Many condensed matter systems are such that their collective excitations at low energies can be described by fields satisfying equations of motion formally indistinguishable from those of relativistic field theory. The finite speed of propagation of the disturbances in the effective fields (in the simplest models, the speed of sound) plays here the role of the speed of light in fundamental physics. However, these apparently relativistic fields are immersed in an external Newtonian world (the condensed matter system itself and the (...) laboratory can be considered Newtonian, since all the velocities involved are much smaller than the velocity of light) which provides a privileged coordinate system and therefore seems to destroy the possibility of having a perfectly defined relativistic emergent world. In this essay we ask ourselves the following question: In a homogeneous condensed matter medium, is there a way for internal observers, dealing exclusively with the low-energy collective phenomena, to detect their state of uniform motion with respect to the medium? By proposing a thought experiment based on the construction of a Michelson-Morley interferometer made of quasi-particles, we show that a real Lorentz-FitzGerald contraction takes place, so that internal observers are unable to find out anything about their ‘absolute’ state of motion. Therefore, we also show that an effective but perfectly defined relativistic world can emerge in a fishbowl world situated inside a Newtonian (laboratory) system. This leads us to reflect on the various levels of description in physics, in particular regarding the quest towards a theory of quantum gravity. (shrink)

It is argued that an unheralded moment marking the beginnings of relativity theory occurred in 1889, when G. F. FitzGerald, no doubt with the puzzling 1887 Michelson-Morley experiment fresh in mind, wrote to Heaviside about the possible effects of motion on inter-molecular forces in bodies. Emphasis is placed on the difference between FitzGerald's and Lorentz's independent justifications of the shape distortion effect involved. Finally, the importance of the their `constructive' approach to kinematics---stripped of any commitment to the physicality of the (...) ether--- will be defended, in the spirit of Pauli, Swann and Bell. (shrink)

In der vorliegenden Arbeit wird über die verschiedenen Aspekte der sogenannten FitzGerald-Lorentz-Kontraktion berichtet. Nach einem kurzen Abriß der Entwicklung der Ätherkonzeption wird eine Beschreibung des Michelson-Morley Versuchs gegeben und seine Rolle in der Entstehungsgeschichte der speziellen Relativitätstheorie diskutiert. Anschließend wird die Kontraktionshypothese vorgestellt und die Frage erörtert, ob die Kontraktion „wirklich“ oder nur „scheinbar“ ist. Einige Gedankenexperimente werden vorgestellt, die zeigen, daß die Kontraktion bewegter Körper kein bloßer Schein ist. Ferner wird die noch bei Einstein unklare Beantwortung nach der Frage (...) der Sichtbarkeit der Längenkontraktion durch die Analyse der Begriffe „Beobachten“ und „Sehen“ aufgehellt. Abschließend wird auf die Frage nach der Falsifizierbarkeit der Kontraktionshypothese eingegangen, die von Popper aufgeworfen wurde. (shrink)