Dec 7, 2021 06:22 PM
(This post was last modified: Dec 7, 2021 07:12 PM by C C.)
The cliché has it that the Copenhagen interpretation demands adherence without deep enquiry. That does physics a disservice
https://aeon.co/essays/shut-up-and-calcu...-mechanics
EXCERPTS (Jim Baggott): . . . What are we supposed to make of this? If we interpret the wave function realistically, as a tangible physical thing, we then have to figure out how it ‘collapses’ to produce a spot at only one location out of all the other probable locations on the screen. Such a collapse implies what Einstein in 1927 called ‘an entirely peculiar mechanism of action at a distance’ – an anathema of ghostly physical effects transmitted instantaneously across space with no apparent direct cause, now generally referred to as the ‘measurement problem’. For Einstein, the lack of any kind of physical explanation for how this is supposed to happen meant that something is missing; that quantum mechanics is in some way incomplete.
Bohr disagreed. He argued that in quantum mechanics we have hit a fundamental limit. What we observe is quantum behaviour as projected into our classical world of direct experience. As we cannot transcend this experience, we have to accept that the wave function has no physical significance beyond its relevance to the calculation of probabilities. We must be content with a ‘purely symbolic’ mathematical formalism that works. The wave function doesn’t collapse (and there’s no peculiar action at a distance) because it doesn’t actually exist, and so there is no measurement problem. In other words, all we can know is the electron-as-it-appears in different experimental arrangements. We can never know what the electron really is.
This is an empiricist, ‘antirealist’, or (to some) an ‘instrumentalist’ interpretation, which judges a theory to be largely meaningless except as an instrument to connect together our empirical experiences. Such an antirealist theory doesn’t necessarily deny the existence of an objective reality [...], nor does it necessarily deny the reality of unobserved electrons, however we imagine them. But it does deny a direct and exact correspondence between the wave function and the things that the wave function purportedly describes. The formalism appears simply to encode our experiences of quantum phenomena in ways that allow us to calculate the probability that this or that will happen next. Quantum mechanics is complete, and we just need to get over it.
This, in essence, is the Copenhagen interpretation of quantum mechanics, named for the location of Bohr’s Institute for Theoretical Physics in Denmark. [...] In a letter to Erwin Schrödinger in May 1928, Einstein called it a ‘tranquilising philosophy’.
The popular reading of subsequent history suggests that Bohr emerged the victor in the debate [...] and the Copenhagen interpretation became a dogmatic orthodoxy. The Northern Irish physicist and quantum dissident John Stewart Bell was one of only a few physicists of the time prepared to push back against this orthodoxy, writing in 1981...
[...] in Physics Today magazine in April 1989 by N David Mermin, [...] Mermin expressed some personal discomfort with the Copenhagen interpretation. He wrote: ‘If I were forced to sum up in one sentence what the Copenhagen interpretation says to me, it would be “Shut up and calculate!”.’ Mermin’s meme would go on to become part of modern quantum folklore.
More years passed. Some commentators began to hint that ‘Shut up and calculate’ had actually been coined not by Mermin but by the charismatic US physicist Richard Feynman. In a follow-up column for Physics Today published 15 years later, Mermin was able to convince himself that it was indeed he who first used the phrase in the context of quantum foundations. He was also in no doubt about who was to blame, as he drew on
[...] the ‘Copenhagen interpretation’ didn’t actually exist as such until the mid-1950s ... And this version of Copenhagen is largely an invention of the German physicist Werner Heisenberg, seeking rehabilitation with the international physics community after the war. Heisenberg’s interpretation differed from Bohr’s in many key respects, particularly in the former’s willingness to admit a substantial subjective element.
Make no mistake, the physicists of the 1950s understood that there was an orthodox interpretation. But what was known only vaguely from the early 1930s as the Kopenhagener Geist...
[...] Unlike in Europe, theoretical physics in universities of the prewar US was not the lofty preserve of a few exalted specialists, able to exert influence through the unquestionable authority of an academic hierarchy, until death. Physics departments in the US were more inclusive, collaborative and inherently democratic, with theorists working directly alongside their experimentalist colleagues...
This practical mindset extended to the students, most of whom had [...] ‘at one time or another taken the family car apart and had put it together again’. Such ‘hands-on’, ‘can-do’ instincts fit comfortably within a culture that, from the 19th into the 20th century in the US, reputedly paid less attention to philosophy than any other country in the civilised world, and which had continued to foster, in the words of the historian Richard Hofstadter, a deep-seated anti-intellectualism...
The dominance of a more philosophically inclined European physics was soon to be ended by an avalanche of discoveries in nuclear physics in a time of impending war, the forced emigration of leading European physicists [...] It would be the bolder, brasher, more empirical ‘hands-on’ style of US theoretical physics that would come to dominate the postwar world.
[...] In a quick follow-up discussion with me in July 2021, Mermin confessed that he now regrets his choice of words. Already by 2004 he had ‘come to hold a milder and more nuanced opinion of the Copenhagen view’... So, at what point did it become fashionable to gather together all the ills of quantum mechanics – all those conundrums that arise only in realist interpretations – and bundle them into a demonised version of the antirealist Copenhagen interpretation?
The motives are fairly obvious. [...] Those more inquisitive physicists and philosophers looking to develop a more realist alternative interpretation needed a better foil, a more meaningful straw man to knock down.
[...] ‘Everybody pays lip service to Bohr,’ Bohm explained in 1987, ‘but nobody knows what he says. People then get brainwashed into saying Bohr is right, but when the time comes to do their physics, they are doing something different.’ Overlook (or ignore) its fragmented nature and questionable paternity, and the ‘Copenhagen interpretation’ is a great platform on which to build your counterarguments, or deepen discontent in order to foment your revolution. Or sell a few more books.
One of my favourite examples of this trend is an article by the US theorist Bryce DeWitt published in 1970 in Physics Today: ‘According to the Copenhagen interpretation of quantum mechanics,’ he wrote, ‘whenever a [wave function] attains a [certain form pertaining to measurement] it immediately collapses.’ DeWitt was seeking to validate an alternative reality based on the idea of ‘many worlds’, and no doubt his contrived version of Copenhagen helped him to breed discontent with the prevailing orthodoxy.
The timing is about right. The work of Bohm in the late 1950s, and Bell in the ’60s, had, by the early ’70s, led to another extraordinary conclusion. A so-called ‘locally real’ interpretation of quantum mechanics in which entities like photons or electrons are assumed to have intrinsic properties all along – and not just at their point of observation or measurement – makes predictions that differ from ‘ordinary’ quantum mechanics.
It was realised that these predictions could be tested experimentally. Such tests have been performed at regular intervals ever since, with ever-increasing sophistication and precision, confirming that, despite how reasonable they might seem, all locally real interpretations are quite wrong. These experiments have, nonetheless, spawned entirely new disciplines – of quantum information and quantum computing – demonstrating that exploration of seemingly pointless philosophical issues can have profound practical consequences.
[...] Mermin should be forgiven for following a trend that, by 1989, was entrenched in the quantum cultural mindset. I did much the same in my first book on quantum mechanics, published in 1992. We have both since learned to be more circumspect; we have to acknowledge that a dogma of indifference to philosophical questions was at least as much to blame for the rejection of foundational enquiry as anything Bohr might have said.
Of course, the first to give expression to a meme such as ‘Shut up and calculate’ can claim no ownership over it and cannot control how others will use it. Irrespective of the historical rights and wrongs, those who continue to use it as a term of abuse directed at the Copenhagen interpretation are perfectly at liberty to do so.
But there is a growing number of commentators who are both familiar with the history and prepared to call this out. The purpose of this essay is to help you do the same... (MORE - missing details)
https://aeon.co/essays/shut-up-and-calcu...-mechanics
EXCERPTS (Jim Baggott): . . . What are we supposed to make of this? If we interpret the wave function realistically, as a tangible physical thing, we then have to figure out how it ‘collapses’ to produce a spot at only one location out of all the other probable locations on the screen. Such a collapse implies what Einstein in 1927 called ‘an entirely peculiar mechanism of action at a distance’ – an anathema of ghostly physical effects transmitted instantaneously across space with no apparent direct cause, now generally referred to as the ‘measurement problem’. For Einstein, the lack of any kind of physical explanation for how this is supposed to happen meant that something is missing; that quantum mechanics is in some way incomplete.
Bohr disagreed. He argued that in quantum mechanics we have hit a fundamental limit. What we observe is quantum behaviour as projected into our classical world of direct experience. As we cannot transcend this experience, we have to accept that the wave function has no physical significance beyond its relevance to the calculation of probabilities. We must be content with a ‘purely symbolic’ mathematical formalism that works. The wave function doesn’t collapse (and there’s no peculiar action at a distance) because it doesn’t actually exist, and so there is no measurement problem. In other words, all we can know is the electron-as-it-appears in different experimental arrangements. We can never know what the electron really is.
This is an empiricist, ‘antirealist’, or (to some) an ‘instrumentalist’ interpretation, which judges a theory to be largely meaningless except as an instrument to connect together our empirical experiences. Such an antirealist theory doesn’t necessarily deny the existence of an objective reality [...], nor does it necessarily deny the reality of unobserved electrons, however we imagine them. But it does deny a direct and exact correspondence between the wave function and the things that the wave function purportedly describes. The formalism appears simply to encode our experiences of quantum phenomena in ways that allow us to calculate the probability that this or that will happen next. Quantum mechanics is complete, and we just need to get over it.
This, in essence, is the Copenhagen interpretation of quantum mechanics, named for the location of Bohr’s Institute for Theoretical Physics in Denmark. [...] In a letter to Erwin Schrödinger in May 1928, Einstein called it a ‘tranquilising philosophy’.
The popular reading of subsequent history suggests that Bohr emerged the victor in the debate [...] and the Copenhagen interpretation became a dogmatic orthodoxy. The Northern Irish physicist and quantum dissident John Stewart Bell was one of only a few physicists of the time prepared to push back against this orthodoxy, writing in 1981...
[...] in Physics Today magazine in April 1989 by N David Mermin, [...] Mermin expressed some personal discomfort with the Copenhagen interpretation. He wrote: ‘If I were forced to sum up in one sentence what the Copenhagen interpretation says to me, it would be “Shut up and calculate!”.’ Mermin’s meme would go on to become part of modern quantum folklore.
More years passed. Some commentators began to hint that ‘Shut up and calculate’ had actually been coined not by Mermin but by the charismatic US physicist Richard Feynman. In a follow-up column for Physics Today published 15 years later, Mermin was able to convince himself that it was indeed he who first used the phrase in the context of quantum foundations. He was also in no doubt about who was to blame, as he drew on
vivid memories of the responses my conceptual inquiries elicited from my professors – whom I viewed as agents of Copenhagen – when I was first learning quantum mechanics as a graduate student at Harvard [...] ‘You’ll never get a PhD if you allow yourself to be distracted by such frivolities,’ they kept advising me, ‘so get back to serious business and produce some results.’ ‘Shut up,’ in other words, ‘and calculate...’
The phrase has since become deeply embedded in the literature on quantum foundations, repeated in academic papers and in popular articles and books. It has become a handy put-down, an easy slight, a catchy synonym, summarising in just four words everything that is wrong with a dogmatic, orthodox interpretation that [...] leaves just too many unanswered questions. For those seeking to push a preferred realist alternative, such as Sean Carroll in his bestselling popular book Something Deeply Hidden (2019), ‘Shut up and calculate’ is the perfect foil, tantamount to declaring enough is enough, demanding that we look again.[...] the ‘Copenhagen interpretation’ didn’t actually exist as such until the mid-1950s ... And this version of Copenhagen is largely an invention of the German physicist Werner Heisenberg, seeking rehabilitation with the international physics community after the war. Heisenberg’s interpretation differed from Bohr’s in many key respects, particularly in the former’s willingness to admit a substantial subjective element.
Make no mistake, the physicists of the 1950s understood that there was an orthodox interpretation. But what was known only vaguely from the early 1930s as the Kopenhagener Geist...
[...] Unlike in Europe, theoretical physics in universities of the prewar US was not the lofty preserve of a few exalted specialists, able to exert influence through the unquestionable authority of an academic hierarchy, until death. Physics departments in the US were more inclusive, collaborative and inherently democratic, with theorists working directly alongside their experimentalist colleagues...
This practical mindset extended to the students, most of whom had [...] ‘at one time or another taken the family car apart and had put it together again’. Such ‘hands-on’, ‘can-do’ instincts fit comfortably within a culture that, from the 19th into the 20th century in the US, reputedly paid less attention to philosophy than any other country in the civilised world, and which had continued to foster, in the words of the historian Richard Hofstadter, a deep-seated anti-intellectualism...
The dominance of a more philosophically inclined European physics was soon to be ended by an avalanche of discoveries in nuclear physics in a time of impending war, the forced emigration of leading European physicists [...] It would be the bolder, brasher, more empirical ‘hands-on’ style of US theoretical physics that would come to dominate the postwar world.
[...] In a quick follow-up discussion with me in July 2021, Mermin confessed that he now regrets his choice of words. Already by 2004 he had ‘come to hold a milder and more nuanced opinion of the Copenhagen view’... So, at what point did it become fashionable to gather together all the ills of quantum mechanics – all those conundrums that arise only in realist interpretations – and bundle them into a demonised version of the antirealist Copenhagen interpretation?
The motives are fairly obvious. [...] Those more inquisitive physicists and philosophers looking to develop a more realist alternative interpretation needed a better foil, a more meaningful straw man to knock down.
[...] ‘Everybody pays lip service to Bohr,’ Bohm explained in 1987, ‘but nobody knows what he says. People then get brainwashed into saying Bohr is right, but when the time comes to do their physics, they are doing something different.’ Overlook (or ignore) its fragmented nature and questionable paternity, and the ‘Copenhagen interpretation’ is a great platform on which to build your counterarguments, or deepen discontent in order to foment your revolution. Or sell a few more books.
One of my favourite examples of this trend is an article by the US theorist Bryce DeWitt published in 1970 in Physics Today: ‘According to the Copenhagen interpretation of quantum mechanics,’ he wrote, ‘whenever a [wave function] attains a [certain form pertaining to measurement] it immediately collapses.’ DeWitt was seeking to validate an alternative reality based on the idea of ‘many worlds’, and no doubt his contrived version of Copenhagen helped him to breed discontent with the prevailing orthodoxy.
The timing is about right. The work of Bohm in the late 1950s, and Bell in the ’60s, had, by the early ’70s, led to another extraordinary conclusion. A so-called ‘locally real’ interpretation of quantum mechanics in which entities like photons or electrons are assumed to have intrinsic properties all along – and not just at their point of observation or measurement – makes predictions that differ from ‘ordinary’ quantum mechanics.
It was realised that these predictions could be tested experimentally. Such tests have been performed at regular intervals ever since, with ever-increasing sophistication and precision, confirming that, despite how reasonable they might seem, all locally real interpretations are quite wrong. These experiments have, nonetheless, spawned entirely new disciplines – of quantum information and quantum computing – demonstrating that exploration of seemingly pointless philosophical issues can have profound practical consequences.
[...] Mermin should be forgiven for following a trend that, by 1989, was entrenched in the quantum cultural mindset. I did much the same in my first book on quantum mechanics, published in 1992. We have both since learned to be more circumspect; we have to acknowledge that a dogma of indifference to philosophical questions was at least as much to blame for the rejection of foundational enquiry as anything Bohr might have said.
Of course, the first to give expression to a meme such as ‘Shut up and calculate’ can claim no ownership over it and cannot control how others will use it. Irrespective of the historical rights and wrongs, those who continue to use it as a term of abuse directed at the Copenhagen interpretation are perfectly at liberty to do so.
But there is a growing number of commentators who are both familiar with the history and prepared to call this out. The purpose of this essay is to help you do the same... (MORE - missing details)
