What is information in quantum mechanics

Information and quantum physics

Epistemological considerations on the importance of the quantum teleportative "transmission" of information

In the discussion, prominently promoted by Anton Zeilinger from the Institute for Experimental Physics at the University of Vienna, about possible applications of the findings of quantum physics, the term, in a broader sense the concept or theory of information, plays a decisive role ("It ultimately turns out that information is a essential building block of the world is "). Controversial technological developments such as quantum cryptology, quantum teleportation or fast information processing by quantum computers are in prospect.

The theory of quantum physics has been repeatedly and impressively tested in methodically refined empirical experiments in the last few decades (breakthrough in quantum physics, quantum flow under the Danube). It must be regarded as one of the best empirically confirmed and most successful physical theories of modern times, not least due to successful technical applications such as lasers. The discussions about possible applications suggested by the more recent quantum mechanical experiments (the dream of "beaming"), however, cannot be denied a certain naivety with regard to an information theory on which quantum physics is based.

The phenomenon of "entanglement", which has been confirmed experimentally in many cases, as well as the quantum mechanical effect of superposition (stable Schrödinger cats), calls into question the classic (Newtonian) concept of a "punctiform", unambiguous locality of events or entities. "Entangled" elementary particles, such as photons, can still be in instantaneous, ie not delayed, "interaction" if they are "spatially" "separated" from one another. Even the speed of light is not limiting; Einstein therefore spoke of a "spooky long-distance effect". Regardless of this quantum mechanical effect, which has been confirmed many times, the classic view is apparently applied unreservedly in the discussion about possible quantum teleportations: The point here is to transfer information. In the microcosm of the quantum world, however, local things are to a certain extent "smeared". The view that information is "transmitted" here is therefore extremely problematic. Namely, it presupposes the local separation of the different (?) Particles, which is just called into question in the case of the entanglement of elementary particles in quantum physics. Or to put it another way: The interpretation that it is not a quantum teleportative “transmission” of information between two locally separated laboratories that crosses the Danube, but that the construction of a spatially “smeared” laboratory has succeeded, is just as plausible. It would be questionable here to speak of a successful “information transfer”.

Problems of Conventional Formulation of Information

When there is talk of the transmission of information, the classic model of communication is assumed: Here, information is exchanged between "senders" and "receivers" or even (reciprocally) transmitted. This classic view of information and communication in the field of quantum physics is clearly demonstrated by the fact that Zeilinger illustrates his idea of ​​“quantum teleportation” using the sender-receiver representatives “Alice” and “Bob”. This may be due to popular scientific advances, but it is misleading because the epistemological problem horizon of quantum physics makes it necessary to use a more abstract conceptual version of the term information or communication as a basis.

The strictly possible separation between the subject of knowledge and the object of knowledge, observed from a classical perspective, is called into question by quantum physics. In the scientific recording of the microcosm, the (measurement) problem appears that the level of the subject of knowledge, the recipient of “objective” information, can in principle no longer be separated from the object of knowledge. The levels are entangled with one another at an elementary level. In relation to the horizon of these phenomena, the subject and object sides are, so to speak, bound to elementary "units" (waves or particles?) On both sides and can therefore no longer be categorically strictly separated. Precisely for this reason, it can be assumed that the concept of information may play a decisive role. It is a term that, turning away from the Cartesian subject-object dualism, can possibly unite the subjective and objective domain of phenomena and thus take into account the epistemological knowledge that quantum physics generates (has). Linked to this would be a departure from the classic model of information transmission, i.e. the model that requires subjects to be strictly separated locally as senders and receivers.

In the discussion about possible technical applications of quantum physics (such as quantum teleportations) it would not only be misleading, but also contradictory, to conceptually couple the concept of information to strictly spatially separated individuals (in Zeilinger's example “Alice” and “Bob”). The strict spatial separation between “Alice” and “Bob” is a prerequisite for the classic concept of information in order to speak of a transfer of information in a meaningful way. It is therefore necessary to fall back on a more abstract concept of information, a concept of information that is independent of a link to the paradigm of transmission.

Information is a difference which makes a difference

In fact, what we mean by information - the elementary unit of information - is a difference which makes a difference.

Gregory Bateson's conception of information is itself to be called classic in its abstract simplicity.

Information taken in this way does not anticipate the reference level to which the term is to be understood. It is possible to relate it to social systems, i.e. to understand it at the level of the operation of communication. Difference here, for example: bad weather, not nice - which makes the difference: excursion tomorrow, not today. However, it can also be used without problems on the level of neural systems; E.g. difference, related to the synaptically coupled neurons A, B and C: only neuron A fires, not neuron A and B - which makes the difference: neuron C does not fire instead of fire. Since quantum physics raises the epistemological problem of whether information must be assigned to an objective reality or understood as a subjective construction, an information concept that does not anticipate a decision in this regard is of high methodological value in the construction of theories. Because it is precisely this uncertainty that crystallizes the multitude of more or less plausible interpretations of quantum mechanics, such as the Copenhagen Interpretation, the Bohmian Interpretation or the Many Worlds Interpretation.

Bateson's conceptual conception does not suggest that information has to be essences or substances that can then be transferred. Rather, information in this abstract way is understood to be strictly operational, procedural and thus independent of specific locality or substance. And thus also independent of a referential reference to subjects as senders or receivers of information, which anticipates a specific epistemological perspective. This is methodologically fruitful insofar as quantum physics calls into question conventional epistemological perspectives. In the sense of a possible epistemological insight, it is therefore forbidden to prematurely base the interpretation of those quite strange quantum mechanical effects such as "entanglement" on a conventional view from an epistemological point of view. - Zeilinger, for example, suggests an essentialist concept of information linked to the paradigm of transference:

We [...] suggest a principle of quantization of information as follows. An elementary system represents the truth value of one proposition. [...] We now note that the truth value of a proposition can be represented by one bit of information with “true” being identified with the bit value “1” and “false” identified with the bit value “0”. Thus our principle becomes simply: An elementary system carries 1 bit of information.

Anton Zeilinger: (A Foundational Principle for Quantum Mechanics, p. 635

Incidentally, it remains Zeilinger's secret why an “elementary system” represents the “truth value”, as “1 bit of information” is precisely due to the difference between “truth value” (1) and “false value” (0 ) certainly. But apart from that, an essentialist version of information, i.e. a conception that is based on carriers of information (“elementary system”) and thus fundamentally from the transfer of information, is associated with massive problems, especially in epistemological terms. How exactly is the transition of this information understood as essences or substances from the sender to the recipient? A problem that leads straight to the center of the mind-body problem that has been discussed for centuries. This can be understood as a follow-up problem to Cartesian dualism, which is called into question by the results of quantum physics and, viewed in this way, once again offers an occasion to distance yourself from classical information theories based on the transference paradigm. Recent biological-cybernetic research gives reason to assume that neural systems are informative, as research by Gerhard Roth shows. In this context, neural systems could be considered as addressees in the sense of senders or receivers from the perspective of classical information theory. In the more recent system-theoretical-cybernetic perspective, however, information is constructed on the basis of system-specific operations, and thus entirely in line with the conception of information according to Bateson. The apparently fundamental epistemological problem of how the initially and superficially plausible idea of ​​a transfer of information can be concretized becomes obsolete. In the elaboration of a “theory of social systems” by the sociologist Niklas Luhmann, Bateson's basic idea is certainly used in the most differentiated and fruitful way.

Even with the empirically obvious and seemingly trivial phenomenon that the information itself leads to information being destroyed - repeated information is no longer information - can theoretically hardly be grasped with an essentialist conception of information. It is true that one could fall back on subjectivisms here - "Oh, that is no longer information, it is old, I already know it, I have already heard" - but such a plausibility check would have to be understood and understood completely independently of the specific essentialist explanatory model of information would thus refer to its weakness of explanation. With reference to Zeilinger's “elementary systems” as the carrier of exactly “1 bit of information”, the mentioned “trivial” phenomenon can hardly be explained. Why should repeated information (or information transfer) have the effect of destroying information precisely to those "elementary systems" as carriers of information?

Bateson's conceptual formulation of information, on the other hand, makes it very easy to theoretically grasp the problem of information destruction through (repeated) information. The repeated information creates a difference between “information” and “information (repeated)”, the characteristic of which is that no difference is made (any more) and, according to Bateson's conceptual definition, cannot (no longer) be understood as information. Through repetition, information (a difference which makes a difference) is transformed into non-information (a difference which makes NO difference (anymore)). It speaks for the fruitfulness of Bateson's concept of information that it can explain the everyday, common phenomenon that information is destroyed by (repeated) information. It is a phenomenon that may seem trivial in its everyday life, but it certainly cannot be theoretically grasped in a trivial way.


If the findings of quantum physics are taken seriously, they must consequently also have an impact on a theory of information or the factual processing of information. These are effects above all from an epistemological point of view. With the possibility of "entangling" elementary particles, quantum mechanics suggests fundamentally questioning the principle of a one-to-one locality of entities that is valid for classical physics. For example with reference to the ideal type of “mass points” in Newtonian physics. In the discussion about quantum teleportation, for example, the phenomenon of “entanglement” of elementary particles, which fundamentally questions the locality of units, is taken as the starting point for the considerations, but remains in the further discussion without any conceptual effect on the formulation of the concept of information. This becomes obvious when the phenomenon of "entanglement" is to be made usable for quantum teleportative information transmission. The paradigm of a transfer of information, however, presupposes that different levels (such as "Alice" and "Bob" as sender / receiver) regarding locality can be easily distinguished.

In the absence of a discussion of the question of whether the collapse of the classical paradigm of an unambiguously based locality of entities through the theory of quantum mechanics must not also have an impact on a theory of information, at least a lack of problem awareness becomes apparent. A conception of information based on its transmission ultimately requires clear spatial distinctions (sender - receiver). This lack of awareness of the problem is all the more serious since the more recent experiments show that effects can be expected not only on an elementary level, but also on a macroscopic level. This would also reach the horizon of “senders” and “receivers” of information.

The phenomenon of entanglement, which becomes evident in quantum physics, can therefore suggest that a more abstract version of the concept of information should be used as a basis, which avoids implicitly associating information with locality (in relation to "sender" and "receiver") and substantiality (in Reference to “carrier” of information). Bateson's concept offers precisely these advantages. The concept of information is understood here independently of the classical paradigm of a “transfer” and is thus in line with the often strange effects of quantum physics. A major part of this alienation is caused by a classic understanding of information linked to sender and receiver, which is no longer up-to-date, at least apparently no longer in quantum physics. (Jörg Räwel)

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