Richard Feynman the farther of Quantum Electrodynamics or “OED” realized the significance of the Thompson’s double slit experiment because it demonstrates the inseparability of the wave and particle properties of particles and felt a complete understanding of quantum mechanics could be gleaned from carefully thinking through its implications.
However it also allows one to understand the physical connection between quantum mechanics and the space-time universe of Einstein.
The double slit experiment is made up of “A coherent source of photons illuminating a screen after passing through a thin plate with two parallel slits cut in it. The wave nature of light causes the light waves passing through both slits to interfere, creating an interference pattern of bright and dark bands on the screen. However, at the screen, the light is always found to be absorbed as discrete particles, called photons.
When only one slit is open, the pattern on the screen is a diffraction pattern however, when both slits are open, the pattern is similar but with much more detailed. These facts were elucidated by Thomas Young in a paper entitled “Experiments and Calculations Relative to Physical Optics,” published in 1803. To a very high degree of success, these results could be explained by the method of Huygens–Fresnel principle that is based on the hypothesis that light consists of waves propagated through some medium. However, discovery of the photoelectric effect made it necessary to go beyond classical physics and take the quantum nature of light into account.
It is a widespread misunderstanding that, when two slits are open but a detector is added to determine which slit a photon has passed through, the interference pattern no longer forms and it yields two simple patterns, one from each slit, without interference. However, there ways to determine which slit a photon passed through in which the interference pattern will be changed but not be completely wiped out. For instance, by placing an atom at the position of each slit and monitoring whether one of these atoms is influenced by a photon passing the interference pattern will be changed but not be completely wiped out.
However the most baffling part of this experiment comes when only one photon at a time impacts a barrier with two opened slits because an interference pattern forms which is similar to what it was when multiple photons were impacting the barrier. This is a clear implication the particle called a photon has a wave component, which simultaneously passes through both slits and interferes with itself. (The experiment works with electrons, atoms, and even some molecules too.)”
As was mentioned earlier, one can understand this experiment in term of the physical properties of space-time and Relatively because they tell us wave energy moves continuously through space and time time unless it is prevented from by moving through time by someone observing or something interacting with it. This would result in its energy being confined to three-dimensional space. The science of wave mechanics also tells us the three-dimensional “walls” of this confinement will result in its energy being reflected back on itself thereby creating a resonant or standing wave in three-dimensional space. This would cause its wave energy to be concentrated at the point in space where a particle would be found. Additionally, wave mechanics also tells us the energy of a resonant system, such as a standing wave which this confinement would create can only take on the discrete or quantized values associated with its fundamental or a harmonic of its fundamental frequency. This means the particle quantum mechanic calls a photon would have an extended volume equal to the wavelength associated with its standing wave.(Note the boundaries or “walls” of its confinement would be defined by its wave properties. If an electromagnetic wave is prevented from moving through time it will be reflected back on itself. However, that reflected wave still cannot move through time therefore it will be reflected back creating a standing wave. Putting it another way wave itself defines its boundaries because if it cannot move though time it MUST STAND in place in the form of a standing wave.)
As was mentioned earlier one can use the above to demonstrate the physical connection between quantum mechanics and the space-time universe of Einstein.
Briefly it shows the reason why the interference pattern remains when one photon at a time is fired at the barrier with both slits open or “the most baffling part of this experiment” is because, as mentioned earlier it is made up of a standing wave therefore it occupies an extended volume which is directly related to its wavelength.
This means a portion of its energy could simultaneously pass both slits, if the diameter of its volume exceeds the separation of the slits and recombine on the other side to generate an interference pattern. This would occur because wave energy is allowed to move freely through time.
However, when its energy is prevented from moving through time by contacting the screen its energy will be will confined to three-dimensional space causing it to be concentrated in a standing wave that as mentioned earlier would define the particle properties of a photon.
Additionally because the energy of the standing wave which earlier was shown to define a photon is dependent on its frequency the energy of the particle created when it contacts the screen must have the same energy. Therefore, were it appears on the screen will be determined by where the interference of the wave properties from each slit combine to produce enough energy to support its particle properties.
It also explains why the interference pattern disappears, in most cases when a detector is added to determine which slit a photon has passed through. this is because the energy required to measure which one of the two slits it passes through interacts with it causing the wavelength of that portion to change so that it will not have the same resonant characteristics as one that passed through the other slit. Therefore, the energy passing thought that slit will not be able to interact, in most cases with the energy passing through the other one to form an interference pattern on the screen.
However it also explains why, as was mentioned “there are ways to determine which slit a photon passed through that will cause a change in the interference pattern but will not completely wiped it out.
The fact that the interference pattern can still occur even if a measurement is made is because if the energy passing through one of the two slits is altered by a relatively small amount compared to what it originally was, classical wave mechanics tells us it will be able to interact to form a slightly different resonant system with a slightly different interference pattern on the other side than would be the case if no measurement was taken.
However, this also means there should be a quantifiable minimum value of interaction between a measuring device and a photon that will permit the interference pattern although somewhat altered to be reestablished on the other side after measuring which slit the photon passes through.
Copyright Jeffrey O’Callaghan Apr. 2021