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Layman question: what constitutes observation in the world of quantum physics ? The article suggests that stronger light means less quantum effects, but isn't o

Layman question: what constitutes observation in the world of quantum physics ? The article suggests that stronger light means less quantum effects, but isn't observation a binary thing, so something is either watched or not.

ars 11y ago
Observation means interaction. So a stronger light means it interacts more extensively with something else. It does NOT mean a human. It can interact with anything, another particle even.
- gpvos 11y ago
  Obviously it is not about observation by a human; I don't think anyone on here thinks we are special magical creatures when it comes to quantum physics. However, not all interactions with another particle count as an observation, and I think the poster asked for a more precise description of the boundary, and why it would not be a boundary but actually appears to be a continuum.
  - gnaritas 11y ago
    > I don't think anyone on here thinks we are special magical creatures when it comes to quantum physics. The general public does, most explanations of the double slit experiment you can find lead people to believe that mind affects reality because the word observation confuses people into thinking consciousnesses is involved.
  - jsprogrammer 11y ago
    Humans observe smells through quantum physics.
deleted 11y ago
[deleted]
Strilanc 11y ago
Any effect that is conditional on the state and thermodynamically irreversible counts as a measurement. One way to do a partial measurement is to make the conditional effects less orthogonal to each other, e.g. cause a target qubit to conditionally rotate by 22 degrees instead of a full 180 degrees. Another possible concept for a partial measurement is not distinguishing between all of the cases. For example, if a system can be in the x=-1, x=0, or x=1 cases then it's possible to do a measurement that distinguishes x=-1 from x in {0,1} without collapsing all the way down to x=0 or x=1.
- Keyframe 11y ago
  and thermodynamically irreversible So anything related to light then as well?
  - kawa 11y ago
    If you make the opening shot in billiards, the balls are all over the table in the end. In principle you could now make another shot which restores the original, ordered position, but in practice it's impossible. So the opening shot is called 'irreversible'. Same thing goes for many things, for example letting some hydrogen gas out of a gas bottle: The gas will never go back into the bottle by itself (even if there is a very very small probability that this may happen, in practice it never will). Because the behavior of this kind of systems is described in thermodynamics those systems are called "thermodynamically irreversible". In the end it simply means that its much more easy to break things than to assemble them again (which also leads to the concept of the always increasing entropy).
dandelion_lover 11y ago
> isn't observation a binary thing https://en.wikipedia.org/wiki/Weak_measurement https://en.wikipedia.org/wiki/Weak_measurement
kawa 11y ago
Observation means: Interaction with a 'classical system'. Now because of entanglement this also works if we look at chains of interactions: Interaction with another single atom for example is no observation, but if this other atom interacts with a 'classical system' at some point earlier or later we have again an 'observation'. Now 'classical systems' are systems made of so many elements that we can only make statistical statements about it because we can't ever determine the state of each of it's constituents. I suspect for some time now that this is also the source for the "quantum randomness". In principle, everything is deterministic, but to observe something we always have interactions with a "big classical system" (in the end it's always our brain). And because we don't know the exact state of those systems but only statistical averages, quantum mechanics looks random for us, even if it's perfectly deterministic in itself. But that's my personal view of the matter.
- deleted 11y ago
  [deleted]
- JabavuAdams 11y ago
  The first couple of paragraphs are a great summary. Prof. Binney has some interesting observations on the non-physicality of quantum measurement (the formalism). One of the postulates of QM is that after a measurement the system is in a well-defined state (the one we measured). But this is aphysical. It's an artifact of the deliberate choice to formally model measurement in a way that simultaneously recognizes that all measurements disturb the measured system, while also wanting to abstract away the particular hardware used. So, I'm starting to see wavefunction collapse and the whole Copenhagen interpretation as artifacts of the the formalism, not any kind of physical truth.
gaze 11y ago
Not true. Observation can happen on a continuum. See quantum backaction of a variable strength measurement by hatridge et al

ars 11y ago

Observation means interaction. So a stronger light means it interacts more extensively with something else. It does NOT mean a human. It can interact with anything, another particle even.

gpvos 11y ago
Obviously it is not about observation by a human; I don't think anyone on here thinks we are special magical creatures when it comes to quantum physics. However, not all interactions with another particle count as an observation, and I think the poster asked for a more precise description of the boundary, and why it would not be a boundary but actually appears to be a continuum.
- gnaritas 11y ago
  > I don't think anyone on here thinks we are special magical creatures when it comes to quantum physics. The general public does, most explanations of the double slit experiment you can find lead people to believe that mind affects reality because the word observation confuses people into thinking consciousnesses is involved.
- jsprogrammer 11y ago
  Humans observe smells through quantum physics.

deleted 11y ago

[deleted]

Strilanc 11y ago

Any effect that is conditional on the state and thermodynamically irreversible counts as a measurement. One way to do a partial measurement is to make the conditional effects less orthogonal to each other, e.g. cause a target qubit to conditionally rotate by 22 degrees instead of a full 180 degrees. Another possible concept for a partial measurement is not distinguishing between all of the cases. For example, if a system can be in the x=-1, x=0, or x=1 cases then it's possible to do a measurement that distinguishes x=-1 from x in {0,1} without collapsing all the way down to x=0 or x=1.

Keyframe 11y ago
and thermodynamically irreversible So anything related to light then as well?
- kawa 11y ago
  If you make the opening shot in billiards, the balls are all over the table in the end. In principle you could now make another shot which restores the original, ordered position, but in practice it's impossible. So the opening shot is called 'irreversible'. Same thing goes for many things, for example letting some hydrogen gas out of a gas bottle: The gas will never go back into the bottle by itself (even if there is a very very small probability that this may happen, in practice it never will). Because the behavior of this kind of systems is described in thermodynamics those systems are called "thermodynamically irreversible". In the end it simply means that its much more easy to break things than to assemble them again (which also leads to the concept of the always increasing entropy).

dandelion_lover 11y ago

> isn't observation a binary thing https://en.wikipedia.org/wiki/Weak_measurement https://en.wikipedia.org/wiki/Weak_measurement

kawa 11y ago

Observation means: Interaction with a 'classical system'. Now because of entanglement this also works if we look at chains of interactions: Interaction with another single atom for example is no observation, but if this other atom interacts with a 'classical system' at some point earlier or later we have again an 'observation'. Now 'classical systems' are systems made of so many elements that we can only make statistical statements about it because we can't ever determine the state of each of it's constituents. I suspect for some time now that this is also the source for the "quantum randomness". In principle, everything is deterministic, but to observe something we always have interactions with a "big classical system" (in the end it's always our brain). And because we don't know the exact state of those systems but only statistical averages, quantum mechanics looks random for us, even if it's perfectly deterministic in itself. But that's my personal view of the matter.

deleted 11y ago
[deleted]
JabavuAdams 11y ago
The first couple of paragraphs are a great summary. Prof. Binney has some interesting observations on the non-physicality of quantum measurement (the formalism). One of the postulates of QM is that after a measurement the system is in a well-defined state (the one we measured). But this is aphysical. It's an artifact of the deliberate choice to formally model measurement in a way that simultaneously recognizes that all measurements disturb the measured system, while also wanting to abstract away the particular hardware used. So, I'm starting to see wavefunction collapse and the whole Copenhagen interpretation as artifacts of the the formalism, not any kind of physical truth.

gaze 11y ago

Not true. Observation can happen on a continuum. See quantum backaction of a variable strength measurement by hatridge et al