Copenhagen Interpretation of QM

Marchesk

The Copenhagen Interpretation of Quantum Mechanics denies that the wave function is describing anything real. Rather, it's describing the range of possibilities a quantum property can resolve to (become discrete) upon measurement. This range has the distribution of a wave, and thus the notion of probability waves. The resulting measurement is fundamentally random, although the wavefunction describing the probability of the measurement being a certain value is itself deterministic.

This raises several questions:

1. What determines a measurement? Even molecules can exhibit the same behavior that electrons and photons do in the double-slit experiments.

2. How does a quantum property transition from possibility to a single value? This would be the issue of the so-called wave function collapse.

3. Why is the probability distribution wave-like? If it's not real, then how does the math work out? What makes the wavefunction descriptive? How are mere possibilities interfering, cohering, entangling, etc?

4. Do normal, macro-scale objects exist when we're not "looking"? I recall reading that Bohr and Einstein debated whether the moon was still there when they turned their backs. Bohr, being the champion of the Copenhagen Interpretation, argued it was just a range of possible states.

5. Early enough in the universe, everything would have been on the scale of subatomic particles, so how did the macro-scale universe where measurements take place come to exist? If the Copenhagen interpretation is correct, then the early Big Bang was just a probability space, not something real. Does that mean a measurement took place?

6. Does gravity have a wavefunction? Is mass only discrete when measured? What would the implication of that be for GR?

Rich

My view is that the so-named Copenhagen Interpretation, was a well-meaning attempt by Bohr to draw a line between the Schrodinger Equation and the metaphysics that may result from the equation, which is is stark contrast to the metaphysics that competing theories, such as General Relativity, might presume. Einstein at times was quite adament about the mathematics of his theories should be elevated to a concrete metaphysics.

But not all early QM theorists, such as De Brogle, felt as bound as Bohr, and did present a concrete view of the reality of the Quantum equation. De Broglie was brow beaten by Bohr and Heisenberg to accept the Copenhagen stance, but this did not prevent De Broglie from writing essays concerning the metaphysics, in particular his discussion of Bergson's metaphysics and it's possible compatibility with QM. Later Bohm resurrected the De Broglie real wave theory and himself extended his thinking into a description of a holographic universe.

Not much theoretical work is performed nowadays that may impact QM metaphysical interpretations, but recent experimental results from an NIST are noteworthy in its support of "spooky action at a distance" being a real aspect of quantum metaphysics.

http://phys.org/news/2015-11-nist-team-spooky-action-distance.html

javra

1. What determines a measurement? Even molecules can exhibit the same behavior that electrons and photons do in the double-slit experiments. — Marchesk

Even proteins (large molecules). So in the normal functions of a cell, some of its microscopically observable parts can hold particle-wave duality when on their own. But can the cell still be a functioning whole if its molecular parts do not pertain to a stable macro-reality? When looking through a microscope at microscopic life we all say “no”. Beats me how this happens; however, given what we know of QM and bio, it nevertheless does: macro-level reality as we know it becomes stabilized at the level of microscopic life--or, if one prefers, microscopic sentience.

4. Do normal, macro-scale objects exist when we're not "looking"? I recall reading that Bohr and Einstein debated whether the moon was still there when they turned their backs. Bohr, being the champion of the Copenhagen Interpretation, argued it was just a range of possible states. — Marchesk

This then is part of the stable macro-reality that, as aforementioned, somehow gets stabilized at the level of microscopic life. The question posed might be more applicable to the physics of multiple worlds than to the issue of QM.

I’ll for now skip my opinions on the other questions (not that I have an opinion for all of them).

tom

1. What determines a measurement? Even molecules can exhibit the same behavior that electrons and photons do in the double-slit experiments. — Marchesk

It doesn't matter what determines a measurement. All that matters is that you can predict probabilities associated with whatever you decide to measure.

2. How does a quantum property transition from possibility to a single value? This would be the issue of the so-called wave function collapse. — Marchesk

As you said, wavefunctions are not real - they are not elements of reality - so they don't really collapse either. Wavefunctions are purely epistemic.

3. Why is the probability distribution wave-like? If it's not real, then how does the math work out? What makes the wavefunction descriptive? How are mere possibilities interfering, cohering, entangling, etc? — Marchesk

Most integrable functions of position (or whatever basis you prefer) look a bit like waves, or wave-packets. Probability distributions are just another well-behaved wave-like function. Wavefunctions however are not probability distributions, but probability amplitudes, and in general they don't look like waves because they exist in Hilbert space as a ray of unit length.

Your other questions are meaningless. Shut up and calculate instead. If you don't like being told what to do, tough! Probabilities are normative.

4. Do normal, macro-scale objects exist when we're not "looking"? I recall reading that Bohr and Einstein debated whether the moon was still there when they turned their backs. Bohr, being the champion of the Copenhagen Interpretation, argued it was just a range of possible states. — Marchesk

Not so sure about that. Copenhagen requires the existence of classical physics, particularly as a place for probabilities to be calculated. It's called "Complementarity".

5. Early enough in the universe, everything would have been on the scale of subatomic particles, so how did the macro-scale universe where measurements take place come to exist? If the Copenhagen interpretation is correct, then the early Big Bang was just a probability space, not something real. Does that mean a measurement took place? — Marchesk

I'm not sure that these questions have any meaning under instrumentalist theories like Copenhagen.

6. Does gravity have a wavefunction? Is mass only discrete when measured? What would the implication of that be for GR? — Marchesk

Gravity? You mean space-time curvature I hope, and no, space-time is real.

Metaphysician Undercover

Gravity? You mean space-time curvature I hope, and no, space-time is real. — tom

Oh the fantasies that people make up to justify their beliefs.

Rich

↪tom

Space-time is as real as probability waves. Einstein's greatest feat was transforming Lorentz's transformation equations into fodder for sci-fi writers. A magnificent example of science elevating its concocted mathematical equations into a rather strange metaphysics.

Marchesk

Your other questions are meaningless. Shut up and calculate instead. If you don't like being told what to do, tough! Probabilities are normative. — tom

Yeah, but part of science is asking why phenomena appears the way it does. What's going on behind the scenes? Imagine if Newton and Einstein had stopped at an equation for gravity and told everyone to shut up about the reality behind the equation.

The related concern is why should Schrodinger's equation work at all? Just saying that it fits experimental data is no answer at all. I was watching a video last night where Brian Green brought in four people to discuss the various interpretations of QM. One of them summed up the measurement problem as asking the question: what sort of world do we live in to get the sort of results that the double slit experiment gives us?

Marchesk

Gravity? You mean space-time curvature I hope, and no, space-time is real. — tom

Gravitons, I would presume. And space has quantum foam, where virtual particles pop in and out of existence, creating energy that supplies most of the mass for particles.

Rich

I think we should stick with gravity. Much more concrete than the lavish notion of space-time. I feel the pull of gravity and yes, gravity will have an effect on things.

Marchesk

↪Rich

But then how do you account for all the things that General Relativity does? Gravitational lensing of stars and Galaxies, Mercury's orbit, neutron stars and black holes, gravity waves, time dilation, the Big Bang and inflation, red shifting of distant galaxies, etc?

And there's the fact that acceleration gives you the same force as gravity, which is what led Einstein to GR.

tom

Yeah, but part of science is asking why phenomena appears the way it does. What's going on behind the scenes? Imagine if Newton and Einstein had stopped at an equation for gravity and told everyone to shut up about the reality behind the equation. — Marchesk

Absolutely! My view is that Copenhagen Interpretation should be discounted as a scientific theory because it is non-explanatory. But then I adhere to the conception of science as a purely explanatory endeavour. Instrumentalists strongly disagree!

The related concern is why should Schrodinger's equation work at all? Just saying that it fits experimental data is no answer at all. I was watching a video last night where Brian Green brought in four people to discuss the various interpretations of QM. One of them summed up the measurement problem as asking the question: what sort of world do we live in to get the sort of results that the double slit experiment gives us? — Marchesk

A more difficult question to answer is "why should the Heisenberg equation work at all?".

I would suggest that you follow through some of the many derivations of the Schrödinger equation on the web. QM is actually intimately associated with deep classical theories, particularly Hamiltonian-Jacobi mechanics. The ONLY difference is the the commutator is non-zero!

Rich

↪Marchesk

I am not suggesting that the equations are incorrect or that they do not have some usefulness - albeit quite limited. What I am suggesting is the elevation of the mathematical abstraction to the level of some metaphysical theory of the universe, in particular the notion of some 4D space-time continuum. It is unnecessary though no doubt fun for sci-fi buffs.

Rich

In regards to the double slit conundrum, the Bohm-De Broglie real wave-particle interpretation handles it quite eloquently as long as you can tolerate non-local action at a distance. I personally have no problem with the notion since a holographic wave universe seems quite reasonable.

tom

Gravitons, I would presume. And space has quantum foam, where virtual particles pop in and out of existence, creating energy that supplies most of the mass for particles. — Marchesk

You presume too much. Gravitons are a nice idea, but there is zero evidence for them. As far as we can tell, physics takes place in a space-time.

Copenhagen Interpretation of QM

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