3 ms·

What Happens in a Measurement?

15 points by Jasamba 11y ago

amelius 11y ago
Summary in plain English?
- goerz 11y ago
  Traditionally, in quantum mechanics a measurement "breaks the system": the state of the system is instantaneously modified in a way that does not follow the normal equation of motion (the Schrödinger equation). This is known as the "collapse of the wave function". The paper shows that there is a way in principle to include the measurement apparatus also within the quantum description, in such a way that the interaction with the system causes the system to eventually evolve into a state that corresponds exactly to the one that results from the traditional collapse of the wave function (but without a "break" in the description). It therefore supports the idea that classical behavior is an emergent phenomenon from the underlying quantum behavior, and that there is no fundamental classical-quantum divide
  - dzdt 11y ago
    Thanks! Since I took quantum in college years ago I had the picture that this must be how it works. Is this at all controversial, among serious physicists?
    - Jasamba 11y ago
      They seem intrigued and eager for further investigation from what i see, the paper showed up on my fb feed through a famous senior physicist sharing it and calling it interesting. ;)
      - goerz 11y ago
        It's definitely interesting! ;-)
    - goerz 11y ago
      Probably not overly controversial, but still a conjecture. That is, nobody has shown how exactly classical physics emerges from quantum mechanics (specifically, the measurement problem). Note that this is a separate and more fundamental issue from how simple quantum systems under certain conditions can show quasi-classical behavior, e.g. the "coherent state" of a quantum oscillator, or the common "let h-bar go to zero"
ivan_ah 11y ago
Some previous work on understanding measurement through decoherence: http://perimeterinstitute.ca/personal/rblume-kohout/thesis/thesis.ssp.pdf http://perimeterinstitute.ca/personal/rblume-kohout/thesis/t... Could someone explain the Lindblad equation in plain English?

15 points by Jasamba 11y ago

amelius 11y ago

Summary in plain English?

goerz 11y ago
Traditionally, in quantum mechanics a measurement "breaks the system": the state of the system is instantaneously modified in a way that does not follow the normal equation of motion (the Schrödinger equation). This is known as the "collapse of the wave function". The paper shows that there is a way in principle to include the measurement apparatus also within the quantum description, in such a way that the interaction with the system causes the system to eventually evolve into a state that corresponds exactly to the one that results from the traditional collapse of the wave function (but without a "break" in the description). It therefore supports the idea that classical behavior is an emergent phenomenon from the underlying quantum behavior, and that there is no fundamental classical-quantum divide
- dzdt 11y ago
  Thanks! Since I took quantum in college years ago I had the picture that this must be how it works. Is this at all controversial, among serious physicists?
  - Jasamba 11y ago
    They seem intrigued and eager for further investigation from what i see, the paper showed up on my fb feed through a famous senior physicist sharing it and calling it interesting. ;)
    - goerz 11y ago
      It's definitely interesting! ;-)
  - goerz 11y ago
    Probably not overly controversial, but still a conjecture. That is, nobody has shown how exactly classical physics emerges from quantum mechanics (specifically, the measurement problem). Note that this is a separate and more fundamental issue from how simple quantum systems under certain conditions can show quasi-classical behavior, e.g. the "coherent state" of a quantum oscillator, or the common "let h-bar go to zero"

ivan_ah 11y ago

Some previous work on understanding measurement through decoherence: http://perimeterinstitute.ca/personal/rblume-kohout/thesis/thesis.ssp.pdf http://perimeterinstitute.ca/personal/rblume-kohout/thesis/t... Could someone explain the Lindblad equation in plain English?