3 ms·
Ok fine: The sun for example is not physically in the place it appears to be due to the 8 minutes of light travel time and the fact it moves about one diameter
by SiempreViernes 9y ago
Ok fine: The sun for example is not physically in the place it appears to be due to the 8 minutes of light travel time and the fact it moves about one diameter across the sky in two minutes.
I just feel that if you talk about where the sun appears to be you can infer from context that I talk about actual sky positions and motions, not the inferred global state of the solar system, but here we are.
Anyway, the central fact in my argument is that the light that reaches us from the sun has travelled for 8 minutes, and so shows us now^1 where the sun would have been on the sky^2 8 minutes ago if we then had observed it by superluminal means.
Now, that there are no superluminal means to observe the sun with (as far as we know) is not crucial to the point because there are other situations where one mode of observation carries older information than other. That is the example of observing^3 the distant air plane with sound waves, and then with the supersonic means of light waves. The sound waves emitted at a given point in time reach you after the light waves emitted at that same instant, and so it looks^4 like the plane is at a different position than the sound is coming from. Since most of us rely mostly on sight, the sound is judged to be erroneous, but clearly we could just as well pick the sound position to be the baseline, which we do for instance if the plane is hidden by a cloud.
Also, in the spirit of your objection, you are almost completely wrong, in an exact technical way, when you say that
> the light rays that it hits at every point are always pointing back to the exact physical center of the sun
Because the sun is so close, it is in fact NOT a point, but it resolves to a disk, and since most of the disk is not on the one (infinitesimally thin) light ray that points back trough "the exact physical centre of the sun", most of the light does not point exactly there.
1: By which I mean a given instant in time, and due to how close the sun is and our reasonable velocity relativity of simultaneity is not important
2: Here "on the sky" means what position in an earth co-moving sky coordinate system
3: Again, I am talking about the motion of objects across the sky, in an earth co-moving sky coordinate system. The various and important ways that the example objects differ are neglected if they do not matter for the observed motion in the sky.
4: That is, you see optical waves with your eyes and infer from that a specific sky position different from the one reconstructed by your brain based on the sound waves detected by your ears.