Why physicists refuse to measure the one-way speed of light directly?
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From: Sam Wormley on 11 Jan 2010 11:22 Physics FAQ: How is the speed of light measured? http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html Physics FAQ: What is the experimental basis of Special Relativity? http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html 3.2 One-Way Tests of Light-Speed Isotropy http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#one-way_tests Note that while these experiments clearly use a one-way light path and find isotropy, they are inherently unable to rule out a large class of theories in which the one-way speed of light is anisotropic. These theories share the property that the round-trip speed of light is isotropic in any inertial frame, but the one-way speed is isotropic only in an �ther frame. In all of these theories the effects of slow clock transport exactly offset the effects of the anisotropic one-way speed of light (in any inertial frame), and all are experimentally indistinguishable from SR. All of these theories predict null results for these experiments. See Test Theories above, especially Zhang (in which these theories are called �Edwards frames�). Cialdea, Lett. Nuovo Cimento 4 (1972), pg 821. Uses two multi-mode lasers mounted on a rotating table to look for variations in their interference pattern as the table is rotated. Places an upper limit on any one-way anisotropy of 0.9 m/s. Krisher et al., Phys. Rev. D, 42, No. 2, pg 731�734, (1990). Uses two hydrogen masers fixed to the Earth and separated by a 21-km fiber-optic link to look for variations in the phase between them. They put an upper limit on the one-way linear anisotropy of 100 m/s. Champeny et al., Phys. Lett. 7 (1963), pg 241. Champeney, Isaak and Khan, Proc. Physical Soc. 85, pg 583 (1965). Isaak et al., Phys. Bull. 21 (1970), pg 255. Uses a rotating M�ssbauer absorber and fixed detector to place an upper limit on any one-way anisotropy of 3 m/s. Turner and Hill, Phys. Rev. 134 (1964), B252. Uses a rotating source and fixed M�ssbauer detector to place an upper limit on any one-way anisotropy of 10 m/s. Gagnon, Torr, Kolen, and Chang, Phys. Rev. A38 no. 4 (1988), pg 1767. A guided-wave test of isotropy. Their null result is consistent with SR. T.W. Cole, �Astronomical Tests for the Presence of an Ether�, Mon. Not. R. Astr. Soc. (1976), 175 93P-96P. Several VLBI tests sensitive to first-order effects of an �ther are described. No �ther is detected, with a sensitivity of 70 m/s. Ragulsky, �Determination of light velocity dependence on direction of propagation�, Phys. Lett. A, 235 (1997), pg 125. A �one-way� test that is bidirectional with the outgoing ray in glass and the return ray in air. The interferometer is by design particularly robust against mechanical perturbations, and temperature controlled. The limit on the anisotropy of c is 0.13 m/s.
From: Androcles on 11 Jan 2010 11:44 "Sam Wormley" <swormley1(a)gmail.com> wrote in message news:rPGdnRQjJNPTzdbWnZ2dnUVZ_r5i4p2d(a)mchsi.com... > Physics FAQ: How is the speed of light measured? > > http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure_c.html Proper method: speed = distance/time. Why do shitheads refuse to measure the one-way speed of light directly?
From: GogoJF on 11 Jan 2010 12:15 On Jan 11, 10:22 am, Sam Wormley <sworml...(a)gmail.com> wrote: > Physics FAQ: How is the speed of light measured? > > http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/measure... > > Physics FAQ: What is the experimental basis of Special Relativity? > http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html > > 3.2 One-Way Tests of Light-Speed Isotropy > > http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#... > > Note that while these experiments clearly use a one-way light path and > find isotropy, they are inherently unable to rule out a large class of > theories in which the one-way speed of light is anisotropic. These > theories share the property that the round-trip speed of light is > isotropic in any inertial frame, but the one-way speed is isotropic only > in an æther frame. In all of these theories the effects of slow clock > transport exactly offset the effects of the anisotropic one-way speed of > light (in any inertial frame), and all are experimentally > indistinguishable from SR. All of these theories predict null results > for these experiments. See Test Theories above, especially Zhang (in > which these theories are called Edwards frames). > > Cialdea, Lett. Nuovo Cimento 4 (1972), pg 821. > Uses two multi-mode lasers mounted on a rotating table to look for > variations in their interference pattern as the table is rotated. Places > an upper limit on any one-way anisotropy of 0.9 m/s. > > Krisher et al., Phys. Rev. D, 42, No. 2, pg 731734, (1990). > Uses two hydrogen masers fixed to the Earth and separated by a 21-km > fiber-optic link to look for variations in the phase between them. They > put an upper limit on the one-way linear anisotropy of 100 m/s. > > Champeny et al., Phys. Lett. 7 (1963), pg 241. > Champeney, Isaak and Khan, Proc. Physical Soc. 85, pg 583 (1965). > Isaak et al., Phys. Bull. 21 (1970), pg 255. > Uses a rotating Mössbauer absorber and fixed detector to place an upper > limit on any one-way anisotropy of 3 m/s. > > Turner and Hill, Phys. Rev. 134 (1964), B252. > Uses a rotating source and fixed Mössbauer detector to place an upper > limit on any one-way anisotropy of 10 m/s. > > Gagnon, Torr, Kolen, and Chang, Phys. Rev. A38 no. 4 (1988), pg 1767. > A guided-wave test of isotropy. Their null result is consistent with SR. > > T.W. Cole, Astronomical Tests for the Presence of an Ether, Mon. Not. > R. Astr. Soc. (1976), 175 93P-96P. > Several VLBI tests sensitive to first-order effects of an æther are > described. No æther is detected, with a sensitivity of 70 m/s. > > Ragulsky, Determination of light velocity dependence on direction of > propagation, Phys. Lett. A, 235 (1997), pg 125. > A one-way test that is bidirectional with the outgoing ray in glass > and the return ray in air. The interferometer is by design particularly > robust against mechanical perturbations, and temperature controlled. The > limit on the anisotropy of c is 0.13 m/s. One-way path vs. one-directional path: This is an example of a one-way path: I get in may car, drive down to the end of the block, hang a right, drive down to the next block, hang a left- I might even go around the block a few times- while doing this, I maintain a one-way path. This is an example of a one-directional path: I get in my car and start driving in a straight line. I can drive as far as I want, as long as I maintain a straight line. The examples you refer are bi-directional, or multi-directional- although they are of one path. I think what kenseto is trying to say, "Why do physicists refuse to measure a one-way speed of light directly?"- implies this one- directional approach.
From: glird on 11 Jan 2010 12:38 On Jan 11, 10:23 am, Igor wrote: > On Jan 11, 8:59 am, kenseto wrote: > >< The one-way speed of light is physical distance dependent. BTW that's why they invented a new definition for a meter length: 1 meter=1/299,792,458 light second. Using this definition the one-way speed of light is c by definition.> >< No, you've got it backwards. The speed of light in vacuum is a universal constant and the meter is defined based on it and the time standard. Whether the speed of electromagnetic radiation in a vacuum is actually c is an entirely different issue. > Maybe you need to stop confusing the two. One is a convention and the other is physics. Do you understand the difference? "At the 1983 Conference Generale des Poids et Mesures, the following SI (Systeme International) definition of the metre was adopted: The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. This defines the speed of light in vacuum to be exactly 299,792,458 m/ s. This provides a very short answer to the question "Is c constant": Yes, c is constant by definition!"!! and a bit further on: "Today, high energy physicists at CERN in Geneva and Fermilab in Chicago routinely accelerate particles to within a whisper of the speed of light. Any dependence of the speed of light on reference frames would have shown up long ago, unless it is very slight indeed. "But what if we pursued the original theory of Fitzgerald and Lorentz, who proposed that the ether is there, but is undetectable because of physical changes in the lengths of material objects and the rates of clocks, rather than changes in space and time? For such a theory to be consistent with observation, the ether would need to be completely undetectable using clocks and rulers. Everything, including the observer, would have to contract and slow down by just the right amounts. Such a theory could make exactly the same prediction in all experiments as the theory of relativity; but in that case the ether would be no more than a metaphysical construct unless there was some other way of detecting it--which nobody has found." Nobody HAD found. It has now been found. It is called "dark matter" because it is invisible. It is invisible because it doesn't reflect light, it transmits it in all directions from any given point. That's because it is a continuous non-particulate space- filling material that doesn't have a reflective surface. >< Maybe you need to stop confusing the two. One is a convention and the other is physics. Do you understand the difference? > There isn't any. glird
From: eric gisse on 11 Jan 2010 12:39
kenseto wrote: > Why physicists refuse to measure the one-way speed of light directly? > The answer: http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html > The one-way speed of light is physical distance dependent. > BTW that's why they invented a new definition for a meter length: 1 > meter=1/299,792,458 light second > Using this definition the one-way speed of light is c by definition. > > Ken Seto |