Double Slit Detector Debate Project producer David Watkinson proposes an experiment to decide the answer to a question for which there are opposing views between physicist Tom Campbell and quantum physicists that Watkinson interviewed at Texas A&M.

The Proposal

Comments (2 with 7 Responses)


Tom notes that the key factor is whether or not the which-slit information will be available to a resident within physical matter reality (PMR). It is not the chunks of information that matter, but the probability that those chunks of information will be seen, noted, observed, etc by a PMR resident. The which-slit information might be stored at the top of some mountain completely in tact, but if there is only a 0.00000000001 probability that that information will be available to a PMR resident (specifically a human), then the detection screen results will be consistent with an interference pattern. If the probability is such that the same which-slit information might be later available to a PMR resident, then the detection screen result would be consistent with that of a particle.

Maintaining historical consistency in PMR is the driving force. So in the case of the DCQE experiment, the information that is “obfuscated” is in fact erased. A book contains information as a result of the order and arrangement of the characters. If that arrangement and order is obfuscated, then the information within that book is lost. Reading the characters would not yield any understanding. The characters might still be there, but the information not. Likewise with the DCQE experiment. The data is still technically “collected” at D1 and D2, but the which-slit information is indeterminate. Which-slit remains unknown.

At 7:48 in your video, Dmitri exactly summarizes this by saying, “If there is a possibility to obtain the which-way information, then, in principle, the information is there.” This statement is in full agreement with what Tom is saying. If there is some probability that the information will be available to a PMR resident, then the particle will act like a particle and land directly behind the given slit.

Even Anton Zeilinger, though not likely to have fully agreed with Tom, stated: "It is sufficient to destroy the interference pattern, if the path information is accessible in principle from the experiment or even if it is dispersed in the environment and beyond any technical possibility to be recovered, but in principle still ‘‘out there.’’ The absence of any such information is the essential criterion for quantum interference to appear."
-Anton Zeilinger from: Experiment and the foundations of quantum physics

In Tom’s discussions, “out there” could be that the information is stored on a hard drive, on paper, on a camera, or simply in the head of a physicist who saw the which-slit data before it was destroyed. Again historical consistency is the key. If, for example, that physicist is already considered to be a bit untrustworthy or “off” by his peers, then the system has some wiggle room. Again, the key is that historical consistency is maintained in this reality.

What would likely blow the minds of many and resolve much of the confusion related to Tom’s discussion of this topic is if somebody would carry out Tom's envelope example - his logical equivalent to the DCQE experiment ( I tried to contact Dean Radin some time back via Facebook to see if it was something that he could do, but I did not hear back from him. I’m certain he is very busy and receives mounds of emails and messages. However, such an experiment - if carried out in the way that Tom describes - would be headline news.

That is my limited understanding anyway. I certainly support and appreciate the push the to probe and test such things. Very nice job explaining the DCQE experiment and kudos for pressing for more experimentation!

Responses (1 with 2 Responses)

Erased or not erased?

You say, 'the information that is “obfuscated” is in fact erased." But I disagree because there is no possibility of obtaining information about the photon until it reaches the detector screen (ignoring for a second Dean Radin's experiments on using the minds' eye to view the photon as it travels). Therefore, there can be no information until it is detected. If the photon goes to D1 or D2 then we simply don't have path information because of the way it traveled. To erase would mean we do have the information (i.e. the photon is detected and because of where it's detected we could obtain which-path information), and then some time later that information is "erased" and disappears from our physical reality before anyone has a chance to check the results. We do it all the time on hard drives, why not try it on a double slit experiment?

Responses (2 with 0 Responses)

Justin is proving Tom wrong

Justin quoted: "The key is not so much about the moment that the information is obtained but instead related to the potential (or probability) that the information will be obtained." This is in disagreement with Tom that wrongly believes that the information needs to be recorded.


You said, "there is no possibility of obtaining information about the photon until it reaches the detector screen." Do you mean the detection screen as in D0, or detectors as in D1-D4?

The authors of the DCQE experiment specifically use the term "erasure" and "erased:" "The which-path or both-path information of a quantum can be erased or marked by its entangled twin even after the registration of the quantum." The key is not so much about the moment that the information is obtained but instead related to the potential (or probability) that the information will be obtained. The which-slit information (or lack there of) exists in potential after the result at the detection screen (D0). In fact, one could argue that some of the information is first obtained when the photon hits the detection screen (D0). For example, if the result on the detection screen is consistent with an interference pattern, then we know that the paired photon must arrive at either D3 or D4 shortly after.

It might be most accurate to say that they erased the potential for the information to be obtained. I do understand your point. Again, the experiment that would seal the deal, so to speak, would be to mimic the envelope example discussed by Tom Campbell... hard drives would work just fine. Then there would be no confusion or disagreement that the data existed and was later erased.

I think Dean Radin is just the man to do it. I'm keeping my fingers crossed.

This question posed on a physics forum

I found this forum ( which addresses the same question. Although they get off on a tangent, the initial responses agree with the physicists you talked to in the car. It doesn't matter if the data is "collected", the machine doing the measurement forces the wavefunction to collapse...otherwise it couldn't be measured. To measure the particle's position that particle must take on a certain position, thereby collapsing the wavefunction. It shouldn't then matter if the data is available to us later when we look at the results. This makes sense, until we think about the delayed choice quantum eraser which requires no measurement (i.e. interference with the particle/photon). Now the collapse is not due to any machine measuring the photon and forcing it to take a certain position/spin in order for the measurement to occur. The collapse is entirely dependent on whether or not we have "information" about the photon. But, the central question is: Does this information need to be available at the time the results are viewed by a conscious observer? Could we erase the data that shows which-path information before looking and still get the same results. Really, we need to run the delayed choice quantum eraser experiment without the "eraser" part, i.e. only with detector's 3 and 4. Then we need a true "eraser" which would involve erasing the detector data (for D3 and D4) before we looked at the results of detector 0. In the described scenario, the photon was never interfered with before reaching the detector. However, the which-path information is still determined at the time the photon reaches a certain detector. However, if that information is not stored by the detector for later retrieval, then no human could ever become aware of that information and in a sense it would be like it never existed (it was never recorded, no one ever saw it--it was simply detected for a millisecond before being erased from the detector's memory) I have no idea if we would get a particle pattern or interference pattern. We need this experiment to know what's causing the collapse. Is it the mere presence of which-path information about the photon at any time during the experiment regardless of whether or not the data is available when the results are checked? Is it the presence of which-path information that's available (or potentially available) to a conscious observer when the experiment is checked? You see, we can't decide this question with the classical double-slit experiment because in that experiment a machine is involved which interferes with the photon. But in this "delayed quantum eraser" setup the particle is never interfered with so we can rule out that as causing the collapse.

Responses (3 with 1 Response)

The key

The key thing that would make the experiment work is the which-way information being available and then erased. The detector must detect the photon, registering it so that at the time of detection the which-path info. is theoretically available. However, within a split second, that information must be deleted from existence with no possibility of retrieval.

Responses (1 with 0 Responses)


I think that's the idea. The "Under Construction" sign on the website will come down soon and we'll reach out to physicists to see if someone will do the experiment.

We still need the experiment performed

Dan, I think you've made an excellent summary of why we need the experiment performed as you described it to finally settle the debate. It is not enough to say (as someone did on the physicsforum), "No, it has not been proved in any experiment and it is just a plain wrong claim." That sort of proclamation, as well as the argumentum ad hominem on the forum don't help. However, as soon as we finish preliminary beta testing (sometime this week), we'll reach out to more physicists including the ones in the debate to see if anyone is interested in doing the experiment or has further comment on the subject.

minor correction

"Is it the mere presence of which-path information about the photon at any time during the experiment regardless of whether or not the data is available when the results are checked" I meant to say, "the presence of which-path information when the photon hits the detector." Obviously which-path info could theoretically be available and then made unavailable before it gets detected. I think the key moment is the point where the photon reaches the detector.

Questions (2 with 1 Response)


To "question to physicists" video


Why DCQE experiment is not done again by those who can make it ( with new details – erasing memorised information after colecting data …) Every disagrement will Imediately be solved (is sombody making a joke?).

Responses (1 with 0 Responses)


There is no need to do it again. The DCQE was demystified already.