Is light always in motion?  If so is it relative to the speed of light away from the source?
337266
Um, well it depend on how you consider light. If you consider it as a stream of photons, then you might say that if you measure the positions of each of those photons it doesn't have velocity.\nIf you say it is a wave and always in motion then it is not relative to your velocity, exactly. Even if you were travelling at 30000000mph the light would still appear to be travelling at 3x10to the power of 8 m/s away from you. Light is the fixed speed limit for the universe. But at the far reaches where the material of space itself is expanding into nothing, it is expanding at a speed greater than the speed of light because that speed limit only applies to objects moving within the universe.
966236
No matter how fast you go or think you are going, light always appears to be going the speed of light.\n\nEven if you are going 0.99999999999 c from the viewpoint of an outside observer, you would still see light traveling at the speed of light around you. Now, light sent by objects moving at 0.9999999999 c towards you (those "ahead" of you) would be severely blue-shifted and light from objects moving away from you at that speed (those "behind" you) would be severely red-shifted.\n\nBut light from any object moving the same speed as you would look perfectly normal. In fact if you covered the windows of your spaceship (it better be a spaceship, since you won't be in any atmosphere for very long), you wouldn't know you were moving at all!
442563
There's a number of ways to answer this.  Einstein's theory of Relativity says that all things are moving at the speed of light through spacetime, with stationary objects moving wholely in the time dimension.  As you start moving, some of your velocity is directed away from time and in a physical dimension.  When you approach the speed of light, you are traveling very little in the time dimension and mostly in the physical dimesions.  If you actually reached the speed of light you would experience no time whatsoever; your entire trip across the universe would be one instantaneous flash.  However, the faster you travel, the more difficult it is to travel even faster.  When you are traveling relativistically, Newton's second law of F=ma no longer applies.  You continue adding force, but rather than creating acceleration, you'll begin gaining mass.
908254
If the flash light is stationary then the light would always be seen at the same distance (for example if the distance between you and the flash light is 100m at start, you would always see the light as 100m away from you) as the starting time as this involve relative velocity. however if you are holding on the flash light then it would be the same as you standing on 1 spot and turning on the flash light as the  velocity of the flash light would be the speed of light + the speed of you moving which is also equal to the speed of light as well. If you want to further understand it then you could go read more about relative velocity.
972241
Firstly, please allow me to substitute your term "speed" for the more accurate term "velocity".\n\nAll particles and waves have an intrinsic velocity  in a vacuum.  The subatomic particle which makes up light is the photon.  The photon travels at an average maximum velocity of 3x10^8 m/sec in a vacuum.  For the exact numerical speed, here is a good source\n\nhttp://en.wikipedia.org/wiki/Speed_of_light\n\nbut for the purposes of almost all calculations, 3x10^8m/sec is used.  There are physical forces which can slow down the speed of light, and the chief force is gravity.\n\nDarkness is the absence of light, and therefore, the absence of any photons. Therefore, the concepts of speed and velocity are not applicable.\n\nP.S.  There is only one particle theorized to be faster than the speed of a photon, or more aptly put, faster than the speed of light.  That subatomic particle is the "tachyon".  It is further theorized that , because it is travelling faster than the speed of light, it is also travelling backward in time.\n\nP.P.S.  Many of the theories in physics are derived from solutions to various "so-called" unsolvable problems derived from math theory.  In this sense , physics and math go hand in hand.  Therefore, many physics theories are simply supported by math equations until a real life proof can be generated, characterized properly, qualified, and quantified.  The problem here is that just because a math equation may have a solution , it alone BY NO MEANS is proof in and of itself of the existence of subatomic particles and physical phenomenae.  It can only be used as a measuring stick,of sorts,  in order to look for the existence, and therefore, FORMAL PROOF of such phenomenae.
506771
Actually by what Einstein explained, da light will still be in  front of da car, it won't go behind u no matter how fast u r going even if u r faster dan da speed of light. Weird? rit. I too thought so, It was explained in discovery channel. Well I'll try 2 explain it 2 u, But it wud hav been easier if I cud actually show it by som animations. When u r travellin at da speed of light, time stops. Ya it does. Time is somthin like per user setting, it is unique for u & each & every one. Think dat ur carrying an Einstein's clock, which is a simple devise with 2 mirrors facing each other with a photon bouncin of the mirror. Each time it bounces from a mirror u'll hear a tic sound, that will b 1 second for u. Say u travel at a speed little less dan light u r movin forward but da photon has 2 move a lot more distance than it initially had been, which was in a straight line, but now it's motion will b som what like a hypotenuse, so it has 2 travell more distance dependin on ur speed. So ur 1 sec will not be da same as 1 sec is for som 1 on earth. So actually ur headlight will be actually movin faster dan u no matter what
989387
The only thing that can travel at the speed of light is light. So basically yes.
227315
Speed of light in vacuum is given, but light travels at constant speed in any medium, but the magnitude of the speed might be different than any other medium. There was a discussion about that here before. You might wanna check that.
555954
Updated 1997 by PEG.\nOriginal by Philip Gibbs 1997.\n\n\nI am driving my car at the speed of light and I turn on my headlights.  What do I see?\n\nSadly this question and all others about experiences at the speed of light do not have a definitive answer.  You cannot go at the speed of light so the question is hypothetical.  Hypothetical questions do not have definitive answers.  Only massless particles such as photons can go at the speed of light.  As a massive object approaches the speed of light the amount of energy needed to accelerate it further increases so that an infinite amount would be needed to reach the speed of light.\n\nSometimes people persist: What would the world look like in the reference frame of a photon?  What does a photon experience?  Does space contract to two dimensions at the speed of light?  Does time stop for a photon?. . .  It is really not possible to make sense of such questions and any attempt to do so is bound to lead to paradoxes.  There are no inertial reference frames in which the photon is at rest so it is hopeless to try to imagine what it would be like in one.  Photons do not have experiences.  There is no sense in saying that time stops when you go at the speed of light.  This is not a failing of the theory of relativity.  There are no inconsistencies revealed by these questions.  They just don't make sense.\n\nDespite these empty answers, nobody should feel too put down for asking such questions.  They are exactly the kind of question that Einstein often asked himself from the age of 16 until he discovered special relativity ten years later.  Einstein reported that in 1896 he thought,\n\n``If I pursue a beam of light with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as a spatially oscillatory electromagnetic field at rest.  However, there seems to be no such thing, whether on the basis of experience or according to Maxwell's equations.  From the very beginning it appeared to me intuitively clear that, judged from the standpoint of such an observer, everything would have to happen according to the same laws as for an observer who, relative to the earth, was at rest.  For how, otherwise, should the first observer know, i.e., be able to determine, that he is in a state of fast uniform motion?  One sees that in this paradox the germ of the special relativity theory is already contained.  Today everyone knows, of course, that all attempts to clarify this paradox satisfactorily were condemned to failure as long as the axiom of the absolute character of time, viz., of a simultaneous, unrecognizedly was anchored in the unconscious.  Clearly to recognize this axiom and its arbitrary character really implies already the solution to the problem.''\n\nIn 1905 he realised how it could be that light always goes at the same speed no matter how fast you go.  Events that are simultaneous in one reference frame will happen at different times in another that has a velocity relative to the first.  Space and time cannot be taken as absolute.  On this basis Einstein constructed the theory of special relativity, which has since been well confirmed by experiment.\n\nQuestions of relative velocity in relativity can be answered using the velocity subtraction formula v = (w - u)/(1 - wu/c2) (see relativity FAQ: velocity addition).  If you are driving at a speed u relative to me and you measure the speed of light in the same direction (w = c in my frame), the formula gives v the speed of light in your reference frame as, v = (c-u)/(1 - u/c).  For any speed u less than c this gives v = c so the speed of light is the same for you.  But if u = c the formula degenerates to zero divided by zero; a meaningless answer.\n\nIf you want to know what happens when you are driving at very nearly the speed of light, an answer can be given.  Within your car you observe no unusual effects.  You can look at yourself in your mirror which is moving with the car and you will lo
1081423
the speed of light is constant no matter what your reference frame is, so the light from your headlights travels at the speed of light (as seen by you in the moving car and by a person standing on the side of the road)
990328
The speed of light is always constant in any reference frame.\n\nNo matter the reference frame, an observer will always measure the speed of light in a vacuum to be exactly,\n299,792,458 m/s.
688056
This question comes up very regularly. If you do a search you will find it has been answered dozens of times in the past few months.\n\nThe speed of light is an absolute constant. It doesn't matter what speed you are travelling at the light will always be travelling away from you at the same speed: the speed of light.\n\nThe freaky part is that the light from your headlights would seem to be travelling away form you at the speed of light (C), but to an observer who was sitting still the light would also appears to be travelling away from them at the speed of light. How can that happen? Well it's one of the tricky bits of relativity, but part of the solution lies in understanding that although light never slows down or speeds up relative to any observer it does change frequency.\n\nSo to you the light from your headlights will look quite normal, but to someone sitting still your headlights will appear to be emitting x-rays. The light would be invisible to them.\n\nThe corrolary of that is that any light approaching your windshield will be equally shifted into the x-ray part of the spectrum. Although the headlights will be emitting visible light, any time they strike an object and reflect back they will reflect back extremely low frequency light that is invisible to the human eye.\n\n\nSo no, it won't do a damn bit o good to turn on your headlights. That's not because the light won't travel, it will travel just fine. The problem will be that any light that reflects back off the road will be invisible to the human eye.
184096
Light travels at a constant, finite speed of 186,000 mi/sec
263084
The speed of light in a vacuum is constant.\n\nThe speed of light varies in other media.  It varies from medium to medium, such as glass versus copper.  It also varies within a medium depending mainly upon the density of the medium.  For example, the speed of light through air varies with the density of the air.
661036
Yes. Theoretically, if you try to determine the 'place' of a photon 'exactly' as if it is a particle, you will not be able to detect it's velocity. And when you want to know its 'exact' speed, you will have no idea about where it is, just like a wave.
630475
Theory of Relativity- Light is the one speed that does remain constant.
996962
The speed of light is a constant (186,000 mi per second) and does not change based on what it is travelling through.