On 12/5/2012 5:17 PM, Craig Weinberg wrote:
On Wednesday, December 5, 2012 1:41:43 AM UTC-5, Brent wrote: On 12/4/2012 9:14 PM, Craig Weinberg wrote:On Tuesday, December 4, 2012 6:27:42 PM UTC-5, Brent wrote: On 12/4/2012 12:32 PM, Craig Weinberg wrote:On Tuesday, December 4, 2012 2:52:25 PM UTC-5, Brent wrote: Kinda depends on what you mean by 'available'.� If the entangled photon is allowed to hit a wall and be absorbed, it is only 'available' to a kind of Maxwellian demon who can discern the thermal atomic motions and trace them back to get which-way infomation - but the interference pattern is destroyed anyway.� If the entangled photon is simply allowed to fly out the window and off to infinity it is 'available' many years later to an inhabitant of some extra-solar planet - and the interference pattern is destroyed in our present.� What if the inhabitant of the extra-solar planet catches the photon in a lens just like the quantum eraser?The interference would be destroyed.� Note that the way the experiment works (and necessarily so) is that the photons detected at the interference plane have to be post-selected to pair up with those either erased or not on the other leg.� So since an extra-solar observer could only catch a small fraction of the photons, the interference would erased in the corresponding small fraction of those hitting the interference plane. You could look for a temporal rather than spatial interference pattern. That way there would be a chance that if any photons were received they might continue to stream for long enough: "The latest experiment is radically different because the slits exist in time not space, and because the interference pattern appears when the number of electrons at the detector is plotted as a function of their energy rather than their position on a screen. The work was performed at the Technical University of Vienna in collaboration with physicists from the Max Born Institute in Berlin, the Max Planck Institute for Quantum Optics in Munich and the University of Sarajevo. Paulus and co-workers focused a train of pulses from a Ti:sapphire laser into a chamber containing a gas of argon atoms. The pulses were so short � just 5 femtoseconds � that each one contained just a few cycles of the electric field. The team was able to control the output of the laser so that all the pulses were identical. The researchers could, for example, ensure that each pulse contained two maxima of the electric field (thatis, two peaks with large positive values) and one minimum (a peak with a large negative value). There was a small probability that an atom would be ionized by one or other of the maxima, which therefore played the role of the slits, with the resulting electron being accelerated towards a detector. If the atom was ionized by the minimum, the electron travelled in the opposite direction towards a second detector. The team registered the arrival times of the electrons at both detectors and then plotted the number of electrons as a function of energy. The researchers observed interference fringes at the first detector because it was impossible to know if an electron counted by the detector was produced during the first or second maximum. There was no interference pattern at the second detector because all the electrons were produced at the same time at the minimum. However,when the phase of the laser was changed so that there was one maximum and two minima, interference fringes were seen at the second detector but not at the first. �We have complete which-way information and no which-way information at the same time for the same electron,� says Paulus. "It just depends on the direction from which we look at it."� -http://physicsworld.com/cws/article/news/2005/mar/02/new-look-for-classic-experiment <http://physicsworld.com/cws/article/news/2005/mar/02/new-look-for-classic-experiment>I looked at the paper. It doesn't show the detector arrangement, but from the description I don't see that it can obtain which-way and no-which-way for the *same* electron.I think that they are using two detectors on the same wave, so that each one of the twin peaks on one detector which produce no-which way interference patterns is also a single peak on the opposite detector which produces the which way no-interference pattern. It's staggered like a zipper.
The peaks are in the EM field. They're detecting electrons. The electron has a Schrodinger wave of probability associated with it - but detections are all particle like and must be either in the forward or backward direction. The interference only appears when you accumulate many detections. So I don't see anyway the data can refer to which-way and interference 'for the same electron'.
What if the inhabitant naturally has eyes which function as quantum erasers?Those wouldn't be eyes.� The eraser focuses the photons on the same spot whichever slit they went through so the 'eyes' that would erase the information are 'eyes' that can't resolve the slits. Maybe more photoreceptors than eyes, but they can still discern light from dark, so they could be used as eyes of a sort, especially if their brain accumulated light-dark patterns over time...i.e. more like optical ears.But if they don't detect the direction of the photon with sufficient resolution then they won't act as erasers of the interference pattern. Maybe it could detect a red shift? Would that be enough?
No, there's no way that red shift would tell which slit.
I think that the term 'eraser' is fundamentally misguided.
No, it's a good term. It emphasizes that in general one must do something to cancel out or erase the information that would otherwise distinguish the two cases, photon thru the left slit and photon thru the right slit. People usually understand that if you detect which-way information the interference is destroyed, but they don't understand that if you don't detect it but it is still available in the universe the interference is also destroyed - and 'available' means 'available in principle', even though it may not be available in practice (as when the photon gets absorbed in a wall or flys out the window).
What it seems like is that we are looking at the arrow of time with a microscope, and seeing how events themselves are realized, through a conservation of semantic continuity.
??
What if the inhabitant has one eye which is a quantum eraser and one which isn't?Depends on which one detects the photon. Yes, that's the point. If you don't know which one, how does the interference pattern know?'It knows' because you have to select out the photon detections corresponding the ones whose partner went in the detector eye in order to see the interference. Not sure I get that.
If some of the auxiliary photons are detected by the which-way eye, then their partners don't form an interference pattern. The partners of the others do form an an interference pattern. When the experiment is done the pattern is built up by detecting many photons what constitute a mix of the two and so you see a pattern that is intermediate between interference and no interference. After the fact, using the coincidence timing, you pick out which ones are paired with the which-way eye and which aren't and that separates the ensembles into no-interference and interference - after the fact.
What if the inhabitant has a cat in a box with a cyanide capsule triggered by...What if you read the papers yourself. I try but find the jargon distracting.I don't see any jargon.� It's just that real experiments are messier and have more details to explain than thought experiments. That's no excuse for omitting a clear summary of what was learned and why.
And there's no excuse for not including a diagram of the experimental arrangement. Brent -- You received this message because you are subscribed to the Google Groups "Everything List" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/everything-list?hl=en.
