AetherCosPlay Aberration or Starlight

Work in Progress:

On 2026-06-26 on the Earth Awakenings Discord server Piezo and MCToon had this conversation:

Insert conversation here

In the comments section of that video TruthNerds wrote this response: A flat Earther found a formula which he doesn't understand and put some numbers in it. When has that ever happened before! (Warning, long post … see Brandolini's Law)

Anyway, Geo claims that Alan calculated the expected stellar aberration in Airy's failure experiment and that it doesn't match SR. By plugging in different light speeds, apparently. 😂

Ok, insider joke? I'll elaborate.

Let's first look at what Geo means by Bradley's formula. The classical formula is derived assuming that light propagates as a wave with a given speed in a stationary medium, aka aether, and the application of Newtonian mechanics.

It is θ - arctan(sin θ / (v/c + cos θ)) where θ is the angle of movement relative to the viewing direction, v is speed and c is the speed of light.

Then there's the relativistic formula, which is θ - 2 arctan(sqrt((1-v/c)/(1+v/c)) * tan(θ/2)). The relativistic formula reduces to the classical formula for v << c. Furthermore, for θ = 90° and v<<c, both reduce to v/c (in radians) as an approximation.

Ok, first, let's do some calculations, plain 90° aberration with Earth's average orbital speed gives about 0.0996 mrad (about 20.5 arcseconds) both for the classical and for the relativistic formula. It really makes no difference at those speeds!

Now, what did Alan presumably do to model Airy's experiment? Changing θ makes no sense, we want to keep that constant for comparability. Changing v makes no sense because Earth's speed wouldn't change. So he must've modified c. And that is hilarious!

Why? Well, for how Bradley's formula was derived, it would make sense because it is originally based on the assumption of a wave propagating through the aether. Slower wave propagation would thus affect the aberration angle.

But it doesn't make any sense to vary c in the relativistic formula! The relativistic formula is not derived from any assumption about a wave propagating through a fixed medium, it is based on the Lorentz transformation and the postulates of Special Relativity:

1. The laws of physics are the same in all inertial frames. 2. The speed of light in a vacuum (denoted c) is the same for all observers.

The speed of light to plug into the relativistic formula is always that same c, it has nothing to do with wave propagation in a medium. The formula follows from a coordinate transform in 4D spacetime. I.e. it is derived geometrically. It doesn't care about whether the light goes through a vacuum, air, water, glass or what have you.

Alan is once again debunking himself: If (classical) aether theory were correct, then Airy's experiment should have detected a change in aberration angle consistent with Bradley's formula (using different c).

Airy did not detect such a change, which is entirely consistent with SR. Alan therefore must straw man SR and misapply the relativistic formula in order to try and discredit it.

Reply

2 replies 2 @TruthNerds @TruthNerds Member (5 years, 9 months) Received one of the highest number of hearts from you Publicly subscribed to you (6 years)

• 3 days ago

PS: The speed of light is actually the same in all media if you take the front velocity of a light pulse. That might also be called the speed of causality. What changes in water is the phase velocity. While this is very important for some optical effects, namely refraction, it is irrelevant for the derivation of the relativistic aberration formula.

PPS: Why do we still use the classical formula? It is simpler and a good approximation for non-relativistic speeds. However, we now know to also only use constant c in it. Then the formula's original derivation becomes invalid, but it remains valid as a numerical approximation. (It can be independently derived as an approximation of the SR formula.)