Timeline for What constitutes an observation/measurement in QM?
Current License: CC BY-SA 3.0
11 events
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| Dec 20, 2023 at 8:16 | comment | added | JustAMartin | Has there been a practical experiment that would clearly distinguish that the outcome is determined by the measurement with a physical detector and not by conscious subjective awareness of the signal from the detectors? It might be as simple as keeping the slit detectors turned on and letting the detector signals reach the recording device (whatever it is), but not recording and not becoming subjectively aware of the particle's path. Will the screen show the interference pattern or not when the path is measured but not recorded for later inspection? | |
| Nov 6, 2012 at 18:06 | history | edited | Arnold Neumaier | CC BY-SA 3.0 |
added quote by Wheeler
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| S Nov 6, 2012 at 16:00 | history | suggested | juanrga | CC BY-SA 3.0 |
typos corrected. Changed pdf by abs in arxiv, because abs allows to download other formats and gives additional info as publication journal, versions, trackbacs...
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| Nov 6, 2012 at 15:45 | review | Suggested edits | |||
| S Nov 6, 2012 at 16:00 | |||||
| Nov 5, 2012 at 12:25 | comment | added | Arnold Neumaier | - ''the physicist outside the box may choose a superior treatment''. Even in principle (i.e., having the whole universe at his disposal but bound to the physical laws) a physicist cannot gather enough information to choose a treatment accurate enough to determine the state of a bottle of gas well enough to represent the state without dissipation. | |
| Nov 5, 2012 at 12:25 | comment | added | Arnold Neumaier | @LubošMotl: ''Irreversibility in Nature is never perfect'' - only according to an idealized theoretical model that assumes (against better knowledge) that one can change something without having to observe the required information and without having to set up the corresponding forces that accomplish the change. This can be done in principle only for very small or very weakly coupled systems. | |
| Nov 5, 2012 at 10:13 | comment | added | Luboš Motl | Irreversibility in Nature is never perfect, it's always a matter of approximations, and there's no objective threshold at which one could say that "now it's really irreversible". With a good enough knowledge of the velocities and positions, one may reverse some evolution and prepare a state whose entropy will decrease for a while. It's exponentially difficult but not impossible in principle. The same thing with decoherence. If one traces environmental degrees of freedom, and in principle he can, he may reverse certain amounts of decoherence, too. Decoherence is very fast but never perfect. | |
| Nov 5, 2012 at 10:11 | comment | added | Luboš Motl | The only problem with your assertion is that in the quantum framework, measurements and other "records" are subjective as well. Many people may agree about them, and they usually do, but in principle, others may disagree. The gedanken experiment known as Wigner's friend illustrates this clearly. A friend chosen in a box may "know" that some record of a measurement is already there and became a fact, but the physicist outside the box may choose a superior treatment and describe the physicist inside by linear superpositions of macro-different states. | |
| Nov 5, 2012 at 9:42 | comment | added | Arnold Neumaier | @LubošMotl: The resuts of statistical mechanics resulting in equilibrium and nonequilibrium thermodynamics are extremely well established, and show that there is nothing subjective at all in irreversibility. We observe it every moment when we look at fluid flow of water or air. - If the basic laws are in principle reversible this has no bearing on the real universe as it is impossible in principle that an observer inside the universe can reverse the universe. The real universe as_observed_by_objects_inside is irreversible, and measurements are permanent records for these observers. | |
| Nov 5, 2012 at 7:18 | comment | added | Luboš Motl | Well, except that irreversibility is always a subjective matter. Many subjects may agree it's irreversible for them but in principle, the situation is always reversible and an agent tracing the "irreversible" phenomena exponentially accurately could do it. | |
| Nov 4, 2012 at 15:47 | history | answered | Arnold Neumaier | CC BY-SA 3.0 |