VARIABLE SPEED OF LIGHT (HOW IS RELATIVITY POSSIBLE?)

If an observer on top of a tower emits light, an observer on the
ground measures the speed of the light to be increased:

http://www.damtp.cam.ac.uk/user/hsr1...notes12_02.pdf
Harvey Reall, University of Cambridge: "...light falls in the
gravitational field in exactly the same way as a massive test
particle."

http://membres.multimania.fr/juvastr...s/einstein.pdf
"Le principe d'équivalence, un des fondements de base de la relativité
générale prédit que dans un champ gravitationnel, la lumière tombe
comme tout corps matériel selon l'acceleration de la pesanteur."

http://www.youtube.com/watch?v=TNWngpw2vr0
Brian Cox: "Light falls at the same rate in a gravitational field as
everything else."

http://www.wfu.edu/~brehme/space.htm
Robert W. Brehme: "Light falls in a gravitational field just as do
material objects."

The fact that "light falls in a gravitational field just as do
material objects" has an important implication. Let us consider two
initially stationary observers, A and B, at some distance apart in an
inertial system. A emits a flash of light towards B just as B starts
accelerating towards A so that, when B and the flash meet, B has a
speed v relative to the original inertial system. If "light falls in a
gravitational field just as do material objects", then B measures the
speed of the flash to be c'=c+v. In other words, the speed of light
(relative to the observer) varies with the speed of the observer:

http://a-levelphysicstutor.com/wav-doppler.php
"vO is the velocity of an observer moving towards the source. This
velocity is independent of the motion of the source. Hence, the
velocity of waves relative to the observer is c + vO. (...) The motion
of an observer does not alter the wavelength. The increase in
frequency is a result of the observer encountering more wavelengths in
a given time."

http://physics.ucsd.edu/students/cou...cs2c/Waves.pdf
"Doppler Shift: Moving Observer: Shift in frequency only, wavelength
does not change"

http://www.expo-db.be/ExposPrecedent...%20Doppler.pdf
"La variation de la fréquence observée lorsqu'il y a mouvement relatif
entre la source et l'observateur est appelée effet Doppler. (...) 6.
Source immobile - Observateur en mouvement: La distance entre les
crêtes, la longueur d'onde lambda ne change pas. Mais la vitesse des
crêtes par rapport à l'observateur change !"

http://www.radartutorial.eu/11.coherent/co06.fr.html
"L'effet Doppler est le décalage de fréquence d'une onde acoustique ou
électromagnétique entre la mesure à l'émission et la mesure à la
réception lorsque la distance entre l'émetteur et le récepteur varie
au cours du temps. (...) Pour comprendre ce phénomène, il s'agit de
penser à une onde à une fréquence donnée qui est émise vers un
observateur en mouvement, ou vis-versa. LA LONGUEUR D'ONDE DU SIGNAL
EST CONSTANTE mais si l'observateur se rapproche de la source, il se
déplace vers les fronts d'ondes successifs et perçoit donc plus
d'ondes par seconde que s'il était resté stationnaire, donc une
augmentation de la fréquence. De la même manière, s'il s'éloigne de la
source, les fronts d'onde l'atteindront avec un retard qui dépend de
sa vitesse d'éloignement, donc une diminution de la fréquence."

http://www.phys.uconn.edu/~gibson/No...6_3/Sec6_3.htm
Professor George N. Gibson, University of Connecticut: "However, if
either the source or the observer is moving, things change. This is
called the Doppler effect. (...) To understand the moving observer,
imagine you are in a motorboat on the ocean. If you are not moving,
the boat will bob up and down with a certain frequency determined by
the ocean waves coming in. However, imagine that you are moving into
the waves fairly quickly. You will find that you bob up and down more
rapidly, because you hit the crests of the waves sooner than if you
were not moving. So, the frequency of the waves appears to be higher
to you than if you were not moving. Notice, THE WAVES THEMSELVES HAVE
NOT CHANGED, only your experience of them. Nevertheless, you would say
that the frequency has increased. Now imagine that you are returning
to shore, and so you are traveling in the same direction as the waves.
In this case, the waves may still overtake you, but AT A MUCH SLOWER
RATE - you will bob up and down more slowly. In fact, if you travel
with exactly the same speed as the waves, you will not bob up and down
at all. The same thing is true for sound waves, or ANY OTHER
WAVES."

Pentcho Valev