Speed of Light: A universal Constant?
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From: George Dishman on 27 Mar 2005 15:26 "sean" <jaymoseley(a)hotmail.com> wrote in message news:40f80aa1.0503270548.6412b1a2(a)posting.google.com... > > Hi George > About an earlier point you made.. > > (George quote) > The radius of Jupiter is about 71,500 km while the radius of > Io's orbit is 421,600km. That means that its motion is almost > transverse at the time of a transit, the component of the > speed directed towards Earth is reduced to only 2.98 km/s so > the time difference is only 0.05s > (George unquote) > > What you calculate above isnt the difference between Jupiters > max speed away from earth and its minimum but rather the > difference between Ios speed and Jupiters speed relative to > earth, depending on whether or not Io is orbiting towards earth > or away from earth around jupiter. Actually this earlier paragraph did that: "George Dishman" <george(a)briar.demon.co.uk> wrote in message news:d1vkr5$3c1$1(a)news.freedom2surf.net... > > "Jim Greenfield" <jgreen(a)seol.net.au> wrote in message > news:e7b5cc5d.0503232023.1e8326bf(a)posting.google.com... >> >> I don't know what the time difference in the 'signal' time interval >> would be for Io due to c-v as it is regressing from earth, and c+v as >> it approaches, but I think it would only be of the order 1 second, not >> 1,000. > > Not a bad guess :-) The orbital speed of Io is 17.34 km/s > so the time difference between approaching and receding is > about 0.3s. However, that is when the motion of Io is > directly towards or away from the Earth. The one you quote is for the speed at the start and end of a transit. > Of course that would be much > smaller than the difference between Jupiters max speed away > from earth and its minimum speed away from earth. Surprisingly, no, it is considerably larger. Io's speed around Jupiter is faster than Jupiter's speed round the Sun. See below. > So your > above point is irrelevent isnt it? Shouldnt one be calculating > the difference between the max speed that Jupiter is moving > away from earth and the minimum speed it is moving away from > earth and then calculate how many more seconds this difference > in speed would be for a non sr wave to travel to earth would be? It depends on how you are going to make the measurement.If you could compare the time delays about 0.9 days apart, you get a simpler measurement because the planetary motions have changed little in that time and are common. Jim's earlier paragraph described that so I followed his lead. The trouble though is that you have to accurately determine when Io is moving directly towards or away from you which is very difficult. Roemer's measurements, and those Stan has to work with, are for transits, the time when Io crosses the edge of Jupiter's disc which leads to the much smaller time difference I calculated in the second paragraph. > I can only rough calculate but it seems that if lets say if Jupiter > were moving away from earth at 1,000k/s faster at its fastest speed Jupiter's mean orbital speed is only 13.07 km/s. Even Mercury manages less than 48km/s! (As an exercise, you might like to find the orbital radius at which the speed would be 1000km/s and compare it to the radius of the Sun.) > away from earth than its fastest speed towards earth then this > would give a 1000 second difference as Stan says. In other words > if the difference between Jupiters speed relative to Earth was > 1000k/s then that would be the difference Stan needs? The speed of Earth is 29.79 km/s so with a bit of trig I find the maximum speed of Jupiter measured radially from a point on the Earth's orbit is 2.52km/s. That maximum happens when the line from Jupiter to the Earth is a tangent to the Earth's orbit. The distance from Earth to Jupiter at that time is 5.1AU which means that, when Jupiter is ahead of the Earth and we are catching it up, the light would take 0.0215s longer than SR suggests to reach us. while it would take then same amount less when we have passed Jupiter and it is chasing us about half a year later, a total difference of only 0.043s. The effect of Io's orbital motion is about seven times larger at peak speed and still slightly larger even between the start and end of a transit. Stan's calculation is valid but it is just repeating Roemer's calculation of the speed of light. It proves Ralph Sansbury wrong but not SR. George
From: George Dishman on 27 Mar 2005 15:31 "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message news:Xns96248E1F275A4WQAHBGMXSZHVspammote(a)130.39.198.139... > "George Dishman" <george(a)briar.demon.co.uk> wrote in news:d21o60$lo6$1 > @news.freedom2surf.net: > >> >> Turn slowly around in a circle, say in ten seconds. >> The Andromeda Galaxy is about 2 to 3 million light >> years away. In a coordinate frame that rotated with >> you, the galaxy and all the light in it moved about >> 15 million light years in ten seconds. > > Amazing, and the angular momentum of all that supraluminal mass was > concerved too. > > I suspect that if I was on a rotating platform with equipment to measure > the speed of light from the Andromeda Galaxy... I would find that it still > moves at c. > > The earth is such a platform. > > However, I get your point. Cool. > It appears that you have just demonstrated that unlike linear motion, > where > there is no absolute frame of reference, where rotation is concern, there > is an absolute frame of reference and radial velocities must be measured > with respect to THAT frame of reference. Yes, SR is a simplification because it works with inertial frames, although you can handle acceleration with care, centrifugal forces and all that, but it treats acceleration as absolute. I believe GR does away with that and can even handle acceleration as relative but I don't know it well enough to be sure. HTH George
From: PD on 27 Mar 2005 17:05 kenseto wrote: > "PD" <pdraper(a)yahoo.com> wrote in message > news:1111770058.196421.21200(a)l41g2000cwc.googlegroups.com... > > > > kenseto wrote: > > > "bz" <bz+sp(a)ch100-5.chem.lsu.edu> wrote in message > > > news:Xns96217F0FC3412WQAHBGMXSZHVspammote(a)130.39.198.139... > > > > "kenseto" <kenseto(a)erinet.com> wrote in > > > > news:24Z%d.14316$cC6.10056(a)fe2.columbus.rr.com: > > > > > > > > > What you said is hogwash. If we define that the wave length of a > > > > > specific light source remains constant in all frames then the > > observed > > > > > Doppler shift is due to the varying speed of light from these > > different > > > > > sources. > > > > > > > > > > > > > Are you going to say that doppler shift of sound is ALSO due to > > varying > > > > the speed of sound? A car drops a fire cracker on the ground and > > sets off > > > > a fire cracker on the hood of the car at the same time. The 'bang' > > from > > > > the fire cracker on the ground and the one on the hood of the car > > reach me > > > > at the same time. The bang from the one on the hood of the car is > > dopplar > > > > shifted, the one on the ground is not. They both travel through the > > same > > > > air. Why should one travel at a different speed than the other? > > > > > > I assume that you mean that the fire cracker is at rest wrt the > > ground when > > > it goes off. In that case there is no Doppler shift. The fire cracker > > on the > > > car would be Doppler shifted. The sound generated by that fire > > cracker would > > > be closer to the detector with the passage of incremental time and > > this is > > > the cause of the doppler shift. There is no valid way to measure the > > speed > > > of sound from a moving fire cracker because there is no valid way to > > measure > > > the distance between the fire cracker and the detector at rest when > > the fire > > > cracker generate the first sound wave. > > > > Oh, good Lord. I can't believe you said such a thing. Never mind light. > > First pick up a book and learn what causes the Doppler effect in sound. > > Jiminy. Whoowhee. > > Hey idiot....what do you think that causes Doppler shift?? Hint: Changing > distance with time between the source and the detector. Therefore the > observed Doppler shift can be interpreted as that the speed of sound (or > light) arriving from a moving source is different than that if the source > and the detector are at rest wrt each other. This conclusion is based on the > assumption that the wave length remain constant whether the sound (or light) > wave is generated by a stationary source or a moving source wrt the > detector. > > Ken Seto No, what causes Doppler shift is that successive wavefronts are closer together because the source is moving in the same direction as the wavefronts. However, the wavefronts are still traveling at the same speed as they would for a stationary source. The speed is the same, but the wavelength (the distance between wavefronts) is smaller, and therefore the frequency is higher. Next! PD
From: Henri Wilson on 27 Mar 2005 19:31 On Sat, 26 Mar 2005 00:10:05 -0000, "George Dishman" <george(a)briar.demon.co.uk> wrote: > >"Henri Wilson" <H@..> wrote in message > >>>As we have discussed before, ballistic theory is >>>disproved by the Sagnac Experiment. >> >> Bull. The reason for the fringe shift has nothing to do with light speed. >> It is due to the fact that the mirrors rotate slightly during the time >> light >> travels between them. The two opposite beams are deflected in opposite >> directions. > >We went over that last time. You got the >geometry wrong, the beams are deflected >such that they maintain the angle between >them at the interferometer. No they don't. Just draw a simple diagram. The angular deflection of the beam at each miror is double the angular change of the mirror during the travel time. For three mirrors, the total angular difference is 16 x rotation during total light travel time. Like I said, whether c or c+v is used is of little consequence. > >You also talked of the curvature of the >paths in the rotating frame but the effect >of that on the path length is second order >and the same for both directions so it >cancels out. We have been over all of this >before and you never came up with a workable >explanation. Don't use the rotating frame. There is too much room for misinterpretation. > >> Note: A fibre ring is like an infinite number of mirrors with an >> infiniteimal >> angular change at each one. Same effect overall. > >Except that the effect on the path length >of the deflection is second order so the >limit of an infinite number of infinitesimal >deviations is zero. > >Sorry Henri, Ritzian theory unquestionably >predicts no output in the Sagnac Experiment >and yet it exists. Go ahead and show your >calculations if you think you can explain >how the first order output arises. Let the light travel time around the four mirror system be 10 ns. An apparatus rotation of (2pi/3600) radians/hour (0.1 deg/hr) should result in a deflection difference between the two beams of 12 x 3 (m) x 10/3600/10^8 metres/sec. That is 10^-9 m/sec. or 0.001 um. ~ 500 x wavelength? How wide is a fringe? > >George > HW. www.users.bigpond.com/hewn/index.htm Sometimes I feel like a complete failure. The most useful thing I have ever done is prove Einstein wrong.
From: Henri Wilson on 27 Mar 2005 19:34
On Fri, 25 Mar 2005 23:29:16 GMT, Sam Wormley <swormley1(a)mchsi.com> wrote: >Henri Wilson wrote: >> On Thu, 24 Mar 2005 23:13:18 GMT, Sam Wormley <swormley1(a)mchsi.com> wrote: >> >> >>>Henri Wilson wrote: >>> >>>>On Tue, 22 Mar 2005 16:52:39 GMT, Sam Wormley <swormley1(a)mchsi.com> wrote: >>>> >>>> >>>> >>>>>kenseto wrote: >> >> >>> The speed of light is constant. >> >> >> 'c' is a universal constant. >> >> Light moves at 'c' wrt its source. >> > > And light moves at 'c' wrt its observers! And which experiment demonstrates that? HW. www.users.bigpond.com/hewn/index.htm Sometimes I feel like a complete failure. The most useful thing I have ever done is prove Einstein wrong. |