Michael Pohlig

Karlsruhe Institute of Technology | KIT

In the context of teaching relativity, one encounters two situations in which two observers age at different rates. Usually, these effects are treated as if they were independent of each other. Often one is referred to as special-relativistic, the other as general-relativistic. We show that both are special cases of an effect which follows naturall...

We consider the Earth moving through empty space at 30 km/s (in the sun’s frame of reference). Associated with this motion is a convective flow of kinetic and internal energy. Since there is high pressure inside the earth, and since the earth is moving, there is yet another “hydraulic” energy flow. This latter is what this article is about. Althoug...

We learn and teach classical mechanics essentially as it was developed by Newton. The theory is more than 300 years old, but still useful for many purposes. However, even in contexts where it produces correct results, it has a flaw: it uses actions at a distance. In addition, it is not able to describe the transport and storage of energy in the gra...

Gravitation is still taught largely in a way that suggests the existence of action-at-a-distance. A theory without such shortcomings, gravitoelectromagnetism, was proposed by Heaviside in 1893, but it did not become well-established because many effects it describes are very small and the later emergence of general relativity seemed to make a theor...

Mathematical derivations alone do not necessarily lead to physical understanding. Tools that can replace the mathematical treatment of a physical process and at the same time increase the physical understanding are computer-aided modeling programs, also called system dynamics software. Examples of such software are Stella, Berkeley Madonna, Wensim,...

The teaching of relativity usually starts with kinematics: The invariance of the speed of light, clock synchronization, time dilatation and length contraction, the relativity of simultaneity, Lorentz transformation and the Minkowski diagram. The change of the reference frame is a central topic. Only afterwards problems of relativistic dynamics are...

“What is heat?” was the title of a 1954 article by Freeman J. Dyson, published in Scientific American. Apparently, it was appropriate to ask this question at that time. The answer is given in the very first sentence of the article: heat is disordered energy. We will ask the same question again, but with a different expectation for its answer. Let u...

At school and university, gravity is taught essentially in the Newtonian way. Newtonian mechanics originated at a time when there were no fields, when energy did not exist as a physical quantity, and when one still had to be satisfied with the concept of actions at a distance. A theory without such shortcomings, Maxwell’s electromagnetism, came int...

We discuss a paradox from the field of relativistic thermodynamics: Two heat reservoirs of the same proper temperature move against each other. One is at rest in reference frame SA, the other in reference frame SB. For an observer, no matter in which of the two reference frames he is at rest, the temperatures of the two reservoirs are different. On...

We discuss a paradox from the field of relativistic thermodynamics: two heat reservoirs of the same proper temperature move against each other. One is at rest in the inertial reference frame SA, the other in SB. For an observer, no matter in which of the two reference frames he is at rest, the temperatures of the two reservoirs are different. One m...

1 What changes Newtonian Mechanics into the Special Theory of Relativity? Usually, in introducing in the Special Theory of Relativity we begin by discussing the failure of the MICHELSON-MORLEY experiment. FITZGERALD's hypothesis, elaborated by LORENTZ stated that all bodies in motion should be shortened in the direction of their velocity. He be-lie...

We introduce an atomic model that avoids some of the worst dissonances. According to this model, the electron is not point-like but extended. The square of the wave function is interpreted as the density of a fluid, the electronium. On the basis of the electronium model suggestive pictures and animations of the atom can be generated. We shall see a...

Entropy is known to be one of the most difficult physical quantities. The difficulties arise from the way it is currently introduced, which is due to Clausius. Clausius showed that the ratio of the process quantity heat and the absolute temperature is the differential of a state variable, which he called entropy. About 50 years later, in 1911, H. L...