Role of Observer in Double Slit Experiment

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In summary, the double slit experiment shows that when an observer checks to see the particles passing through the slits, the interference pattern disappears. This suggests that the method of observation, not the act itself, is responsible for this discrepancy. However, recent research using weak measurements and post-selection has provided an observationally grounded description of the propagation of quantum particles in a two-slit interferometer. This research also suggests that interactions, rather than the act of observation, may be responsible for the collapse of the wavefunction.
  • #1
Astralos
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In the double slit experiment, there is interference between the fired particles when both slits are opened. Yet, when an observer checks to see what's actually going on by looking at the slits as the particles pass through them, the interference disappears. In other words, the particles act like particles when they are observed, yet they act like waves when they are not observed. Why does this happen, and what does it mean? Certainly, particles don't have a consciousness with which to deduce, "Oh snap, they're watching me--I better go straight through and not make a scene."
 
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  • #2
Actually, the act of observation itself is not necessary to destroy the interference pattern. The possibility of observation is enough. If you shined a light between the screen and the slits, WITHOUT actually observing to see which hole each electron went through, there would be no interference pattern.
 
  • #3
Matterwave said:
Actually, the act of observation itself is not necessary to destroy the interference pattern. The possibility of observation is enough. If you shined a light between the screen and the slits, WITHOUT actually observing to see which hole each electron went through, there would be no interference pattern.

Does that not suggest that the method of observation (in this case, the light) is responsible for the discrepancy, NOT the act of observing?
 
  • #4
http://www.cbc.ca/m/rich/technology/story/2011/06/02/science-heisenberg-uncertainty-steinberg.html [Broken]

"We are all just thrilled to be able to see, in some sense, what a photon does as it goes through an interferometer, something all of our textbooks and professors had always told us was impossible," Aephraim Steinberg, a physicist at the University of Toronto's Centre for Quantum Information and Quantum Control, said in a statement.

The results were published Thursday in Science.

EDIT: more details:

Science, 3 June 2011:
Vol. 332 no. 6034 pp. 1170-1173
DOI: 10.1126/science.1202218

Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer

Sacha Kocsis1,2,*,
Boris Braverman1,*,
Sylvain Ravets3,*,
Martin J. Stevens4,
Richard P. Mirin4,
L. Krister Shalm1,5, and
Aephraim M. Steinberg1,†

Abstract

A consequence of the quantum mechanical uncertainty principle is that one may not discuss the path or “trajectory” that a quantum particle takes, because any measurement of position irrevocably disturbs the momentum, and vice versa. Using weak measurements, however, it is possible to operationally define a set of trajectories for an ensemble of quantum particles. We sent single photons emitted by a quantum dot through a double-slit interferometer and reconstructed these trajectories by performing a weak measurement of the photon momentum, postselected according to the result of a strong measurement of photon position in a series of planes. The results provide an observationally grounded description of the propagation of subensembles of quantum particles in a two-slit interferometer.
 
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  • #5
It suggests that really interactions are the culprit, in fact, the decoherence theory has made quite a bit of headway into this matter; however, the wave function collapse is still somewhat interpretation based, so I can't say for sure.
 

1. What is the Double Slit Experiment?

The Double Slit Experiment is a fundamental experiment in quantum mechanics that involves sending particles, such as photons or electrons, through two parallel slits and observing the resulting interference pattern on a detector screen.

2. How does the Double Slit Experiment work?

In the Double Slit Experiment, particles are sent one at a time through two parallel slits and then detected on a screen behind the slits. The particles behave like waves and interfere with each other, creating an interference pattern on the screen.

3. What is the role of the observer in the Double Slit Experiment?

The role of the observer in the Double Slit Experiment is to measure or observe which slit the particle passes through. This measurement causes the particle to behave like a particle instead of a wave, and the resulting interference pattern on the screen disappears.

4. Why is the role of the observer important in the Double Slit Experiment?

The role of the observer is important in the Double Slit Experiment because it demonstrates the concept of wave-particle duality in quantum mechanics. The observer's measurement affects the behavior of the particles, showing that they can behave like both waves and particles.

5. What are the implications of the Double Slit Experiment on our understanding of reality?

The Double Slit Experiment challenges our classical understanding of reality by showing that particles can behave like waves and that our observations can affect the behavior of these particles. It highlights the strange and counterintuitive nature of quantum mechanics and raises questions about the fundamental nature of reality.

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