Why does light have a FIXED speed????

why06 · Jul 29, 2006

If light speed is the fastet anything can ever go than why does it have a fixed speed - and 186,000 miles per second at that. 1. Why is this the fastest ligh can go 2. Can it only go this fast on earth 3. What equations brought this conclusion? <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

nova_explored · Jul 29, 2006

a photon travels at C, and is considered the upper bound in speed for many reasons. Namely: a photon carries information but does not exhibit any change in information. every other particle changes as it moves, as it changes it velocity, it's information changes as well. Photons do not. (they have no charge and can adapt to other enviornments, however breaking free again, they immediately assume the original properties with no exchange with mass or other particles.) For this reason it is considered a massless particle, also exhibiting the traits of a wave function. Since it is completely neutral, there is no interference, except by an atmosphere. Here it can slow down, but again, leaving the environment, it immediately resumes the constant C. and it is a constant for that matter. no additional energy is required to accelerate a photon to C. it immediately resumes C. and 186,000 just happens to be that speed that a photon resumes to. It was einstein's special relativity that brought this into light (pun intended). i'll let others bring forward the equations that use, and successfully reveal C, and it's attributes. hope that helps. <div class="Discussion_UserSignature"> </div>

mikeemmert · Jul 29, 2006

Because that's the way it is. Seriously. That the speed of light is a fixed constant of the Universe is not a dictat from authoritarian scientists. It was a fundamental discovery of the nature of the coordinate system itself. The Machaelson-Morley experiment to determine from which direction the speed of light was the highest, therefore determining Earth's direction with regard to "fixed" space, had an unexpected result: there was no such direction. The speed of light was the same in all directions. Michaelson and Morely and numerous other scientists repeated the experiment with ever increasing accuracy but always got the same result. Therefore, several theories of physics had to be thrown out. Einstein later showed that the entire coordinate system for measuring positions and velocities had to be thrown out and based on an unvarying speed of light. The corrections are negligible at low speeds, but at high speed, lengths are shortened. In fact, even time itself is affected by very high speeds.

derekmcd · Jul 29, 2006

Here's a real kicker... the speed of light is observed to be the same regardless of the relative motion of the observer. If I am traveling at 50% sol and turn on a flashlight, those photons will still travel at 300,000k/s away from me... a stationary observer in relation to me will also see those same photons traveling at 300,000k/s. That is what really makes it a fundamental constant of nature. <div class="Discussion_UserSignature"> <div> </div> <div>"If something's hard to do, then it's not worth doing." - Homer Simpson</div> </div>

alkalin · Jul 29, 2006

Here’s my take on light. I must warn that these notions are not standard physics concepts, so these ideas will not be seen by someone knowing physics as correct, so I’m sure that this will be pointed out. But I just want to give a little different perspective. Light has a wave that can be understood as spin. All other matter has a wave that can be understood as spin as well. It is the spin of the wave that gives light its fundamental velocity, but in relation to the spin of other nearby waves. So if you test the velocity of light on a test bench, its velocity will always be the constant we measure due to the nearness to the matter in the bench. It will make no difference as to the test bench orientation. Hence the failure of MM. Again these are speculations only, but spin can be equated to vibration, which string theory is all about. But importantly, this also implies that in the universe light velocity is not a constant everywhere relative to us. There would never be any proof of this statement just as there is no proof that light is a constant everywhere. But it would be true as someone here pointed out that if you traveled at great velocity and put light out in front of you, it would travel at c relative to you at first. But it would change wavelength and velocity as soon as it came close to other matter that traveled at other velocity. There would be a Doppler shift, which would change the wavelength to blue for someone in front of you. How would these views change our concepts of the universe? Well, we need to deal with other factors that effect light and its apparent shift. It was thought many years ago that light could not change its wavelength in free space since at the time no mechanism was apparent, so Walla, the expanding universe was born based on the Doppler principle alone. Today we know better about such things as correlation, but expansion notions of the universe keep expanding only in the minds of current cosmo

Saiph · Jul 29, 2006

why does light travel at 186,000 mph? Because of the way electricity and magnetism interact. Each force can induce the other. A changing electric field creates a magnetic field. A changing magnetic field creates an electric field. And of course, since a changing electric field is...well, changing, the magnetic field it creates is also changing which then creates a changing electric...and you get the idea. The rate at which these fields can create/change eachother, and thus propagate through space, is a fundamental property of the two forces. The speed, calculated from this "rate of induction", is found to be 1/sqrt(mu*epsilon). Mu and Epsilon are the two fundemental constants that govern the strength of magnetic and electrical interactions, and they're constant. As such the speed of light is constant (within a given medium). The highest speed for light, is when those constants have the smallest value...and that's in a vacuum. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

nova_explored · Jul 29, 2006

spin of the photon (1 i think) is a measure of angular momentum, or the amount of energy of the system. That light is only one limit in the electromagnetic spectrum (albeit the quantum - or base form), doesn't change velocity of the entire system, which is constant (see Saiph's post for the reason for this). <div class="Discussion_UserSignature"> </div>

enigma10 · Jul 30, 2006

So then, how fast does a nutrino travel? Axioms? Curious. <div class="Discussion_UserSignature"> "An organism at war with itself is a doomed organism." - Carl Sagan </div>

derekmcd · Jul 30, 2006

I'm sure you meant per second <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <div> </div> <div>"If something's hard to do, then it's not worth doing." - Homer Simpson</div> </div>

vandivx · Jul 30, 2006

<blockquote>In reply to:<hr />1. Why is this the fastest ligh can go<hr /></blockquote> I'd say that light always goes at speed c no matter what when it actually does 'go' what I want to say by that is that light goes slower in mediums like air and various materials because it gets absorbed and reemited on its way, if it weren't for this 'stopping', its speed would be as usual c but speed of light in materials or atmosphere is normally measured by the time it traverses between some points A and B macroscopicaly distant and that includes many such points where light got stopped before it continued on its journey to another such stopping point...so from that point of view, if you measure speed over longer distance in a medium, you get speed less than c vanDivX <div class="Discussion_UserSignature"> </div>

docm · Jul 30, 2006

Bottom line: light can go any speed between zero and c, depending on the transmission media, its refraction index and the environment. <div class="Discussion_UserSignature"> </div>

rhodan · Jul 30, 2006

From Ames Laboratory:<ul type="square">REVERSING AND ACCELERATING THE SPEED OF LIGHT Ames Laboratory researchers use metamaterials to alter light's path, speed AMES, IA – Physicist Costas Soukoulis and his research group at the U.S. Department of Energy’s Ames Laboratory on the Iowa State University campus are having the time of their lives making light travel backwards at negative speeds that appear faster than the speed of light. That, folks, is a mind-boggling 186,000 miles per second – the speed at which electromagnetic waves can move in a vacuum. And making light seem to move faster than that and in reverse is what Soukoulis, who is also an ISU Distinguished Professor of Liberal Arts and Sciences, said is “like rewriting electromagnetism.” He predicted, “Snell’s law on the refraction of light is going to be different; a number of other laws will be different.” However, neither Soukoulis nor any other scientist involved in efforts to manipulate the direction and speed of light can do so with naturally occurring materials. The endeavor requires exotic, artificially created materials. Known as metamaterials, these substances can be manipulated to respond to electromagnetic waves in ways that natural materials cannot. Natural materials refract light, or electromagnetic radiation, to the right of the incident beam at different angles and speeds. However, metamaterials, also called left-handed materials, make it possible to refract light at a negative angle, so it emerges on the left side of the incident beam. This backward-bending characteristic of metamaterials allows enhanced resolution in optical lenses, which could potentially lead to the development of a flat superlens with the power to see inside a human cell and diagnose disease in a baby still in the womb. ...( Full story)</ul>

vandivx · Jul 30, 2006

<blockquote>In reply to:<hr />The rate at which these fields can create/change eachother, and thus propagate through space, is a fundamental property of the two forces. The speed, calculated from this "rate of induction", is found to be 1/sqrt(mu*epsilon). Mu and Epsilon are the two fundemental constants that govern the strength of magnetic and electrical interactions, and they're constant. As such the speed of light is constant (within a given medium). The highest speed for light, is when those constants have the smallest value...and that's in a vacuum.<hr /></blockquote> the question should then be reformulated, instead of asking why the speed of light is what it is, we could ask why are the values of Mu and Epsilon what they are or alternatively, why are electric and magnetic fields found to be interacting at the rate that they do as to the thread title, <blockquote>In reply to:<hr />Why does light have a FIXED speed????<hr /></blockquote>answering that would mean putting in place new theory, physicists would answer 'because the speed of light is natural constant, one among the many measured', that's the best they can come up with today vanDivX <div class="Discussion_UserSignature"> </div>

Saiph · Jul 30, 2006

rhodan....that makes my head hurt. I've heard of similar things before, and it's all very...strange, but cool. As for why the value of mu and epsilon are what they are, at least in a vacuum: well, they're "fundamental constants"...so we don't know why, they just are. As for why a medium has a particular value, its the way the material retards and interferes with EM waves by the presence of the charged atomic particles. In the photon picture it's emission and aboprtion of individual photons creating a lag time. In the wave picture, it really is slowing the speed of light due to the presence of matter. Both pictures give you the right answer. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

nova_explored · Jul 30, 2006

that is really fascinating stuff. very cool. (especially about the lense technology to see into the human cell) <div class="Discussion_UserSignature"> </div>

nova_explored · Jul 30, 2006

Neutrino has mass so it is some specific upperbound limit below the constant (speed of light.) The neutrino is an elementary particle. It has half-integer spin (egin{matrix}frac{1}{2}hbarend{matrix}) and is therefore a fermion. All neutrinos observed to date have left-handed chirality. Although they had been considered massless for many years, recent experiments (see Super-Kamiokande, Sudbury Neutrino Observatory, KamLAND and MINOS) have shown their mass to be non-zero. Because it is an electrically neutral lepton, the neutrino interacts neither by way of the strong nor the electromagnetic force, but only through the weak force and gravity. Because the cross section in weak nuclear interactions is very small, neutrinos can pass through matter almost unhindered. For typical neutrinos produced in the sun (with energies of a few MeV), it would take approximately one light year (~1016m) of lead to block half of them. Detection of neutrinos is therefore challenging, requiring large detection volumes or high intensity artificial neutrino beams. from wikipedia excerpt on the 'neutrino'. http://en.wikipedia.org/wiki/Neutrino more interestingly: Chirality Massless particles — such as the photon, the gluon, and the (hypothetical) graviton — have absolute chirality: (better known as helicity) a given massless particle appears to spin in the same direction along its axis of motion regardless of point of view of the observer. http://en.wikipedia.org/wiki/Chirality_%28physics%29 This goes with those reference frames and 'test benches' referred to: A massless particle moves with the speed of light, so a real observer (who must always travel at less than the speed of light) <div class="Discussion_UserSignature"> </div>

rhodan · Jul 30, 2006

rhodan....that makes my head hurt. I've heard of similar things before, and it's all very...strange, but cool. These metamaterials are materials nature, or the Universe, can not produce. Well, nature produced the human brain of course, so all our actions and thoughts are still very much part of nature, but I hope you understand what I'm getting at; these metamaterials are not a natural phenomenon. So, in a way, by creating them, we're adding something to the Universe, bend (designed to interact with EM waves) or extend (by creating something new) its rules a bit, so hence the freaky interaction with light? It makes the impossible possible? I'm glad it makes your head hurt, because mine nearly exploded. <img src="/images/icons/wink.gif" />

kmarinas86 · Jul 30, 2006

As for why the value of mu and epsilon are what they are, at least in a vacuum: well, they're "fundamental constants"...so we don't know why, they just are. As for why a medium has a particular value, its the way the material retards and interferes with EM waves by the presence of the charged atomic particles. If you want a butt easy answer to this question first you must assume the speed of light is c in all mediums. To do the fix, assume that when the speed of light slows down that it's actually "time dilation" so that a refractive index of 2 corresponds to a time dilation of 2. Then time dilation is simply 1/(v*sqrt(mu*epsilon)), where v is the velocity of light using our units of time (as if we possessed the coordinate time frame). In this case, you assume that time runs at different speeds inside different mediums (e.g. time would run slower in diamond than it would in glass). As for force in netwons, being in units of kg m/s^2, it would increase with the square of the time dilation (i.e. the forces just look weaker than they really are due to time dilation making them "slow motion"), and with energy (gravitational potential energy, kinetic energy, etc.) - still the square of the time dilation. kg*m/C^2 (i.e. permeability) would remain the same, whereas permittivity ((C^2*s^2)/(kg*m)) it would be inversely proportional to second power of the time dilation (i.e. this would mean that permittivity is overestimated by a factor equal to the second power of the time dilation) such that sqrt(permittivity*permeability) is overestimated by the factor for time dilation. As for the values of mu and epsilon, they're like the constant G, that is, they depend on the units we use to define them. If we use different units we (in just about all cases) will get a different "magnitude".

why06 · Jul 31, 2006

Okay say if the say if this interaction took place faster ....would light be faster? What could possibly cause this interaction to only occur at 186,000 miles per second? <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

why06 · Jul 31, 2006

Also say since in the idea of quantum mehcanics space-time is bumpy and radically different on the sub-atomic level then on the macroscopic levels. Maybe this light moves at the speed that space-time fluctuates on the microscopic level. Possibly if space-time was different on the sub-atomic level light would take place at a different speed If this is the case then can other electro-magnetic itner-actions take place a a higher speed? OR AM I MISSING Something!? <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

vandivx · Jul 31, 2006

<blockquote>In reply to:<hr />Okay say if the say if this interaction took place faster ....would light be faster?<hr /></blockquote> [puts on Ned Flanders head] Yes, indeedly-doodly [takes off Ned Flanders head] light is the electromagnetic interaction (as Maxwell first realized) and so yes, it would <blockquote>In reply to:<hr />What could possibly cause this interaction to only occur at 186,000 miles per second?<hr /></blockquote> aaah, that nobody knows (of course, as always exceptions can occur, one should never say never or nobody because there may be somebody, at least there usually is somebody) it doesn't always have to occur at this speed but it does so at this point in time and space that we currently find ourselves in vanDivX <div class="Discussion_UserSignature"> </div>

Saiph · Jul 31, 2006

yep, van's got it right. The idea of the constants being different (thus the rate of interaction) is one that's been tossed around as a possible explaination for the "inflationary" period of the big bang model of universal expansion. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

why06 · Aug 1, 2006

Are you saying that light can travel faster in other portions of space? -Possibly? <div class="Discussion_UserSignature"> <div>________________________________________ </div><div><ul><li>your move...</li></ul></div> </div>

Saiph · Aug 1, 2006

possible, and it is something people are looking for. If the fine constant (mu and epsilon term in the speed of light) was different in the past, to explain inflation period, the speed of light would be different then, and so it would be different at that distance from us (remember distance = time in the past!). However, to date no indications of such a systematic shift in the speed of light have been found, nor of small local variations. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

vandivx · Aug 1, 2006

not being experimentalist, wouldn't it be hard to detect altered speed of light since it can hide behind frequency shift if for example light started out in deep space with speed different from c suppose speed of light in early universe was less than c, in that case the light we receive from there would be redshifted even if there was no recession velocity redshift due to the general expansion of universe however the expansion is there and we can't tell how much of the redshift is due to to each effect, in the end we may just mistakenly believe the distant galaxies to be farther out than they really are measurement of speed of light in distant space is likely quite problematic I imagine (that sentence may earn the understatement of the year award very likely) can we even measure speed of light on the outskirts of our galaxy in some direct fashion, that is not deducting it indirectly from some phenomena, I don't think so typically the speed of light is taken as one of the basic givens to interpret the data we get from space, not the other way vanDivX <div class="Discussion_UserSignature"> </div>

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