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That CAN'T be true! / Re: Is the speed of light constant for all observers?
« on: 02/11/2017 17:13:02 »Which is why the Relativistic model of Doppler shift is the only valid one. If you assume that light travels at a fixed speed relative to the source and not so to the receiver, you get one answer for Doppler shift, if you assume that The light travels at a fixed speed relative to the receiver and to the source you get another answer. If you assume that light travels at a fixed speed relative to both as measure by both (due to the fact that receiver and source measure time and space differently due to their relative motion), then you get a third answer.QuoteI can do the same assuming that the light does travel at c with respect to the Earth.This is true, but there is a subtle difference. If light were traveling at c relative to the observer then the time taken from emission to reception would depend upon the distance from sender to receiver at the time of emission. This would lead to some strange effects. Let's say that Algol is 93.5 light-years from Earth. The Earth is at the maximum distance away from Algol and is approaching Algol. Every time an eclipse occurs the Earth is closer to Algol. This means that the period of time between eclipses will be shorter. 93.5 years later, when the Earth is closest to Algol, the Earth will start receiving those eclipses. So we would have the strange effect of having a shorter period of time between eclipses as the Earth is moving away from Algol.
At the moment the light from one eclipse of Algol occurs, Algol is a certain distance from Earth. If Earth and Algol are moving apart at 66629 mph, then 2.867321 days later, when the light for the next eclipse occurs, Algol will be 4585121.54 miles or 24.6162 light seconds further away from the Earth when that light leaves, This means that the light from this eclipse, traveling at c relative to the Earth, take 24.6162 seconds longer to travel to the Earth than the light from the earlier eclipse did. If the eclipses occurred 2.867321 days apart at Algol, the Earth would see them 24.6162 seconds or 0.00028491 days further apart 2.867321 + 0.00028491 =2.86760591 days apart which is also close to the given time. (quibbling about the small difference here does no good because the Earth's orbital speed itself varies by some 2240.3 mph (.6223 miles per sec) over over the course of an orbit, which would result in a larger difference in answers than what we got.)
The point is that I can get the same type of spacing between observed eclipses by assuming that light does travel at c relative to the Earth.
And as I've already indicated, we have done experiments to find out which model gives the correct answer, and the Relativistic model came out the winner.
This was demonstrated some yeas ago with in a practical situation. NASA had sent a pair of probes to one of the moons of one of the gas giants. One of pair was a lander and the other an orbiter. The lander would send info to the orbiter to be relayed back to Earth. The problem was that there was a glitch in the communication between the two. A communication protocol had been set up that required a very narrow frequency tolerance between the two and they were offset from each each other and they couldn't talk back and forth. The solution they came up with was to adjust the orbit of the probe so that when it was receiving from the lander, their relative velocity was just the right magnitude for Doppler shift to correct for the offset.
So here's the thing. Relativistic Doppler shift only depends on the relative velocity difference between source and receiver, while a model that assumes that the speed of light relative to the one doing the measuring depends on it motion, then the Doppler shift depends on both the source's and receiver's motion with respect to some fixed frame. Now we are dealing with an receiver which is orbiting a moon, which is in turn orbiting a planet, which in turn is orbiting the Sun. This means that after every orbit of the probe, the Moon will have moved some in its orbit and will be moving at a slightly different velocity relative top the Sun than is was before, this means that both the Orbiter's and lander's velocities will have changed, which in turn changes the Doppler shift. Thus in order to keep the shift to the precise value needed for the correction, NASA would have had keep adjusting the orbiter's orbit. They didn't. (If they had, it would have meant that there was something amiss with the prediction of Relativistic Doppler shift and there would have been quite a stir in scientific circles.)
The problem you are having is that you are trying to apply Newtonian physics to a universe that operates by Einsteinian rules.
The Earth measures light coming from Algol as moving at c relative to the Earth both when it is moving towards and away from Algol. The Earth now has a different velocity relative to the Earth 6 months from now or 6 months ago, and thus measures time and space differently. (This is the whole gist of Relativity, it involves a whole new model for space and time than Newtonian Physics uses.)
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