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Delayed Choice Quantum Eraser Question 
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#19
Feb1813, 09:07 AM

P: 915

The idler's state during collapse is not controllable/predeterminable 


#20
Feb1813, 01:04 PM

P: 161

San K: indeed.



#21
Feb2013, 08:33 PM

P: 342

Even though you can't decide the particular value you'll get for the observable you are measuring on the idler photon, you can decide which observable to measure. Don't you think that that would affect the statistics on the other side? Even if this was possible, given the fact that both measurement events are spacelike, this sould not imply retrocausality, but it would imply fasterthanlight signaling. I know most people think that in Dopfer's experiment coincidence counting is the only way to get an interference pattern, but I am not convinced yet.



#22
Feb2013, 08:42 PM

P: 342

Ruth, If after making a measurement, or having some quantum state recorded in a stable way (decoherence or "collapse" in the language of CI) you have a definite state, then the set of all these outcomes in the past, present and future could be mapped on a diagram, constituting what could be called "a block model". Wouldn't it ? This is if we think that there is only one outcome after measurement, which all oneworld interpretations (not only TI) propose.



#23
Feb2013, 08:44 PM

P: 342




#24
Feb2013, 11:07 PM

P: 161

Regarding sending a signal into one's own past: in order to do this using FTL signalling you have to collaborate with someone in a different inertial frame, both parties using FTL signalling. Wiki has a pretty good discussion of this here: http://en.wikipedia.org/wiki/Minkowski_diagram (under 'speed of light as a limit'). The problem is that each observer just sends a FTL signal to the other observer based on their observation of an event, but they have have no way of knowing whether that event was a 'signal' or not. 


#25
Feb2013, 11:11 PM

P: 161




#26
Feb2113, 07:48 AM

P: 342




#27
Feb2213, 07:16 AM

P: 342

We can also imagine that the weather this year will show some kind of definite evolution which we can't predict either. But we can imagine that at the end of the year we'll be able to put the actuall data in a diagram. We usually imagine a single future, not a series of possible ones. Of course if can consider the different alternatives and their probability in order to make some decision, such as what crop to plant now if that's what we do. But usually have the belief that the future will be one. I think that's the usual way to look at things. Of course there is the manyworlds interpretation where all possible paths of evolution count and are "real" and the consistent histories where we consider different histories but only one is part of reality. I'll appreciate your opinion on this and it would be nice to hear from Dr. Chinese. 


#28
Feb2513, 10:47 AM

P: 342




#29
Feb2613, 10:15 PM

P: 161

Causality is a very slippery notion indeed. I do address this in Chapter 7 of my book.



#30
Feb2813, 10:32 AM

P: 342

Thanks, Alex 


#31
Feb2813, 12:51 PM

P: 161



#32
Feb2813, 01:02 PM

Sci Advisor
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#33
Feb2813, 03:24 PM

P: 342




#34
Feb2813, 05:13 PM

P: 161

Thanks Dr. Chinese! :)



#35
Apr2713, 04:56 PM

P: 342

Ruth, I have now read chapter 7. In it you say: "As noted in Chapter 1, traditional approaches to measurement in quantum theory inevitably end up needing to invoke an ‘observing consciousness’ in order to ‘collapse’ the wave function (or state vector) and bring about a determinate outcome, necessitating speculative forays into psychophysical parallelism" I would like to understand if this means you see psychophysical parallelism as a problematic concept and if this is so, why you think there is a problem with it. Thanks. 


#36
Apr2813, 12:12 AM

P: 161

I view psychophysical parallelism as problematic in the context of interpreting physical theory because it is so speculative, and because it does not appear to be based on any sort of physical theory. As Kent has noted, "we don't have a good theory of mind." In Chapter 1 I quote from Kent (2010): "“...the fact that we don't have a good theory of mind, even in classical physics, doesn't give us a free pass to conclude anything we please. That way lies scientific ruin: any physical theory is consistent with any observations if we can bridge any discrepancy by tacking on arbitrary assumptions about the link between mind states and physics.” (A. Kent, 2010, from Many Worlds? Everett, Quantum Theory, and Reality , p.21)



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