Wave function collapse Definition and 88 Threads

In quantum mechanics, wave function collapse occurs when a wave function—initially in a superposition of several eigenstates—reduces to a single eigenstate due to interaction with the external world. This interaction is called an "observation". It is the essence of a measurement in quantum mechanics which connects the wave function with classical observables like position and momentum. Collapse is one of two processes by which quantum systems evolve in time; the other is the continuous evolution via the Schrödinger equation. Collapse is a black box for a thermodynamically irreversible interaction with a classical environment. Calculations of quantum decoherence show that when a quantum system interacts with the environment, the superpositions apparently reduce to mixtures of classical alternatives. Significantly, the combined wave function of the system and environment continue to obey the Schrödinger equation. More importantly, this is not enough to explain wave function collapse, as decoherence does not reduce it to a single eigenstate.Historically Werner Heisenberg was the first to use the idea of wave function reduction to explain quantum measurement.

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  1. J

    Wave Function Collapse: Does Interaction of Photons & Objects Force It?

    While I was daydreaming in my boring math class today I came across a weird problem. What ACTUALLY causes a wave function to collapse. I had a discussion with my teacher the week prior and she was telling me that it has something to do with your brain. I didnt really believe her, I just thought...
  2. J

    Under what circumstances does the wave function collapse?

    The hypothesis that a conscious observer collapses the wave function has been discarded, right? The real reason is that the particle you use to measure the other disrupts the wave function, forcing it to choose an eigenvalue. So since we are able to remove the conscious observer as the...
  3. L

    Decoherence and Wave Function Collapse

    Hi, I was wondering whether we are sure (I know, strong word) that decoherence is the mechanism that takes us from the quantum world to our classical world. Correct me if I'm wrong, but basically decoherence is a phenomenon where we have a bunch of quantum states that, when piled onto each...
  4. Q

    Wave function collapse in QED?

    Does the measurement problem ("wave function collapse") or something similar somehow manifest itself in QED and other quantum field theories? Is it somehow built-in into the propagators etc. "away from sight"? If so, how does it affect the theories and is this a problem, which needs to be...
  5. C

    If you measure the energy of a system how does wave function collapse

    Hey. Given that if you measure the energy of a wave function, the wave function must collapse to the eigenstate corresponding to the eigenvalue measured. Does that mean when you measure the energy of a wave function it must collapse the wave function into one of these stationary states...
  6. F

    Does the environment cause wave function collapse

    I came across this statement by bhobba in another thread and it got me to thinking, if the "environment" itself is capable of collapsing the wave function, then how is it possible to produce an interference pattern in a double slit experiment? After all, the particle isn't traveling through a...
  7. morrobay

    Has Wave Function Collapse Been Verified Experimentally ?

    In QM theory entangled particles or photons are in superposition for spin (spin up or spin down) or for polarization angles. When one of the space like separated pair is measured for a spin or polarization observable, the wave function collapses and the other particle is then in a...
  8. atyy

    Wave function collapse in curved spacetime

    In flat spacetime, there isn't any problem with wave function collapse. I think that's the "textbook" position, although the only citation I have off the top of my head is the discussion in http://arxiv.org/abs/0706.1232 (section 1.1). How about in curved spacetime (working in the regime where...
  9. E

    How gravity affects wave function collapse

    Apologies if these questions have been answered before - I didn't have any luck with google. Something has bugged me for a while about quantum experiments like Schrödinger's cat where a 'black box' system is theorized to be in a superposition of states until observation causes wave function...
  10. stevendaryl

    Wave Function Collapse and Entropy

    I don't want to argue about whether the notion of "wave function collapse" is a good way of understanding quantum mechanics, or not. For the purposes of this discussion, let's just adopt uncritically the naive approach to quantum mechanics, that: Between measurements, the system evolves...
  11. J

    Unraveling the Mystery of Observation & Wave Function Collapse

    Hi, I've done a lot of personal research on the internet trying to understand what exactly is happening in this experiment but I keep seeing contrasting information about what the role of observation actually had on the experiment. What I understand is that when they try to figure out which...
  12. T

    Information Theory on Wave Function Collapse

    I was trying to understand wave function collapse in terms of superposition, but I ran into some problems when relating back to information theory/entropy. It is given in the definition of information in terms of entropy energy is needed to transfer information. That is something we have always...
  13. G

    What happens when a detector does not find a particle in state |4>?

    Homework Statement A particle is in the state 1/2 |1> - 1/2 |2> + 1/2 |3> - 1/2 |4> A detector is placed to measure state |4>. What the particle's wave function collapses into, if the detector does not find a particle Homework Equations <i|j> = delta (i, j) The Attempt at a...
  14. N

    Wave Function Collapse: Quantum Mechanics by Griffith

    i was going through the quantum mechanics book by griffith and on the very first chapter i read that the wavefunction of the quantum particle collapse on measurement. and if the interval between the succesive measurement is shorter the particle will be found at the very same location. the...
  15. USeptim

    Wave function collapse by orbital angular momentum operator Lz

    I have some doubts about the implications of the orbital angular operators and its eigenvectors (maybe the reason is that I have a weak knowledge on QM). If we choose the measurement of the z axis and therefore the Lz operator, the are the following spherical harmonics for l=1...
  16. U

    Wave Function Collapse and Bayesian Probabilty

    I'm curious as to whether or not there is a connection to be drawn between the phenomenon of wave function collapse and the idea of Bayesian inference. I began thinking about this within the context of one of the variants of the Monty Hall problem. If you have one kid, what's the probability...
  17. G

    Wave function collapse for Schrödinger's cat

    I have what is probably a very basic question about the Schrödinger's cat thought experiment. As I understand it, in order for the counter tube to break and release the deadly poison, the Geiger counter must measure whether or not an atom decays. So, why doesn't that measurement collapse the...
  18. I

    Wave function collapse with Young's double slits.

    I have a question regarding Young's double slits experiment. To my understanding, wave function of a photon somehow collapses according to the probability function (which has a interference pattern). But at the very moment the wave hits the screen, it seems to me that there should be no...
  19. N

    Wave Function Collapse: Atom's Non-Stable State

    consider a atom who's single electron is made to jump into conduction band ,after some time the electron will come into it's valence band by releasing the quanta of energy but if an observer observes the electron in it's excited state continuously it's wave function will collapse to bring about...
  20. andrewkirk

    Why doesn't wave function collapse contradict Schrodinger equation?

    The postulates of quantum mechanics include: (1) Schrodinger's equation describes how the wave function of a system changes over time, and appears to make the wave function continuous over time. (2) When a measurement is made of quantity m, the wave function instantly changes to an...
  21. L

    Question about wave function collapse

    I’ve been fascinated with the different QM interpretations since I discovered them… but I want to sort of restrict my imagination to more solid ideas. I know about the Double-Slit experiment and that there are many misconceptions about the correct definition of an ‘observer’ and what role the...
  22. N

    Is Consciousness involved in wave function collapse?

    Hello: I know it's a rather subjective title. But I am no expert in the subject and I've read a lot of information in the Internet that is contradictory. I have read that the collapse of the wave function requires interaction with an observer. But is that collapse in any way related to the...
  23. B

    Does the Wave Function Predict the Most Likely Position of an Electron?

    Hi. I have a simple question- Does the wave function describe probability of finding a particle in a certain state upon collapse of the wave function?
  24. L

    Can the wave function collapse before being measured?

    N.B. I am not trying to send information back in time or generate infinite free energy (also I couldn't find how to delete the other thread but could a moderator please delete it for me) If you could send classical information signals faster than light, then according to relativity you could...
  25. C

    Exploring Wave Function Collapse and the Double Slit Experiment

    I'm still wrestling with the whole uncertainty principal / wave function collapse idea. Obviously a basic building block of QM, I'm having a hard time understanding the real world evidence which supports these QM piles. 1. So from my understanding, the uncertainty principle tells us it is...
  26. M

    How does a wave function collapse?

    Hi. I've asked the question many times (as I'm sure many others have) why does the particle behave differently once it has been observed? Does that not mean it knows it has been observed? How does it know? The only answer I get is: "observing destroys the wave function" , but that doesn't...
  27. B

    Measuring Spin - wave function collapse

    It is my understanding that a measurement of S_z followed by a measurement of S_y will result in a particle which is in an eigenstate of S_y . But it appears that a measurement of say S_y followed by a measurement of S_x results in zero. I see this from a question in which I am asked to...
  28. C

    Description of Wave Function Collapse

    Hello, I'm new to Physics Forums, so I apologize if this question seems somewhat uninformed, but I have recently started studying quantum mechanics, and was curious about the idea of the wave function collapse, and how, from what I can tell, it seems to be approached completely independently...
  29. L

    Wave function collapse and the statistical nature of quantum states

    Sorry for a (maybe) dumb question, but... I understand that according to QM, the description of the situation for a particle or system is described by a linear superposition of the wave functions of all the possible states (eigenstates) of the system. When a measurement is made, the wave...
  30. zonde

    Wave function collapse and entanglement

    Sorry people but some quantum mysteries look quite trivial to me. Wave function collapse for photons is actually subsampling of whole sample of photons. That way wave function collapse can happen instantaneously in the whole experimental setup or even backwards in time. Photon entanglement...
  31. elfmotat

    Having trouble understanding the wave function collapse.

    What about the act of observation actually causes a particle to break the superpostion and "decide" what its state is? What property does the observer posses that changes the the way particles behaves?
  32. MTd2

    Wave function collapse causes gravity? (article title)

    http://arxiv.org/abs/0902.1464 Does wave function collapse cause gravity? Authors: Lajos Diósi (Submitted on 9 Feb 2009) Abstract: We give a twist to the assumption - discussed in various earlier works - that gravity plays a role in the collapse of the wave function. This time we discuss...
  33. P

    Electron wave function collapse

    As far as I understand it, an electron exists as a probability cloud around an atom, representing all the possible places it could be. Then when we make an observation the wave function collapses to one point where we see the electron. So what happens if we keep looking at it? Does the elctron...
  34. U

    Why Is Wave Function Collapse Unnecessary in Bohmian Interpretation?

    why is not need for introducing a true collapse in bohmian interpretation?
  35. T

    Wave Function Collapse: Why Does Observation Matter?

    Why is it that when observing an electron or photon it causes the wave function to collapse, surely the photons that cause this collapse were still "colliding" with it when we wern't looking. Or does it only collapse the wave function from the observers viewpoint? (I'm abit of a noob so if...
  36. B

    Wave Function Collapse in Quantum Mechanics: Understanding Probability

    Hello. In QM we can determine the probability of any event ocurring given the wavefunction. Once we actually take a measurement the particle 'picks' a state to be found in. so my question is how do we know a priori that the particle is in two or more states at the same time before we make a...
  37. M

    Finding Wave Function Collapse

    Scientists wan't to know where wave function collapse occures. I have found at least one. Take the experiment of shooting electrons through two holes that are close together and seeing where they land at a detection screen on the other side. If you shut one hole you get a particle or lump...
  38. H

    Exploring Quantum Mechanics: Wave Function Collapse

    Hate to ask another one of these questions, but I've just read something about the collapse of the wave function that does not seem consistent with other accounts I've read about it. From what I understand, the wave function of a system is collapsed automatically by interaction with another...
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