Fortunately, this situation never occurs till now. If photon does have static mass, then we should observe the attractive force between photons, and this attractive force among photons will make the photons self focusing, then all photons will focus together that will be terrible situation due to the huge energy concentrated at one point. In literature, some scientists propose the photon has static mass but is still not accepted generally yet. Where F is the force resulting from the interaction between the electromagnetic spacetime and “pure” spacetime, which is an attractive force among the photon m is the mass of the photon. Following the Newton mechanics, if we ignore the difference between dt for “pure” spacetime and dt’ for electromagnetic spacetime, then we get To do so, we have to mo- ve faster than the electromagnetic wave to get out of the electromagnetic spacetime, that means c − c' 0. If we hope to measure the absolute speed of light, we have to stay outside the electromagnetic spacetime. That is why we always get the same speed of light which is irrelative to whether the light source is moving or not.
That means the electromagnetic wave speed is the same as that of “pure” spacetime we lived in, then, we can’t independently determine the speed of light because we can’t find independent reference for this measurement. (8), we found they all keep the same formulation as standard wave equation. Where c’ is the electromagnetic wave propagation speed. Now we consider the variation of electric and magnetic fields with time for light.įortunately, Maxwell already did the work one hundred years ago. This means that any point in the spacetime behaves as a wave, which we can call the spacetime wave. (6) is the same as the wave equation, where the parameter c corresponds to the wave propagation speed. (4), we obtainīy defining, where c is the speed of spacetime variation, then, we have This result tells us that any point in our spacetime can be described by Eq. Supposing our universe is homogeneous in all direction, then, we haveĪnd using L to represent all the space dimensions, The more familiar words to publics are “empty” and “vacu- um”, but we prefer to use “pure spacetime” here and following.). Therefore, we can suppose (x, y, z, −it) to represent the spacetime (We can call “pure spacetime”. Then, the following question arises: does the spacetime change? Based on the astronomy observation, the spacetime not only changes but also changes in accelerating. In order to understand why the speed of light is constant, we have to make clear what is spacetime? The spacetime is the universe around us, which includes x, y, z, three space dimensions and t, one time dimension. As a first step in this effort, we have to go back to the beginning of the question: why the speed of light keeps constant? If it is true, why the light passing the sun does not follow the curved spacetime formed by the earth and the sun?Īll these questions make scientists explore the deep meaning of our universe or spacetime. Based on the relativity theory, the earth doesn’t turn around the sun but just follows the curved spacetime which is formed by the earth and sun. Only under this condition, there exists the possibility for the speed of light to keep as a constant. If the space is really curved and time is inflated, the ratio of space over time must keep constant. In the relativity theory, Einstein told us the curved space and inflation of time.
Einstein didn’t give the reason why the speed of light is constant, therefore, till now we still can’t understand how and why it is. When Einstein setup the relativity theory, he supposed the speed of light is constant and furthermore, nobody in our universe can go faster than the light. In the process of understanding the universe, the speed of light is a puzzle for human being to explain, that is, it doesn’t matter whether the light source is moving toward or away from us, we got the same speed of light.
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