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bhobba

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Hi All

This is an outgrowth of the following thread:

https://www.physicsforums.com/threads/light-photons-waves-particles-wave-particle-duality.934063/

OK first we need to clear up a few misconceptions about Einsteins view of QM. It is often said Einstein didn't believe in QM. That's really a half truth - he initially didn't and tried many ways to disprove it - his last attempt being the famous clock in a box argument solved by Bohr. For a modern take on it see here:

https://arxiv.org/pdf/1203.1139.pdf

As an aside - the paper says 'At first Bohr didn’t know how to reply to the Einstein’s paradox'. That's a bit of an understatement. Evidently it shook him to his core. Long into the night he labored to resolve it - he was really worried. But finally he resolved it. Einstein was seen sitting there, smiling and literally tipped his hat to Bohr - he knew he was beaten - and by his own equivalence principle at that.

From that point on he never attacked the actual consistency of QM - he accepted it as a correct theory. However until his dying day he believed it incomplete - ie it was just an approximation to a more complete theory, had some hidden variables or something like that. We have versions today he would be happy with such as DBB - although if I remember correctly he thought it was a bit too naive The statements he believed it actually wrong or didn't understand it are incorrect. As I mentioned in my previous post in the other thread he believed Dirac's presentation was the best treatment and kept a copy of his book close at all times. He knew QM very well. He even came up with his own interpretation that got rid of the issues he thought QM had. His main objection was in fact to Copenhagen whose main tenants at that time (it's modern version is likely different because it contains things we now know are strictly speaking wrong such as the wave-particle duality - these days many Copenhagenists have taken on Consistent Histories which is lot more complete and modern) I will detail (from a site that detailed them - there is a bit of variation on exactly what they are) so we can see just what Einstein did not like:

1. A system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system. (Heisenberg)

2. The description of nature is essentially probabilistic, with the probability of an event related to the square of the amplitude of the wave function related to it. (The Born rule, after Max Born)

3. It is not possible to know the value of all the properties of the system at the same time; those properties that are not known with precision must be described by probabilities. (Heisenberg's uncertainty principle)

4. Matter exhibits a wave–particle duality. An experiment can show the particle-like properties of matter, or the wave-like properties; in some experiments both of these complementary viewpoints must be invoked to explain the results, according to the complementarity principle of Niels Bohr.

5. Measuring devices are essentially classical devices, and measure only classical properties such as position and momentum.

6. The quantum mechanical description of large systems will closely approximate the classical description. (The correspondence principle of Bohr and Heisenberg)

Popularizations concentrate on he didn't like probabilities coming into it. That's not quite right - he made foundational contributions to statistical mechanics and had no trouble with that. No it was something else - in fact it was number 1:

A system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system. (Heisenberg)

He did not like this at all, and in fact it was an anathema to his view of an objective reality that Einstein believed science explained - not described - no he thought science explained the world around us:

'I want to know how God created this world. I'm not interested in this or that phenomenon, in the spectrum of this or that element. I want to know His thoughts, the rest are details.'

This is Einsteins real objection - non locality etc is just one of the means he wanted to show it cant be like that. That is the crux of the matter.

Just as an aside both Bohr and Einstein were wrong as Weinberg explains:

http://physicstoday.scitation.org/doi/full/10.1063/1.2155755

What do I believe? I believe the purpose of science is to describe - not explain mind you, although it will often shed light on that - but to describe it. Like for example saying two apples sit on a table is not actually two apples sitting on the table - but just describing it - this is often paraphrased as the map is not the territory.

Are real numbers reality? Well simply look at their definition. Have a look at the least upper bound axiom? Is that real? How would you even test it? No - its not real, like a table that kicks back if you kick it. What it is, is simply, like English, something that has proven useful in describing reality - whatever that is.

Added Later:

I forgot to mention - is the above philosophy - possibly - I will leave it to others to decide that one - but point taken. Feynman was like me - a bit anti philosophy. That in itself is a philosophy - as I said before likely a lot of circularity in these foundational issues.

Thanks

Bill

This is an outgrowth of the following thread:

https://www.physicsforums.com/threads/light-photons-waves-particles-wave-particle-duality.934063/

OK first we need to clear up a few misconceptions about Einsteins view of QM. It is often said Einstein didn't believe in QM. That's really a half truth - he initially didn't and tried many ways to disprove it - his last attempt being the famous clock in a box argument solved by Bohr. For a modern take on it see here:

https://arxiv.org/pdf/1203.1139.pdf

As an aside - the paper says 'At first Bohr didn’t know how to reply to the Einstein’s paradox'. That's a bit of an understatement. Evidently it shook him to his core. Long into the night he labored to resolve it - he was really worried. But finally he resolved it. Einstein was seen sitting there, smiling and literally tipped his hat to Bohr - he knew he was beaten - and by his own equivalence principle at that.

From that point on he never attacked the actual consistency of QM - he accepted it as a correct theory. However until his dying day he believed it incomplete - ie it was just an approximation to a more complete theory, had some hidden variables or something like that. We have versions today he would be happy with such as DBB - although if I remember correctly he thought it was a bit too naive The statements he believed it actually wrong or didn't understand it are incorrect. As I mentioned in my previous post in the other thread he believed Dirac's presentation was the best treatment and kept a copy of his book close at all times. He knew QM very well. He even came up with his own interpretation that got rid of the issues he thought QM had. His main objection was in fact to Copenhagen whose main tenants at that time (it's modern version is likely different because it contains things we now know are strictly speaking wrong such as the wave-particle duality - these days many Copenhagenists have taken on Consistent Histories which is lot more complete and modern) I will detail (from a site that detailed them - there is a bit of variation on exactly what they are) so we can see just what Einstein did not like:

1. A system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system. (Heisenberg)

2. The description of nature is essentially probabilistic, with the probability of an event related to the square of the amplitude of the wave function related to it. (The Born rule, after Max Born)

3. It is not possible to know the value of all the properties of the system at the same time; those properties that are not known with precision must be described by probabilities. (Heisenberg's uncertainty principle)

4. Matter exhibits a wave–particle duality. An experiment can show the particle-like properties of matter, or the wave-like properties; in some experiments both of these complementary viewpoints must be invoked to explain the results, according to the complementarity principle of Niels Bohr.

5. Measuring devices are essentially classical devices, and measure only classical properties such as position and momentum.

6. The quantum mechanical description of large systems will closely approximate the classical description. (The correspondence principle of Bohr and Heisenberg)

Popularizations concentrate on he didn't like probabilities coming into it. That's not quite right - he made foundational contributions to statistical mechanics and had no trouble with that. No it was something else - in fact it was number 1:

A system is completely described by a wave function ψ, representing an observer's subjective knowledge of the system. (Heisenberg)

He did not like this at all, and in fact it was an anathema to his view of an objective reality that Einstein believed science explained - not described - no he thought science explained the world around us:

'I want to know how God created this world. I'm not interested in this or that phenomenon, in the spectrum of this or that element. I want to know His thoughts, the rest are details.'

This is Einsteins real objection - non locality etc is just one of the means he wanted to show it cant be like that. That is the crux of the matter.

Just as an aside both Bohr and Einstein were wrong as Weinberg explains:

http://physicstoday.scitation.org/doi/full/10.1063/1.2155755

What do I believe? I believe the purpose of science is to describe - not explain mind you, although it will often shed light on that - but to describe it. Like for example saying two apples sit on a table is not actually two apples sitting on the table - but just describing it - this is often paraphrased as the map is not the territory.

Are real numbers reality? Well simply look at their definition. Have a look at the least upper bound axiom? Is that real? How would you even test it? No - its not real, like a table that kicks back if you kick it. What it is, is simply, like English, something that has proven useful in describing reality - whatever that is.

Added Later:

I forgot to mention - is the above philosophy - possibly - I will leave it to others to decide that one - but point taken. Feynman was like me - a bit anti philosophy. That in itself is a philosophy - as I said before likely a lot of circularity in these foundational issues.

Thanks

Bill

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