Modern physical theories are deterministic in the sense that once we know the current state of the world, we can, in principle, predict all the future states. This was true for classical (pre-quantum) theories, this is true for modern quantum physics. On the other hand, we all know that we can make decision that change the state of the world -- even if, for most of us, a little bit. This intuitive idea of free will permeates all our life, all our activities -- and it seems to contradict the determinism of modern physics. It is therefore desirable to incorporate the idea of free will into physical theories. In this paper, we show that in quantum physics, free will leads to nonconservation of energy. This nonconservation is a microscopic purely quantum effect, but it needs to be taken into account in future free-will quantum theories.
As we are accustomed to everyday life, we may find quantum phenomena to be strange. If quantum phenomena were to happen often in our macroscopic world, we would react as if we had seen a ghost. A person to whom we were talking could move to another seat out of our sight in a moment, or his/her face could change. We might question if we are who we are. Fortunately experiencing quantum phenomena in everyday life is extremely hard. However, interestingly, quantum physics predicts that quantum phenomena can occur in the macroscopic world, regardless of our everyday experience. If that prediction is correct, why is experiencing quantum phenomena hard? Such a seemingly contradictory discussion was clearly raised by Schrodinger in his thought experiment, the so-called ‘Schrodinger cat paradox.’ Haroche’s group and Wineland’s group have independently performed experiments on the paradox. In this article, I discuss the historical background and the physical implications of the Schrodinger cat paradox.
Quantum fluids are fluids, indeed. We have seen in the previous chapter what it means from a classical physics point of view. But quantum fluids are by definition ruled by quantum physics, as well. The goal of this chapter is to introduce some key concepts of quantum physics necessary to understand what makes a fluid a quantum one or rather what quantum property makes an ensemble of particles a quantum fluid. We are here precisely at the edge of our basic intuition of quantum physics. Indeed, one usually associates the notion of quantum object to a microscopic nature and it may thus a priori seem paradoxical to link the word quantum to a macroscopic object, such as the notion of fluid. Thinking it over a bit deeper, quantum physics is certainly present at all scales and we are confronted with quantum mechanics through the many electronic devices which have invaded our everyday life. And it actually turns out that, as we will see later on, most of these quantum devices are directly connected to the notion of quantum fluids, the case of electron fluids being certainly the most common one in such devices. Quantum physics has for sure deeply modified our everyday life. But it has also changed our perception of the world, and as we shall see in this chapter, it is precisely this new vision of the world which allows us to understand the concept of quantum fluids underlying so many physical systems.