Re: The first postulate is a truism.

On Mon, 23 Jun 2025 17:20:59 +0000, J. J. Lodder wrote:

LaurenceClarkCrossen <clzb93ynxj@att.net> wrote:
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On Sun, 22 Jun 2025 11:25:52 +0000, J. J. Lodder wrote:
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Mikko <mikko.levanto@iki.fi> wrote:
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On 2025-06-20 18:55:34 +0000, LaurenceClarkCrossen said:
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On Fri, 20 Jun 2025 9:06:49 +0000, Mikko wrote:
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On 2025-06-19 17:37:29 +0000, LaurenceClarkCrossen said:
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Perplexity:
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"The First Postulate of Special Relativity
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Statement of the First Postulate
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The first postulate of special relativity, also known as the principle
of relativity, states:
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The laws of physics are the same in all inertial frames of
reference."
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"truism
/?tr?iz?m/  n. a statement that is obviously true and says nothing new
or interesting. —truistic/tr?istik/ adj." -Oxford American.

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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.

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Your reply does not explain how it is not obviously true and nothing new
that wasn't already known long before Einstein.

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I did explain. And what I said was indeed known long before Einstein.
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If the first postulate were a truism nobody would ever have believed
otherwise. But ancinet literature shows that the opposite belief was
common.

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Indeed.
In particular Maxwell's equations were generally believed before 1905
to hold only in one prefered frame. (the rest frame of the aether)
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Einstein's postulate applied to electromagnetism
was new and revolutionary, and seen as such at the time,
(by those who mattered)
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Jan

Jan, thank you for a steel man of the first postulate.
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Was Einstein qualified to declare this for all of physics, or was he
mainly acquainted with electromagnetism?

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Einstein was a generalist.
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So, before Einstein, electromagnetism was the only field of physics
believed to not apply to all frames?

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In 1900 there was Newtonian mechanics, and electromagnetism.
What other fields of theoretical physics do you see?
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Is there no other equation expressing a law of physics that is not true
in every frame of reference?
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The law of free fall (v=gt) is for one frame, and Newton's gravity
formula (F= MG/r^2) for another.
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Wouldn't the aether include all reference frames?

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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'.
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Einstein solved all that once and for all,
by making electromagnetism frame-independent too,
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Jan

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