By Perig Gouanvic
Reposted from Pi alpha
Reflecting on the Double Slit Experiment
What do particles know?
The so-called ‘double-slit experiment’ is a demonstration that light and matter can display characteristics of both classically defined waves and particles. It is also said that it displays the 'fundamentally probabilistic nature' of the universe at the quantum scale.
The original intuition of Thomas Young (back in 1802) was to reproduce the cancellation of water waves, but with light; the double slit was simply used to yield two exactly identical light sources (the same, divided in two). Notice the straight lines that seem to radiate from the source of the water waves: they are made of the cancellation of each other, and are analogous to the dark regions on the five-step picture (below), a true depiction of the impact of electrons in an experiment made by Tanamura.
In the de Broglie–Bohm theory (also called the Bohm interpretation) of quantum physics, the reason why single particles seem to interfere ‘with themselves’, in other words, the reason why, in the double-slit experiment, even single particles ultimately form a figure of interference despite of the fact that they are not emitted as beams but one after the other (see the 5-step process, below), is because each of these particles have a kind of pilot wave which does interfere with itself in some circumstances like the double slit apparatus. The analogy of the sonar helps to explain the phenomenon : picture a dolphin who would have to echolocate through two holes and you get the picture!
Bohm had many analogies for the quantum potential, his revised version of the pilot wave. The sonar is one of them. The information given by the surroundings guides the dolphin, it is called 'active information'
However, what this analogy leaves unattended is the fact that particles do not "send" signals to the surrounding and do not "wait" for this signal to bounce back. Another analogy far remote from the sonar one, was given by Bohm : each particle is like a piece of an hologram, each contains information about the whole, but each is concretised in a specific context.
The 'echolocation' process would be more like a pulsation between the particle as a located entity and the particle as one concretion of the whole. Pulsating infinitely rapidly between being-discrete and being-the-whole, the particle would be more like a process taking the form of an object.
What kind of "thing" can be everything half of the time and something the rest of the time?
Humans, for starters. We, as particles, tend to forget that we also are the whole, each night. We dream.
Reposted from Pi alpha
What do particles know?
The so-called ‘double-slit experiment’ is a demonstration that light and matter can display characteristics of both classically defined waves and particles. It is also said that it displays the 'fundamentally probabilistic nature' of the universe at the quantum scale.
The original intuition of Thomas Young (back in 1802) was to reproduce the cancellation of water waves, but with light; the double slit was simply used to yield two exactly identical light sources (the same, divided in two). Notice the straight lines that seem to radiate from the source of the water waves: they are made of the cancellation of each other, and are analogous to the dark regions on the five-step picture (below), a true depiction of the impact of electrons in an experiment made by Tanamura.
In the de Broglie–Bohm theory (also called the Bohm interpretation) of quantum physics, the reason why single particles seem to interfere ‘with themselves’, in other words, the reason why, in the double-slit experiment, even single particles ultimately form a figure of interference despite of the fact that they are not emitted as beams but one after the other (see the 5-step process, below), is because each of these particles have a kind of pilot wave which does interfere with itself in some circumstances like the double slit apparatus. The analogy of the sonar helps to explain the phenomenon : picture a dolphin who would have to echolocate through two holes and you get the picture!
Bohm had many analogies for the quantum potential, his revised version of the pilot wave. The sonar is one of them. The information given by the surroundings guides the dolphin, it is called 'active information'However, what this analogy leaves unattended is the fact that particles do not "send" signals to the surrounding and do not "wait" for this signal to bounce back. Another analogy far remote from the sonar one, was given by Bohm : each particle is like a piece of an hologram, each contains information about the whole, but each is concretised in a specific context.
The 'echolocation' process would be more like a pulsation between the particle as a located entity and the particle as one concretion of the whole. Pulsating infinitely rapidly between being-discrete and being-the-whole, the particle would be more like a process taking the form of an object.
What kind of "thing" can be everything half of the time and something the rest of the time?
Humans, for starters. We, as particles, tend to forget that we also are the whole, each night. We dream.
I much enjoyed the creative thread, Perig, that you wove between Niels Bohr’s ‘complementarity’—the particle-wave duality you describe—and ‘particles dreaming.’ Bohr, himself, recognized the metaphysics running hand-in-hand with the physics. He thought about complementarity in expansive terms, much beyond quantum physics, including in the social sciences and, in particular, as an explanation of many matters in his other field of great affection, philosophy. An example of Bohr’s interest along these lines was the complementarity of yin-yang of eastern philosophy. So ardently, in fact, that he chose to design his own coat of arms, whose centerpiece was the yin-yang symbol—bearing the inscription “Contraria sunt complementa [opposites are complementary]”! In the general vein of ‘particles dreaming’, you might agree with Bohr that likewise “A physicist is just an atom’s way of looking at itself.”
ReplyDeleteMy understanding of Bohr’s complimentarity is about how our language is limited by our observational experience but it is necessary for our depicting the world. We have to use the classic language (particles and waves, where an observation has no interference with its objects) to describe the non-classic phenomena (quantum, where an observation does interfere with its objects). It is like that if we have to use the language of Yin and Yang to describe something that is actually neither, we should tell people how they are used in a complimentary way.
ReplyDeleteMmmm... I agree with your intuition, Chengde- but isn't the whole issue about the two things not being complementary but irreconcilable? Like being red all over or green or over but not red and green all over? As my philosophy tutor used to say... (lacking more imagintive examples)
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