The inner and the outer world
In the ‘Quantum Physics & the Mind’ course that I lecture at the Academy of Humanities in Utrecht, The Netherlands, the study assignment is an essay about which insights quantum physics has yielded for the student. In one such an essay, a student wrote that she could well understand the interference pattern that results in the double slit experiment, but that she did not get clear why, as soon as one of the slits is observed, the interference pattern disappears. Musing about the small but important difference between those two experiments, I realized that the problem for many may be found in our usual subject-object stance.
The ordinary double slit experiment – where it is not observed through which slit the object or quantum wave goes – is a clear example of how we usually do experiments. We are not physically involved and observe the results from a third person perspective. That is the way we observe the world, as we have been used to do so from childhood, as if the perceived world is not part of our inner world.
As an aside, I assume that it is the quantum wave and not the materialized object that passes through one of the slits. That explains the observed loss of interference just as well and does not contain the additional unnecessary assumption that the object materialized for a moment in the slit even though it was not directly observed there. The assumption that the object materializes in the slit originates probably from the preference we have for the idea of the permanence of matter. The assumption that the state wave is a probability wave as long as it is not observed is sufficient to explain the phenomena without anything materializing anywhere on its path to the detector. If the state wave reduces itself to just one slit, the probability that we would have found the particle there, if we had actually observed there in the slit, is indeed 100%. However, a 100% probability is only just a number in our mind and not the same as a material presence. Probability is not matter.
But as soon as we notice that our mere observation has an effect on the result in the experiment – the state wave changes its behavior, even retroactively, to pass only through one of the two slits – we ourselves become a part of the experiment. Our knowledge, our spiritual inner world, becomes entangled, literally, with the perceived material outer world. Which is absolutely something we are not used to. The intellect – that is the way we interpret the world – no longer understands what happens and backs away. Confusion arises.
The illusion of separate inner and outer worlds
How can this confusion be resolved? The logic is in itself simple and correct. Einstein saw it as early as 1920 (and he was very opposed to what it implied). If you can determine in some way the slit that the particle has passed, it is no longer possible that the outcome is that it has passed through both slits, even if this happens in the form of a probability wave. The probability in one of the slits should become 100%, zero in the other. Those outcomes, passing two slits and passing only one of the slits, are logically and mutually exclusive. The wave therefore conforms clearly its behavior to our knowledge of the world. At that crucial moment, the intellect realizes a violation of its deeply ingrained stance of “I am in here and the world is out there and they are both independent of each other“. Which results in confusion and not being able to understand. I think the only solution to understand this is to let the logic come in through quiet introspection. Ask yourself if you are really sure – from positive experience – if the inner and outer world are separate worlds. The acceptance of the idea that the inner world and the outer world are strongly connected and influence each other must take time. Be patient.
The usual interpretation is that the object materializes in the slit when it is observed and then continues again as quantum wave on its way to the detector. See insert aside above. The result – the disappearance of the interference pattern – is indistinguishable from the expected effect of the reduction of the wave to one slit. In the first case, the observer’s inner world has a slightly different effect on the outer world, materialization of the object in the slit instead of the reduction of the wave. Does the difference matter? Not a bit really.
In other words, the outer world is a part of the world of the mind. Which would explain the phenomenon of synchronicity excellently. Synchronicity becomes something that should be expected. How it is possible that we – each aware individual – have an inner world that is not separate from the outside world, is then made understandable by assuming that that seeming individuality, de personal inner world, ultimately is also an illusion, a special form of a constrained perspective. This also sheds light on the consensus question that was an insurmountable problem for Eugene Wigner.
How to actually observe the slits
‘Observing’ the slits is a metaphorically intended expression in these experiments. We only need to be able to determine by measurement the slit through which the object went. This is usually done by using two entangled photons, where one of them is sent through the slits and the other one provides us the information about its twin sister.
Doing three-slit experiments
The question of what happens when ‘observing’ only one of the three slits in a three-slit experiment is of course also interesting here. This question comes up often when I’m giving my course on quantum physics and the mind. With three slits where only one of them is ‘observed’ we have some information, but not enough to know each time which slit the object went through. If we don’t observe the object’s passing – a probability of 2:3 – the state wave will pass through the other two slits. Interference of these two synchronous waves will then occur.
But, if we do ‘observe’ an object passing the observed slit, which means that the probability wave is reduced to the observed slit, then there will be only a single wave coming from the ‘observed’ slit, so no interference. The pattern of fringes, which becomes discernible when we fire a large enough amount of photons, becomes less distinct. The clear fringes and the spread-out spot become superimposed. The less information we can have about the path followed, the stronger the wave behavior becomes. The more information we can have, the stronger the particle behavior will be shown. Which is confirmed in a Korean experiment that I discuss elsewhere. That experiment showed that there is a mathematical relation between information and wave-particle behavior.
So, the illusion is not that of the experience of an illusionary material world, the illusion is one of separation between the mental and the material. There is no hard impenetrable separation between the inner and outer world. Observation: the inner world is undeniably ‘real’. So, the outside world therefore too.
The meaning of what should be understood as real changes accordingly.
Paul J. van Leeuwen graduated in applied physics in Delft TU in 1974. There was little attention to the significance of quantum physics for the view on reality at that time. However, much later in his life he discovered that there is an important and clear connection between quantum physics and consciousness.