Double-slit Experiment Questions

[rmw]

There has been short pause while acquired a camera that can take decent photos.

Before we even get to single slits, double slits or even a simple sharp edge, I am having a problem with the beam itself. attached is a photo of the beam spot on a door at about 6.67 metres from the laser. Ir's a mess. I want to understand the granularity of the beam spread and why it spreads so much. I am assuming it is associated with internal reflections inside the laser housing, but I want to know more about that . have just viewed teh photo, it's rubbish and I don't know how to upload a decent versio of it

Edited November 3, 2010 by rmw

[michel123456]

There has been short pause while acquired a camera that can take decent photos.

Before we even get to single slits, double slits or even a simple sharp edge, I am having a problem with the beam itself. attached is a photo of the beam spot on a door at about 6.67 metres from the laser. Ir's a mess. I want to understand the granularity of the beam spread and why it spreads so much. I am assuming it is associated with internal reflections inside the laser housing, but I want to know more about that . have just viewed teh photo, it's rubbish and I don't know how to upload a decent versio of it

 

I am not an expert, but I think the surface of the target is too porous. You need a smoother surface. I would try with very thin glass from microscope equipment, or glass-ceramic, like the babyliss flat iron your girlfriend use to make her hair.

And also on the picture, you get the image of reflection from the dust in the air. I am afraid you wont get correct results by photographying from a distance, even in a dust-free room. The target should be a photographic plate. With all the above mentionned inconvenient.

 

Note what i said in previous post: the photograph you get comes from reflected light. If reflection was null, you would not see anything. How do they manage to avoid reflection in this kind of experiment?

 

I voted for you post, rmv. I am touched by your approach. It is much more difficult than simply browsing, as we do all here. Good for you.

Edited November 4, 2010 by michel123456

[swansont]

There has been short pause while acquired a camera that can take decent photos.

Before we even get to single slits, double slits or even a simple sharp edge, I am having a problem with the beam itself. attached is a photo of the beam spot on a door at about 6.67 metres from the laser. Ir's a mess. I want to understand the granularity of the beam spread and why it spreads so much. I am assuming it is associated with internal reflections inside the laser housing, but I want to know more about that . have just viewed teh photo, it's rubbish and I don't know how to upload a decent versio of it

 

Laser diodes have large divergences as well as astigmatism, and it's not trivial to correct both simultaneously. Cheap laser pointers have cheap optics. And then there's speckle

[michel123456]

I learned something today.

[steevey]

After reading up on particle-wave duality and the double-slit experiment, I came upon this in the article.

 

The most baffling part of this experiment comes when only one photon at a time is fired at the barrier with both slits open. The pattern of interference remains the same, as can be seen if many photons are emitted one at a time and recorded on the same sheet of photographic film. The clear implication is that something with a wavelike nature passes simultaneously through both slits and interferes with itself — even though there is only one photon present. (The experiment works with electrons, atoms, and even some molecules too.)

http://en.wikipedia....slit_experiment

 

 

Would someone care to try and explain this? Or do we just not know enough as of yet to understand why this happens?

 

Elementary particles are also waves, that's it. What they are a wave of, is existence itself. Why does it work like this exactly? We don't know. Could be something to do with distance being an illusion, could be something to do with all matter existing in all possible places simultaneously but we can't see it, could be some extra dimension thing, etc. When you have a wave of probability, the wave is always there even after you observe it, however the information of an single point of bundle of matter is what we see.

 

Here's a simulation for you

Edited November 27, 2010 by steevey

[Higgs0123]

The most baffling part of this experiment comes when only one photon at a time is fired at the barrier with both slits open. The pattern of interference remains the same, as can be seen if many photons are emitted one at a time and recorded on the same sheet of photographic film. The clear implication is that something with a wavelike nature passes simultaneously through both slits and interferes with itself — even though there is only one photon present. (The experiment works with electrons, atoms, and even some molecules too.)

 

Elementary particles are also waves, that's it. What they are a wave of, is existence itself. Why does it work like this exactly? We don't know.

 

I am sorry, but this response ["particles are also waves... waves of existence..."] strikes me as unrelated concepts without coherent meaning.

 

As I understand it, per quantum field theory, a particle (photon, electron,etc.) spreads out as it travels from place to place like a wave; but is detected only in a single location like a particle. What does the traveling? The so-called wave function; which represents the probability of finding the particle at a certain place and time.

 

 

 

The latter repeats a common confusion. First, you can't write the Schrodinger wave (probability) equation for the photon because it has zero rest mass. Second, the wave of the photon is real and actual; Maxwell's equations describe it and it registers on an oscilloscope (which the Schrodinger wave will never do). Third, you are mixing a physical entity (a photon or electron) with a mathematical/calculated entity (the Schrodinger equation) and asking the latter to influence the path of the former. This makes the Schrodinger equation prescriptive rather than descriptive. Some interpretations argue for the physical reality of the probability wave (Objective Collapse) but they have not received much support

 

So if single photons pass through a double slit at separate time intervals and yet still form a diffraction pattern with their individual "impacts" then each photon must be interfering with itself through the double slit as the above quote indicates. This says the photon is a wave since only waves can produce interference patterns. But each photon registers at a space point so does this prove it is a particle when passing through the slit and before it has terminated? It does not; it merely says that whatever the photon is, it registers/terminates upon matter at a space point. Keep two things in mind here: 1. when the photon registers on matter at a space point it has already terminated and ceases to be a photon (although some photon energy may re-emit as a new photon); 2. we are all slaves of classical physics concepts and we think that anything moving through space and "impacting" matter at a point must be a projectile (particle). There is no hard proof of this assumption; there could be real entities we do not know about that collapse at a space point.

An interesting reinterpretation of photon termination (Wave-Particle Duality) argues that when photons terminate upon matter their space-dispersed, stored (potential) mass collapses at a space point thus simulating particle impact. This potential mass could be the entity "we do not know about."

 

One hundred years of debate and we are still searching for an answer...

[immortal]

I think we should stick to the copenhagen interpretation of QM. We can not use QM to describe what is happening at the slits when single photons are passed through it. We can only know where it has registered in the photographic film and we can make predictions about it. If we introduce a detector to see through which slit it has passed then we have destroyed the interference pattern.

 

Recent experiments indicate that the interference pattern is destroyed not due to Heisenberg's uncertainty principle. I think we really don't understand what we mean by measurement. What we need is an explanation of what is going on in the act of measurement.

[IM Egdall]

Recent experiments indicate that the interference pattern is destroyed not due to Heisenberg's uncertainty principle. I think we really don't understand what we mean by measurement. What we need is an explanation of what is going on in the act of measurement.

 

Could you please give us a link to these recent experiments?

Edited November 30, 2010 by I ME

[immortal]

Could you please give us a link to these recent experiments?

 

I actually read it here My link

 

I hope you can search the original article by yourself.

 

This might help you

 

"Thanks to Nature and The New Scientist. Further reading "Origin of quantum mechanical complementarity probed by a 'which-way' experiment in an atom interferometer," S. Durr, T. Nonn, G. Rempe, Nature vol. 395, p. 33. "An End to Uncertainty," Mark Buchanan, The New Scientist 6 March 1999, "Light's spooky connections set distance record," Mark Buchanan, The New Scientist, 28 June 1997."

[IM Egdall]

I actually read it here My link

 

 

 

Terrific link. Thank you!