Here is the Fraunhofer singles slit interference Plt.plot(dots, np.random.normal(size=len(dots)),'.') If np.random.uniform() < pattern(w,d,l,x): Don't rely on this as either "good code" or "good physics" - it was purely designed to illustrate the concepts above. If you are interested in reproducing a graph like this, here is the (rather crummy) code I used to generate it. But in each case, an individual photon lands in just one place. In the first plot you have just a few dots, with no pattern in the next row, a pattern starts to emerge in the bottom row, the interference pattern is clear. I wrote a little simulation to demonstrate this - each plot has ten times more dots than the one before. The act of going through the slit changes their wavefunction in such a way that the probability of them landing at a particular point on the screen is no longer uniform but when they do land, they land in a particular location it is only by observing a large ensemble of photons that you start to see this pattern emerge - there will be more dots in some regions than in others. Now when you roll the dice just once, you get a particular sum (like the photon hitting the screen at just one place) if you roll the dice many times, and plot the number of occurrences of each sum, you get a triangular distribution (example after 500 random rolls):Īnd so it is with photons going through slits. Any other number has fewer possible combinations). If I asked you to guess the number, your best guess would be "7", because for a pair of dice, the probability of the sum being 7 is higher than any other value (1-6, 2-5, 3-4, 4-3, 5-2, 6-1 are the 6 rolls that could get you 7. But for a given roll, you only see a specific sum - for example, 5. This is where probability comes into play - similar to the example given by Anna V, if you roll a pair of dice, the sum could be any number from 2 to 12. Here is the fun bit: the single photon could have appeared just about anywhere on the screen - but it only appeared in one place. In quantum mechanics, they say "the wave function collapses". But when the photon "wave" interacts with the screen, the photon can only be observed at a single place. The result of this is that the wave, after the slit, gets certain peaks and troughs - there are certain "preferred" directions for the wave, while the amplitude in other directions is diminished. The dual slit experiment attempts to demonstrate this duality.Īs the photon "wave" passes through the slits, it actually passes through both slits, like a wave would. The behavior of a photon is at times best described by calling it a particle at other times, its behavior looks like that of a wave. However, it is clear from the various comments on this page that you are looking for deeper insight, and that the concept of a "photon interfering with itself" is confusing and potentially misleading. Thus, the short answer to your question is "yes, you would just see a dot". When a single photon hits a screen, it can only create a dot at the point where it is detected.
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