Our physical world view currently has some gaps.
One of the most fundamental problems is that the established theories of the micro and macrocosm - quantum field theory and general relativity - do not fit together in their current form.
They should, however, not only out of a desire for standardization, but also because there are areas of overlap between the two theories.
A theory of quantum gravity is particularly essential for the theoretical understanding of black holes and the Big Bang, where the curvature of space-time becomes infinite in the context of general relativity.
The fact that physical quantities assume infinite values in both cases is described with the concept of singularity.
Physicists understand the occurrence of such singularities as an indication that
Sibylle Anderl
Editor in the feuilleton, responsible for the "Nature and Science" department.
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However, it is still unclear which theory of quantum gravity could replace the theory of relativity.
There are a large number of different approaches, the best known being string theory and loop quantum gravity.
The former strives for a unified theory of all four basic physical forces by attributing elementary particles to the oscillations of one-dimensional "strings".
The latter attempts, more modestly, to reconcile relativity with quantum theory by quantizing space-time on tiny scales.
However, there is a problem in assessing which of the various approaches is the right one: the empirical data is scarce.
At least we now have astrophysical observations, such as neutral hydrogen radiation and the cosmic background radiation, that shed light on conditions in the early Universe.
Quantum cosmological models, in which theories of quantum gravity are combined with cosmological models, can be confronted with these observations.
But even these data do not provide particularly strong indications for the nature of quantum gravity.
For this reason, physicists like to invoke theoretical guiding principles such as elegance and simplicity, although their justification can be doubted.
Interdisciplinary dialogue
Discussions about the principles of theory choice, but also the preoccupation of quantum gravity with the nature of space-time create a natural proximity between theoretical physics and philosophy.
In mid-June, philosophers and physicists – experienced scientists together with doctoral students from both disciplines – met on the Canadian shore of Lake Huron to promote interdisciplinary exchange within the framework of a philosophy of cosmology, also at the level of young scientists.
The summer school was organized by the Rotman Institute of Philosophy at Canada's University of Western Ontario with support from the Templeton Foundation.
Physicists in particular had high hopes for exchanges with philosophers.
Philosophers as conceptual experts
Co-organizer Chris Smeenk justified the fact that philosophers are particularly suitable for a constructive dialogue by saying that the strength of philosophers is a special precision in dealing with terms: "In cosmology we find a mixture of different terms that were introduced to cover very different roles to play.” Philosophers could help to test the fruitfulness of concepts and work out which existing intuitions they capture.
An example is the concept of singularity, for which there are many different definitions.
If a theory of quantum gravity aims to resolve the singularities that appear in the general theory of relativity, it must be clarified conceptually what exactly is meant by this.
However, the cooperation still has one blemish, as was repeatedly admitted at the workshop: So far, there has been no example of the input of philosophers having really led to a physical breakthrough.
Unless this is due to a fundamental problem of interdisciplinary discourse, one can hope that this will change soon, because one thing is certain: the relationship between physicists and philosophers is intensifying.