Does Cherenkov Radiation in atmosphere break the speed of light?
368030
The speed of light in matter is always less than the speed of light in a vacuum. It is the speed of light in a vacuum that cannot be exceeded. If a particle goes faster than the speed of light in whatever matter is around, Cerenkov radiation is given off. The radiation itself is a form of light, but it is made when something else goes through matter at a speed faster than light in that matter. \n\nFor example, the speed of light in water is only 75% of the speed of light in a vacuum. If a particle goes through water at 85% of the speed of light in a vacuum, Cerenkov radiation will be emitted.
811313
I believe it is expanding.  The speed og light, c, is the cosmic speed limit for objects or radiation within spacetime.  Spacetime itself can (hypothetically) expand faster than c, though what the limit to this might be I don't know.  Special relativity is not violated since there is no object being accelerated.
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.
353005
No. But, from the POV of the photon, they are everywhere along the path of the photon at once. See the answer on "lorentz contraction", because it's right, but I just wanted to clarify that photons are not, in fact, *everywhere* at once.\n\nOh, and from the POV of any subluminous velocity, no, they propagate at the speed of light, naturally.
1035026
The image of the laser beam would be moving faster than the speed of light.\n\nHowever, this does not violate Einstein's special relativity (the fact that nothing can travel faster than the speed of light).  The image of the laser beam is not a "thing", i.e. something with mass.
399905
We've actually run experiments that EXCEEDED the speed of light - which means the observer detected a particle before it left the emitter.  Wish I still had the link to give you.\n\nWeird science.  But real.
681287
OK-Simple and understandable.\nLight is actually small quanta of energy called photons.\nWhen these photons are propagated or travel through a medium, they are only allowed to travel as fast as the medium will allow.\nHydrogen will only let light travel at a certain speed, and that speed is always the same for light travelling through hydrogen.\nLight actually has a different constant for each medium that it is propagated through.\nSo regardless of how fast the light source is travelling, the photons will only propagate at a set speed.\n\nThe closest example would be sound waves. They can only travel at a certain speed as well within a given medium. Once the source of the sound catches up to and passes the sound, it creates a sonic boom.\nSo again, regardless of the speed of the jet, the sound it creates can only go so fast.\n\nThe constancy of the speed of light actually applies to the speed within the medium through which it is being transferred.\n\n\nHope this helps
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.
1109557
1) You must first of all be aware that radio waves, light, infrared, x-rays, all these are electromagnetic radiation, only with different frequencies; they are pure energy, without mass, transmitted through space by photons at the speed of light. That is the fastest way of communication there can be in the universe, assuming that nothing travels faster than the speed of light.\n\n\n2) Radio waves were chosen from the electromagnetic spectrum because they include the Water Hole, which is the band of electromagnetic frequencies between 1420 MHz and 1640 MHz. This is the band between the hydrogen line and the strongest hydroxyl spectral line, and is notable because it is a quiet region between two notable frequencies; The combination of hydrogen and hydroxyl yields water (the "water" part of the name); the "hole" part refers to the sudden drop in radio noise (the universe background radiation) within this band. Several SETI programs, including SETI@home search in the Water Hole.\n\n\n3) It has been proposed that higher frequency signals, such as lasers operating at visible light frequencies, may prove to be a fruitful method of interstellar communication; at a given frequency it takes surprisingly small energy output for a laser emitter to outshine its local star from the perspective of its target.\n\nOther more exotic methods of communication have been proposed, such as modulated neutrino or gravitational wave emissions. These would have the advantage of being essentially immune to interference by intervening matter, but are very difficult to generate or detect with current technology.\n\nSending physical mail packets between stars may prove to be optimal for many applications. While mail packets would likely be limited to speeds far below that of electromagnetic or other light-speed signals (resulting in very high latency), the amount of information that could be encoded in only a few tons of physical matter could more than make up for it in terms of average bandwidth.Starting in 1979, Robert Freitas advanced arguments for the proposition that physical space-probes provide a superior mode of interstellar communication to radio signals, then undertook telescopic searches for such probes in 1979 and 1982.
600967
No there is no 'summation' of speeds involved with light.  Light is Electro-Magnetic Energy, although light travels as particles as well as waves.  In this Universe the speed of light is a constant, roughly 186,000 miles-per-second, or 300,000 km/sec or 300 Mega-Metres / sec.  Unless some POWERFUL external force acts upon light, it cannot change speed.  This entails the gravity of black-holes and such. (Not even light can escape from them.)\n\nA vehicle might weigh somewhere in the neighbor-hood of 3,300 lbs. (Approximately 1,500 Kg, for those of you who have not learned to count properly, just yet ...)\nCheck out da' math ...\n\n60mph = 100 kmph = 27.77r mps. \n(1,500 Kg x 27.77r mps) / 9.81 mps = ~ 4,246 N\n\nI doubt, very seriously, that a little over 4,000 Newtons is enough force to even put a dent in the factor of light-speed.  For more info, look-up Einstein's Theory of Realtivity' (Although I believe 90% of it to be short-sighted ancient crap ...)  This subject is covered in it ...\n(umm covered in Einstein's Theory, not copvered in crap .. which err .. is the same thing at times ...
223333
Light is a bit pardoxical in that it exhibits characteristics of both a wave and particle, depending how you test it.  In physics this phenomena is referred to as the wave-particle duality (see 2nd ref below) and will probably never be fully resolved until physicists succeeds in finding the long sought unified theory meant to bridge the gap between gravity and electromagnetics.\n\nTo answer your question the maximum speed of light in a vacuum is approximately 3 x 10^8 m/s
113572
I too would be veeerrrrry interested in seeing some evidence for this claim from a non-creationist source. I keep an eye out for this sort of thing out professional as well as personal interest and I can't recall seeing anything like it.\n\nRoger are you absolutely certan that you haven't misundertsood the phase velocity experiments of Wang? They were done around that time (published 2000 IIRC). But they never shattered the speed of light or anything like that, no  did Wang et al ever make such a claim.\n\nTo help you out Roger, folow the link below? Is that what you arehtinkng of? If so you have misunderstood the results entirely.\n\n" Wang et al. (2000), who produced a laser pulse in atomic cesium gas with a group velocity of 310+/- 5 C. In each case, the observed superluminal propagation is not at odds with causality, and is instead a consequence of classical interference between its constituent frequency components in a region of anomalous dispersion (Wang et al. 2000)."\n\nIOW the speed of light wasn't exceeded by a particle, massless or not. It was the speed of the frequency change wihtin the medium that was 300 times faster than light. Perhaps the easiest way for a layman to understand this is to imagine one of those Newton's Cradle's toys. (see link 2). \n\nWhen you let go of one ball the motion is tranferred through the two intervening balls to the other end, causing that ball to fly up. That motion is is transmitted at near enough the speed of sound. IOW when the dropped ball hits the suspended balls the motion is passed along at the speed of sound. \n\nBut, and this is important, the ball itself wasn't travelling at the speed of sound. Nor did the ball on the end fly out at Mach 1 just because the motion was tranferred at MAch 1. The motion of the drooped ball was transferred at Mach 1, but at no stage was the ball or anyhting else actually travelling at Mach 1.\n\nWang's experiments did approximately the same thing using photons rather than metal balls. By some very clever work they managed to induce a phase change within the Cesium medium. In essence the Cesium atoms became the middle balls in newtons cradle. When light  hit an atom on one side it caused a phase change that was then passed on to the next atom, then the next and so forth, all at 300*C. But it was the phase change that was moving at that speed, not photons, not even electrons, just a phase change.
297054
heres the info:\n\nNobody has ever managed to ride a beam of light, although Einstein in his youth imagined what it might be like to do so. Such thinking eventually lead to the special theory of relativity. Although it is still impossible for anyone to travel on a light ray, physicists have managed to stop a laser beam in its tracks! This amazing result builds on earlier work by a research group led by Lene Hau in which light was slowed to 38 miles per hour.\n     Light in a medium travels somewhat slower than 300,000 kilometers per second, its speed in a vacuum. This effect, known as refraction, is responsible for the bending of light in passing from one medium to another. In an ultracold gas of sodium atoms, the index of fraction varies significantly with the frequency of light. The gas is normally opaque, but when the sodium atoms are bathed with secondary "controlling" laser light of a particular frequency, the medium becomes transparent and light can pass through it. Due to the varying index of refraction, a primary laser pulse slows down when it enters the gas. It also becomes greatly compressed. A pulse with a length of one kilometer gets squeezed into a tiny unit one one-thousandth of a meter in length. When the light pulse exits the region of sodium atoms, it expands back to its original length zooming off at 300,000 kilometers per second again. \n     To bring the light to a standstill, Dr. Hau and her co-workers turn off the secondary controlling laser light after the impinging laser beam has entered the ultra cold sample. The medium becomes opaque. One would think that the laser pulse would be absorbed by the sodium atoms. Instead, the information about the light wave is encoded in the atoms. When the controlling laser light is turned back on, the atoms reconstruct the laser beam. It continues its propagation though medium and then out the sample. If the time during which the beam is halted is not too long, the shape of the reconstructed beam coincides to a high degree with the original shape.\n     Imagine a train one kilometer in length consisting of thousands of cars traveling at 300,000 kilometers per second. Suddenly, the track becomes rough, causing the front engine and subsequent cars to come to a screeching slowdown. With the train now moving at 38 miles per hour, the cars pile up and are crushed to the size of an ant. Then a magician snaps her finger and the train disappears but leaves an imprint on the dirt between the tracks. With a second snap of the finger, the imprint vanishes while the ant-sized train reappears and moves forward at 38 miles per hour again. Then the train encounters smooth track. The engine speeds off at 300,000 kilometers per second, and as subsequent cars enter the smooth track region, they too rapidly speed off so that the entire accordion-like structure unfolds. Remarkably, little damage to the train occurs.\n     "Impossible!" You say. Well, in the case of a train, it is impossible because the deformation of metal is an irreversible process. But light is more accommodating and can be stretched or compressed more readily. Still, Dr. Hau's team has done what seems to be magical. Why isn't the light absorbed and lost? How can the atomic information reconstruct the beam? Why isn't the beam greatly distorted when it leaves the sample? The answers to these questions reside in the miracles of quantum mechanics, the dynamics that control the microscopic world of atoms and their interactions with light.\n     A major technological breakthrough has occurred. If low cost means are found to manipulate light in the above manner, then computers and communications will be revolutionized. One can imagine using light instead of electrons to perform computational processes. Such photonic machines would calculate at many times the rate of current computers.
25993
No.  No terrestrial object can travel at the speed of light.  If you were traveling at the speed of light you would literally dissentigrate from the millions of pounds of air resistance pinning you down.
1107829
There is no question that light obeys its speed limit. And I agree with the many others who said that light will travel to infinity unless it is absorbed by matter. But what if there were a distance limit? Now it may not make sense to say that a photon of light has a distance limit, but it could possibly be correct that photons of light have a lifetime, albeit very very long. \n\nScience theorizes that the 3-degree Kelvin background radiation we see everywhere is what is left from the initial Big Bang. Based on this temperature, cosmologists tell us the universe is somewhere between 11.2 billion to 20 billion years old. BUT, what if photons decay like radioactive particles and have a half-life? What if their half-life were 1 billion years? There would be too much 3-degree background radiation around to be explained by a universe between 11.2 billion and 20 billion years old. So the universe would have to be much younger and as a consequence, much smaller. \n\nYour question provoked a cool idea which I'm sure has been provoked' before.
697266
In a vacuum, the speed of light is 299,792,458meters per second and sound is 344meters per second at sea level and 70deg Fahrenheit.\n\nHowever, these speeds are dependent on various outside factors--namely the material they are passing through.
612849
NO energy, matter, or information has EVER been observed to exceed the speed of light.\n\nTheoretically, there are particles known as "tachyons" ( see wikipedia ) that travel ALWAYS in excess of that of light but never AT or BELOW that speed. Although never observed, their theoretical existence has sent many physicists to look for them ( or their trails ! ) \n\nthere are many abstract entities that "travel" faster than light.  for example, the shadow of a large celestial object ( a planet say ) on another celestial object can be observed to move at great speeds.  a shadow however is not a real entity ( i.e. mass or energy ) and it cannot convey information.