Why don’t classical and quantum physics go together? Are we dealing with two different worlds or are they just two different descriptions?

A world or a universe can only have one physics. It can hardly be assumed that different laws of nature prevail in the microcosm described by quantum physics than in the mesocosm or macrocosm, for which classical physics is responsible.

Let’s assume that there are two kinds of laws of nature, one made by nature, the other by us humans. The two are not identical. This means that ‘our’ laws of nature describe nature as we see it. This description is best achieved in the mesocosm with which we are familiar. We are adapted to this by evolution and are able to create rules with the help of which we can understand the mesoscopic world. By creating our laws of nature, we formulate, as it were, a (mesoscopic) ontology of the world.

So you can say that the phenomenology of the mesoscopic world leads to an ontology in classical physics. In the microscopic world, this ontology does not succeed, one remains in a phenomenological description in the form of statistics, because our mesoscopic measuring instruments do not correspond to the microscopic scales.

Quantum mechanical phenomena such as the “spooky action at a distance” indicate that at the lowest level, the world must be seen as a coherent field. The field is not an ontological concept, but a phenomenological one. If we were as small as a photon, we could formulate an ontology of the very smallest. And only then would there be a unified physical theory.

Therefore, conversely, it makes no sense to try to apply quantum mechanics to the macroscopic world — and this also applies to philosophical conclusions. For this reason, structural realist considerations based on quantum mechanical considerations, such as those of John Worrall, are pointless. One would want to justify a (macroscopic) ontology with a (microscopic) phenomenology.

Against this background, a unification of classical and quantum physics is therefore not possible, unless new laws are found on both sides and categorically unified.

To achieve this, it would have to be possible to ascribe properties to matter, whatever we want to understand by that. In the mesoscopic world, this is easy for us to do by characterizing a molecule, for example. At the quantum level, where we speak of fields, properties can no longer be ontologically assigned to individual particles, because they appear to us both as particles and as waves.

The properties of matter are therefore not intrinsic, but they are an attribution made by us, no matter which interpretation of quantum mechanics we use.

The question of what holds the world together at its core — and by this we actually mean what makes up the world in the smallest — is wrongly posed, because there is no innermost that we can ontologically label with properties.

So we take two looks at the world, a quasi-ontological one at the mesoworld and a phenomenological one at the microworld.

The same applies accordingly to the macro world of the cosmos. Again, we observe phenomena for which we cannot create an ontology, starting with the Big Bang.

So the world is relativistic for us. Thus, the Kantian ‘thing-in-itself’ does not exist. In the Critique of Pure Reason, however, Kant still described the thing-in-itself as recognizable in the sense of the essence of things. Later, he described it as unrecognizable. In the earlier version, therefore, it resembles the being that Husserl meant in the context of his view of nature, which is to be achieved by the method of eidetic reduction.

This reduction to the essentials is therefore the starting point of any ontology that we can establish. And we can — as far as possible — assign properties to this essence, at least in the mesoscopic world.