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.
Fig. 10 The alley Marktgasse at 0.95 c.
The snapshot is taken at the
same position as in figure 5. Here, the change in intensity has
also been taken into account.
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.