what is the speed of light?
474792
(m)\n\nThe speed of light in a vacuum is exactly 299,792,458 metres per second (or 1,079,252,848.8  km·h-1, which is approximately 186,282.397 miles per second, or 670,616,629.4 miles per hour). This value is denoted by the letter c, reputedly from the Latin celeritas, "speed", and also known as Einstein's constant. Note that this speed is a definition, not a measurement, since the fundamental SI unit of distance, the metre, has been defined since 1983 in terms of the speed of light—one metre is the distance light travels in a vacuum in 1/299,792,458 of a second. The speed of light through a transparent medium (that is, not in vacuum) is less than c; the ratio of c to this speed is called the refractive index of the medium.
185936
At ground zero, a significant fraction of the speed of light. However at a short distance it diminishes to the speed of sound.
327223
1 lightyear is the distance a beam of light can travel in a vacuum in one year.  Given that the speed of light is roughly 3*(10^8) meters per second, or about 670.6 million miles per hour, then 93 million miles is about 1.58*(10^-5) lightyears.  Another way to look at it, is that it takes about 7.21 minutes for light from the sun to reach earth, and they are roughly 93 million miles apart.
71455
http://en.wikipedia.org/wiki/Speed_of_light#Measurement_of_the_speed_of_light
344154
Scientists have defined the speed of light in a vacuum to be exactly 299,792,458 meters per second (about 186,000 miles per second).\n\nThis definition is possible because since 1983, scientists have known the distance light travels in one second more accurately than the definition of the standard meter. Therefore, in 1983, scientists defined the meter as 1/299,792,458, the distance light travels through a vacuum in one second. This precise measurement is the latest step in a long history of measurement, beginning in the early 1600s with an unsuccessful attempt by Italian scientist Galileo to measure the speed of lantern light from one hilltop to another.\nMicrosoft ® Encarta ® 2006. © 1993-2005 Microsoft
426222
The speed of light is the same no matter where it is. It is 299,792,458 meters per second.
676715
The speed of light is the upper limit of speed in our space-time universe. Nothing here can be faster. And no car or any other macroscopic object can be equal to the speed of light. But the question is a thought experiment, hence, a good one indeed. Questions like this were raised by Einstein and Relativity became part of modern physical theory.\n\nSince the speed of light is an upper limit, the light from the headlamp of the relativistic car cannot be faster than the car. You won't see them in front.
1186727
It is a failing of the current theories of physics that the values of the key fundamental constants - of which c is one - cannot be derived but have to be measured and inserted into the equations. In other words, no-one knows what determines the speed of light.\n\nIt is true that the permittivity and permeability of free space are related to the speed of light, but the relationship is the other way around - they are what they are because the speed of light is what it is.\n\nThere have been two sources of thoughts that the speed of light may vary over time. One is theoretical, because it may help the sums work better when describing the early universe (i.e. moment after the big bang).\n\nThe other is experimental, and is controversial as it has not been independently confirmed (see link). This involves looking at light from galaxies so far away the light took billions of years to reach us - ie we are looking back to the early universe. But the measurements show a change in the fine structure constant, and not c directly, so there could be other sources of the discrepancies if the measurements are correct.
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The speed of light is a CONSTANT and has the symbol c in Science and is measured in meters per second.\n\nc (the speed of light) is equal to 3 times 10 to the power 9.\n\nNow 3x10*9 meters per second equals 3000000000 meters per second. (3 then nine zeroes!).\n\nc is important in physics because nothing can go faster than  c. \n\nNothing can go faster than the speed of light and as Einstein showed with the Theory of Relativity (a very important theory in physics) when an object (mass if you will) approaches c it gets bigger and bigger!! \n\nIf it gets to c then its mass will become infinite - this is impossible! An object with infinite mass! Hence it is impossible to reach the speed of light. \n\nHope this helps.
532772
nothing but light can travel at light speed.  the faster you go, the more energy it requires to accelerate.  at speeds that are close to the speed of light, you would need what is basically an infinite amount of power to accelate.  with current technology, it is impossible.  the only reason light can travel that fast, is because when it is created it is already traveling that fast.  it doesnt have to accelerate.
61325
the Flash @ speed of light ;)
406703
the speed of light is c=3*10 at the 8-th power  m/s\ndark means 0 light
630475
Theory of Relativity- Light is the one speed that does remain constant.
1103100
Here's the equation T = T' / sqrt[1- (v^2/c^2)]\n\nT is time measured by an observer at rest.  T' (read: T prime) is time measured by a moving observer.  v is the moving observer's velocity and c is the speed of light.\n\nThe speed of light is very fast.  So if v is 100 mph or 10 000 mph when you divide it by a number like c (186000 mps that's miles per second so a huge amount of miles per hour)  the v^2/c^2 value is zero and T = T'/sqrt (1) which is T = T'/1 so there is no measurable difference.  \n\nBut plug in 9/10 c for v.  That means an object going 9/10 the speed of light.  You get T = T' / sqrt[1-(9/10c)^2/c^2]\n\nc^2 cancels out and you get T = T'/[sqrt 1-(81/100)] T would be 2.2 times T'.  More time transpired for the non moving observer.\n\nHow did we get the equation?  Einstein was really smart.
846108
i dont know the exact speed but its faster than the light. want proof darkness is always been there before the light. " at first there was darkness then ...'let there be light" - genesis
547699
Its a myth that thought is particularly fast- We can measure the speed that signals travel along nerves, in the spinal cord, brain, etc, and it's around 20-60 meters/second.  Not nearly as fast as light (186,000 miles/second).  Photons don't "accelerate" to the speed of light-that speed is a stable property of photons, thus they are going that speed at the instant they are created-they dont start from motionlessness and speed up.\n*edit* Mich is right-light can be slowed and accelerated, but again, a photon upon creation does not accelerate to it's maximum speed (whatever that is given the medium that it's in)-it starts life going at that speed.  All light does *not* travel at 186,000 miles/sec- that is the speed of light in a vacuum-the speed varies with the medium that light is traveling through.  The speed of light through normal clear glass, for example, is around 120,000 miles/sec.
475201
velocity is just a term that means "speed" - the distance traveled per time unit \n\nthe "speed of light" is a number - the actual speed (velocity) that light travels, usually reported in meters/second (distance/time)