Hello everybody, I am absolutely a novice in physics and although I generally have a good grasp of math I am pretty sure my knowledge of it is quite far from the one required by quantum physics. However, I am very interested to its main concepts and for this reason I am reading an introductory book on the subject: "How to teach quantum physics to your dog" by Chad Orzel which I think is a very good source for novices to learn at least the basics theories. However, I couldn't properly understand the quantum eraser experiment and, so I was wondering if you guys could help me with that. Surfing on the internet I saw that there are many different versions of the experiment and the most discussed one seems to be "the delayed choice quantum eraser". However this is the version explained on the book (or at least that is my understanding of it) for which I couldn't find any other explanation online: If we cast a beam of light polarized at 45° through two slits, one where we put a vertical polarizer and the other where we put a horizontal polarizer, there is a 50% possibility for each photon to pass through the right slit and a 50% possibility to pass through the left slit. When we do this we don't see the production of an interference pattern. I couldn't understand why should it be "unexpected" not to observe an interference pattern in this case. Namely, if the photon will pass through one of the two slits but not the another one (as I understood is the case when we put polarizers) it is like saying that we are "forcing" the photon to pass through just one slit and, therefore there will be no interference with "the photon with itself" due to its wave nature (as it happens when there are no polarizers). So it seems to me pretty natural that we don't see an interference pattern (it is a distruptive effect of our measurement device that again "forces" the photon to pass from just one slits when it normally would have passed from both). If the photon will still pass through both the slits even with polarizers (assuming that this is possible which I don't know) then the "two" photons (it is still the same one but sort of "duplicated" for the effect of its wave nature) will be one horizontally polarized and the other vertically polarized and, so there will be no interference between the two waves and again no interference pattern. As you noticed, my doubts are related to the part before the actual experiment of "quantum erasure" that happens when we put another polarizer at 45° degree before the detector and we see the reoccurence of the interference pattern. Thank you all in advance for your answers.