Is light always in motion? If so is it relative to the speed of light away from the source?
341703
Yes, and no- The theory of relativity states that light moves at the same speed regardless of the viewer-it is "special relativity".  If you are riding a beam of light, and switch on a flashlight, that light will speed away from you at the speed of light.  However, to a person standing still behind you, both you and the beam of light you just sent out, are traveling at the same speed.  So, light is always in motion, but it is not relative to the source.  Light, no matter how fast you are moving or in what direction, always travels relative to you (and everything else) at the same speed.  All that will happen is a change in the frequency of the light.
630475
Theory of Relativity- Light is the one speed that does remain constant.
381943
As the others have said, all light travels at exactly the same speed.  This is even true if the observer and/or the  light source are moving very very fast.  Once this was proved by experiment, everyone was very upset until Einstein figured it out and showed that time and space can distort. If you want a real bad headache, you can read all about this.  If it doesn't give you a headache, become a physicist!
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.
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.
30733
If you were traveling at the speed of light, whether or not your lights work would probably be the least of your concerns.\n\nIn reality, the laws of physics prevent any object from traveling faster than the speed of light.\n\nSomething that is perhaps just as interesting, however, is what happens as your vehicle APPROACHES the speed of light.  Take a look at some of the work done by Einstein to get a general idea on that.
468247
The speed of light is constant, approximately 300,000km/second. \n\nThe principals of relative motion are that if you are travelling at a speed, and you look at something else travelling at another speed, your perception of the speed of that something else will be the difference between your two speeds. For example if you are travelling 60, and you get overtaken by someone going at 70, you perceive them to be travelling at 10, since they travelling at 10 relative to you. \n\nHowever, you can never perceive the speed of light to be anything different than it's constant value. Therefore, if you travel at half the speed of light, time actually slows down to half of what it normally is, since this is the only way for the speed of light to remain constant. \n\nTherefore if you travel at the speed of light, time stands still. To answer your question, I don't know what you'd see, but probably nothing!\n\nTheres a more complicated explanation involving the magnetic and electric fields of a photo of light, but that's the basics.
10713
no, only things traveling at speeds close to the speed of light experience the distortion of time.  Light itself doesn't have mass or anything, it's an electromagnetic wave.  And even if it did, time is only distorted for the thing thats moving at the high velocities, so you wouldn't ever know it.
13401
It's true that the speed of light is constant no matter what speed at which you or the source is moving.  This is a fundamental postulate of relativity, and there is no explination.  It's just accepted because our experiments indicate that it is true.  You used the formula "lights speed + X = actual speed"  this type of velocity addition is called "Galilean".  It turns out that speeds don't actually add that way.  Far out.\n\nWhere is the rest of the energy? Good question.  The frequency of the light you observe from the sun DOES depend on how fast you and it are moving.  The energy of each photon is given by E = hf, where f is the frequency of light.
706572
The answers already given are generally correct for light travelling in a vacuum. However, the speed of light slows down when it travels through any material substance (the exact amount depends on the material).
71955
Here are two explanations (neither particularly satisfying I will tell  you in advance.)\n\nThe first is that the speed of light (in a vaccuum) is a property of the universe that is measured the same by everyone, regardless of their motion relative to anyone else. This is a true statement born out by experiment, but it implies some very weird stuff.  One is that distance and time are not measured the same by people in relative motion.  Another is that you can never get closer to a beam of light going away from you (i.e. go faster than the speed of light).  If you could, you would measure the speed of light differently than someone else, and you would be special.  The basic idea behind relativity is that, with regard to the laws of physics, no one is special.  \n\nThe second unsatisfying answer is E=mc^2.  In order to go faster, you have to accelerate.  Acceleration takes energy, and an accelerating body has more mass than a body in a constant state of motion (increase E in that equation m has go up, because c is the constant speed of light).  It just so happens that the mass doesn't go up in proportion to the rate of acceleration, but in relationship to how close you are to the speed of light.  Everytime you halve the distance between your speed and the speed of light, your mass doubles, and the amount of effort needed to get that next bit of acceleration doubles.  Getting to the speed of light would require infinite energy.
592518
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\nIgnore what the previous poster said, he is completely incorrect. The 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.
133450
well, the usual rules of physics at such speed don't apply. so when you turn the headlights, the light will travel from them at approximately the usual speen of light, and i guess you won't notice anything unusual..\nfor more information check the subject at wikipedia. and the following subject: Constant velocity from all reference frames
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.
24020
Neglecting the lengthy derivation of why light speed travel is impossible, the first postulate of relativity is that light has the same velocity regardless of how fast you're moving.  So, at ANY speed you can achieve in your car, when you turn the lights on you'll see the waves moving away from you very very quickly.
1149766
No, photons of light all travel at the same speed.  The different colors are because the photons oscillate at different frequencies, and the different frequencies of light are refracted (bent) at different angles with respect to the intersection with the surface of the prism (which is what the diamond acts as).  Yes, all the color frequencies exist withing white light.  In fact, pure white light almost never exists.  The spectrum of light from sources like the sun, fluorescent or incandescent bulbs all have flaws which can be read when they spectrum is spread out by a prism.  These flaws are indicative of the type of material that is producing the light.