A classic double-slit experiment

[Moreno]

It is speculated that a consciousness of an observer could affect the classic double-slit experiment outcome. Could it really be a case? Is it possible that it is just a particles (let say photons) which affect the electrons and change their behavior? How can you make an observation without using some physical mediators (like photons) and avoid their interaction with an observed particles (like electrons)?

[QuantumT]

Consciousness as the factor in the measurement effect is one interpretation. But most physicists don't subscribe to that.
I myself am also fascinated with the collapse of the "wave function", and looking for proof of what exactly causes it.
One clue could be the simulation "hypothesis", where matter only takes shape when needed. But that is unfalsifiable, and thereby bad science.
Another clue could be the many worlds interpretation. But that is equally unfalsifiable.

We just don't know why.

Edited February 24, 2019 by QuantumT

[Strange]

8 hours ago, Moreno said:

It is speculated that a consciousness of an observer could affect the classic double-slit experiment outcome.

The "classic" double-slit experiment uses waves (it can be done with ripples in water, sound light, etc). You can observe the waves going through the slits without affecting the outcome.

So I assume you mean the quantum version of the experiment where only one photon or electron goes through the slits. (If so, this thread should be moved.)

Quote

Is it possible that it is just a particles (let say photons) which affect the electrons and change their behavior? How can you make an observation without using some physical mediators (like photons) and avoid their interaction with an observed particles (like electrons)?

The quantum version of the experiment uses entangled pairs of particles: one particle goes through the double slit apparatus, while the other goes to a detector. The detector measures the spin of the particle which can be used to deduce which slit the other particle went through. The particle that goes through the apparatus is not measured or affected at all.

This has nothing to do with consciousness. You can set up the experiment and make sure no one looks at the "which slit" information; you get the same result. 

[Moreno]

5 hours ago, Strange said:

The "classic" double-slit experiment uses waves (it can be done with ripples in water, sound light, etc). You can observe the waves going through the slits without affecting the outcome.

Most commonly a version with electrons passing double slit is mentioned. I'm not sure if any quantum entanglement (or spin) is involved. Usually they don't mention this. They claim electrons start to behave like particles when observed.

[Strange]

26 minutes ago, Moreno said:

Most commonly a version with electrons passing double slit is mentioned.

So this is the quantum, not classical, version.

27 minutes ago, Moreno said:

I'm not sure if any quantum entanglement (or spin) is involved. Usually they don't mention this.

Quantum entanglement is used to measure which slit an electron went through. Directly measuring an electron (or photon) at one of the slits would destroy the particle. Measuring an entangled pair means that the particle going through the slit is not (directly) affected.

This may not be mentioned in simplified descriptions as it may just be considered an implementation detail, but it is actually crucial.

30 minutes ago, Moreno said:

They claim electrons start to behave like particles when observed.

I really don't like the description in terms of wave vs particle behaviour, but it is frequently used. I think it misses the point.

[swansont]

6 hours ago, Strange said:

So I assume you mean the quantum version of the experiment where only one photon or electron goes through the slits. (If so, this thread should be moved.)

!

Moderator Note

Yes, this sounds like what is being discussed. Moved to Quantum.

 

52 minutes ago, Moreno said:

Most commonly a version with electrons passing double slit is mentioned. I'm not sure if any quantum entanglement (or spin) is involved. Usually they don't mention this. They claim electrons start to behave like particles when observed.

That's the "physics lite" description, where you still have one foot in the classical world, and describe things in terms of classical waves and classical particles (billiard balls). It's more nuanced than that.

[Carrock]

9 hours ago, Strange said:

So I assume you mean the quantum version of the experiment where only one photon or electron goes through the slits. (If so, this thread should be moved.)

The quantum version of the experiment uses entangled pairs of particles: one particle goes through the double slit apparatus, while the other goes to a detector. The detector measures the spin of the particle which can be used to deduce which slit the other particle went through. The particle that goes through the apparatus is not measured or affected at all.

 

3 hours ago, Strange said:

So this is the quantum, not classical, version.

Quantum entanglement is used to measure which slit an electron went through. Directly measuring an electron (or photon) at one of the slits would destroy the particle. Measuring an entangled pair means that the particle going through the slit is not (directly) affected.

These seem to me, rightly or wrongly, like oversimplified descriptions with details essential for (my) understanding omitted. And I suspect you meant "Directly measuring an electron at one of the slits would destroy the interference pattern."

Please provide reference(s) and/or more info.

[Strange]

40 minutes ago, Carrock said:

These seem to me, rightly or wrongly, like oversimplified descriptions with details essential for (my) understanding omitted. And I suspect you meant "Directly measuring an electron at one of the slits would destroy the interference pattern."

Please provide reference(s) and/or more info.

I will admit "destroy the electron" was not good phrasing! Detection would destroy a photon. In the case of an electron, it would be absurd by whatever sensor technology was used, but not actually be destroyed. It might be possible to detect the passage of an electron because of its change, but I am not aware of any technology that is sensitive enough to detect a single electron that way.

I did search earlier for a good description of how the double slit experiment is actually carried out and couldn't really find anything. But I have just noticed that Wikipedia has a reasonably good description of the experimental setup for the delayed choice quantum eraser experiment. This is more complicated but shows the principles involved.

https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser#The_experiment_of_Kim_et_al._(1999)

[Carrock]

Thanks for the reference which I read a while ago but lost.

I think it's worth reading in its entirety, particularly for its description of how action at a distance can, by delayed choice, either provide essential  information to show an interference pattern or show which slit the entangled particle passed through... all with information limited to lightspeed.

 

[yuanxue60616]

if there is no wave, then no collapse of the wave.

but need explain the interference and why observe cause it disappear.

[swansont]

6 hours ago, yuanxue60616 said:

if there is no wave, then no collapse of the wave.

but need explain the interference and why observe cause it disappear.

Interference is what you get when you add two waves together.

Why observation causes wave function collapse is a question of philosophy. Physics does not explain why it happens. It observes (in that model and interpretation) that it does.

[yuanxue60616]

3 hours ago, swansont said:

Interference is what you get when you add two waves together.

Why observation causes wave function collapse is a question of philosophy. Physics does not explain why it happens. It observes (in that model and interpretation) that it does.

I do not think it is a question of philosophy, still a question of physics. just do not have a physics explanation now.

superposition principal is equal to include the middle, means it do not need two waves to cause Interference

[swansont]

6 minutes ago, yuanxue60616 said:

I do not think it is a question of philosophy, still a question of physics. just do not have a physics explanation now.

Even if there were, there would be an unexplained "why does it happen that way". There is no point where that ends.

 

[Phi for All]

1 hour ago, yuanxue60616 said:

superposition principal is equal to include the middle, means it do not need two waves to cause Interference

!

Moderator Note

You have a thread discussing this speculative notion. Do NOT introduce it in mainstream topics, since that's hijacking, and against the rules.