The simulated images of the bike ride through virtual Tübingen where the speed of light is 30 km/h, are all in colour. Actually, however, we should see quite different colours because of the Doppler effect and also quite different levels of brightness. E. g., when moving at 95% of the speed of light and looking forward, radiation with wavelengths between 2.5 μm and 5 μm in the rest frame of the street would be visible light to the moving observer - he would see the street in infrared light. Looking backward, wavelengths from the ultraviolet (65 - 130 nm) would be shifted into the visible part of the spectrum. The shift in wavelength is always linked with a scaling of the amplitude: When looking forward, the intensity is increased, when looking backward, it is reduced. The observed brightness therefore changes for two reasons, firstly because the spectrum is scaled in amplitude and secondly because a different spectral range moves into the visible.
In general, the change in brightness is much more dramatic than the change in colour. It then makes the surroundings appear very bright in the direction of motion and increasingly darker towards the side.
Since we do not have spectra of the houses in the old city centre of Tübingen at our disposal, we cannot make a realistic simulation of brightness and colour. Figure 13 therefore only illustrates the impact of the intensity change in a qualitative way.
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