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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: sci.physics.relativity
Subject: Re: Division by zero
Date: Sat, 1 Feb 2025 11:36:25 +0200
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On 2025-02-01 08:14:08 +0000, Thomas Heger said:

> Hi NG
> 
> I'm actually not really certain, but found an error in Einstein's 'On 
> the electrodynamics of moving bodies' which is quite serious.
> 
> 
> See page six, roughly in the middle:
> 
> There we find an equation, which says this:
> 
> ∂τ/∂y= 0

Do you mean on page 899 (9th page of the article) in §3?
The operation is not division but a partial derivative.

> Now, 'tau' is a time belonging to the moving system k.

Yes, but it is also a number that is computed from coordinates of K.

> This system k moves along the x-axis of system K with velocity v, while 
> x- and xsi-axis coincide and etha- and y axis remain parallel.
> 
> In other words v_y is permanently zero,

Yes,

>  or: ∂y=0.

No. ∂y is not a number but a part of an operator. There are points with
different values of y and ∂/∂y refers to a line where t, x, and z (but not
y) have the same value at every point.

See https://en.wikipedia.org/wiki/Partial_derivative

-- 
Mikko