Take the description of the collapse in Nature Loves to Hide, by physicist Shimon Malin:

In this chapter we zero in on the mystery at the heart of Quantum Mechanics. 'The collapse of the quantum state'. The collapse is, whereby in an act of measurement, the potential becomes actual. An elementary quantum event is created out of a background of potentialities.

The process is atemporal occurring outside space and time and leads to an actual appearance of an event in spacetime. The idea of an atemporal process may seem strange but it is neither new nor obsolete. It is an integral part of Platos worldview and Whiteheads.

On this reading, conceptually speaking, the collapse of a quantum state ought to be called actualisation.

Consider a man. He can measure an apple, he can hold it in his hand. But he cannot hold the air. The air had to 'actualise' or 'condense' before he can hold it, before he can measure it.

Collapse is named from the purely mathematical conception of a quantum state, it collapses into an eigenstate whose eigenvalue can be measured.

Surely a mathematical description does not tell us what something is. I can measure, for example, the mass of an apple, but this does not tell me what an apple is.

The reason why, of course, collapse remains as a signifier in discoursing about QM is that there is no conceptual consensus on how to interpret QM; whereas there is a consensus on its mathematical description. Collapse, then, as a descriptive signifier, is the lowest common denominator in explanatory interpretations.

Is actualisation, given Malins description, a good stand-in?

  • This topic is a minefield for the layman and tempers run high in the profession so I wouldn't dare say much, but calling it 'actualisation' makes a lot of sense to this non-physicist.
    – user20253
    Jan 17 '18 at 11:59
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    @PeterJ: For sure. There's a review of Malins book by Philosophy Now if you're interested. I was just thinking that if there is actualisation there must be its opposite, potentialisation. Much of Malins account reminds me of Parmenides, strangely enough. Whereas the atomists introduced space for atoms to move in, Aristotle introduced potentiality for change to occur. I think, on the whole, this is the better account. But I'm probably one of the very few who thinks so... Jan 17 '18 at 12:47
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    The Wikipedia article on matrix mechanics (en.wikipedia.org/wiki/Matrix_mechanics#Matrix_basics) suggests a conflict between Einstein (wave-particle duality) and Bohr (discrete energy states and quantum jumps) as part of the problem with understanding "collapse". The wave function tries to give a path for the particle when we are not looking at it. This function "collapses" with a measurement which is all we observe. Getting away from the collapse metaphor seems like a good thing. Actualization sounds promising, but there is nothing that is collapsing as I see it. Jan 18 '18 at 5:18
  • I've read Malin since you mentioned him. I think the word "choice" needs to be part of the description based on his reference to Dirac's use of the word to describe the collapse. The move from potentialities to actualization describes the full process. What I am puzzling over is why the process takes time if there is nothing underlying the potentialities. I will try to provide an answer to your question based on this book after I go over it again. Feb 10 '18 at 19:55
  • @Frank Hubeny: I recall that was in response to a question that Malin put to Dirac and Dirac said: Nature makes choices. This suggests that he doesn't believe strict determinism holds since in that picture no choices are made. Feb 10 '18 at 20:25

"Give me a long enough lever, and a fulcrum upon which to put it, and I will move the world." -Archimedes

"Give me a razor fine enough, and I will split hairs." -Cort Ammon

I love playing with words, and using this word or that. In the end, the reality is that the best word for describing something is the word which conveys the meaning the best. Sometimes that requires using a non-standard word, and other times the existing typical word is simply the best choice for communication.

When trying to find the "best" word for this concept, it's worth noting that it does not appear in all interpretations. The Copenhagen interpretation has it, but MWI and Pilot wave interpretations do not. So whatever term one uses should remember that other interpretations are equally credible, even if they don't use the term. MWI and Pilot Wave interpretations have a concept of something being measurable, so I fear using a powerful term like "actualize" for Copenhagen and Copenhagen alone is a dangerous precedent.

"Collapse" has a nice feel in Copenhagen, as the quantum waveform has subtle nuances which are permanent lost upon this kind of event, like a tower of cards collapsing into a pile of cards. It conveys a sense of loss that I find fits well with Copenhagen, but which does not necessarily appear in other interpretations.

Another word that might join the fray is "realize," because "realism" is a concept which already has a meaning in the world of quantum mechanics, and there's some fun connections there.

If one wanted to write a book on the philosophy of quantum physics, and wanted to tie this concept of collapse into the concept of actualization from philosophy, I don't think anyone would find it troubling (who am I kidding, it's philosophy... someone will find it troubling!). But I think making the claim that it is misnamed is a bit strong.


Not being acquainted with proper philosophical methods I will restrict myself to a physical chemists interpretation of the semantic problem.

The system, that which is being probed, exists in a so-called superposition of states. We use this language because we find that when we perform an experiment specific to probing what state the system is in, we may obtain different values each time (note that the system is prepared identically prior to each experiment, the only variable being time). Having performed sufficient such replicate experiments, we obtain a probabilistic distribution describing the likelihood that a particular value will be observed. The idea of obtaining different results from an experiment performed on replicas of a system is of course not necessarily strange, for we could equally well perform the following classical experiment: we have a box full of a mixture of colored balls which are continuously shaken about. We perform an experiment to see what is in the box by sticking our hand into the box (without looking) and withdrawing a ball. The ball is then returned to the box and the experiment is repeated sufficient times to obtain a distribution of the color probability to the desired accuracy.

What is different about the QM system, then? Where does the analogy fail? When we remove the ball we are separating the ball from the system, that is, the immediate product of the experiment is two distinguishable subsystems: (1) the ball and (2) the remaining box+balls. The two subsystems preserve all of the information of the original system. There is no loss of information. What about in QM? When we perform the experiment, the system loses information permanently. We cannot continue to probe the sytem to extract information about the original system. The only way to obtain more information is to repeat the experiment on a new pristine system. This is why the word "collapse" is used. It suggests a dramatic perturbation that renders lost any information about the full range of possible experimental outcomes.

  • Well-put. I think the fact that the talk of "collapse" of physical waves predates quantum mechanics to be a factor as well, but that's pure speculation.
    – Philip Klöcking
    Apr 18 '20 at 14:25

Electron orbits would then be 'unactualised'. Many quantum phenomena 'reach' in their uncollapsed state, like a particle in a potential well tunnelling through a barrier it shouldn't be able to cross. A probability wave represents many points, a detection or interaction one, so collapse is not entirely innappropriate.


Calling the transition from potentiality to actuality in a quantum event a “collapse” presents a non-agent description where the actual event that is observed makes a specific measurement. The potentiality cannot be observed directly but it is represented by a wave function that allows alternate possibilities. Going from alternate possibilities to a specific measurement is the collapse of those possibilities to something specific.

In the case of someone making a choice there is nothing odd about this. In that case the person has multiple possibilities and chooses one of them. Again the possibilities could be said to collapse into one measurement, but since this is an acknowledged agent the agent can be said to choose regardless of what one believes about free will or determinism.

This means there are at least two ways of looking at the transition from potentialities to one actuality. It could be viewed as a collapse of those potentialities where a non-agent particle is assumed to be involved or it could be viewed as a choice between alternate possibilities where an agent is assumed to be involved. Given Malin’s quote of Dirac describing the collapse as “nature makes a choice” ("Nature Loves to Hide", Chapter 11) suggests that choice could be used in place of collapse.

However, using “choice” implies some sort of agent making that choice. Using “choice” suggests we should look for evidence that the agency at the quantum level is more than metaphor. Other possible descriptions such as “actualization” or “manifestation” hide the idea of this agency. They look at what happens as a completed observation. They also hide that there were many alternatives that could have actualized or manifested but did not. They are no better than using the word “observation” which also hides the alternatives available prior to the observation and the choice from or collapse of those alternatives at the end of the process.

If one can establish agency of some sort at the quantum level, this implies that "choice" is the right word to use because it is real. That means there is free will at the quantum level. The Conway and Kochen Free Will Theorem uses the assumption of human experimenters having free will to conclude that the quantum system also shares in that free will, but whether humans have free will or not is not universally accepted. Also this does not clarify what kind of agency might be at the quantum level although it might clarify what agency means at our level. It only shows that free will must be there if we have free will.


"Actualization" might suggest that before the collapse there was nothing "actually" there. The wave function tells us where we might find it if we look for it, but it is a big step to claiming that it really is not there until we do. For example it will still be exerting a gravitational field, by virtue of having nonzero energy. On the other hand if I conceive a sculpture is is genuinely not there until I actualize it in my studio. Or at least, that is a plausible understanding.

So one clarification must be what precisely you wish to mean by "not actualized" vs "actualized".

Having made that clarification, you may ask ten quantum physicists their views on your definition and you will receive at least twelve different judgements, all wildly conflicting. The widely adopted Copenhagen interpretation is basically "Don't think about it, we can never know".

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