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From: helbig@asclothestro.multivax.de (Phillip Helbig (undress to reply))
Newsgroups: sci.physics.research
Subject: Re: Apparent rotation
Date: 12 Jan 2023 08:23:17 GMT
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From: helbig@asclothestro.multivax.de
In article , Luigi Fortunati
writes:
> Phillip Helbigundress to reply mercoled=EC 11/01/2023 alle ore 09:32:14
> ha scritto:
>
>>> Why bother the distant universe if rotation (like any other
>>> acceleration) are "absolute"?
>>>
>>> Matter is made up of atoms with a nucleus inside.
>>>
>>> If we rotate the matter (ie the atoms) the nuclei that "float" inside
>>> them "push" outwards and generate centrifugal force opposed by the
>>> centripetal force of the molecular bonds.
>>>
>>> The presence of these two opposing internal forces of matter is
>>> confirmed by the internal tension of the rotating bodies.
>>
>> Yes. No-one debates the fact that accelerations are absolute. The
>> question is WHY that is the case. Imagine an empty universe with one
>> object in it, say a merry-go-round. Should it be possible to tell if it
>> is rotating, as it would be under normal conditions? If so, with
>> respect to what is it rotating? There is nothing else in the Universe.
>
> There is a contradiction in what you write.
>
> First you say that accelerations are absolute and then you ask "with
> respect to what is it rotating?".
It is an empirical fact that they are absolute. But the very word
"rotation" implies that it is rotating with respect to something. But
what?
> If they are absolute, they cannot depend on the reference!
Another way of looking at it is that they provide an absolute reference,
absolute space, a Newtonian idea which some think Einstein did away
with.
> I say that the "real" rotations (those where centripetal and
> centrifugal forces are manifested) are absolute and the "apparent"
> rotations (those where neither centripetal nor centrifugal forces are
> manifested) are relative.
I am sitting on a chair. If I can feel it pushing on me, then I am
really being accelerated, as opposed to someone thinking I am because of
some strange coordinates. (Ignoring for the moment that I also feel it
pushing on me at rest in a gravitational field.)
> In an empty universe there could be only real rotations, those where
> the question "with respect to what is it rotating?" it has no reason to
> exist, being absolute and not relative.
Right. But do such real rotations imply some sort of absolute space?
It's a hard question. Einstein spent years thinking about it.
>> Some would claim that there would be no way to tell in such a case, i.e.
>> no inertia.
>
> I did not get this.
That is a claim some people make. If one thinks that what determines a
real acceleration is acceleration relative to some average of mass in
the Universe, then it makes sense for inertia to be proportional to such
mass.
> Do you think that in a completely empty universe there would be no
> centripetal and centrifugal forces?
I don't know.
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