What is Wave function collapse: Definition and 86 Discussions

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

    B New hypothesis of continuous wave function collapse

    In standard quantum mechanics, the wavefunction remains in a superposition of multiple possible states until it is "measured" or observed, at which point it collapses into one definite state. However, in this new model, there is no special role for measurement or observation. Instead, all...
  2. Y

    I Collapse of particle wave function and single Universe wave function?

    Hi All, Sorry for a silly question from a curious but not properly initiated: why a concept of a particle wave function "collapse" upon "observing" even a thing given that there is only one Universe wave function that this particle is a part of? As I understand this, once a particle has...
  3. zaramahdi

    A Can particles appear and disappear "with" a cause?

    The first thing we need for this is to define what a particle is... It is an object that has specific intrinsic properties and is described by a wave sign How to measure it? This is done by the interaction of the particle to be measured with the measurement system. When measuring, the wave...
  4. P

    I How non-conscious can an Observer be and cause wave function collapse?

    Please help me find websites describing easy to understand experiments discovering how little of a Conscious Observer is needed to cause wave function collapse? Is just a sensor, that "could have been" attached to a reporting device, that "could have been" looked-at by a Conscious Human...
  5. S

    I Exploring Wave Function Collapse: The Role of Conscious Observation

    Do scientists still entertain the idea that wave function collapse requires a conscious observer? Is it possible? Why/not?
  6. B

    Decoherence vs Observer Wave Function Collapse & MWI: Questions

    I have a couple of questions about decoherence vs. observer wave function collapse and multi-worlds interpretation. Am I right that Zeh's decoherence theory does not involve an observer, and esp not a conscious observer? Also, am I right that his theory does not involve or align with the...
  7. lektroon

    I Are Nicolas Gisin's Intuitionist Mathematics Theories Compatible with SR and GR?

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  8. C

    B How is energy transferred from a wave to a photon?

    This is just a curiosity to me. My interest is from the position of a layman (as you will see from my description below). In the double slit experiment it shows a wave passing through both slits and interfering with itself to create an interference pattern. This is how I understand it... From...
  9. E

    B Question about quantum superposition

    All of my speculation is based on my current understanding of quantum physics as an art high school student who just has this as an interest, which is in no way at a quantum physicist's level so I apologize if this question is stupid. Also sorry for my English. Most, if not all of you reading...
  10. B

    B Entangled particle decoherence question

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  11. TheHeraclitus

    B Objective-collapse theory, collapse for large objects

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  12. Sciencemaster

    I Exploring Wave Function Collapse and Measuring Particles

    Hello! Let's say we have a wave function. Maybe it's in a potential well, maybe not, I think it's arbitrary here. This wave function is one-dimensional for now to keep things simple. Then, we use a device, maybe a photon emitter and detector system where the photon crosses paths with the wave...
  13. O

    B Schrödinger's cat measurement

    In the Schrödinger's cat thought experiment in its standard configuration, before the experimenter opens the box that contains the cat, has any relevant QM measurement been made by any objects involved in this instance of this experiment? My speculation/understanding: Yes, the cat knows (is...
  14. Lexovix

    B Wave Function Collapse using faulty recording devices.

    Hey there! I have two questions regarding the Double Slit Experiment and the Wave Function Collapse. How effective does a measuring device have to be to cause a collapse? As in, say that every second the device has a 50% chance to turn off or on for one second, does the collapse still occur...
  15. hyksos

    A Wave Function Collapse and Thermodynamic Irreversible Processes

    Very early in the development of thermodynamics, it was realized that the 2nd Law of Thermodynamics is not a law fundamental to the fabric of our cosmos, but only becomes true in the limit of the number of particles. It was none other than Boltzmann himself who realized and articulated this...
  16. Sciencemaster

    I Does the wave function spread more quickly after it is observed?

    For the sake of this question, I am primarily concerned with the position wave function. So, from my understanding, the wave function seems to 'collapse' to a few states apon measurement. We know this because, if the same particle is measured again shortly after this, it will generally remain in...
  17. danielhaish

    I Why quantum wave function collapse is not consider a signal?

    I read about the non-communication theorem and I understand why when changing one practical will not change the other . But suppose that there is two observers that doing the double slit experiment, but using it with two entanglement practicals. observer one should send signal of yes or...
  18. StevieTNZ

    B "Test of wave function collapse suggests gravity is not the answer"

    https://phys.org/news/2020-09-function-collapse-gravity.html An interesting article I saw yesterday. However, both Nature articles (the summary [https://www.nature.com/articles/s41567-020-1026-2] and the actual technical paper [https://www.nature.com/articles/s41567-020-1008-4]) are behind a...
  19. ngrunenberg

    B How do quantum computers find a solution?

    Apologies in advance if this is a stupid question, I'm not the brightest. I recently listened to Scott Aaronson's conversation with Lex Fridman, and an interview he did for Scientific American, regarding quantum computing (QC from now on) and have a question regarding how a QC finds a solution...
  20. Lynch101

    B Entanglement & Wave Function Collapse

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  21. Sophrosyne

    Is the concept of "wave function collapse" obsolete?

    Summary: In the past, physicists talked of the phenomenon of "wave function collapse" very freely, whereas now there seems to be some reservation about it. Why? In reading older popular physics literature, physicists used to talk about "wave function collapse" freely and more often...
  22. Silvio Macedo

    I Wave function of particle / quantum field in space, also in time?

    Quantum fields have wave functions that determine a particle position in space. It solves non-locality, double-slit paradox, tunnel effect, etc. What if the wave function is also in time? Won't it solve the breaking of causality at quantum level? (Delayed Choice/Quantum Eraser/Time) Not much...
  23. T

    I Locality and Wave Function Collapse Implications

    OK, so I'm trying to work out a few ideas regarding locality. I've studied at the undergrad level in the past (including quantum), but with professors that slaved away at proving math constructs and never bothered to indulge in clarifying the context of any concepts, so I'm pretty weak here...
  24. Sandeep T S

    I Wave function collapse in a double slit experiment

    Is anyone did experiment on wave function collapse in double slit experiment. Could you please share information about that, and also share research paper about that experiment. What kind of observation done here, what kind of equipment used for that?
  25. Sophrosyne

    B How to think of molecular orbitals quantum mechanically

    The electrons in a molecule are said to be in a quantum superposition state in terms of their position/spin/momentum. But when you look at a molecule like water at a chemical level, it has a very specific shape corresponding to the P orbitals of the outer shell of the Oxygen atom. The two...
  26. J

    I Would this experiment prove consciousness causes collapse

    Firstly i would like to say that i am not advocating the need for a conscious observer to collapse the wave function but i just want to know whether the methodology behind this experiment would prove or disprove this idea. The experiment would be similar to the quantum eraser experiment except...
  27. D

    B The Nature of Measurement and Interaction in Quantum Mechanics

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  28. C

    B Meaning of Wave Function Collapse

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  29. E

    I Wave function collapse and measurement rule

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  30. Thejas15101998

    I Wave Function Collapse: Quantifying Quickness

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    B Why does a the Wave Function collapse?

    Why does a wave function collapse when we observe a particle? I would like to know why something that is in Super Position suddenly chooses a particular position when observed? If something is in all positions or states. How does the particle choose a particular state? What is the decision...
  32. P

    I Concerning the Nature of Quantum Measurement....

    I'm well aware of the common adage and quantum fact that, until a particle is measured by some sort of instrument, it exists in a state of superposition, can interfere with itself, etc. My questions pertains to the definition of "measurement". In order for something to qualify as a measurement...
  33. ohwilleke

    I Is Gravity Dynamically Emergent From Wave Function Collapse?

    A clever new paper explores the notion that the reduced Planck's constant in the quantum analogy to Newton's constant for macroscopic quantities though a hybrid quantity that generalized the Compton wavelength and the Schwarzschild radius. This allows for a linkage between the Einstein equations...
  34. M

    I Trying to model wave function collapse

    Lets assume there is an observable represented by the operator, ##\hat{A}##. It follow (I think) that the observed values and allowed states obeys an equation of the following form\begin{equation}\hat{A}|\psi^i\rangle=\lambda_f|\psi_f\rangle\end{equation} where $$|\psi^i\rangle = initial \ \...
  35. J

    B Measuring velocity and interference?

    If I measured the velocity of an electron what happens to its position? Does it collapse into a specific position or is it still uncertain? Here's a thought experiment... we measure the velocity of an electron and then send it through the double slit at the same time. Does the electron still...
  36. J

    B How does sideband detection work in a Penning trap?

    http://depts.washington.edu/uwptms/research.html I'm having a hard time understanding how the sideband detection works. They say that they use an rf drive to observe the particle in the trap. But what is an rf drive and how does it observe the particle? Also, when this rf drive is put into the...
  37. N

    B Interference pattern after a particle is detected?

    Say we have a particle, like an electron in a double slit experiment. And say that we have a measuring apparatus to detect it right after its fired out of the electron gun. And after that it goes through the double slit and hits the detector plate. Would we see an interference pattern? If the...
  38. FreeThinking

    I Is entanglement severed by wave function collapse?

    What has confused me for a long time is the interaction between superposition and entanglement. That is, what happens when one member of a pair of entangled particles passes through a filter that selects for an observable that is incompatible to the observable in which the pair is entangled...
  39. E

    I On Wave Function Collapse and Accuracy of Energy Measurment

    I have a concern about having some wave function psi, that is originally a superposition of many eigenstates (energies). Traditionally, it is said that the square of the coefficient of each of the component eigenfunctions represents the probability of measuring this particular energy eigenstate...
  40. I

    B Is the wave function collapse asymmetrical in time?

    Suppose the Copenhagen interpretation is correct. And we reverse time, what happens. If a wave function has collapsed, and we found a particle somewhere. Now, I turn back time( just hypothetically), what would happen? Would the wave function uncollapse and would the particle then appear at some...
  41. Bill Myk

    I Strong Force and Wave function collapse

    Why does STRONG FORCE fail regarding complex structures of sub atomic particles when wave functions collapse @ entangled superpositions. Why does it not continue to function keeping the particles bound yet unentangled with the observed Eigenstate being it was originally binding such particles @...
  42. P

    "Wave function Collapse" 'proof' articles

    I have seen a number of references to apparent experimental "proof" of wavefunction collapse www.nature.com/articles/ncomms7665 However, I am still seeing propagation of the "Many Worlds" theory, which, and I admit that my understanding is limited, but the MW hass at its very core, a necessary...
  43. Hybrid

    The Two-State Vector Formalism

    Within Two-state vector formalism is the universe probabilistic or determined? I have read into this interpretation, but I cannot figure out which. Thanks guys https://en.wikipedia.org/wiki/Two-state_vector_formalism http://www.tau.ac.il/~yakir/yahp/yh165.pdf...
  44. Hybrid

    I Many Worlds - Superdeterministic?

    Forgive me if this question has been asked previously on this board, but I cannot seem to find anything similar having searched around earlier. I suppose this blog entry written by the Physicist Robert Oerter linked below has accurately reflected how I feel about Many Worlds: "But now you see...
  45. abrogard

    B What Is Surprising About Wave Function Collapse?

    Excuse my ignorance. I've been googling trying to understand but they always seem to just state it without explaining why. They say the electron could be anywhere within this area of probability but we don't know why until we look and then the wave function 'collapses' and we know where it is...
  46. H

    Interpretation of a wave function collapse

    Suppose the system is in a state of superposition of two determinate states (of an observable) and has equal probability of getting each determinate state, when observed. An observation forces the collapse of the wave function to either one of the determinate state (say, states A and B). Since...
  47. B

    Explain delayed choice quantum eraser without consciousness

    I'm trying to understand the delayed choice quantum eraser experiment without consciousness. As I understand it, photons will either interfere or not depending on whether or not "which-path" information is randomly hidden and rendered unkowable to the experimenter. That is, rather the by any...
  48. C

    Difference Between Two Thoughts on Wave Function Collapse?

    I've recently been reading the book The Dancing Wu Li Masters which is supposed to be a very basic introduction to quantum physics. I have a question on the following quote: "Up to now, we have said that the collapse occurs when somebody looks at the observed system. This is only one point of...
  49. 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...
  50. 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...
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