• In a nutshell... no. The speed of light depends upon where you're measuring it (the 'medium' in which the light is travelling). In a vacuum, the speed of light has been measured to be approximately 300,000,000 meters per second; but in air, water, or other materials (mediums) light does not move quite so fast. For a list of different mediums and the recorded speeds of light through them, follow the following link:
  • If we are on the subject of relativity, yes Einstien proved that light (in a vacuum) is a constant. He proved that nothing in the universe is travelling at the speed because as you near the speed of light your mass increases exponentially so something travelling at the speed of light would have an infinitely large mass. He also said that time is not a constant. So it would be true to say that the speed of light is a constant and time isn't.
  • Yes. The speed of light is always 3*10 ^ 8 m/s. However, it appears to take longer to move through matter (like glass, or air, or water) because it is absorbed and re-emitted by atoms, meaning it effectively has to travel a longer distance. But the photons themselves are always moving at c.
  • NO! It is not...well not always. As light passes through matter such as glass or water, it actually slows. Current experiments have shown that it is possible, using plasma and lasers, to slow light to around 30 some-odd miles per hour. Later experiments using the same method have actually trapped light. Reversal of the plasma state (the lasers where used to turn a gas into plasma) allowed the light to escape at it's normal speed later, completely intact at any time the experimenter saw fit. So, it is, but it isn't.
  • This is several questions. 1) Has the speed of light been the same over the life of the universe? This is currently unknown, but there is some evidence it may have been faster in the past. 2) Is the speed of light the same in all materials? No, generally the denser the material the slower the speed. 3) Is the speed of light in a vacuum the same in all directions at all speeds when measured in modern times? Yes. One experiment found that the speed of light was the same in all directions to an accuracy of better than 2 parts in a thousand million million. 4) Is the value of the speed of light constant? In 1983 the speed of light was fixed to be 299792458 metres per second exactly. This is because the speed of light is so constant, that it makes more sense to define distances in terms of the speed of light instead of the other way about.
  • When using the speed of light in a formula, it is a constant value- 300,000 kilometers / 186,000 miles per second. Those numbers will always remain constant in math/physics equations, such as Albert Einstein's Law of Relativity, E=mc^2 (energy equals the mass of an object multiplied by the speed of light squared). Certain transparent and translucent objects can slightly change the speed of light, such as glass, plastic and water. These objects can refract, or bend, light. Because light passes through these objects and bends, you can see images of objects that do not look real. For example, if you have a pole or stick in a swimming pool or river, it looks like it is bent on an angle right under the surface of the water. This is due to the refraction of light.
  • Yes, In free space The speed of light depends upon the media it is traveling through. Light or photons are one of the most observed physical effects. Actually , their is still lots to learn about the photons. In effect ,the nature of light is still quite a mystery. Is it a particle or a wave? Optical experiments done over years of research show its both and has truely mysterious properties. Completely described in Quantium . The experts dont think so. but hey, what do i know
  • Speed of light is mathematically constant, but it has been found that it was originally faster than it's present speed, i.e 3*10^8 m/s (in vacuum). But the reason for this is not known till now. It might be so because right now we do not possess the mathematical and physical proficiency needed to answer this question. Hence, the speed of light may not really be constant. A useful website:

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