UPDATE 1-Particles found to break speed of light | Reuters
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UPDATE 1-Particles found to break speed of light | Reuters
 
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Sigh. I guess there really are NO absolutes in this universe of ours.
http://www.reuters.com/article/2011/09/22/science-light-idUSL5E7KM4CW20110922 -tj ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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Of that you can be absolutely sure.
--Doug
On Thu, Sep 22, 2011 at 2:53 PM, Tom Johnson <[hidden email]> wrote:
Sigh. I guess there really are NO absolutes in this universe of ours. ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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Administrator
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So the speed of light differs depending on medium, right? Is this also true for neutrinos? If so, change in materials in the path could possibly make a difference. The study was through the earth, not via conduits.
Sounds like a question for Howel White tomorrow!
-- Owen
On Thu, Sep 22, 2011 at 3:00 PM, Douglas Roberts <[hidden email]> wrote: Of that you can be absolutely sure. ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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The speed of light is relative, apparently.
Actually, I'm betting on measurement error. As was pointed out on Slashdot, it would only take a few centimeters of wire not properly taken into account to cause this apparent result.
--Doug
On Thu, Sep 22, 2011 at 6:21 PM, Owen Densmore <[hidden email]> wrote: So the speed of light differs depending on medium, right? Is this also true for neutrinos? If so, change in materials in the path could possibly make a difference. The study was through the earth, not via conduits. Doug Roberts [hidden email] [hidden email] ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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Administrator
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For folks interested in /.'s unusual (i.e. not all rants) comments, see: http://goo.gl/NRtuv
Several of the /.ers read the research in reasonable detail.
-- Owen
On Thu, Sep 22, 2011 at 6:28 PM, Douglas Roberts <[hidden email]> wrote: The speed of light is relative, apparently. ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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In reply to this post by Owen Densmore
This is in response to the question, "So the speed of light differs
depending on medium, right? Is this also true for neutrinos?" Actually, there is an important sense in which one can (and should) say that the speed of light does NOT depend on the medium! See my article http://matterandinteractions.org/Content/Articles/Refraction.pdf If you accelerate charges, they radiate light. Light consists of traveling waves of electric and magnetic fields; you can see a video about electromagnetic waves titled "Electric Fields, Cell Towers, and Wi-Fi", a presentation I made to Santa Fe city government staff: http://www4.ncsu.edu/~basherwo There is an extremely important though underrated property of charges and fields called the "superposition principle": The value of the electric or magnetic field at a location in space is the vector sum of all the fields contributed by all the charges in the Universe, AND THE CONTRIBUTION OF ANY PARTICULAR CHARGE IS UNAFFECTED BY THE PRESENCE OF OTHER CHARGES. It is the capitalized portion of the principle that despite its innocent-sounding content leads to quite counterintuitive consequences. For example, you've probably heard that a metal container shields out electric fields made by charges outside the container. False! There is no such thing as "shielding". By the well validated superposition principle, the field at any location inside the metal container includes the field contributed by external charges. However, it LOOKS as though the metal prevents the field from getting in, because the external charges "polarize" the metal by shifting the mobile electrons in the metal, and the polarized metal contributes an additional electric field inside the container that is equal in magnitude but opposite in direction to the field contributed by the external charges. The effect is indeed as though the metal "shielded" the interior, but the actual mechanism has nothing to do with "shielding", and the field due to the external charges is most definitely present inside the container. Consider a cubical box with metal walls, and there's a positive charge to the right of the box. That positive charge makes an electric field through the region, and that field causes (negatively charged) mobile electrons in the metal to move to the right, toward the external positive charge. That makes the right side of the box have an excess negative charge, and it leaves the left side with a deficiency of electrons, hence a positive charge. By convention, the direction of electric field is said to be in the direction that a positive charge would be pushed, so the electric field inside the box due to the external positive charge is to the left. Note that the "polarization" charges, negative on the right side of the box and positive on the left side of the box, contribute a field inside the box to the right. The 1/r squared character of the electric field of point charges leads to the surprising result that the field inside the box contributed by the polarization charges is exactly equal in magnitude and opposite in direction to the field contributed by the external charge, so the vector sum of the field contributions of all the charges is in fact zero inside the box, as though the metal "shielded" the interior. In fact, if one claims that the box "prevents the field of external charges getting into the box", there's an flaming inconsistency, since the polarization charges would make a nonzero electric field inside the box, uncompensated for by the field due to the external charge, and in violent disagreement with measurements that show that the electric field inside the box is zero. Back to the case of light, which is produced by accelerated charges. If you accelerate charges for a short time, they radiate a short pulse of light. Let's accelerate some charges somewhere off to the left, for a short time. Light (electric and magnetic fields) propagates in all directions, but we're interested in the light traveling to the right, toward a detector (which could be a camera) some known distance from the "source" (the accelerated charges). We measure the time from when we briefly accelerated the charges to when we detect the light a known distance away. Divide distance by time and get the speed of light in air, 3e8 m/s. Now let's repeat the experiment, except that there's a thick slab of glass between the source and the detector. You've surely heard that "light travels much slower in glass than in air", so you would expect the light to take significantly longer to reach the detector now that the glass is in place. But that's not what happens! You find the same time interval between the emission and the first light reaching the detector, and you determine the same 3e8 m/s speed as before! And you must, because the field at any location in space is the vector sum of the field contributions of all the charges in the Universe, unaffected by the presence of other charges (in this case, the electrons and protons in the glass). The fields radiated by the accelerated charges are unaffected and reach the detector in the same amount of time as before. However, there is an effect. As the electric field passes through the glass, it accelerates the electrons and protons (it accelerates the electrons much more than the protons, due to their very low mass). These accelerated electrons radiate electromagnetic radiation, like any accelerated charges. The traveling fields of this re-radiation also come to our detector, so that the shape of the pulse we receive is altered from what we saw without the glass, because there are now additional field contributions that were not present in the absence of the electron-containing glass. The first bit of light shows up on time, but then the situation becomes quite complicated. An important special case is that where the source charges off to the left are accelerated not for a short time, but continuously, sinusoidally up and down (which involves accelerations as the charges move faster and slower and turn around). If you turn on this sinusoidal radiation abruptly, of course you'll first see some light at the detector on time, with or without the glass being present. But let the sinusoidal acceleration of those source charges continue for a long long time. It can be shown that the vector sum of this radiation and the re-radiation from electrons accelerated in the glass leads to a detection of sinusoidal radiation, and that sinusoidal radiation has a phase which is shifted. That is, the peaks come at a different time than they did without the glass. In fact, in the "steady state", the peaks come later than they used to, and the lateness is proportional to how thick the glass is. It is a useful shorthand to say that the "light travels more slowly in the glass", as that description is consistent with the phase delay of peaks in the sinusoid, in the steady state, even though the speed of light in the glass is the usual 3e8 m/s. (The initial transient is messy, and not a simple sinusoid.) Richard Feynman in the famous Feynman Lectures on Physics discusses this quantitatively in Chapter 31 on "The Origin of the Refractive Index".The "refractive index" is usually denoted by n, and it is common practice to say that "the speed of light in a medium with refractive index n is 3e8/n m/s". But in fact the speed of light is a universal quantity. Although it is very often convenient to pretend that the speed of light is slower in glass, that's just a calculational convenience -- it's a misleading description of what's really going on. In fact, the refractive index and "speed of light" in glass is different for different frequencies of the sinusoidal radiation, because different frequencies of electric field affect the motion of the electrons differently in the glass. Bruce ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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A couple afterthoughts on the speed of light:
The interaction of the electric field of the light with the matter (glass or whatever) can be (for nonobvious reasons) well modeled by the electric field exerting a force on an outer electron in an atom as though the electron were bound to the atom by a spring-like force, with damping. The details of the spring stiffness and damping depend on the material and on the frequency of the electric field. In some materials this works out in such a way that in the downstream electric field (the sum of the field contributed by the accelerated source charges and the re-radiation by the accelerated electrons in the material) the peaks can actually be earlier than in the absence of the intervening material, in which case it looks as though the speed of transmission is actually faster than 3e8 m/s. But it is of course still the case that the first detection downstream occurs at 3e8 m/s. As to whether the (apparent) speed of propagation of neutrinos would differ in different materials, I think not. The change in phase speed for light is due to the rather strong interaction of light with matter, leading to re-radiation. Neutrinos have an amazingly small probability of interacting with matter, which is why one can detect them after they've traveled hundreds of kilometers through solid rock. So I wouldn't expect matter to have any effect on the speed of neutrinos. Bruce ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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In reply to this post by Bruce Sherwood
Obligatory xkcd toon - http://xkcd.com/955/
On 9/22/11 10:27 PM, Bruce Sherwood wrote: > This is in response to the question, "So the speed of light differs > depending on medium, right? Is this also true for neutrinos?" > > Actually, there is an important sense in which one can (and should) > say that the speed of light does NOT depend on the medium! See my > article > > http://matterandinteractions.org/Content/Articles/Refraction.pdf > > If you accelerate charges, they radiate light. Light consists of > traveling waves of electric and magnetic fields; you can see a video > about electromagnetic waves titled "Electric Fields, Cell Towers, and > Wi-Fi", a presentation I made to Santa Fe city government staff: > > http://www4.ncsu.edu/~basherwo > > There is an extremely important though underrated property of charges > and fields called the "superposition principle": The value of the > electric or magnetic field at a location in space is the vector sum of > all the fields contributed by all the charges in the Universe, AND THE > CONTRIBUTION OF ANY PARTICULAR CHARGE IS UNAFFECTED BY THE PRESENCE OF > OTHER CHARGES. > > It is the capitalized portion of the principle that despite its > innocent-sounding content leads to quite counterintuitive > consequences. For example, you've probably heard that a metal > container shields out electric fields made by charges outside the > container. False! There is no such thing as "shielding". By the well > validated superposition principle, the field at any location inside > the metal container includes the field contributed by external > charges. However, it LOOKS as though the metal prevents the field from > getting in, because the external charges "polarize" the metal by > shifting the mobile electrons in the metal, and the polarized metal > contributes an additional electric field inside the container that is > equal in magnitude but opposite in direction to the field contributed > by the external charges. The effect is indeed as though the metal > "shielded" the interior, but the actual mechanism has nothing to do > with "shielding", and the field due to the external charges is most > definitely present inside the container. > > Consider a cubical box with metal walls, and there's a positive charge > to the right of the box. That positive charge makes an electric field > through the region, and that field causes (negatively charged) mobile > electrons in the metal to move to the right, toward the external > positive charge. That makes the right side of the box have an excess > negative charge, and it leaves the left side with a deficiency of > electrons, hence a positive charge. > > By convention, the direction of electric field is said to be in the > direction that a positive charge would be pushed, so the electric > field inside the box due to the external positive charge is to the > left. Note that the "polarization" charges, negative on the right side > of the box and positive on the left side of the box, contribute a > field inside the box to the right. The 1/r squared character of the > electric field of point charges leads to the surprising result that > the field inside the box contributed by the polarization charges is > exactly equal in magnitude and opposite in direction to the field > contributed by the external charge, so the vector sum of the field > contributions of all the charges is in fact zero inside the box, as > though the metal "shielded" the interior. > > In fact, if one claims that the box "prevents the field of external > charges getting into the box", there's an flaming inconsistency, since > the polarization charges would make a nonzero electric field inside > the box, uncompensated for by the field due to the external charge, > and in violent disagreement with measurements that show that the > electric field inside the box is zero. > > Back to the case of light, which is produced by accelerated charges. > If you accelerate charges for a short time, they radiate a short pulse > of light. Let's accelerate some charges somewhere off to the left, for > a short time. Light (electric and magnetic fields) propagates in all > directions, but we're interested in the light traveling to the right, > toward a detector (which could be a camera) some known distance from > the "source" (the accelerated charges). We measure the time from when > we briefly accelerated the charges to when we detect the light a known > distance away. Divide distance by time and get the speed of light in > air, 3e8 m/s. > > Now let's repeat the experiment, except that there's a thick slab of > glass between the source and the detector. You've surely heard that > "light travels much slower in glass than in air", so you would expect > the light to take significantly longer to reach the detector now that > the glass is in place. But that's not what happens! You find the same > time interval between the emission and the first light reaching the > detector, and you determine the same 3e8 m/s speed as before! And you > must, because the field at any location in space is the vector sum of > the field contributions of all the charges in the Universe, unaffected > by the presence of other charges (in this case, the electrons and > protons in the glass). The fields radiated by the accelerated charges > are unaffected and reach the detector in the same amount of time as > before. > > However, there is an effect. As the electric field passes through the > glass, it accelerates the electrons and protons (it accelerates the > electrons much more than the protons, due to their very low mass). > These accelerated electrons radiate electromagnetic radiation, like > any accelerated charges. The traveling fields of this re-radiation > also come to our detector, so that the shape of the pulse we receive > is altered from what we saw without the glass, because there are now > additional field contributions that were not present in the absence of > the electron-containing glass. The first bit of light shows up on > time, but then the situation becomes quite complicated. > > An important special case is that where the source charges off to the > left are accelerated not for a short time, but continuously, > sinusoidally up and down (which involves accelerations as the charges > move faster and slower and turn around). If you turn on this > sinusoidal radiation abruptly, of course you'll first see some light > at the detector on time, with or without the glass being present. But > let the sinusoidal acceleration of those source charges continue for a > long long time. It can be shown that the vector sum of this radiation > and the re-radiation from electrons accelerated in the glass leads to > a detection of sinusoidal radiation, and that sinusoidal radiation has > a phase which is shifted. That is, the peaks come at a different time > than they did without the glass. In fact, in the "steady state", the > peaks come later than they used to, and the lateness is proportional > to how thick the glass is. It is a useful shorthand to say that the > "light travels more slowly in the glass", as that description is > consistent with the phase delay of peaks in the sinusoid, in the > steady state, even though the speed of light in the glass is the usual > 3e8 m/s. (The initial transient is messy, and not a simple sinusoid.) > > Richard Feynman in the famous Feynman Lectures on Physics discusses > this quantitatively in Chapter 31 on "The Origin of the Refractive > Index".The "refractive index" is usually denoted by n, and it is > common practice to say that "the speed of light in a medium with > refractive index n is 3e8/n m/s". But in fact the speed of light is a > universal quantity. Although it is very often convenient to pretend > that the speed of light is slower in glass, that's just a > calculational convenience -- it's a misleading description of what's > really going on. In fact, the refractive index and "speed of light" in > glass is different for different frequencies of the sinusoidal > radiation, because different frequencies of electric field affect the > motion of the electrons differently in the glass. > > Bruce > > ============================================================ > FRIAM Applied Complexity Group listserv > Meets Fridays 9a-11:30 at cafe at St. John's College > lectures, archives, unsubscribe, maps at http://www.friam.org > ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
Re: UPDATE 1-Particles found to break speed of light | Reuters
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In reply to this post by Bruce Sherwood
Another comment about the speed of light in matter:
When in the steady state light is traveling through glass, the frequency of the light in the glass (how many cycles of the sine function occur per second) is the same as the frequency of the light in the air. The speed with which a crest of the sine wave advances (the phase speed) is the distance between crests (the wavelength) divided by the time for one cycle, which is 1/frequency. Because the phase speed is slower in the glass, the wavelength is shorter in the glass than in the air: the crests are pushed closer together. Bruce ============================================================ FRIAM Applied Complexity Group listserv Meets Fridays 9a-11:30 at cafe at St. John's College lectures, archives, unsubscribe, maps at http://www.friam.org |
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