Groups > sci.physics.relativity > #600038

Re: Kinetic Energy formula check - a series of short burn rockets, and see how the velocity adds up.

From	Thomas Heger <ttt_heg@web.de>
Newsgroups	sci.physics.relativity
Subject	Re: Kinetic Energy formula check - a series of short burn rockets, and see how the velocity adds up.
Date	2023-01-22 08:24 +0100
Message-ID	<k346klF78caU1@mid.individual.net> (permalink)
References	(12 earlier) <tq6nuu$3b8ve$1@dont-email.me> <k2poiiFi1jiU1@mid.individual.net> <tq9ojl$12dv7$1@dont-email.me> <k2sd92Fud77U1@mid.individual.net> <tqccu9$1n9f5$1@dont-email.me>

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Am 19.01.2023 um 22:33 schrieb Volney:
> On 1/19/2023 3:28 AM, Thomas Heger wrote:
>> Am 18.01.2023 um 22:33 schrieb Volney:
>>> On 1/18/2023 3:22 AM, Thomas Heger wrote:
>>>> Am 17.01.2023 um 19:04 schrieb Volney:
>>>>
>>>>>> Such inertial frames require absense of gravity, which we earthlings
>>>>>> obviously cannot provide.
>>>>>
>>>>> As usual in physics, especially then, things are tested to within an
>>>>> error limit, where it can be shown the error from the existence of
>>>>> gravity or whatever is smaller than measurement errors or outcome
>>>>> error.
>>>>>
>>>>> Secondly, this is theoretical, it's what happens when there is no
>>>>> gravity even if such a situation is difficult or impossible to
>>>>> reproduce
>>>>> in real life. Just like Einstein's trains, moving at a substantial
>>>>> fraction of c, with observers able to time flashes from lightning
>>>>> bolts
>>>>> as a train passes an embankment aren't real.
>>>>>
>>>>>> But in such a dark and gravity free inertial frame, you have
>>>>>> abolutely
>>>>>> nothing, which could eventually help you to measure absolute
>>>>>> velocity.
>>>>>
>>>>> And Einstein doesn't try to use any absolute velocity. He says simply
>>>>> here's a frame where the equations of Newton's mechanics hold good.
>>>>> Are
>>>>> you going to complain that Einstein didn't discuss moving objects
>>>>> around
>>>>> and accelerating them to test Newton's mechanics?
>>>>>>
>>>>>> In that scenario you always need something, where you could base your
>>>>>> position vectors on.
>>>>>
>>>>> You, the observer, say "Here's the origin".
>>>>
>>>> That would be actually correct, but was not, what Einstein said.
>>>
>>> He defined a frame in which 'equations of Newton hold good'. Period. He
>>> defined the origin. No other reference frame necessary.
>>>>
>>>> I personally use a concept I call 'subjectivism', which states, that
>>>> all observers would naturally take the own position and base
>>>> observations upon that.
>>>
>>> Thus, Einstein use the perspective of an unnamed observer and called
>>> this frame "the stationary frame". That's really just a name, it has no
>>> special features like being "absolutely stationary" in some way.
>>
>> What Einstein had in mind is not important, but what he wrote in his
>> text.
>
> But he didn't need to write things his peers were well acquainted with,
> such as the definition of an inertial reference frame.


Einstein wrote such a definition with: a coordinate system in which the 
equations of Newtons mechanics hold good.

That is what Einstein wrote and what we should take as his definition.

Other definitions could float around among his peer, but we need to take 
his words verbatim and use definitions as he defined terms.

Other terms in use among physicists could safely be used without 
definition. For instance the terms 'acceleration' or 'force' would not 
need to be defined. These have well accepted meanings among physicists 
and could be used accordingly.


>> I wrote a critique about 'On the electrodynamics of moving bodies' and
>> didn't attempt to read his mind in a psychoanalysis.
>>
>> It is simply irrelevant, what Einstein really wanted, if he didn't
>> write that in his paper.
>
> Except things there was no need to write what you claim is needed.
> Remember who his target audience was!

Sure. He wrote for physicists.

But that was not the problem I had adressed.

The problem was, that even physicists need to know, what Einstein 
actually wanted to say.


>> Also subsequent papers are irrellevant for a review, because at the
>> time of the article those didn't exist.
>>
>> That's why I'm allowed to ignore Einstein's real intentions, if they
>> were not put into words and those into the text.
>
> You can't ignore things established in the field of interest. Does he
> need to prove 2+2=4 if he uses that in his paper? How about everything
> Galileo said about inertial frames?

Well, Gallileo is certainly quotable. But without a quote, it wouldn't 
be possible to know, whether Einstein meant Gallileo or not.


>> Sure, 'the perspective of an unnamed observer' would make sense, but I
>> cannot find such a statement in the text.
>
> It wasn't necessary. The first part of his kinematics section explains
> the frame he is going to use.


But "a coordinate system in which the equations of Newtons mechanics 
hold good" does not contain " unnamed observer".

You simply must not 'fill in the blanks' with your own preoccupied 
knowledge, but can take only, what is actually written.

To fill the blanks would make things appear in a text, which simply are 
not there. And it would make also different 'copies' possible, if 
different readers fill the blanks differently.



>> Contrary to your view, Einstein gave the impression, that he wanted to
>> measure velocity against a static and well defined universe.
>
> No, he didn't. He used the definition of an inertial frame without
> boring his intended audience (not you) what an inertial frame was.


Well, that's not a particularily boring question in the topic of relativity.

But Einstein gave in fact a definition of the coordinate system called 
'stationary' and used that.

That is good enough, but would not define 'stationary' properly, because 
Newton's equations are not restricted to absolutely stationary systems.

>> This was actually a self-contradicting statement, because Einstein
>> also wrote, that Newton's absolute space would not exist.
>
> Since he wasn't intending to measure any velocity "against a static
> universe", this claim is irrelevant.


Sure, but against what else did he want to measure 'stationary'?

...


TH

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