Jump to content
Science Forums

Recommended Posts

(This is the first part of a work in progress that explores the Wheeler Delayed Choice Quantum Eraser Experiment)


The quote below is false and unfortunately contains two common misinterpretations of the quantum eraser experiment.

“Which-path information destroys interference pattern"..."the act of observing which-slit causes the object to behave as a particle"... "by erasing the which-slit information, the object returns to behaving as a wave" 

Below is a video showing how “marking” the two light paths in a double slit experiment with polarizing films destroys the familiar interference pattern. The explanation is that having knowledge of which-path (left or right) the photons took through the slits destroys the interference pattern even if we only have the ability of obtain that knowledge at a future time. 


I give the author of the video credit for recognizing that the the pattern he got with the polarizing films was a diffraction pattern and not a pattern characteristic of light as a particle. A diffraction pattern is also an example of light acting as a wave. Light beams fan-out as they pass the edge of an opaque object. This is known as diffraction. When light passes through a narrow slit, diffracting waves from one side of the slit interfere with those from the other side. The author also correctly recognized that the complex interference pattern he got without the polarizers was a two slit interference pattern on top of a diffraction pattern. His amateur analysis of the experiment was more accurate than many explanations from highly “creditable” sources.  Having which-path information does not cause light to behave as a particle. Light is always a wave.

The correct explanation for why orthogonal polarized light does not interfere was given by Fresnel and Argo two centuries ago and it has nothing to do with which-path information. Which-path information was a modern corruption.

A simple test of the which-way hypothesis is to repeat the experiment as described in the video above except using circular polarizing films rather than linear polarizers. The two beams from the double slit can be “marked” with circularly polarized light giving us which-path information, but it is my experience in doing so, that having circular which-way information does not destroy interference. 

Ordinary clear cellophane tape “Scotch” tape is an excellent quarter wave circular polarizing film. Unlike linear polarizers, circular polarizers become orthogonal at 45 degrees rather than 180.  I tried different ways of mounting the films but applying the clear tape to opposite halves of a microscope slide was the easiest. 

The proper mounting can be tested by observing the films through a polarizing film or a pair of polarized sunglasses while holding the films against the light of a flat screen monitor. One side of the films should be dark while the other is light and the light and dark should switch sides as the film is rotated.

I used a red laser for my experiment rather than green because that is what I had. 

A just-for-fun demonstration can be done by applying several layers of clear tape at different angles to a glass surface and looking at the glass through a pair of polarized glasses against the white light of a flat screen monitor. You should see a kaleidoscope of colors. 

I have read about many experiments with light but I have never found an experiment like the one I described that used circularly polarized light with the double slit to see what would happen. Certainly someone must have tried this before. I would be interested in knowing if anyone knows of such an experiment. Perhaps, no one has tried because which-path theory claims it is impossible? 

I would also be interested in hearing if anyone has repeated my experiment or what I did to get the “wrong” result. 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...