Physics is to be regarded not so much as the study of something a priori given, but rather as the development of methods for ordering and surveying human experience.
Niels Bohr

Dobbiamo inventare il mondo per inquadrarvi le nostre sensazioni, ma non dovremo mai considerarlo come uno schema rigido e fisso, come una costruzione definitiva: esso non è che il risultato provvisorio di uno sforzo di sintesi.
Bruno de Finetti

At the heart of two basic theories of physics, quantum theory and statistical mechanics, lies the concept of probability. In the modern Bayesian view, probability theory in turn constitutes an extension of logic: Rather than merely describing limits of relative frequencies, it is regarded much more broadly as a framework for reasoning in the face of uncertainty. Could it be, therefore, that some of our fundamental laws of physics reflect but "laws of thought"; i.e., consistency requirements of some – at times counterintuitive – algorithm for plausible reasoning?

The challenges – both conceptual and practical – posed by probabilities may vary with the scale considered. While the microscopic realm confronts us with the peculiarities of quantum versus classical probabilities, the macroscopic realm brings with it the notions of entropy and irreversibility, and in particular, the need to understand the emergence of a macroscopic dynamics which may have an entirely different quality than its microscopic counterpart. These have been recurrent themes in my recent research efforts, some of which are detailed below.

Quantum probability

Quantum theory is an inherently probabilistic theory. Outcomes of measurements are no longer certain. Rather, they must be assigned probabilities not as a result of insufficient knowledge, but as a matter of principle. While the rules governing these probabilities exhibit many similarities with classical probability theory, there are also some profound differences. I like to elucidate these similarities and differences, as they offer an interesting perspective on the conceptual basis of quantum theory. Moreover, on a more practical level, I have developed statistical tools for the reconstruction of quantum states on the basis of incomplete or noisy data. I have also considered the case where not just the states but also their time evolution must be modelled probabilistically.

from: T. Koga and Y. Sekine, NTT Tech. Rev., Vol. 10 No. 9 Sep. 2012
from: T. Koga and Y. Sekine, NTT Tech. Rev., Vol. 10 No. 9 Sep. 2012

Macroscopic dynamics

While the dynamics of microscopic systems say, individual atoms or molecules is governed by few basic equations such as the Schrödinger and Maxwell equations, macroscopic systems may evolve according to a plethora of seemingly unrelated and ad hoc macroscopic transport equations. I am interested in how these macroscopic equations can be derived from the underlying microscopic dynamics; or in case the latter is not known, how they can be inferred from experimental data. I have also explored the link between macroscopic transport equations, effective forces, and renormalization.

Space, time, and particles

My early research focused on the production of Higgs particles (at the time not yet discovered experimentally), supersymmetric particles, and other heavy, hypothetical particles in heavy-ion collisions. Today I maintain an amateur interest in the geometry and symmetries of spacetime, as well as in the theory of gravity.