When the speed of light will be decreased?
“The velocity c of light in vacuum is the same in all inertial frames of reference in all directions and depend neither on the velocity of the source nor on the velocity of the observer” Einstein’s theory of special relativity says that the speed of light in vacuum is always measured the same (at 299,792.458 km/s) however this is only true locally for systems that are inertial, which means not accelerating. From Newton’s second law: if forces exist implies acceleration exists; this means that if you are in a spaceship and fire your rockets then you are not inertial. The other factor besides acceleration is gravity. Albert Einstein himself emphasized in his paper in 1917: “The results of the special relativity hold only so long as we are able to disregard the influence of gravitational fields on the phenomena” In 1915 (10 years after Special Relativity) Einstein developed another theory called General Relativity that deals with gravitational fields and according to this latest theory th
However, the speed of light is not constant as it moves from medium to medium. When light enters a denser medium (like from air to glass) the speed and wavelength of the light wave decrease while the frequency stays the same. How much light slows down depends on the new medium’s index of refraction, n. (The speed of light in a medium with index n is c/n.) The index of refraction is determined by the electric and magnetic properties of the medium. For air, n is 1.0003, for ice, n is 1.31, and for diamond, n is 2.417. The bending of the light you mentioned upon entering a denser medium is how lenses work. Although the speed of light is no longer constant when we think about different media, we do know that light always travels fastest in a vacuum. Nothing can reach speeds faster than c (well that’s not exactly true, see here for more details). Thus from our equation v=c/n, n must always be greater than 1. Light moves slower through denser media because more particles get in its way. Each
