### The minimal realistic interpretation aims to answer this question.

Imagine a 19th century physicist appearing the modern world. He has learn a lot of new things, in particular quantum theory as well as relativity. If he would use a standard course for this, this would not be interesting at all. What makes this thought experiment interesting is to assume that he learns this in a very special, particular way. Namely, he learns the whole mathematical apparatus of bothe theories as it is, then he learns the minimal interpretation, so that he is able to understand how the mathematics is connected with observable results. Everything about other, non-minimal interpretations, he ignores completely - he does not even care to understand them and reject them for one or another reason, he simply does not learn them at all.

### The situation in relativity

In quantum theory, this is at least plausibly imaginable. In relativity, this would be quite difficult, simply because there is no minimal interpretation of general relativity, but only one standard "curved spacetime" interpretation which contains a lot of quite unorthodox and strange metaphysics. I have to thank S.P. Novikov, not a physicist but a mathematician (Fields medalist), for explaining by the way (probably not even intentional) how such a minimal interpretation of general relativity would have to look like. He explained how the solution $$g_{\mu\nu}(x,t)$$ defines for every trajectory of a clock $$\gamma^{\mu}(s)$$ the time shown by this clock being $\tau = \int_{\gamma} \sqrt{g_{\mu\nu}(\gamma(s)\frac{d\gamma^{\mu}}{ds}\frac{d\gamma^{\nu}}{ds}} ds,$ adding simply "and that's all". This "and that's all" shocked me at that time, I thought about it, and recognized, indeed, that's all, one can completely forget about everything else about curved spacetimes and so on, this formula defines a minimal interpretation of general relativity. Fortunately for the purpose of these pages, the situation in quantum theory is much easier, because there exists a minimal interpretation, and this minimal interpretation really contains only what is necessary to make physical sense of the mathematics of quantum theory.

Nonetheless, given that many interpretational questions of quantum theory also have, at least in the background, also the question of compatibility with relativity, these questions also depend on the interpretation of relativity. And here we have to make a similar assumption, namely, that all what our hypothetical scientist has learned is the mathematics and that minimal interpretation of relativity, and that everything beyond this minimal interpretation of relativity is simply ignored.

### Real teaching of quantum theory contains more than the minimal interpretation

But, of course, nobody accepts a minimal interpretation as it is, everybody tries to make sense of it. The teachers as well as the pupils. And de facto the result is that what one really learns is not the minimal interpretation, but some mixture of the minimal interpretation with whatever interpretation the teacher prefers. The point of our thought experiment is to exclude this.

So our hypothetical scientist has learned all the math of quantum theory. This includes not only the minimal math, but also, in particular, all the math of all interpretations, in particular also the math of de Broglie-Bohm theory, Nelsonian stochastics and whatever else. But he has learned only the minimal interpretation of quantum theory, nothing beyond this. While not very realistic, at least in theory this would be sufficient for him to do everything what is necessary in physics, and one can imagine at least in theory that some teachers of quantum theory accept this as an ideal and try to teach this.

### What our hypothetical scientist will do

Our hypothetical scientist is, nonetheless, a human being with typical human interests, and has, in particular, his own metaphysical interests too. As everybody else in the real world, he does not think that mathematics and the minimal interpretation is sufficient. It may be sufficient, at least in principle, for those really interested only in purely pragmatic questions about results of some experiments. Something which may be useful from a technical point of view, for some applications. But it is certainly not why people are interested in doing fundamental physics. Biology or condensed matter physics would be certainly much more interesting for people really interested in this.

So, we are doing physics because we are interested "zu erkennen was die Welt im Innersten zusammenhÃ¤lt" (what holds the world together at the core), else we would do something different. And this is also what our hypothetical scientist is interested in. So, he is not satisfied at all from what he learns from mathematics together with the minimal interpretation.

Instead, he tries to make sense of it. And "making sense" means for him to make it compatible with the classical common sense picture of science which he knows and admires. So, our hypothetical scientist follows the following ideas:

• Forget about all you know about the interpretation of quantum theory, except for the mathematics and the minimal interpretation.
• Try to find an interpretation of quantum theory which makes sense from the point of view of a classical world view.

# Is such an interpretation interesting?

I think it is. Why would one, last but not least, like to object against an interpretation of quantum theory which is compatible with classical common sense, or at least minimizes the conflict between them?

• Even if one prefers another interpretation, it is useful if there exists also an interpretation which is not in conflict with certain common sense principles, simply because it gives the quite useful information that it is not physics, not a conflict with observation which forces one to give up the common sense principle in question, but a deliberate metaphysical decision.
• Then, such a decision may be of interest for students: It is certainly easier to learn an interpretation which is compatible with as much common sense as possible. Whatever the advantages of other interpretations, for most of those who need quantum theory these advantages will be quite irrelevant, because what is necessary for doing real physics - the compatibility with the minimal interpretation - is present too.