When I studied physics (decades ago) there were two exams feared by all students.

One was classical mechanics, a course with the (unofficial) goal to eliminate more than 3/4 of the students. If you wonder how classical mechanics can be so difficult, let me only mention that e.g. Arnold Sommerfeld wrote a four volume master piece about the spinning top. Somehow I passed this exam, which only got me to the next big hurdle: inorganic chemistry.

It was common knowledge among students that the professor had a habit of asking 'weird questions' during the exam and one only had a chance to pass by attending the lectures (where he would mention and discuss them). Unfortunately, those lectures were scheduled early in the morning and since I lived outside the city, it would have meant to get up around 6am or even earlier and this was out of the question for me.

My plan was to skip the lectures, read the book of the professor and bluff my way through the exam.

My luck was that he examined three students at a time, so I had one or two questions and struggling students in front of me to understand what was so 'weird' about this.

It turned out that he was a closet philosopher, e.g. when he asked about the size of a hydrogen atom one could not talk about ångström, but the answer was that an atom does not really have a size because the wave function of the electron extends to infinity.

So when he asked me about the pre-requisit of every measurement, I talked about the basic structure of time and the distinction of past and future (because a measurement is not possible if one cannot distinguish 'before the measurement' from 'after the measurement') and we settled on the fact that the world is inhomogeneous as the basic pre-requisit. Subsequently we discussed the logic of Newton's absolute time and finally he accused me of using a Machian approach and I replied that his methods were close to dialectical materialism (I am not kidding). He was thrilled and I suspect it was not too often that he enjoyed an exam as much as mine.

After discussing transubstantiation he actually asked a few questions about inorganic chemistry and my knowledge about it was unfortunately limited (I remember the oxidation of lanthanum as a stumbling block).

He noticed it, but I still passed the exam (to the great astonishment of my colleagues) at the first try.

I wonder if a subconscious trauma from these exams is the reason I keep writing this blog.

### consistent histories

This post is from one PA member to the other.

First, let me be clear that the interpretation problem in quantum theory is a real problem. Schroedinger's wave function does not match with our direct experience of reality. Several very different proposals have been made on how to solve this problem and in my opinion none of them is very convincing.

Furthermore, decoherence does not solve the measurement problem and this is all there is to say about that.

As for the many worlds proposal, the big problem is to get probabilities right but

if one is interested in consistent histories, there are two good papers about it. We read that

"their explanation of the apparent persistence of quasiclassicality relies on assumptions about an as yet unknown theory of experience".

I think this is the key. We don't have a theory of (conscious) experience and therefore there is an interpretation problem even in classical physics, but usually overlooked and well hidden.

Ernst Mach was one of the few who noticed it but he was pushed to the side long ago.

First, let me be clear that the interpretation problem in quantum theory is a real problem. Schroedinger's wave function does not match with our direct experience of reality. Several very different proposals have been made on how to solve this problem and in my opinion none of them is very convincing.

Furthermore, decoherence does not solve the measurement problem and this is all there is to say about that.

As for the many worlds proposal, the big problem is to get probabilities right but

if one is interested in consistent histories, there are two good papers about it. We read that

"their explanation of the apparent persistence of quasiclassicality relies on assumptions about an as yet unknown theory of experience".

I think this is the key. We don't have a theory of (conscious) experience and therefore there is an interpretation problem even in classical physics, but usually overlooked and well hidden.

Ernst Mach was one of the few who noticed it but he was pushed to the side long ago.

### recently, at the PA meeting

My name is Wolfgang B. and I am a recovering physicist.

Unfortunately, I still need my daily dose of formulas, otherwise my brain begins to come up with crazy ideas.

But recently I found free supply of high quality stuff: quantum field theory and strings.

Perhaps you want to check it out too.

*Hi Wolfgang.*Unfortunately, I still need my daily dose of formulas, otherwise my brain begins to come up with crazy ideas.

But recently I found free supply of high quality stuff: quantum field theory and strings.

Perhaps you want to check it out too.

*OMG! And with problem sheets...*
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