Where can i find a vacuum light?

Does light accelerate in a vacuum? Would you use Calculus to find out the speed of light in a vacuum, seeing as you would have to multiply and divide by 0? How much does light slowdown on earth? How much does Air slow Light down?

• Answer:

  1) Light travels in vacuum at a constant speed. The speed of light in air is 99.97% of the speed of light in vacuum. 2) "The speed of light normally refers the speed of light in a vacuum, and is an important physical constant in modern physics. Light travels at different speeds through different materials, but in vacuum light travels fastest, and the speed does not vary with the color, intensity, or direction of travel. Perhaps more surprisingly, the speed also does not depend on the motion of the light emitter or the observer. Therefore it makes sense to speak of the speed of light, which is the speed of light in vacuum and usually written as c. The speed of light factors into much of modern physics, including special relativity, general relativity, and quantum mechanics. By everyday standards, light travels very rapidly - approximately 300,000 km each second, in vacuum or air. This is roughly a million times faster than sound, and fast enough to circle the Earth more than 7 times in one second. Such a rapid speed is very hard to measure without specialized techniques, and in ancient times the speed of light was the subject of speculation. The first effective measurements of the speed of light were made in the seventeenth century, and were progressively refined. Today, time intervals can be measured extremely precisely, to the point where the metre is now defined officially as the distance light travels in "vacuum" in 1⁄299,792,458 of a second. As a consequence, according to NIST: "… the effect of this definition is to fix the speed of light in vacuum at exactly 299 792 458 m/s." (Further discussion is found later in the subsection Speed of light set by definition.)" "Light is a type of electromagnetic radiation. According to electromagnetic theory, all electromagnetic radiation travels in free space at the speed of light in free space: 299,792,458 m/s. This definition applies regardless of the light's color, intensity, source, or direction. Examples of real media approximating ideal vacuum are: outer space, interstellar medium, interplanetary medium, quantum vacuum, QCD vacuum and ultra-high vacuum. Within experimental error, no variations have been found in the speed of light in these realizable media, so their behavior is well approximated as that of free space. Moreover, observations show the variation of the speed of light as the universe ages is less than two parts in 10^16/year, for both microwaves and visible light." "When a light pulse comprised of multiple frequencies passes through transparent materials, the speed of light is characterized by two speeds: the phase velocity and the group velocity. The phase velocity of light may be found from knowledge of the frequency-dependent refractive index: n = sqrt(εr*μr) = c0/vp where εr is the material's relative permittivity, and μr is its relative permeability. The group velocity of the wave is the speed at which the envelope of the pulse travels through the medium, and is dependent on the frequency content of the pulse as well as the properties of the medium. A wave with different group and phase velocities is said to undergo dispersion. If the light passing through the medium is monochromatic, the phase velocity is often referred to as the "speed of light". When light enters materials its energy is absorbed. In the case of transparent materials (dielectrics) this energy is quickly re-radiated. However, this absorption and re-radiation introduces a delay. As light propagates through dielectric material it undergoes continuous absorption and re-radiation. Therefore when the speed of light in a medium is said to be less than c, this should be read as the speed of energy propagation at the macroscopic level. At an atomic level, electromagnetic waves always travel at c in the empty space between atoms. Two factors influence this slowing; stronger absorption leading to shorter path length between each re-radiation cycle and longer delays. The slowing is therefore the product of these two factors. This reduction in speed is also responsible for bending of light at an interface between two materials with different refractive indices, a phenomenon known as refraction. The refractive index in air is only slightly larger than one. Denser media, such as water and glass, have refractive indices of between 1.3 and 1.5 for visible light. Diamond has a refractive index of about 2.4." Source and further information: http://en.wikipedia.org/wiki/Speed_of_light 3) "Light travels at a slightly slower speed, cg, through a gas than its speed through vacuum c. You may be forgiven for not having noticed this difference because it is generally small; typically a small fraction of a per cent." "the speed of light in air is c/1.000293. 99.97% of the speed of light in vacuum." Source and further information: "Understanding the properties of matter By Michael De Podesta" http://books.google.com/books?id=h8BNvnR050cC&pg=PA131&lpg=PA131