Does this QM experiment show that science is doomed?

  • #51
PeterDonis
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Since we are getting into a discussion of what "exists" means, this thread belongs in the QM interpretations forum. So I have moved it there.
 
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  • #52
Vanadium 50
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Who is saying protons do not exist?
Are you saying that "protons exist" is not the same as "tables exist"??
I think this is arguing against tables existing. After all, we have ~1020 pieces of evidence that protons exist but only ~1010 that tables exist.
 
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  • #53
PeterDonis
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I think this is arguing against tables existing.
If @Lord Jestocost does indeed want to argue that tables don't exist, I'll ask him to bang his head on one and then see if he still thinks so.
 
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  • #54
Lord Jestocost
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Then how exactly do protons exist??
To my mind, questions like „How exactly do protons, neutrons, electrons or atoms etc. exist?“ cannot be answered. Here, I am following Paul Davies who puts it in the following way (in his introduction to Werner Heisenberg’s “Physics and Philosophy”, Penguin Books):

By contrast, the Copenhagen interpretation of quantum mechanics, which Heisenberg here expounds so lucidly, rejects the objective reality of the quantum microworld. It denies that, say, an electron has a well-defined position and a well-defined momentum in the absence of an actual observation of either its position or its momentum (and both cannot yield sharp values simultaneously). Thus an electron or an atom cannot be regarded as a little thing in the same sense that a billiard ball is a thing. One cannot meaningfully talk about what an electron is doing between observations because it is the observations alone that create the reality of the electron. Thus a measurement of an electron's position creates an electron-with-a-position; a measurement of its momentum creates an electron-with-a-momentum. But neither entity can be considered already to be in existence prior to the measurement being made.
What, then, is an electron, according to this point of view? It is not so much a physical thing as an abstract encodement of a set of potentialities or possible outcomes of measurements. It is a shorthand way of referring to a means of connecting different observations via the quantum mechanical formalism. But the reality is in the observations, not in the electron.


Or, to cite John Archibald Wheeler:

In today’s words Bohr’s point – and the central point of quantum theory – can be put into a single, simple sentence. ‚No elementary phenomenon is a phenomenon until it is a registered (observed) phenomenon.‘

Wheeler, J.A. (1983) in “Law without law”, in Wheeler and Zurek (eds.), Quantum Theory and Measurement, Princeton University Press, 182–213.
 
  • #55
To my mind, questions like „How exactly do protons, neutrons, electrons or atoms etc. exist?“ cannot be answered. Here, I am following Paul Davies who puts it in the following way (in his introduction to Werner Heisenberg’s “Physics and Philosophy”, Penguin Books):

By contrast, the Copenhagen interpretation of quantum mechanics, which Heisenberg here expounds so lucidly, rejects the objective reality of the quantum microworld. It denies that, say, an electron has a well-defined position and a well-defined momentum in the absence of an actual observation of either its position or its momentum (and both cannot yield sharp values simultaneously). Thus an electron or an atom cannot be regarded as a little thing in the same sense that a billiard ball is a thing. One cannot meaningfully talk about what an electron is doing between observations because it is the observations alone that create the reality of the electron. Thus a measurement of an electron's position creates an electron-with-a-position; a measurement of its momentum creates an electron-with-a-momentum. But neither entity can be considered already to be in existence prior to the measurement being made.
What, then, is an electron, according to this point of view? It is not so much a physical thing as an abstract encodement of a set of potentialities or possible outcomes of measurements. It is a shorthand way of referring to a means of connecting different observations via the quantum mechanical formalism. But the reality is in the observations, not in the electron.


Or, to cite John Archibald Wheeler:

In today’s words Bohr’s point – and the central point of quantum theory – can be put into a single, simple sentence. ‚No elementary phenomenon is a phenomenon until it is a registered (observed) phenomenon.‘

Wheeler, J.A. (1983) in “Law without law”, in Wheeler and Zurek (eds.), Quantum Theory and Measurement, Princeton University Press, 182–213.
But then, if elementary particles do not "exist" then how come macroscopic things like tables and humans exist??? We know for sure that tables and other people exist.

Another question is how does a light source emit photons when according
to you those photons don't really exist until they are "observed"?

How can a macroscopic light source create non-existing photons???
I.e. How do you create "non-existing" elementary particles??? If you create something then by definition it has to exist, right?
 
  • #56
Lord Jestocost
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But then, if elementary particles do not "exist" then how come macroscopic things like tables and humans exist???
Maybe, you completely misunderstand me. To me the term “existence” means nothing else than the capacity to have effects upon the world with which we “interact”. As a physicist, however, I avoid to make any claims concerning the character of this existence, call it an instrumentalist’s point of view (https://en.wikipedia.org/wiki/Instrumentalism). As Bernard d'Espagnat remarks in "Quantum weirdness: What we call 'reality' is just a state of mind":
"This reality is something that, while not a purely mind-made construct as radical idealism would have it, can be but the picture our mind forces us to form of ... Of what? The only answer I am able to provide is that underlying this empirical reality is a mysterious, non-conceptualisable "ultimate reality", not embedded in space and (presumably) not in time either."
(https://www.theguardian.com/science/blog/2009/mar/17/templeton-quantum-entanglement)
 
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  • #57
vanhees71
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Well, elementary particles indeed have "effects upon the world with which we interact". How else would we have discovered all these critters over the decades?
 
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  • #58
Lord Jestocost
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Regarding the notion "elementary particles" which is used as a matter of convenience, Paul Davies brings it to the point (in his introduction to Werner Heisenberg’s “Physics and Philosophy”, Penguin Books):

And so the language of quantum mechanics employs familiar words, such as wave, particle, position, etc., but their meanings are severely circumscribed and often vague. Heisenberg warns us that: 'When this vague and unsystematic use of language leads us into difficulties, the physicist has to withdraw into the mathematical scheme and its unambiguous correlation with experimental facts.'
 
  • #59
berkeman
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Thread closed for Moderation...

Edit/Update -- after a Mentor discussion, the thread will remain closed.
 
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