How do you account for all the photons and plethora of quantum particles in the box between the double slits and the back wall? Does the particle being shot not interact with the all the particles that must be consuming the space in the box before the back wall? How do we know it’s the same photon traveling the distance to register on the detector wall? Don’t photons ( for example) pass its energy on to the very next one in its path? Maybe it’s just the energy pushing the last photon in line against the wall..?
 A: When you say "account for", I'm interpreting that as asking why doesn't the interaction between the photons/electrons and the environment destroy the interference pattern or lead to decoherence the way macro interactions would?
In that case the answer is detectability. If the photons/electrons interacted with the air in a way that we could detect, prior to hitting the wall, it would destroy the interference pattern.
But they generally don't interact. Light as you know is going very fast and its probability of interacting with an air molecule over a short distance is very very small. Remember there's a LOT of empty space between atoms and molecules especially in a gas. That's why air is generally invisible. And electrons likewise aren't likely to interact with neutral air over short distances because the molecules have no net charge. Even if they caused a slight jostle in a few molecules it wouldn't be remotely enough to detect in most cases.
If you filled the chamber with fog, on the other hand, or ionized gas, to the point where you could see the laser at all points before and after the slits, it would surely destroy the interference pattern.
Plus remember that in the experiments involving single photons and electrons the detection rate isn't 100%. Some surely DO interact with the air, etc., and get thrown off course. We can only say anything definitive about the ones we detect.
A: You take the "particle" characteristic of Photons too far, they are not like atoms or molecules in your box. T do not bump in each other. For the double slit experiment  you have to think of light as a wave.And it has nothing to do with the double slit experiment. If you look at some object, the light comes in your ey without "bumping" to other light particles, otherwise you would not be able to see the object.
