Re: The first postulate is a truism.

Le 21/06/2025 à 23:14, clzb93ynxj@att.net (LaurenceClarkCrossen) a écrit :

On Sat, 21 Jun 2025 10:19:43 +0000, Mikko wrote:
 

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
/ˈtrˌizƏm/  n. a statement that is obviously true and says nothing new
or interesting. —truistic/trˈistik/ 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.

So, Einstein added nothing new. How does that provide a basis for his
new theory? That he accepted the consensus view since Newton?

Read paragraph I.1. in Einstein paper. This is the main point : the meaning of the time coordinate  in an inertial frame.
Up to Einstein (well, it started before with Poincaré and others) it was taken for granted that you don't have to care about the time label of a given event, without justification but the prejudice of existence of some "universal time". Einstein asked for the time coordinate to be defined physically and proposed a procedure (the same one Poincaré proposed before) and he proved that such a procedure is in conflict with absolute simultaneity. Moreover it provides a way to treat space-time as a geometric object (i.e. independent of coordinates), then comes Minkowski, GR, etc.
Einstein expressed for space-time what Pythagoras theorem expressed for space: a coordinate-free invariant.