The double slit is the following experiment. We place 2 slits maybe 5mm apart and each slit very very thin. Send a laser against two of the slits and you will see an interference pattern on a photon counter CCD sitting behind the slits e.g. alternating bright and black fringes. Now this in itself is not strange and proved that the light had wave like properties when first made. We can mathematically match the result quite perfectly using Maxwell's equations. Now around the magical year, 1905, it become evident that light was mediated by photons that are particle like. And assuming this we have a conflict. light seam to be both wave and particle, which notion was considered in the development of Quantum mechanics later in the 20th century. Now it gets weirder. If you lower the count you will indeed see particles hitting the background and if you collect enough of them the interference pattern appears at the target CCD. We can slow this down so much that you can rule out that photons interact between them in some way. Also if you cover a slit, the pattern disappears. We also know that the photon only goes through one slit. This is qute a mystery and the explanation that I will propose, that are quite obvious actually as you do not need to be an expert to understand it, can perhaps explain it all. I have not found this suggested hyothesis in places like quora or stack overflow. It may be that I have missed an important fact that makes me take the wrong conclusions, but as the science has not done it's work to record anything for me to read about it, I feel obligated to investigate this idea and see if it holds water. I am in discussion at redit about it with an expert and we'll see what comes.
The exciting thing that recently happened in the field of the double slit experiment are that now students can perform experiments with two lasers and those can be separated physically and very little information can go between them makeing them interact very small and go through each slit of their own and magically they interact and form the interference pattern. So the conclusion are now that the photons both self interact and interact between them. OK that's fair, but let's assume a refinement of the two-laser experiment. It may be possible to perform this experiment, reducing the photon intensity so much that we most likely can assume, if the pattern appears, that it's not due to photon to photon interaction. But if that's the case they are separated so we should see no interference pattern. Well this experiment have not been done and we do not know what we would see. But basically, according to our current understanding, we should not get an interference pattern as that is similar to the one slit experiment. And if we get one, we need to turn to something else...
The following idea on an alternative theory is actually not hard to understand and it is really strange that internet seam to be void of it. Anyway the basic assumption we must question are if all electromagnetic waves is really an aggregation of photons. Why not a mix of classical EM waves and photons. If you start to analyze how we measure the details of light, like in a CCD or in a spectrum analyzer, you will see that all depends on how matter interact with light by picking up a photon. We actually can't see the EM waves independently of photons part, (with more than statistical meassures that does not resolve individual photons), directly in detail like a CCD of EM receivers. Now imagine that in order to get a high probability count of a photon interaction with matter, you need both! You need a photon and a EM field. As we have pretty good control of the EM field through our calculations, and we know that they form an interference pattern, this means that where the fringes are light, we have a high probability to count a photon, and where the fringe is black we have a low probability to count photons, hence basically explaining everything about the double slit experement quite neatly.
If photons where classical in a sense that they can be constructed by a creative solution to Maxwell, (Mills do this) they must have an EM field associated. Now consider interacting with matter. If we need a very exact amount of energy, to do an energy transition, the photon may be in the ballpark but need some extra glue to really hit the correct level. So now we could motivate that if there is a separate field that can lend the missing energy piece we increase the probability of the transition, and hence we get the correlation between photon count and an external EM field. This idea would raise your eyebrow though. We meassure the energy quite well from the photon, howcome? No we meassure the frequency of the photon, a spectrum analyzer will separate photons with a prism or similar device whihch works due to different frequencies and then count the photons, as all start and end processes demands the exact energy we may not see that the actual true photon energy is a much cruder value. So now you see how a statistical mechanical system mediates exact energy quanta through all source and sink processes, according to all our results, but out in the medium between matter, the photon and the the fields co-exists. This idea also make the energy uptake and radiation processes in the atom a bit more robust which is something that one should factor in.
Note also that I think that Mills model of the photon is basically all we need to model and this is an idea that add a little to this. I know there is a suggestion that it is due to an interaction of the photon with electrons at the slit - which I think Mill's himself suggested. Experts seam to think that this can't work due to it does not fit all the experiments that is done by the double slit. Howerver note that the suggested experiment that shouold be done, would also be able to disprove that idea if interference pattern indeed would show up.
It is actually really strange that you only get photon's on the atom level. In the microwave region we can with an antenna receiver actually meassure quanta related to the photon, this is pure old Maxwell theory, and it does not counter Mills idea of the photon as his photon have parts that you would think is more "traditional" But also with an antenna you can send other fields that coexists that are not related directly to a photon process and these fields coexists on this order of size. So at some point according to QM Maxwell's equations stop exist and you can't use it. If you could there woud trivially be possible other electromagnetically fields that as in the microwave example coexists with photons - mathematically they are there. But actually Maxwell do exist, QM actually combine via a coupling to Maxwell's equations so that you can theoretically explain all our faviorite atom-EM interactions out there, with quite good result! So somehow we have Maxwell's equations but there are this powerful unspecified deamon that convieniently remove all possible solutions when you need that to not get a contradiction.
So we may find, with the experiment discussed above, a whole new dimension that we do not see atm, that are right under our nose. If you are religious I guess you can suspect we found the space where God roam. If you are so inclined you could try to logically motivate this idea if the brain would consists of distributed set of small EM receivers that could connect. I heard from Ericsson engineers that there is a lot of EM noise related to humans. So what next? Judgment day? At least if this is true, God would have had a big LOL for some time (I just love the idea of her enjoying herself while at work). But first things first. Why don't you try to show this, performing the experiment above. If what I suspect is true the Nobel for you would be certain, LOL.