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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: sci.physics.relativity
Subject: Re: The first postulate is a truism.
Date: Tue, 24 Jun 2025 12:38:54 +0300
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On 2025-06-23 21:52:05 +0000, LaurenceClarkCrossen said:

> On Mon, 23 Jun 2025 17:20:59 +0000, J. J. Lodder wrote:
> 
>> LaurenceClarkCrossen <clzb93ynxj@att.net> wrote:
>> 
>>> On Sun, 22 Jun 2025 11:25:52 +0000, J. J. Lodder wrote:
>>> 
>>>> Mikko <mikko.levanto@iki.fi> wrote:
>>>> 
>>>>> On 2025-06-20 18:55:34 +0000, LaurenceClarkCrossen said:
>>>>> 
>>>>>> On Fri, 20 Jun 2025 9:06:49 +0000, Mikko wrote:
>>>>>> 
>>>>>>> On 2025-06-19 17:37:29 +0000, LaurenceClarkCrossen said:
>>>>>>> 
>>>>>>>> Perplexity:
>>>>>>>> 
>>>>>>>> "The First Postulate of Special Relativity
>>>>>>>> 
>>>>>>>> Statement of the First Postulate
>>>>>>>> 
>>>>>>>> The first postulate of special relativity, also known as the principle
>>>>>>>> of relativity, states:
>>>>>>>> 
>>>>>>>> The laws of physics are the same in all inertial frames of
>>>>>>>> reference."
>>>>>>>> 
>>>>>>>> 
>>>>>>>> "truism
>>>>>>>> /?tr?iz?m/  n. a statement that is obviously true and says nothing new
>>>>>>>> or interesting. —truistic/tr?istik/ adj." -Oxford American.
>>>>>>> 
>>>>>>> The first postulate is not a truism. It is possible to imagine a world
>>>>>>> where it is not true and to believe that we actually live in a such
>>>>>>> world.
>>>>> 
>>>>>> Your reply does not explain how it is not obviously true and nothing new
>>>>>> that wasn't already known long before Einstein.
>>>>> 
>>>>> I did explain. And what I said was indeed known long before Einstein.
>>>>> 
>>>>> If the first postulate were a truism nobody would ever have believed
>>>>> otherwise. But ancinet literature shows that the opposite belief was
>>>>> common.
>>>> 
>>>> Indeed.
>>>> In particular Maxwell's equations were generally believed before 1905
>>>> to hold only in one prefered frame. (the rest frame of the aether)
>>>> 
>>>> Einstein's postulate applied to electromagnetism
>>>> was new and revolutionary, and seen as such at the time,
>>>> (by those who mattered)
>>>> 
>>>> Jan
>>> Jan, thank you for a steel man of the first postulate.
>>> 
>>> Was Einstein qualified to declare this for all of physics, or was he
>>> mainly acquainted with electromagnetism?
>> 
>> Einstein was a generalist.
>> 
>>> So, before Einstein, electromagnetism was the only field of physics
>>> believed to not apply to all frames?
>> 
>> In 1900 there was Newtonian mechanics, and electromagnetism.
>> What other fields of theoretical physics do you see?
>> 
>>> Is there no other equation expressing a law of physics that is not true
>>> in every frame of reference?
>>> 
>>> The law of free fall (v=gt) is for one frame, and Newton's gravity
>>> formula (F= MG/r^2) for another.
>>> 
>>> Wouldn't the aether include all reference frames?
>> 
>> Certainly, but the aether was supposed to define a preferred frame.
>> (its rest frame, in which Maxwell's equations were valid)
>> So the problem was how to modify Maxwell's equations
>> to predict phenomena in other frames.
>> Different frames required different modifications,
>> with mutually contradictory views on 'aether dragging'.
>> 
>> Einstein solved all that once and for all,
>> by making electromagnetism frame-independent too,
>> 
>> Jan

> Then relativity still modifies equations of physics using different ones
> for different irfs, making it frame-dependent.

That is strictly false.

-- 
Mikko