The Appearance of Fast Moving Objects

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This project has been presented at .

Short version of a cdrom which may be ordered from U. Backhaus.

classically retarded
relativisticly retarded

U. Backhaus, R. Thiel, Universität Koblenz


The contraction of fast moving bodies in the direction of their velocity is a well-known result of special relativity: Different observers get different results when they measure the length of an object, the shorter the larger the relative speed between observer and object. Much less known is the fact that this so called Lorentz-Fitzgerald contraction is invisible in the following sense: By looking at the moving object or by photographing it one does not observe it as shortened but, on the contrary, as lengthened and, under certain conditions, as deformed or twisted.

The main reason for this surprising effect is the difference between measuring an object and observing it:

simultanous emittation,
registration in succession
emittation in succession,
simultanous registration
Those animations can be generated by the program Retardierung.

The finite value of the speed of light has the consequence that parts of an object with different distances to the observer are imaged at different moments in the past that means, in the case of fast moving objects, due to different positions of the object.

During the last years additional effects have been discussed such as the influence of frequency (Doppler effect) and intensity transformation. Most of the publications cause the impression that these effects are specifically relativistic. We want to stress that most of the effects arrise in classical physics similarily although differently pronounced.

We show several computer animations generated by own raytracing routines. They demonstrate the different effects caused by the finite runtime of light, Doppler effect and intensity transformation due to classical and relativistic theory, respectively. Our main aim is to discriminate classical from relativistic effects and to emphasize the reach of classical theory.

We think generating those animations and considering the demonstrated effects is an excellent opportunity to reflect upon different theories and their implications. Additionally, we consider the generation of those pictures and movies as a good example for the interdependence between theoretical reflections, numerical computing and visualization:

The animations below show the relative motion between a camera and a cube or the printed names of "ALBERT EINSTEIN" (relativistic calculations) and "GALILEO GALILEI" (classical calculations), respectively. They distinguish between the following cases:

In the case of classical theory, the speed of light has a finite measure but does not play the role of a limiting velocity. Therefore, some of the animations show effects arising in classical theory due to superluminal speeds.

By clicking on one of the following pictures you can download a document with the related little animation. That document additionally offers a link to the related high resolution mpeg video. In this internet version, the mpeg videos are not contained.

The simulations of this project have been generated partly for R. Thiel's paper during her examination at the Institut für Physik to become a physics teacher for lower grade secondary schools, partly parallel to this examination and during our following cooperation.

The essential results of R. Thiel's paper:

Der Einfluss der endlichen Lichtgeschwindigkeit auf das Aussehen schnell bewegter Objekte (in German)

are contained in the short version of a speech (in German, too).

Prof. Dr. Udo Backhaus
last modification:  March 28th, 2008