994Mon, 05 Dec 2005 12:16:09 -0800delmoiBy: skallas
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#448006
I don't see how any of this can overcome the Heisenberg uncertainty principle. You're still shooting photons (or some other method) into something to observe it, thus changing its state somewhat.comment:ask.metafilter.com,2005:site.28474-448006Mon, 05 Dec 2005 12:25:02 -0800skallasBy: sergeant sandwich
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#448007
<i>please keep in mind that the cat's alive-or-dead state is A METAPHORE.</i><br>
<br>
what is this supposed to mean? could you elaborate?comment:ask.metafilter.com,2005:site.28474-448007Mon, 05 Dec 2005 12:26:04 -0800sergeant sandwichBy: lumpenprole
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#448032
<i>please keep in mind that the cat's alive-or-dead state is A METAPHORE.<br>
what is this supposed to mean? could you elaborate?</i><br>
<br>
Well, he means metaphor. But the cat example was how Schrodinger described what's weird about quantum particles. Under no circumstances is it supposed to describe the behaviour of a cat in a box with a vial of poison gas. In other words, don't try this at home.comment:ask.metafilter.com,2005:site.28474-448032Mon, 05 Dec 2005 12:39:06 -0800lumpenproleBy: jockc
http://ask.metafilter.com/28474/Does-Feynmans-approach-to-QED-render-the-observer-problem-moot#448200
Uncertainty does not come from disturbing what you are measuring (although that does happen). Uncertainty is because the thing you are measuring either has definite velocity or definite position. It cannot have both. At least that's what Feynman told me.comment:ask.metafilter.com,2005:site.28474-448200Mon, 05 Dec 2005 15:29:08 -0800jockc