Since school times, we know that the speed of light, according to Einstein’s laws, is an insurmountable maximum in the Universe. The distance from the Sun to the Earth passes light in 8 minutes, which is approximately 150,000,000 km. Neptune reaches it only after 6 hours, but spacecraft need decades to overcome such distances. But not everyone knows that the value of speed can vary significantly depending on the environment in which the light passes.
Light speed formula
Knowing the speed of light in vacuum (s ≈ 3 * 10 8 m / s), we can determine it in other media based on their refractive index n. The very formula of the speed of light resembles the laws of mechanics from physics, or rather, the determination of distance using the time and speed of an object.
For example, we take glass with a refractive index of 1.5. Using the formula for the speed of light v = c \ n, we find that the speed in this medium is approximately equal to 200,000 km \ s. If we take a liquid, such as water, then the speed of propagation of photons (particles of light) in it is equal to 226,000 km / s with a refractive index of 1.33.
The formula for the speed of light in air
Air is also an environment. Therefore, it has the so-called optical density. If in a vacuum photons do not encounter obstacles, in the medium they spend some time on the excitation of atomic particles. The denser the medium, the more time is spent on this same excitement. The refractive index (n) in air is 1,000292. And this does not deviate much from the limit of 299 792 458 m / s.
American scientists managed to slow down the speed of light to almost full zero. More than 1/299 792 458 seconds light speed cannot overcome. The thing is that light is the same electromagnetic wave as x-rays, radio waves or heat. The difference is only in the difference between wavelength and frequency.
An interesting fact is the lack of mass of the photon, and this indicates the absence of time for this particle. Simply put, not a second of time passed for a photon that was born several million, or even billions of years ago.