A sudden realisation

[between3and26characterslon]

Sometimes things are really obvious and you just don't notice them.

Here's what I was thinking.

 

If you have electron gun A firing electrons at slits A and B and you will get a difraction pattern.

 

However,

 

If you have one E-gun A firing at slit A and another E-gun B firing at slit B and there is a wall between slit A and B (on the E-gun side) you will not get a difraction pattern.

 

My assumption had always been that electron A inteferes with electron B but this is not the case, electron A inteferes with electron A. (<that's the obvious bit)

This is true when on electron is fired at a time and when 'n' electrons are fired they all interfere with themselves not each other. (<that's what I just realised)

 

Now its said that if you were to fire one electron at a time it will travel through both slits as a wave and interfere with itself on the other side but only of you don't observe it. If you do observe it it will only go through one slit (I beleive this is true regardless whether you observe it before the slits or after the slits)

 

What would you see if you fired a laser at a double slit so that you could see a difraction pattern and then filled your experiment with some smoke. Would you see a single line of light hitting a plate and then fan out in lighter and darker 'fingers'. Is this not making observations throughout the experiment, before and after the slits. Do you not still get a difraction pattern.

 

Maybe I'm not understanding or knowing enough.

 

Your thoughts...

 

(editted for spelling and grammer)

(edited again to spell edited properly)

Edited March 29, 2012 by between3and26characterslon

[derek w]

You cant observe something that small without interfering with it.

[IM Egdall]

If anything you do allows you, in principle, to tell which slit an individual electron went through, then there will be no interference.

[derek w]

yes.but if the results change when you observe then something you did must have interfered.

[questionposter]

Sometimes things are really obvious and you just don't notice them.

Here's what I was thinking.

 

If you have electron gun A firing electrons at slits A and B and you will get a difraction pattern.

 

However,

 

If you have one E-gun A firing at slit A and another E-gun B firing at slit B and there is a wall between slit A and B (on the E-gun side) you will not get a difraction pattern.

 

My assumption had always been that electron A inteferes with electron B but this is not the case, electron A inteferes with electron A. (<that's the obvious bit)

This is true when on electron is fired at a time and when 'n' electrons are fired they all interfere with themselves not each other. (<that's what I just realised)

 

Now its said that if you were to fire one electron at a time it will travel through both slits as a wave and interfere with itself on the other side but only of you don't observe it. If you do observe it it will only go through one slit (I beleive this is true regardless whether you observe it before the slits or after the slits)

 

What would you see if you fired a laser at a double slit so that you could see a difraction pattern and then filled your experiment with some smoke. Would you see a single line of light hitting a plate and then fan out in lighter and darker 'fingers'. Is this not making observations throughout the experiment, before and after the slits. Do you not still get a difraction pattern.

 

Maybe I'm not understanding or knowing enough.

 

Your thoughts...

 

(editted for spelling and grammer)

(edited again to spell edited properly)

 

Particles can still travel as waves after bumping into things, but the shapes of their probability will be altered. If an electron simply hits an atom and nothing more, it doesn't localize to a single point, it just repels, so if electrons hit the smoke atoms they would continue as waves but because of the deflection they would change shape and/or direction.

Measurement that collapses wave functions is more to do with how we observe light, which is only temporary anyway. So relative to you, even if you do observe an electron as a point, the moment you stop observing it, which, impulses from your eyes travel very fast, it statically exists as a wave again.

And, after the electron hits the wall, it goes back to being a wave and following its wave mechanics. What we see is simply the interaction point at which an interaction happened, which is carried by photons.

Edited March 30, 2012 by questionposter

[swansont]

yes.but if the results change when you observe then something you did must have interfered.

 

That's a different use of the word.

[between3and26characterslon]

Particles can still travel as waves after bumping into things, but the shapes of their probability will be altered. If an electron simply hits an atom and nothing more, it doesn't localize to a single point, it just repels, so if electrons hit the smoke atoms they would continue as waves but because of the deflection they would change shape and/or direction.

Measurement that collapses wave functions is more to do with how we observe light, which is only temporary anyway. So relative to you, even if you do observe an electron as a point, the moment you stop observing it, which, impulses from your eyes travel very fast, it statically exists as a wave again.

And, after the electron hits the wall, it goes back to being a wave and following its wave mechanics. What we see is simply the interaction point at which an interaction happened, which is carried by photons.

 

^^ Don't really understand what you are saying^^

 

 

 

The point I was asking about is that the interference in the double slit experiment is not interference between photons or electrons it's that every single photon or electron only ever interferes with itself whether fired individually or en mass.

 

If you were to use two lasers firing at single slits you would not get the same interference pattern so interference can not be between two photons (another interesting experiment would be to split a single source of light into two signals and fire them at two appertures and see if interference happens in this case, I expect it won't)

 

The point is that the electron does not know you are watching, if you detect the electron by using an electromagnetic device you will cause it to only go through one slit. But what would happen if you set up the experiment firing the electron through a reduced pressure gas (one that would illuminate when excited by a high energy electron). Would you see fingers of illuminated gas spreading out from the slits?

[questionposter]

But what would happen if you set up the experiment firing the electron through a reduced pressure gas (one that would illuminate when excited by a high energy electron). Would you see fingers of illuminated gas spreading out from the slits?

 

You would probably just see random patterns because the electrons wouldn't collapse down, they would merely deflect off of the smoke atoms.

Think about right now: There's radio photons that are traveling over many meters with all this air and rock around, yet they don't instantly collapse down as soon as they are emitted...

[derek w]

I was not meaning to imply that the observer interferes.

If the 2 slits were in a sheet of glass,its the atomic structure of the glass that changes the path photons would take from emitter to detector.When the photon reaches the detector,it is absorbed by 1 of the atoms in the detector.

 

Why does the photon go through the slits,because its being forced to by atoms.

[questionposter]

Why does the photon go through the slits,because its being forced to by atoms.

 

Photons aren't forced to do anything, it travels through the slits, and because of it's wave mechanics, it interferes with itself. With the atoms of the sheet with the slits, they simply don't absorb the photon and thus deflect it in some random direction backwards.

Edited March 30, 2012 by questionposter

[derek w]

yeh,from an observers point of view its a solid sheet with 2 slits in it.

from a photons point of view its a forest of atoms with a gap.The photon is not going to make the forest of atoms move,but the forest of atoms force the photon/field to shrink through the gap.Where as glass would not make the photon go through a slit.

[swansont]

yeh,from an observers point of view its a solid sheet with 2 slits in it.

from a photons point of view its a forest of atoms with a gap.The photon is not going to make the forest of atoms move,but the forest of atoms force the photon/field to shrink through the gap.Where as glass would not make the photon go through a slit.

 

The material simply absorbs the photons if they don't hit the slits.

[derek w]

yes.But would I be right in thinking that the field of the photons that go through the slits shrinks?

[swansont]

I'm not sure what you mean by the field of the photons shrinking.

[between3and26characterslon]

Is there anyone sciency here who works in a sciency place with sciency equipment who could carry out a quick experiment to see what happens. Perhaps if anyone's still in education they might have access to the necessary apparatus.

 

My thought is that you will see fingers of light emminating from the slits in a diffraction pattern.

 

 

 

The biggest problem is thinking of waves of light in the same way as waves of water (water being the medium most often used to explain this phenomenon). If a photon is a quanta does this quanta split and go through both slits? Probably not. If the quanta splits is it then spread over the entire diffratcion pattern? Simply, no.

 

A single photon or electron fired one at a time will over an extended period build up a diffraction pattern. The entire photon or electron hits your observation plate (where the diffraction pattern is seen) in one place, it is a particle (Feynman).

 

 

 

By saying the photon knows it is being observered it would suggest the photon also knows it is approaching two slits (what do photons see with?)

 

 

 

A particle fired at two slits will go through only one slit and hit the observation plate in only one place.

 

If you emit a single particle, and you know it's a single particle, and you receive that single particle, and you know you've received a single particle, then why is it not a single particle in between. If you carried out the double slit experiment with laser light (firing x^nth photons) and fill your experiment with just enough smoke to see the laser beam you would see a single beam of light hit the double slits and split into fingers and a diffraction pattern.

 

You will see the beam of light becasue a photon has entered your eye, that photon will have bounced of a particle of smoke. If you can see an uninterupted beam of light followed by several fingers of uniterupted beams of light then at evey point along those beams of light the photon must be a photon.

 

 

 

I'm not trying to rewrite physics here, I'm trying to understand it. I don't work in this field and don't have the equipment to carry out experiments nor the education to know enough to put all the pieces together or the time to do it.

 

What I can do is think and look at things logically which inevitably leads to questions sbout my understanding (or lack thereof).

[questionposter]

yes.But would I be right in thinking that the field of the photons that go through the slits shrinks?

 

It doesn't really "shrink", the number of nodal surfaces just increases.

[derek w]

yes.Greater number of nodes in smaller area.

[swansont]

yes.Greater number of nodes in smaller area.

 

That implies a change in wavelength.

[questionposter]

yes.Greater number of nodes in smaller area.

 

Regardless of however many nodal surfaces a wave has, the wave's existence extends to or at least approaches infinity, so in both instances the actual area of the wave is infinite or at least indefinite.

Edited April 2, 2012 by questionposter

[between3and26characterslon]

Didn't realise this question had been asked so many times before.

 

The photos I've seen show fingers of light eminating from the double slits and the explanations I've read describe a diffraction pattern of light eminating from the double slits when smoke is introduced to the experiment.

 

So a particle is only a particle when it's interacting with something and when not interacting it's a wave?

[swansont]

So a particle is only a particle when it's interacting with something and when not interacting it's a wave?

 

"It's a particle when interacting" is a simplification, but basically yes. The wave-particle duality is more along the lines of "it's a wave but has quantized energy and interacts in a localized region"