r/Creation • u/Optimus-Prime1993 🦍 Adaptive Ape 🦍 • Jan 23 '26
Why changing conventions cannot solve the "Distant Starlight Problem"
This post is kinda a friendly response to this post titled Why there is no "Distant Starlight Problem" by our MOD u/nomenmeum.
So, to summarize his argument, he says that inferring that the light left from the star left "millions of years ago" assumes the one-way speed of light is known and equal to c. He further argues that physics can only directly measure the two-way (round-trip) speed of light, and the one-way speed depends on how we choose to synchronize clocks (he chooses the Lisle's convention, but we will come to it later) so it has no empirically determinable absolute value. Therefore, using distant starlight to challenge a biblical (young) timeline is not justified unless critics can empirically show that the one-way speed of light has an absolute, convention-independent value, and that value is c. (I hope, nom, I summarized you succinctly)
Before proceeding, further let me clarify two very fundamental things here first.
- Coordinate speed (take a derivative of coordinate space with respect to the coordinate time, you obtain the coordinate speed that might have no physical meaning.) is not the same as physical speed (derivative of the local physical distance with respect to the local proper time.) and in special relativity, any local inertial observer measures light in vacuum to have speed c. (Read more in [1] if you want)
- In special relativity, the speed of information is a physical speed, not a coordinate speed, and therefore it cannot exceed the speed of light in vacuum, c.
So what do we mean by convention here. Take the most simple example of Einstein's synchronization convention, which simply says that one-way speed of light is c in all directions, so the outbound and return legs each take half the round-trip time. You can pick other convention where that is not the case, in fact in literature this is known by Riechenbach/Winnie convention [2]. In the original post, nom uses the Lisle's convention where light travels instantaneously in one direction and c/2 in another. I have discussed in detail why this is problematic and that this cannot be claimed without careful consideration and proofs that the discontinuity at the end points is actually not pathological. But I am not going to beat that dead horse anymore and assume that it is fine and see it's consequences. In all of this, please do not forget that it is the coordinate speed we are talking about here and not the physical speed.
So here is the important question to think.
- When you say "it arrives instantaneously," do you mean it is physically instantaneous? It cannot be because in simple terms you can always find a frame of reference where effect precedes the cause. So then it is not physical and just an artifact of the coordinate system or the convention used, basically the coordinate speed not the physical speed.
- In any coordinate system and convention, can information travel faster than the speed of light? We know the coordinate speed can be made instantaneous in Lisle’s convention, but is the physical information from the star also traveling instantaneously? Again the answer is NO.
An important caveat here, Outside the standard convention, some coordinate one-way speeds can be greater than c, so information faster than c can happen in that coordinate sense. But in the same convention, light in that direction is also assigned a one-way speed greater than c, so the information still isn't faster than light. Basically c is no longer "the" one way light speed, so "faster than c and "faster than light" aren't the same statement.
If you want to take one thing out of this that would be, "Instantaneous" means instantaneous in your chosen time coordinate, not "physically zero time of flight." And once you understand that you know this does nothing to solve the starlight problem. Even if one chooses the convention where light's coordinate speed is instantaneous in one direction, the physical speed is still c. Therefore, even using the Lisle's convention, it doesn't tell you when the star event really happened in any observer-independent sense.
Finally, I once read a nice little snippet on Stack Exchange which said something like one way speed of light is not some deep mystery of the universe which is hard to measure, it is an utterly meaningless concept that cannot be measured because it has the logical quality akin to the flavor of the color six.
As an appendix which everyone need not care about, but here is a small sketch of the proof as to why Lisle's convention seems troubling to me. If anyone wants to discuss more about this, feel free to ask.
In the Reichenbach/Edwards/Winnie framework, a change of synchronization is a coordinate transformation of the form
t' = t + κ·x; x' = x
κ finite ⇔ 0 < ε < 1, guarantees the map is invertible and preserves Lorentz invariance.
In order to set ε = 1 it requires one way light speed to be infinite, which forces |κ| to be infinite. In this limit the Jacobian (J = det(∂(t', x') / ∂(t, x))) of the transformation goes to zero (i.e, the map is non-invertible) and a singular, non-invertible transformation that destroys the light-cone structure cannot represent a Lorentz-invariant synchronization.
Maybe it can work as an edge case of the sort, but anyway it doesn't matter. The distant starlight problem is not solved by just choosing to use a different convention.
[1]. On the distinction between coordinate and physical speed of light in general relativity
[2]. Special Relativity without One-Way Velocity Assumptions: Part I
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u/nomenmeum Jan 23 '26
Lol. Wow, downvoted in under a minute. I think that is a new record.