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Newsgroups: sci.physics.relativity
Subject: Re: Approximately 300,000 km/s With Respect To What?
From: nospam@de-ster.demon.nl (J. J. Lodder)
Reply-To: jjlxa31@xs4all.nl (J. J. Lodder)
Date: Fri, 12 Jul 2024 11:55:27 +0200
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Mikko <mikko.levanto@iki.fi> wrote:

> On 2024-07-11 19:58:02 +0000, amirjf nin said:
> 
> > Approximately 300,000 km/s with respect to what?
> 
> Whenever the speec of something is measured it is measured with respect
> to someting else. The report should make clear what is the reference that
> is considered stationary. Usually it is the instruments used in the
> measurement, and usually but not always they are at rest with restpect to
> Earth surface at the place of the measurement.

You really need to have a look at what and how is actually measured,
instead of elaborating your own ideas of measurement.

FYI, in the precision 'speed of light' measurements
that preceded the abolition of the meter in 1983
physicists measured the frequency of a standing wave.
This is a proper measurement in a proper frame,
yielding an obviously dimensionless number. 
(a world scalar of course, being the same in every proper frame.)
It does not involve something going from somewhere.

> Sometimes numbers with units of speed are used for other purposes instead
> of speed, for example in E = mc?, where c has units of speed. In those cases
> the question need not be asked.

Standard error: speed does not -have- a unit.
(except for high school kiddies)
Conversely, 'm/s' is not -a property- of the physical quantity 'speed',
You suffer from misconceptions induced by an 'SI-only' education,

Jan