Can You Really Observe a Wave Function Without Collapsing It?

Click For Summary

Discussion Overview

The discussion revolves around the concept of observing a wave function in quantum mechanics and the implications of such observations, particularly in relation to quantum computers. Participants explore the definitions and interpretations of "observation," the nature of wave function collapse, and the operational aspects of measurement in quantum mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question what is meant by "observing" a state and whether it involves sensory perception, such as seeing or hearing the particle.
  • One participant asserts that caution around quantum computers is unnecessary, as the risk of collapsing a wave function is comparable to that of other lab equipment.
  • There is a suggestion that observing a wave function may be equivalent to applying an operator that changes the state, with a specific mention of measurement operators.
  • A participant introduces the concept of Hermitian operators in relation to measurements.
  • Another participant points out that collapsing the wave function is not a part of the quantum mechanics formalism but is present in certain interpretations, notably the Copenhagen interpretation, which treats it as a change in knowledge rather than a physical process.
  • It is noted that in advanced treatments, observation is described as a quantum process occurring after decoherence, though this raises further unresolved issues.
  • A later reply clarifies that applying a Hermitian operator does not yield the post-measurement state unless the state is an eigenstate, and introduces the concept of projection operators for observed outcomes.

Areas of Agreement / Disagreement

Participants express differing views on the nature of observation and wave function collapse, with no consensus reached on definitions or implications. The discussion remains unresolved regarding the interpretation of these concepts.

Contextual Notes

Participants highlight limitations in the definitions of observation and measurement, as well as the dependence on interpretations of quantum mechanics, which may vary significantly. The discussion also touches on unresolved aspects of decoherence and its role in the observation process.

Debaa
Messages
22
Reaction score
0
What exactly do you mean by observing a state/ collapsing wave function. What is observing? Is it seeing the particle? Hearing?
Also how cautious do you have to be near a quantum computer so that you don't collapse its wave function?
 
Physics news on Phys.org
You don't have to be any more cautious around a quantum computer than around any other lab equipment. As long as you don't trip into the dilution refrigerator and pull all of the wires out in some kind of zany fall, you'll be fine.

The definition you should have in mind for "the state collapsed" is "thermodynamically irreversible effect that depended on the state of the system". It has nothing at all to do with humans.
 
  • Like
Likes   Reactions: Debaa
Debaa said:
What exactly do you mean by observing a state/ collapsing wave function. What is observing? Is it seeing the particle? Hearing?
Also how cautious do you have to be near a quantum computer so that you don't collapse its wave function?

Observing must be equivalent to applying some operator to the wave function which changes the state. Is there a measurement operator?
 
mike1000 said:
Observing must be equivalent to applying some operator to the wave function which changes the state. Is there a measurement operator?
Hermitian operator.
 
Debaa said:
What exactly do you mean by observing a state/ collapsing wave function. What is observing? Is it seeing the particle? Hearing? Also how cautious do you have to be near a quantum computer so that you don't collapse its wave function?

Collapsing is not part of the QM formalism - only of some interpretations. In those interpretations its the instantaneous change in state after an observation. The usual interpretation that has it is Copenhagen where the instantaneous thing isn't worried about because it's simply a state of knowledge that appears in a theorists calculations - its like the Bayesian view of probability - who cares if your knowledge of something suddenly changes.

An observation is trickier. That's because at the beginner and intermediate level its sort of left up in the air as some kind of 'mark' or something that happens here in the common sense classical world. That is a bit of a blemish because QM is supposed to explain that classical world - how can it explain what's assumed in the first place.

In more advanced treatments an observation is a purely quantum process that happens once decoherence occurs without detailing what that is. That way the issue is resolved, but, again without going into details, some problems still remain.

Thanks
Bill
 
  • Like
Likes   Reactions: vanhees71
mike1000 said:
Observing must be equivalent to applying some operator to the wave function which changes the state. Is there a measurement operator?

Debaa said:
Hermitian operator.

This is a common misconception. You do not apply a Hermitian operator that corresponds to a measurement to the state to get the state after the measurement. That will be correct (except the normalization) only if the state is an eigenstate of the operator (so it is unchanged). The correct operator to apply, assuming that repeating the measurement immediately gives the same outcome, is the projection operator corresponding to the observed outcome.
 

Similar threads

Graduate Can particles appear and disappear "with" a cause?
  • · Replies 1 ·
Replies
1
Views
2K
High School Can someone please explain to me the motion of an electron?
  • · Replies 11 ·
Replies
11
Views
3K
Undergrad Is There A Study Showing The Observer Effect Ignoring Conscious Intent?
  • · Replies 3 ·
Replies
3
Views
5K
High School The wave function of the electron doesn't collapse when passing through air?
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad How non-conscious can an Observer be and cause wave function collapse?
  • · Replies 23 ·
Replies
23
Views
9K
High School Why does anyone think gravity might collapse wave function?
  • · Replies 59 ·
2
Replies
59
Views
8K
Undergrad What is an observable exactly?
  • · Replies 3 ·
Replies
3
Views
2K
High School Quantum entanglement and simultaneity
  • · Replies 4 ·
Replies
4
Views
3K
High School The arrow of time (again)
  • · Replies 18 ·
Replies
18
Views
3K
Undergrad How Do We Model Wave Function Collapse After Measuring Particle Location?
  • · Replies 8 ·
Replies
8
Views
2K