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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: sci.physics.relativity
Subject: Re: Division by zero
Date: Sun, 2 Feb 2025 11:38:32 +0200
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On 2025-02-02 08:26:00 +0000, Thomas Heger said:

> Am Sonntag000002, 02.02.2025 um 07:52 schrieb Thomas Heger:
>> Am Samstag000001, 01.02.2025 um 10:36 schrieb Mikko:
>>> 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.
>> 
>> τ was the name of the time coordinate in k and also the name of a 
>> function, which was meant as coordinate transformation between K and k.
>> 
>> The time coordinate of an event in K has also a value in respect to k, 
>> hence time t of K should belong to the parameters of this function τ.
>> 
>> But y should not, because the velocity along the y-axis was assumed to 
>> be zero and the axes of y and eta are assumed to remain parallel.
>> 
>> So we had a function of time tau, which is 'vertical' upon the value zero of y.
>> 
>> In my view, such a function would VERY steep, hence ∂τ/∂y= infinity 
>> (and not zero!)

> For me seemingly ∂y/∂τ= 0 was meant, but ∂τ/∂y= 0 was written.

That "seemingly" is only possible if you don't understand the text
you are attempting to discuss.

The topic at the point is to discuss how τ is determined from x, y, z, and t.
In that context ∂y/∂τ is irrelevat.

You should find out what the symbols in the formulas mean and how the
formulas relate to the surrounding prose before you continue this duscussion.

-- 
Mikko