Does Light Need A Medium ?
A voice is a vibration of the air. When you run out of the house and you say to your wife: "I will be late", she will here your voice lower because you run away. This is so called "Doppler Effect". The same effect is supposed to exist by light. We see the light of the stars that run away in its lower frequencies. The medium of the voice is air. A voice can not move if there is no air as a medium. One could speculate the same is with the light. What could be the medium of the light. Ether is abandoned for 100 years, so let it be in peace. The only “candidate” of the medium of the light is the cosmic space itself.
According to the “A-temporal Gravitation Theory” (see full story on this home page “a-temporal gravitation” ) cosmic space is build up out of quanta of space” (QS) that have a size of Planck. When we heat up the peace of iron, it will emit light, photons. One could interpret photons as a “packets of energy” that from the heated iron transmit via QS of cosmic space; photons jump from one QS to another QS and so on. Like a chain.
The speed of this “chain jumping” of the light is independent of the movement of the source and of the movement of the observer, it is the same in every inertial system. That’s the first postulate of SR: the speed of light is the same in all inertial systems.
Here it is essential to understand that light is not moving through the cosmic space, light is a “chain vibration” of QS of cosmic space and inertial systems are moving through the cosmic space. Einstein idea of a “constant speed of light” in every inertial system is more clear here. All inertial systems move through the medium and light is a vibration of the medium. According to the “Doppler Effect” we detect the light of the inertial systems (a star) that run away from us in its lover vibrations.
Light is not moving through the “space-time” that is only a mathematical construction” (see full story here “Why Mathematics Rules Physics ?”), light is a “chain vibration” of the cosmic space itself.
Light has a double particle-wave nature simultaneously. A single photon jumping from one QS to another along its trajectory is central part - particle. The central part of the photon also changes the vibration of QS around its trajectory that is its circumference part - wave.
In a “double slit experiment” we can settle instruments and observe a "particle part" of the photon or we can settle instruments differently and observe a "wave part" of the photon.
When we settle instruments to observe photon as a a particle, we will observe (detect) particle part of the photon, when we settle instruments to observe photon as a a wave, we will observe (detect) wave part of the photon. Scientist (Observer) should not play any role in this experiment.