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Physics/Theory on the Double-Slit Experiment


QUESTION: Dear Steve Nelson,

I have a theory regarding the disappearance of the interference pattern in a double-slit experiment when a detector is added to the experiment. My theory states that the disappearance of the interference pattern might be due to the magnetic frequency of the electrical detector- the one that is used to see which slit the particle goes through.

To test this theory, a double slit experiment can be conducted with an electrical device other than a detector. It would be a device that emits about the same amount of magnetic frequency as the detector. This device would be turned on and put in the same place a detector would be in a regular double-slit experiment. If the interference pattern disappears, then we might conclude that the reason is the magnetic frequency of the electrical device.

What do you think of this theory? And can you conduct an experiment to test the theory? Thank you.

ANSWER: No, what you propose doesn't make sense at all.  The double slit experiment was originally developed for light, and with passive things like crossed polarizers over the slits one may observe the expected results, no "magnetic frequency" in a polarizer.  Devices to measure the passage of electrons do not typically use magnetic fields with any frequency.  You would use a phosphor screen or some kind of capacitor if you want, you're still disturbing the wave of the electron as it passes through and severely altering the result of the experiment just by putting the thing that interacts to observe the electron.

---------- FOLLOW-UP ----------

QUESTION: Thanks for your opinion. I have some questions:

1. You said that devices to measure the passage of electrons do not typically use magnetic fields with any frequency. Are these devices electrical? If they are, then they would emit magnetic frequency.

2. You mentioned that a phosphor screen or some kind of capacitor might be used. Has a double-slit experiment been conducted with a phosphor screen or some kind of capacitor, then showed the usual result of the disappearance of the interference pattern?

3. There is an article regarding the double-slit experiment which might support the idea that magnetic frequency is involved in the disappearance of interference. A special experiment was conducted. It says in the article: "The researchers used a second counter, called D2, to reveal the final position of the signal photon. First, D2 was placed right next to the slits, so it was able to tell which the signal photon went through. This was used to confirm that the entanglement measurements matched up with the ones from the detector. Then D2 was pulled far enough away from the slits for the photons to interfere. In this position, it measured the complete interference pattern produced by the single photons."

You can read the article at the following link:

It also says: "Similarly, building up the interference pattern requires moving the D2 detector away from the slits, meaning that D1 provides the only information about the trajectory."

My question is: Why does the D2 device have to be moved away from the slits for the interference pattern to exist? If the D2 device is close to the slits, then there is no interference pattern. If it is moved away, there is an interference pattern and it can be observed, even when it is known which slit the particle went through. It could be the magnetic frequency of D2 that is the main factor here.

You keep talking about magnetic frequency.  Devices emit or absorb photons, "magnetic frequency" by itself is not a physical thing.  A photon may have an electromagnetic frequency, but there is no thing that is just "magnetic frequency."  Stop using improper terms that have no meaning.

See here:

Electron diffraction has been observed.  Young's double-slit experiment has been extensively done for light, but not for electrons in the laboratory in a true sense.  So no devices.  Passive polarizers have been done for light, they do not "emit a magnetic frequency" as they are relatively independent of the frequency of light that passes through them.  The article you reference refers to light.  But you're getting into entanglement, which is a whole separate ballgame involving measurement of the second photon and not direct measurement of the first photon.  Entanglement is a poorly-understood phenomenon and much argued about.  You should read up, there are whole books on the quantum theory of light.

For the experiment you read about, D2 was used two separate ways.  First, it was used to confirm that entanglement was working.  Second, it was used to confirm interference patterns.  If you don't know why it had to be moved back from the slits for an interference pattern to occur, then perhaps you've never seen or drawn out the process of slits forming interference patterns...of course there's a distance between the slits and the screen (detector) they're observed (by the detector D2) on.  That's just basic geometry.  If D2 is right behind one of the slits, light from the other one can't just make a right angle and come over to interfere...that's kind of a meaningless question.  Draw an overhead view of it, you'll see.  Detector 2 would be a photomultiplier tube or microchannel plate.  These are direct current electrical devices, they have no frequency on which they operate.

In short, "magnetic frequency" is not even a thing.  


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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