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Groups > sci.physics.relativity > #463071
| From | Thomas 'PointedEars' Lahn <PointedEars@web.de> |
|---|---|
| Newsgroups | sci.physics.relativity |
| Subject | Re: sci.physics.relativity |
| Date | 2018-06-30 18:49 +0200 |
| Organization | PointedEars Software (PES) |
| Message-ID | <34379c3d-4bdc-eca3-e41f-87257530c4e5@PointedEars.de> (permalink) |
| References | (3 earlier) <nf4i2jxkik93.1eojfo62foh97$.dlg@40tude.net> <e6d64558-a1ae-060a-8137-51087cb69f3c@PointedEars.de> <osednT5BsoyWcanGnZ2dnUU7_8zNnZ2d@giganews.com> <2441761.mvXUDI8C0e@PointedEars.de> <plqkyntule4e.9mx1pp9y9h1b$.dlg@40tude.net> |
SolomonW wrote:
> On Thu, 28 Jun 2018 11:08:38 +0200, Thomas 'PointedEars' Lahn wrote:
>> Tom Roberts wrote:
>>> On 6/27/18 8:22 AM, Thomas 'PointedEars' Lahn wrote:
>>>> SolomonW wrote:
>>>>> Newton and Newtonian physics are not quite the same thing.
>>>> First of all, that is nonsense.
>>> No, it is true, fundamentally.
>> No, it is not.
>
> Please explain why you feel that they are the same? For example, do you
> feel that nothing changed after Newton with Newtonian physics after his
> death?
Fundamentally, nothing changed. The idea that something has changed is
based on the ignorance of what Newton actually said or on a
misinterpretation of what he actually meant, and therefore a misconception
of what Newtonian physics is.
For example, one can derive Newton’s second law of motion by application of
the post-Newtonian concept of the action and the Euler–Lagrange equation:
L = T − U,
where L is the Lagrangian, T is the kinetic energy and U is the potential
energy. Then for a single particle with a position with one coordinate we find
L = m∕2 ẋ² − U(x)
∂L∕∂q_i − d∕dt ∂L∕∂q̇_i = 0
∂L∕∂q_i = d∕dt ∂L∕∂q̇_i
q₁ := x
∂L∕∂x = d∕dt ∂L∕∂ẋ
−∂U∕∂x = d∕dt m ẋ
−∂U∕∂x = m d∕dt ẋ = d∕dt m v = d∕dt p = ṗ
F = m ẍ = ̇p (Newton’s version of the 2nd law)
F = m a (Euler’s version of the 2nd law) ∎
And, for example, in all of this, it is *still* implied that there is only
one measure of time, t, that is the *same* for all abservers.
>>> Newton thought that space and time are "absolute". Today, we know that
>>> absolute space and time are irrelevant, because all of the Newtonian
>>> laws of physics are valid in any inertial frame (not just a single
>>> "absolute" frame).
>> But this is not "Newtonian physics".
>
> How is it not "Newtonian physics"?
The idea that space and time are absolute in the way that Newton meant it
(as he has endeavoured to explain, expecting this misinterpretation of his
ideas) is inherent in Newtonian physics as it is being taught today.
> Are you saying an observer using Netonian physics in different inertial
> frame.
I do not know what that is, but it is not a sentence.
> Imagine you have two observers A and B.
>
> A on Earth starts his clock now and measures a planet X,Y,Z position from
> him and its velocity.
>
> B is travelling in a rocket towards the planet. He starts his clock much
> later and measures a planet X,Y,Z position from him and velocity.
>
> All figures will be different and in Newtonian physics none will be wrong.
No. I can only repeat that you do not understand what Newton said and
Newtonian physics says, as compared to *relativistic* physics.
>>> So for the past century (at least), Newton's "absolute space and time"
>>> have had no effect on any modeling using Newtonian physics. IOW: they
>>> are just words with no impact.
>> Incorrect.
>
> Explain why you feel so?
The notions that Newton held about space and time are inherent in what is
being taught as Newtonian physics/mechanics, even when it is not taught
*explicitly* (but in fact it is, especially when one moves in teaching from
Newtonian to relativistic physics).
>>>>> To make Newtonian physics to work you need to have some arbitrary point
>>>>> to measure from, think about an object which is measured with x, y, z
>>>>> directions at a time of t. All these measurements are from some
>>>>> arbitrary point and time.
>>> It actually requires considerably more: an inertial coordinate system.
>>> Just a single point is woefully inadequate.
>> You don’t say.
>
> So we agree that it is even more relative then I stated,
No, we do not agree. (“You don’t say” is an English idiom, a shorthand for
“tell me something that I do not know yet”. Synonyms include “preaching to
the choir”.)
> how does this support your argument of absolute?
Newton assumed absolute space and time, and when we are discussing Newtonian
physics we are using these notions implicitly.
>>>> Once again: You do not understand what “relativity of space and time” in
>>>> “theories of relativity” means.
>>> You are lumping together incommensurate theories -- the concepts of
>>> space and time are CONSIDERABLY different among Newtonian physics, SR,
>>> and GR. But all can be classified as "theories of relativity" -- that
>>> phrase is essentially useless.
>> It is not I who is doing the “lumping together” here.
>
> Indeed, you are arguing that they are separate one is relative, and the
> other is absolute.
I have not argued such a gibberish or anything like it.
--
PointedEars
Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.
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Re: sci.physics.relativity SolomonW <SolomonW@citi.com> - 2018-06-27 21:23 +1000
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Re: sci.physics.relativity SolomonW <SoloomonW@citi.com.au> - 2018-06-29 12:18 +1000
Re: sci.physics.relativity Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-06-30 18:49 +0200
Re: sci.physics.relativity SolomonW <SolomonW@citi.com> - 2018-07-01 13:05 +1000
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