Isn't it true that in some experiments, people have actually sped up & slowed the speed of light?
104857
The speed of light varies depending on the medium it is passing through. The optical density of the material it is passing through is used to find the speed of light through the material. \n\nWhere c is a constant is in a vacuum. If that is what you are referring to, I have no idea.
70170
When someone answers this, I hope they can explain the Doppler effect if they backup Einstein's theory that light maintains a constant speed.
49096
You can't go the speed of light, but even if you were going 99.9999999% the speed of light, yes, you could shine the beam forward, backwards, or sideways, and it would look normal in every direction.  That's the central idea behind relativty.\n\nAnd NO, the light would NOT be going twice the speed of light.  Anyone who says that is BSing you.
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.
1028951
The example of each person going faster than the previous assumes a consistent additive nature of speed which unfortunately falls apart (shown by experimentation) as your speed approaches the speed of light.\n\nSpeed is not absolute in the sense that there isn't a universal stationary reference point.  If there were, then the example will apply.  According to experiments, however, something travelling away from you at light speed will do so regardless of whichever direction you happen to be moving.  This is not something to reason about (nobody arbitrarily made up this rule so that philosophers can find loopholes around); it's just what's been observed so far.\n\nThe Wikipedia article at http://en.wikipedia.org/wiki/Speed_of_light explains it a lot better than I can.  Jump to the section "Constant velocity from all reference frames" for the discussion applicable to this example of yours.\n\nHowever, an article at http://science.howstuffworks.com/news-item6.htm suggests that at least two experiments (pending validation) may have found exceptions?
15796
Its not proven but heres how eistine put it.\n\nThe faster you travel the more you weigh. Since light is the fastest moving thing in the universe if you went faster then that you would way infinite pounds and that would be impossible so you cannot go faster than the spped of light
178453
Ignore the other retards who answered this.  This is actually a very intelligent question.  If you look into Einstein's theory of special relativity, you will see that no matter how fast you go (including light speed itself) light will always appear to be traveling at the same rate to you.  That means that you would still observe your headlights the same as usual.  They would still be ahead of you.  That also means that your time is slowing down greatly.  If there were a video camera on you while you were traveling this fast and someone were watching you on a monitor from the comfort of their own home, it would appear to them that you are almost frozen in time because your time reference would be so slow.  To you, your time would seem to go by at a normal pace.
409498
By traveling faster than the speed of light.  As velocity approaches the speed of light, time slows down.  Traveling faster than light speed then - would make you travel back in time.  Theoretically, it is possible (according to the theory of relativity) but scientifically, it doesn't seem possible.
11066
well first, read my other answer to your question about the speed of sound.  You would probably expect the answer to be the same, and the light to reach the other car, but this is a special circumstance because nothing can travel faster than the speed of light, not even light itself.  when a beam of light is shone ahead of a rapidly moving space vehicle, and is expected to be moving at the speed of light plus the speed of the vehicle, it is still only moving at the speed of light, which is puzzling.  Physicists have defined the speed of light to be the ultimate cutoff point for speed.\n\nAnd also, you wouldn't be able to travel at the speed of light anyway because time would probably stop since it does get slower and slower the faster you go.  Velocity warps time, the faster you go, the slower time moves for you relative to a stationary object.  I've read this, and it is definately true, we had to derive the formula in physics from, and calculate the time, lenghth(which decreases with speed), and mass (which increases with speed) distortion as well.  The effects of this are very negligable unless you are moving at speeds very very close to the speed of light, at least over 90% of the speed of light, and we haven't gotten anywhere close yet.  The denominator of this factor that time, length, and mass are distorted by actually is 1 minus the square root of the speed of light(c) over the speed in which the object is traveling (v), so the reason you can't go faster than the speed of light is because if v was greater than c, then that square root would be greater than one, meaning the denominator would be negative, meaning the factor would be negative, and the light would actually be travelling backwards in time...\n\nIf you find any of this interesting, I highly recommend "The Elegant Universe" by Brian Greene.
27573
No. There is no practical possibility. Humans can't travel at a speed equal to or greater than that of light.
144613
light rays do not move faster or slower than the speed of light.  the speed of light is the speed of light, period.\n\nthat said, light often travels *slower* than c, which is a constant defined as the speed of light IN A VACUUM, approximately 3x10^8 m/s.  here is a way you can actually observe some honest-to-god light traveling slower than c:\n\nstep 1.  find a window.\nstep 2.  look at it.\n\ncongratulations, you have observed light traveling slower than c.  in ANY medium (air, glass, water - you name it) the speed of light is slower than the speed of light in a vacuum.  \n\nin fact, the so-called index of refraction (n, which equals 1.4 for glass) is defined as the ratio of c to the speed of light in that material.  generally, denser materials have a higher index of refraction, and people have been able to make light go REALLY slow by making some very dense materials.  all of this is perfectly consistent with general relativity.\n\nas for FASTER than c:  under certain conditions, it is possible to make photons with a "phase velocity" that is greater than c.  however, when people speak of the speed of light, they usually refer to the "group velocity".  the distinction between phase velocity and group velocity is kind of technical; but phase velocity refers to the speed at which the individual phase fronts propagate through space.  \n\nit is possible to make these phase fronts go faster than c; but because the energy or information or whatever carried by the light travels at the group velocity, the actual speed (as far as stuff like general relativity is concerned) is still less than c.\n\nanyway, all of these results are entirely consistent with general relativity.  in fact, i don't know of any published results of a scientific experiment which are not consistent with GR.  \n\nthe fact that einstein's theory, largely concocted out of the blue from basic principles and logical reasoning, has stood the test of time for so many years is a testament to the genius of the man's work.\n\nhere are some links to learn about phase velocity, group velocity and the speed of light:\nhttp://en.wikipedia.org/wiki/Group_velocity\nhttp://physicsweb.org/articles/news/4/7/8/1
166913
Actually, photons in vaccum are found to travel sometimes faster and sometimes slower than speed of light, but during very brief instants of time. If you are measuring velocities in a distance thats long enough (always in terms of atomic distances) the avarage speed turns to be the speed of light. But if you are measuring shorter distances (I don't know how short it has to be) you have to take into account that maybe you will measure a higher or lower speed than the light speed.\n\nWe can say that photons have a very high probability of travelling at the speed of light, and very small probabilities of travelling a bit faster or a bit slower. If the distance is long enough, the faster velocities will cancel with the slower ones, and the avarage will be light speed.
559732
No, it's not true.  You can only occcupy one person-sized point in space at any given time, no matter how fast it's moving.\n\n\nAs a though experiment, though, if you were to run very much faster than light, it might be possible for you to arrive back at the starting line in time to see the IMAGE of yourself departing.  \n\n\n"There was a young man, named Bright\nWho travelled much faster than light.\nHe went out, one day, in a relative way,\nand came back the previous night."\n\nThe rumbling sound that you can hear is Einstein revolving in his grave, at near-gyroscopic speeds...
1011227
Love to give you specifics, but don't know how.\n\nTheoretically, what you suggest is possible by relativistic theory. There are things called "tachyons" which are these kinds of rays which reverse time - well not "reversing" it, but definitely messing it all around.  Einstein said that nothing could accelerate to faster than speed of light without becoming infinite mass - but "...Einstein said nothing about entities already traveling at that speed or greater..." (Prote in K-Pax).  \n\nSo who knows - is it around the corner for us?  Probably not.  Is it possible?  I love this universe, so I say yes.  Keep surprising me...
596319
There is a big difference between predictions that the speed of sound could not be broken and that the speed of light cannot. It was always known that *some* things can go faster than sound. Bullets for example. The question was whether we would have the technology to get people to that speed.\n\nThe speed of light is very different since we haven't seen *anything* go faster than light in a vacuum. Nothing. Ever. Furthermore, the predictions of special relativity have been verified in particle accelerators when the particles are going to within a hundred thousandth of the speed of light.\n\nAs an example, at Fermilab protons are accelerated to energies of 2TeV. This is over 2000 times the rest mass of those protons. To accelerate something the mass of a *gram* to an equivalent speed would take about the energy of the largest hydrogen bomb ever exploded. This amount of energy would be needed for each gram to get to that speed, so multiply it by 75000 for a medium sized human. And that doesn't count the spaceship they would have to travel in!\n\nNow, this is how much energy is needed to get to speed we *know* about. To go faster would require even more. Unfortunately, we have never seen a wormhole of any type. But the predictions are that the energy requirements would be even more prohibitive than what I just described.
329962
Here is the correct answer....the speed of light is constant IN A VACUUM.  Light is most certainly slowed down by matter, and can be shifted by gravity.
1084318
Actually, the way modern physicists think of it, the question doesn’t quite make sense.  The problem is the “traveling at the speed of light” part, because one of the conclusions of Einstein’s Special Theory of Relativity is that nothing can travel that fast.\n\nInterestingly, though, its was consideration of a similar question that started Einstein down the path toward relativity… Light is best described by Maxwell’s Equations, which predict that any experiement will measure same speed for light in a vacuum.  When Einstein thought about traveling at the speed of light, he realized that there must be a problem.  In fact, Maxwell’s Equations don’t allow for a “standing wave” solution, which is what a light wave would look like if you were traveling at the speed of light. \n\nSo Einsten took things back to basics, which is what he was good at.  Let’s start with what he actually said… His Special Theory of Relativity started with two postulates (or assumptions): 1) that the laws of physics are observed to be the same in any non-accelerated “reference frame” and 2) that the speed of light (c) is observed to be the same for all observers.\n\nThe first assumption basically says that as long as you’re traveling at a constant speed, all your experiments will give the same results.  That seems reasonable.  But the thing about the speed of light always being the same sounds a little odd: the Michelson-Morley experiment (and others) had detected no change in the speed of light when measured from a moving frame of reference, however, and as I already mentioned, Maxwell’s Equations yield a specific value for the velocity of light.\n\nStarting from there, Einstein worked out how to add velocities together, and it comes out to be not simple addition, but a fraction that never gets larger than c. Basically, what happens is that the measurement of time and distance changes, so a physical object (e.g., a spaceship) can never achieve lightspeed.\n\nSo”  That’s a long-winded way of saying that your headlights themselves can’t travel at the speed of light.  If we want to think about them traveling very, very close to the speed of light, however, we realize that the light they emit still travels at lightspeed (as measured by the fast-moving headlights themselves), so they stil work the same way headlights would work on a car traveling much slower.\n\n\nRyan Wyatt\nRose Center for Earth & Space\nNew York, New York