3.4.4.9 Double-Slit Experiments
In 1827, Thomas Young and Augustin Fresnel directed a beam of light through two narrow slits, and they observed interference pattern of light and dark fringes on the screen. Similar pattern also appeared when repeating the experiment on one slit only, which is explained as diffraction, the same behavior that can be demonstrated in water waves. This experiment gave the ultimate demonstration of the wave nature of light. Variations of the double-slit experiment have been performed using electrons, atoms, and even large molecules, and all exhibited the same type of patterns. Thus it has been demonstrated that matter have both particle and wave behavior, as described further in section 4.4.1.
Some physicists then proposed that, since all particles have wave properties, we should expect to diffraction and interference even when only one particle passes through the apparatus at a time, and we allow enough time to develop the pattern. This means that the quantum particle acts as a wave when passing through the double slits, but as a particle when it is detected.
Experiments have been performed later on single photons and other simple and complex atomic particles and objects. The results of many such experiments clearly showed that even though single photons pass through the apparatus only one at a time, interference still occurs, as though it is apparently interfering with itself. Further experiments showed that any observation of “which slit does the photon pass through” causes the collapse of the wave-function of the photon and defines its state, which removes the wave aspect of the photon’s behavior and destroys any interference patterns.
Other advanced setups showed that if this “which path” information is subsequently erased; the interference pattern can be recovered again even after the photons have already made their choice through the slits!
In addition to photons, similar experiments were performed on particles as large as buckyballs, and even macroscopic systems, which all confirmed the previous conclusions.
The fact that photons and other particles exhibit both wave-like properties and particle-like properties is one of the central mysteries in quantum physics. This wave-particle duality conundrum exposes the inadequacy of our conventional conception of the structure and behavior of the microscopic realm. Although Quantum Mechanics provided an adequate mathematical formulation, there is yet no satisfactory interpretation that may explain this ostensible paradox, which challenges our basic intuition.
Bohr regarded this weird quantum behavior of particles as a metaphysical fact of nature, while Richard Feynman (1918-1988) said in his famous Lectures of Physics:
“We choose to examine a phenomenon [Double-slit experiment] which is impossible, absolutely impossible, to explain in any classical way, and which has in it the heart of Quantum Mechanics. In reality, it contains the only mystery. We cannot make the mystery go away by explaining how it works. We will just tell you how it works. In telling you how it works, we will have told you about the basic peculiarities of all Quantum Mechanics.” Feynman et al. (1963)
This weird single particle interference can not be explained without postulating the perpetual re-creation in the inner levels of time. Based on this re-creation principle of the Single Monad Model, a new concept of “temporal entanglement” can be applied to explain both the normal multi-particle and this peculiar single particle interference. In both cases, one wave-function describes the superposition of the two states of the two interfering particles, or waves, but in normal interference this superposition is spatial, on the inner level of time, while in the second case it is temporal, in the outer level of time, i.e. the states of the two interfering particles are entangled through time. Both of these spatial and temporal entanglements are only possible due to the fact that both particles are sequentially created by the Single Monad, which is exactly what gives them the nature of waves and uncertainty, as we shall see further in sections 4.4.1 and 4.4.2, and the very act of observation of one of them causes the collapse of the wave-function, thus determining the behavior of the second particle whether they were separated in space or in time.
This concept of temporal entanglement can also explain other peculiar quantum interference experiments, such as “which path” and the “delayed choice quantum eraser”, but we will leave the discussion on this subject till after we explain the Single Monad Model in chapter IV and the resulting Duality of Time hypothesis in chapter V.