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Byron Jennings | TRIUMF | Canada

View Blog | Read Bio

Reality and the Interpretations of Quantum Mechanics

If there were only one credible interpretation of quantum mechanics, then we could take it as a reliable representation of reality. But when there are many, it destroys the credulity of all of them. The plethora of interpretations of quantum mechanics lends credence to the thesis that science tells us nothing about the ultimate nature of reality.

Quantum mechanics, in its essence, is a mathematical formalism with an algorithm for how to connect the formalism to observation or experiments. When relativistic extensions are included, it provides the framework for all of physics[1] and the underlying foundation for chemistry. For macroscopic objects (things like footballs), it reduces to classical mechanics through some rather subtle mathematics, but it still provides the underlying framework even there. Despite its empirical success, quantum mechanics is not consistent with our common sense ideas of how the world should work. It is inherently probabilistic despite the best efforts of motivated and ingenious people to make it deterministic. It has superposition and interference of the different states of particles, something not seen for macroscopic objects. If it is weird to us, just imagine how weird it must have seemed to the people who invented it. They were trained in the classical system until it was second nature and then nature itself said, “Fooled you, that is not how things are.” Some, like Albert Einstein (1879 – 1955), resisted it to their dying days.

The developers of quantum mechanics, in their efforts to come to grips with quantum weirdness, invented interpretations that tried to understand quantum mechanics in a way that was less disturbing to common sense and their classical training. In my classes in quantum mechanics, there were hand waving discussions of the Copenhagen interpretation, but I could never see what they added to mathematical formalism. I am not convinced my lecturers could either, although the term Copenhagen interpretation was uttered with much reverence. Then I heard a lecture by Sir Rudolf Peierls[2] (1907 – 1995) claiming that the conscious mind caused the collapse of the wave function. That was an interesting take on quantum mechanics, which was also espoused by John von Neumann (1903 – 1957) and Eugene Wigner (1902 –1995) for part of their careers.

So does consciousness play a crucial role in quantum mechanics? Not according to Hugh Everett III (1930 – 1982) who invented the many-worlds interpretation. In this interpretation, the wave function corresponds to physical reality, and each time a measurement is made the universe splits into many different universes corresponding to each possible outcome of the quantum measurement process. Physicists are nothing if not imaginative. This interpretation also offers the promise of eternal life.  The claim is that in all the possible quantum universes there must be one in which you will live forever. Eventually that will be the only one you will be aware of. But as with the Greek legend of Tithonus, there is no promise of eternal youth. The results may not be pretty.

If you do not like either of those interpretations of quantum mechanics, well have I got an interpretation for you. It goes under the title of the relation interpretation. Here the wave function is simply the information a given observer has about the quantum system and may be different for different observers; nothing mystical here and no multiplicity of worlds. Then there is the theological interpretation. This I first heard from Steven Hawking (b. 1942) although I doubt he believed it. In this interpretation, God uses quantum indeterminacy to hide his direct involvement in the unfolding of the universe. He simply manipulates the results of quantum measurements to suit his own goals. Well, He does work in mysterious ways after all.

I will not bore you with all possible interpretations and their permutations. Life is too short for that, but we are still left with the overarching question: which interpretation is the one true interpretation? What is the nature of reality implied by quantum mechanics? Does the universe split into many? Does consciousness play a central role? Is the wave function simply information? Does God hide in quantum indeterminacy?

Experiment cannot sort this out since all the interpretations pretty much agree on the results of experiments (even this is subject to debate), but science has one other criteria: parsimony. We eliminate unnecessary assumptions. When applied to interpretations of quantum mechanics, parsimony seems to favour the relational interpretation. But, in fact, parsimony, carefully applied, favours something else; the instrumentalist approach. That is: don’t worry about the interpretations, just shut up and calculate. All the interpretations have additional assumptions not required by observations.

But what about the ultimate nature of reality? There is no theorem that says reality, itself, must be simple. So quantum mechanics implies very little about the ultimate nature of reality. I guess we will have to leave that discussion to the philosophers and theologians. More power to them.

To receive a notice of future posts follow me on Twitter: @musquod.

[1] Although quantum gravity is still a big problem.

[2] A major player in the development of quantum many body theory and nuclear physics.


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  • http://logicofnature.blogspot.ru/ Gunn Quznetsov

    The Event-Probability Interpretation of quantum mechanics is an updated version of the Copenhagen interpretation. Unlike the Copenhagen interpretation, which assumes the continuous existence of elementary particles, this interpretation considers such particles to be ensembles of their related dot events connected by probabilities. The Event-Probability Interpretation (EPI)[1] is a development of attempts by H. Bergson[2], A. N. Whithead[3], M. Čapek[4][5], E. C. Whipple Jr.[6], and J. Jeans[7] to interpret elementary physical particles as events. The experimental basis for EPI is the Double-Slit Experiment. Theoretical substantiation of EPI is given by Gunn Quznetsov’s works,[8][9] which prove that the concepts and statements of the Quantum Theory are equivalent to the concepts and statements of the probability of dot events and their ensembles.

    Elementary physical particles in a vacuum behave in accord with these probabilities. For example[10] , in accordance with the Double-slit experiment, if a partition with two slits is placed between a source of elementary particles and a detecting screen in vacuum, then interference occurs. But if this system is instead put into a cloud chamber, then the trajectories of the particles will be clearly marked with drops of condensate and any interference will disappear. It seems that any physical particle exists only in those short periods of time when some event occurs to it. And in the other periods of time the particle does not exist, but the probability for some event to occur to this particle remains.

    Thus, if no event occurs between an event of creation of a particle and an event of detection of it, then the particle does not exist during this period of time. There exists only the probability of detection of this particle at some point. But this probability obeys the equations of quantum theory, and we get interference. But in a cloud chamber events of condensation form a chain that traces the trajectory of this particle. In this case the interference disappears. But this trajectory is not continuous—each two points of this line are separated by a gap. The observed movement of this particle arises from the fact that a wave of probability propagates between these points.

    Consequently, the elementary physical particle represents an ensemble of dot events associated with probabilities. Charge, mass, energy, momentum, spins, etc. as they would be seen when the particle is actually observed, are governed by the distribution parameters of the probabilities pertinent thereto. It explains all paradoxes of quantum physics. Schrödinger’s cat lives easily without any superposition of states until the micro event awaited by everyone occurs. Moreover, the wave function disappears without any collapse in the moment when event probability disappears as the event occurs.

    Hence, entanglement concerns not particles but probabilities. That is, when the event of the measuring of spin of Alice’s electron occurs, then the probability for these entangled electrons is changed instantly throughout all space. Therefore, nonlocality applies to probabilities but not to particles. Probabilities cannot transmit any information.

    Quznetsov G 2013 Logical foundation of fundamental theoretical physics (Lambert Academic Publ.)

  • Tienzen (Jeh-Tween) Gong

    Excellent and a very important article.
    The whole issue is about “But what about the ultimate nature of reality?” and should physicists give up on this question and let the philosophers and theologians take the credit?

    I think that this issue can be addressed (not answered) with three points.

    First, “The plethora of interpretations of quantum mechanics lends credence to the thesis that science tells us nothing about the ultimate nature of reality.”
    I have a different opinion about this. Without giving any supporting evidences, I would like presumptively to claim two realities.
    a. Human
    b. A-what: the one which produces galaxies, stars, Earth, life (but not including human-like creatures) and Boltzmann Brain. It is a-what, not a-who.

    The term of ‘physics’ (including the quantum mechanics) which we are talking about today is only an ‘invention’ of human, and, in principle, it can have absolutely nothing to do with the a-what. In some cases, physicists do try to guess something about the a-what and write an invented story about it. In such cases, those invented stories could tell some features about the a-what. Yet, this human/a-what relationship can go a bit more complicated. There could be four a-what in human’s eyes.
    1. A-what-0 (did): did produce galaxies, …, Boltzmann Brain,… , but no human.
    2. A-what-1 (could): although this a-what did not produce unicorn, but it could eventually, at least with its Boltzmann Brain.
    3. A-what-2 (cannot): there is no chance for it to produce a Boeing: 777.
    4. A-what-3 (never): a ghost cannot be ‘materialized’ even by Human.

    Among these five (human and four a-whats), which one is the ultimate nature of reality? Of course, the answer could be ‘none-of-them’. Even with this answer, we (physicists) have got the answer and need not give this privilege to philosophers and theologians.

    Second, “Here the wave function is simply the ‘information’ a given observer has about the quantum system and may be different for different observers; nothing mystical here and no multiplicity of worlds.”
    The above statement is greatly amplified by the recent Black-hole (firewall/information) paradox firestorm. Recently, there is another hot issue, the falsifiability. By definition, a truth (if any) can never be falsified. If it can be, it is not truth. Yet, a truth can always be vindicated and validated, as its deviation must always be falsified.

    As the black-hole by definition is unobservable, physicists can invent all kinds of stories. Yet, most of those stories have the following three parts.
    I. Quantum wave function is ‘information’.
    II. A light-attractor traps lights. That is, the lights can go in but can never come out.
    III. An immortal observer can go into that light-attractor without any harm and can observe the ‘information’ inside of that attractor with only one handicap of incapable of sending his great finding to his colleagues outside of that attractor.

    These great stories can be examined with the life-story of Mr. John, the cat came out alive from the Schrödinger’s cage. By coming out alive, it got too excited and jumped off the roof of the Empire State building. Thus, its life-stories are written with two quantum equations.
    Smiling John = (wave function + … + wave function+ … smile, at the roof of Empire State building) = information (smiling John)

    Pancake John = (wave function + … + wave function + … pancake, at the Street beside the Empire State building after a quantum leap from the roof of …) = information (pancake John)

    Is “information (smiling John) = information (pancake John)” correct? With either answers (Yes and No), the black-hole paradox is no more. But, my personal opinion is that the ‘information paradox’ should use a better name (such as, the quantum wave function paradox), as the information is a bit more than ‘quantum wave functions’.

    Third, what the heck is the ‘quantum mechanics’ anyway, let alone about its ‘interpretations? By all means, there is some weird behaviors about the a-what-0, and that weirdness can be described with the quantum mechanics ‘story’. Yet, however weird it can be, it is simply ‘locked up’ by a box or simply a parenthesis, such as,
    (quantum + … + quantum + … smile) = Smiling John

    That is, however quantum, quantum about it (even with infinite quantum), it simply becomes a deterministic Smiling John. That is, the ‘quantum boy’ can do all his dances but can never go out of a D-box which locks him permanently. This quantum boy is only a rascal kid of the deterministic Daddy, and this is described in the ‘Quantum algebra’ (http://prebabel.blogspot.com/2012/09/quantum-algebra-and-axiomatic-physics.html ).

    When a super, super great mystery is boxed in a box, its greatness is no bigger than that box.

    Of course, the Nature is a bit bigger than the four a-what. So, after all, I did not address this issue of what the ultimate reality is, as I did not address what the Nature is this time.

  • http://www.archidevsys.co.nz Gavin Flower

    Our ‘facts’ & theories are approximations to our perceptions of reality that we feel strongly are a good basis for making decisions about what actions to take – either physical actions or how 2 or more ‘facts’ & ‘observations’ relate to each other to produce new or amended theories.

    For example, we say that the wavelength of photons increase with decreasing energy. A useful concept for designing aerials, and considered a fact. However, is it correct that a very weak photon can be bigger than the Earth??? The equation c = fw (where c = speed of light, f = frequency in metres, w = wavelength in Hz) has been well established by repeated observation, so we can’t sanely reject it – but any interpretation that the wavelength is an object in classical sense, is not so sacred!

    We routinely use calculus, implicitly or explicitly, to relate velocity and acceleration. Calculus assumes that space and time are continuously differentiable, or we could not use the (limit dx –> +0, where ‘+0’ is a delightful nonsense that is informally defined as the smallest positive Real number – there are more rigorous formal definitions of ‘+0’, but they are not as much fun!). However, quantum mechanic says things are quantized: that the more we now how fast something is going, the less precisely we know where it is (can I blame Heisenberg?).

    If space & time were continuously differentiable, and so were ‘solid’ objects (or any cohesive entity) continuously differentiable. We would appear to have a contradiction, as how would one point ‘know’ to stay close to another – as is required for a body to be cohesive (if you pull an object from one end, the whole object moves)? This suggests that at a certain scale, the position of something must be fuzzy in someway, so that contiguous parts of the object overlap in some non-classical sense. So saying that at a particular point in spacetime something can be measured, a convenient approximation for engineering purposes, contradicts what we think we know of reality – arghhh!!! brain explodes…

    So we have several sets of perceptions of reality (notions, theories), or theories we can useful use in different contexts. However, the fun begins when we try to reconcile the different theories that appear to contradict each other.

    notion: thunder happens when the God Thor throws his hammer
    theory: thunder happens when there is a massive electrical discharge in the sky

    Note that the fuzziness in spacetime implies that the distinction between past & future is not as clear cut as we implicitly assume.

    Fortunately, I do not need a rigorous understanding of the True Nature of Spacetime, to successfully kiss my wife!

    However, I am still very much fascinated by the problems of trying to get a handle on the True Nature of Reality…

  • http://crossswords.wordpress.com/ LizR

    Physicists appear to be leaning more towards the Everett interpretation, for several reasons that I will attempt to sum up.

    The “many-worlds” interpretation requires very little information to specify how it works – just the laws of physics, in fact. All other interpretations require some extra information to be specified – what collapses the wavefuntion, for example. Scientists like explanations that are parsimonious with their postulates; this is called Occam’s razor. History shows that reducing postulates multiplies physical entities. Once we had the Earth and some lights in the sky – now we have a universe billions of light years across, which is nevertheless run on very simple principles, arguably far simpler than the Medieval Earth was thought to use.

    The MWI answers one of the big philosophical questions, namely why did things happen this way? It turns out that they didn’t, they happened every possible way – we just find ourselves in this history because someone has to.

    The MWI does NOT answer the question “why is there something rather than nothing?” – but neither do any other interpretations.

  • http://www.triumf.ca/theory/byron-jennings Byron

    The many-worlds interpretation requires a massive unnecessary assumption. Namely that there are many worlds that we are not only unaware of but that make not observational impact on the world we are in.

  • Tienzen (Jeh-Tween) Gong

    @BYRON JENNINGS: “… Namely that there are many worlds that we are not only unaware of but that make not observational impact on the world we are in.”


    Among all physics bloggers, you are the only one who has discussed the most important issue of physics, “What is the ultimate nature of reality (if any)?”

    The basic of atheism is of against the concepts of ‘supernatural (being)’ and the ‘design’ of the universe. Of course, the Christian cosmology is totally nonsense in terms of the modern physics. But, what is the difference between {un-naturalness, tuning} and {supernatural, design}? This neo-atheism is now falling into a trap of no return in its own making. Yet, thus far, the issue of the ‘ultimate nature of reality’ is still elusive in all disciplines.

    In Buddhism, it searches the ‘Ultimate’ with a methodology, the ‘negation’ (emptying out the non-eternal). In Science, it searches the ‘Ultimate’ also with a methodology, the ‘falsifiability’. Now, Buddhism has taken its ‘methodology’ as the ‘Ultimate’ (a total confusion), and physicists are also mistaken the ‘falsifiability’ as the Gospel. For a given destination, it could have many different pathways. Furthermore, the two pathways of above cannot reach the destination by definition, as the true ‘Ultimate’ (if any) must not
    a. be emptied out,
    b. be falsified.

    In a sense, the ‘Ultimate’ is already defined above, but it is operational useless. Thus, I will try to give it an operational definition. The ‘Ultimate’ (if any) must consist of two parts.
    A. It must be ‘eternal’, that is, it is time-independent; not created in-time and cannot be destroyed at the end of time.
    B. It must give rise to ‘this’ universe; an itemized list of realities, such as,
    1. gives rise to nature constants {Alpha, e (electric charge), c (light speed), ħ (Planck constant), etc.},
    2. gives rise to the particle zoo of the Standard Model,
    3. gives rise to quantum principle,
    4. gives rise to unified force equation,
    5. gives rise to dark mass and dark energy,
    6. gives rise to life,
    7. gives rise to arithmetic,
    8. gives rise to … everything in ‘this’ universe.

    Is the ‘Ultimate’ a reality? Is a theory the ‘Ultimate’ theory? Both questions can be answered as the definition of ‘Ultimate’ is now super clear. A failure of any one of the ‘gives rise to’, it cannot be the Ultimate theory. In this short comment, I of course cannot address the details of this long list but would like to talk about the ‘eternal’ very briefly.

    In the book (“Linguistics Manifesto”, ISBN 978-3-8383-9722-1), its central issue is one statement (or thesis), as follow,
    “Every chaotic system can always be described with an ordered system (from a Formal system to Godel to Life system)”. That is, any chaotic system is a ‘shadow’ of an ordered system. Note: biological system is a Life system, but the Life system is much bigger than a bio-system by definition in that book.

    This statement is truly time-independent. Yet, its direct consequence is that any chaotic system (such as the quantum system) can arise from a simple ordered formal system. Although I would not violate the copyright of that book, I could give a simple example here to show the point. A system of two person (I and a ghost) and one game (flipping an American quarter 10 times as a game).

    By playing alone (me only), the probability of the outcome patterns (one head/9 tails; …, 9 heads/one tail, etc.) should all be the same after played a large number (such as, 10^500) of times. Now, the ghost (not visible by me) comes in to mess up my play either randomly or with a system; yet, he is unable to change the outcome when the played number of times is as large as the 10^500. It is not very hard to prove this theorem mathematically. Of course, I will keep it as a conjecture for now. But, with this Ghost-rascal conjecture, it points out that this ‘Ultimate Randomness’ is supremely powerful and eternal, as it can devour all orders. That is, all orders are ‘embedded’ in it too. This is the immanence, not contradiction.

  • http://www.totonboard.com Ashley

    Thanks for the very important article.

  • http://logicofnature.blogspot.ru/ Gunn Quznetsov

    Any information system carries in itself its unidirectioned and irreversible “time” and a metric “space”, bounded with this “time” by the Poincare divisible group transformations.

    Prespacetime Journal| March 2010 | Vol. 1 | Issue 2 | Page 274-275
    Quznetsov G. On Informational Time and Space

  • John Sellers

    Of course there are multiple universes.

    Lets assume a electron comes into being by way of some interaction today on Earth. And let us assume another electron comes into being at the same moment 100 light years away.

    So those two electrons will not and can not interact in any way for the next 100 years. In fact, they could not be more isolated from each other for the next 100 years if they were in separate Universes.

    I maintain they ARE in separate Universes and the wall between those Universes is in fact, 100 light years thick. If you don’t think so, please tell me how the situation is different from being them being in separate Universes. Remember that separate Universes probably can merge or separate if all the Universal rules, whatever they actually are, are followed.

    Some day the electrons will be in the same Universe because they are finally influenced by each other. That is called the collapse of a probability function.

    In the meantime, they are free to be whatever is probable until they finally decide upon their relationship. That sounds like a girl I once dated.

    But lets follow this reasoning to the limit. Every particle in the Universe is separated from every other particle by space-time. And as such they act like they are in separate Universes with walls as thick as whatever space-time is between them.

    So if we define what a Universe is in the right way. Every single particle in the Universe has its own unique Universe to play in, and every time it interacts with another particle, Universes merge. But don’t worry, there are enough to go around.

  • TheMechanicalAdv

    “we just find ourselves in this history because someone has to.”

    What “we”? What “this”? What “someone”? The MWI doesn’t allow such things.

    “Once we had the Earth and some lights in the sky – now we have a universe billions of light years across”

    No. Once we knew only the Earth and some lights in the sky, and then we found our universe billions of light years across. We didn’t simply agree upon it; we looked up, measured the distance with the help of new postulates, and saw for ourselves. And we did it all by observing, experimenting, and striving for the truth about this one universe we all share.

    And now, because of one little detail — waves collapse and you don’t know how or why — you would throw it all away and plunge us back to the ignorant ages of eloquent-makes-right. Pathetic!