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From: Thomas Heger <ttt_heg@web.de>
Newsgroups: sci.physics.relativity
Subject: Re: Relativistic aberration
Date: Wed, 17 Jul 2024 09:05:15 +0200
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Am Dienstag000016, 16.07.2024 um 16:47 schrieb gharnagel:

> 
> Yes, I understand what you're saying.  What needs to be understood is
> just how many molecules make up the normal matter around us (think
> Avogadro's number).  Interstellar space contains between 20 and 50
> hydrogen atoms per cubic cm:
> 
> https://en.wikipedia.org/wiki/Interstellar_medium
> 
> Half of the distance to the Large Magellanic Cloud is outside our
> galaxy,
> so the density is even lower.  At 50/cm3, the entire 168,000 light years
> amounts to only a two meter thickness of hydrogen at STP!  So I'm afraid
> the astrophysicists cannot use that to save their precious
> speed-of-light
> skins.
> 
> "Why is the speed of light so slow when the universe is such a really,
> really big place?" -- G. L. Harnagel



This is a tautology:

What we see in the night sky is actually our own past light-cone.

This means: light is relatively slow for the wastness of the universe, 
hence we can see everything only with a certain delay and the further 
away, the longer the delay, according to x = c* t
(with x= distance in meters, t = delay in seconds).

This 'longer away' is usually measured in light years and the delay in 
years.

Since the night sky shows only a delayed image of past events, the speed 
of light cancels out of the equations and we can put any value into it 
and always get a valid picture of the universe.

So we only assume, that light moves always with ~300 million meters per 
second through the entire universe.

But if light would speed up or slow down, we would not be able to 
measure this, because we always see the own light cone in the night sky 
and c is already embedded into it (for whatever a value c actually has 
in outer space).


TH