It becomes a “science-based” ammunition for modern crackpot spiritualists to give credence to their nonsense and attract millions of educated followers.
That is why an accessible elucidation of the quantum theory of photons becomes so essential. Quantum physics is the most successful theory invented by humankind. It is a mathematical theory whose equations yield a complex (as in “complex numbers”) mathematical function denoted by (pronounced “sigh”), which contains information about the behavior of a physical system. Quantum physics is based on two assumptions about :
- The square of (the absolute value of) is the probability of the behavior of the system. That is why is called the probability amplitude.
- If there are two paths for the system to develop, the total of the system is the sum of the s for each path. This is called the superposition principle.
Superposition principle is an all-embracing law that applies not only to quantum phenomena, but also to ordinary situations. It is, for example, responsible for a boat to go northeast when the engine pushes it northward and the water flow carries it eastward. These two assumptions lead to some strange observations described is the famous double-slit experiment. Take a screen that blocks light. Cut two (very very close) identical slits in it. Cover one slit and send photons (particles of light) one at a time toward the two slits. Collect the photons that pass through the slit on a photographic plate. Quantum theory cannot predict the exact location of each photon on the photographic plate, because it is a probabilistic theory. But, as is true in probability, when you send a large number of photons, the prediction of probability becomes more and more realizable, and the shape of the image determinable. What is the shape of the image formed on the photographic plate after you send a large number of photons? Something like what you see on the right: a single blob. Now cover the first slit and send photons through the second one. The same image is formed on the plate.
… How did the photon in the first experiment know that the second slit was not open? Think about it. … When we fired our photon and it went through the first slit, how did it ‘know‘ that it could go to an area that must be dark if the other slit were open? In other words, how did the photon know that the other slit was closed? There is no definite answer to this question. Some physicists speculate that photons may be conscious!
The repeated use of the word “know” in the quote already hints at a conscious photon. Zukav and the physicists to whom he refers at the end of the quote did not pay attention to the warning in Pseudo-physics 101, a warning that echoes Richard Feynman’s famous quote:
Do not keep saying to yourself … “But how can it be like that?” because you will get ‘down the drain’, into a blind alley from which nobody has escaped. Nobody knows how it can be like that.
Despite Zukav’s claim, there is a definite answer to the question. When one slit is open, there is only one . Square it and you get the probability, which translates into a blob. If the slits are identical, you get identical probabilities and therefore, identical images for the two. When two slits are open, superposition principle tells you to first add the s and then square the sum. The result is not the sum of the squares and the figure on the left above, but an expression which is zero at some points of the photographic plate. A zero probability means zero photons, thus the dark bands in the graph! (N.B. If you know complex numbers, especially their polar representation, then this article shows how the dark bands arise.) Let me repeat my warning in Pseudo-physics 101 in the context of quantum physics (and rephrase Feynman’s quote):
WARNING! Quantum physics is based fundamentally on probability. If you try to “explain” the outcomes of quantum events, you may turn into a crackpot, as have many people, including some physics PhDs.