As far as dark matter goes, if we assume that dark matter has a non-uniform density distribution across the universe, which is only fair considering that we can't directly see it anyway, a star in between two masses of dark matter may, or perhaps surrounded by some halo of dark matter, would have its gravitational field something to contend with
Dark energy and dark matter don't have appreciable gravitational effects over such small distances. Motion within the solar system acts essentially according to Newtonian mechanics, taking into account only gravity as produced by ordinary matter.
You are making this stuff up. For example...
Such would be the case with the sun and Io, both of whose distances can easily be determined by parallax and luminosity.
No that is not how we determine or know the distance to Jupiter, Io, or the Sun.
but simply a way to convey the idea that the distance between the transmitter and the receiver are pre-determined
We don't need to know the location of the transmitter (sun). What is important in Roemer's experiment is knowing the difference in distances between Jupiter and earth at different times.
I ask again what is the purpose of these flights of fancy. You are making up stuff to explain what exactly? I raised the issue that we have evidence that the speed of light was consistent with its current value at a time 160000 years in the past. Carbon dating is only used to estimate dates that are within the last 50,000 years or so, which is sufficient to debunk at least some creationist estimates for the age of the earth. So when is this step change in the speed of light supposed to have happened?
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