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Re: Meditations about the force

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Luigi Fortunati wrote:

> Thomas 'PointedEars' Lahn alle ore 01:34:19 del 16/08/2017 ha scritto:
>> For example (as we are in .relativity), general relativity postulates
>> that the gravitational force (short: gravity) is an illusion, only an
>> *apparent* force, too:
> 
> It is a controversial postulate.

Maybe in past science, or outside of science.  In current science it is not 
controversial at all, given the number of experiments that confirm(ed) it.

There is one particular experiment that confirms it that is performed 
continuously – do you know what it is?
 
> What is the apparent force? It's an illusion!

Correct, except you need to say “an” instead of “the”.  There is not just 
one apparent force.

> The apparent force "seems" to be there but it is not there.

That is what *I* said.

> And how does one distinguish a force from a force that is not there?

I have already told you.

> You control the acceleration!

That statement does not make sense.
 
> If there is acceleration the force is real (F=ma) if there is no
> acceleration the force is apparent, it is an illusion, it is a ghost.
> 
> A ball that rolls without friction seems to advance as though it were
> pushed by a force but there is no force, then?

It is the classical, Aristotelian fallacy that a force would be necessary to 
keep things in motion:

<https://www.youtube.com/watch?v=mYDrufxpW9E>

Newton’s first law of motion already shows that to be false: “A body remains 
at rest or in inertial motion *unless* a force is acting upon it.”

This holds true even in general relativity, but one must redefine inertial 
motion as inertial motion along a spacetime geodesic.

> Then there is no force because the ball moves but does not accelerate!
> 
> The inertia force is illusory (it is apparent) because it does not
> accelerate.

You are contradicting yourself by saying nonsensical things after you said 
right, trivial things just after you have said the opposite, patently wrong 
things.
 
> Instead gravity accelerates and is therefore real and not apparent.

Not in general relativity, where spacetime is dynamic and is curved in the 
presence of energy–momentum.

That general relativity is not just a fancy idea, but corresponds well with 
observation, has been confirmed numerous times and is going to be confirmed 
again, and with even greater precision we hope, during this year’s total 
solar eclipse, on 2017-08-21 UTC.  Watch that space.
 
> Can you give me an example in which gravity is not associated with any
> acceleration?

Ex falso quodlibet.  You are proceeding from the (false) assumption that 
gravity is a real force in the first place.  Of course, *only* if you assume 
that it is a real force, then there has to be a corresponding real 
acceleration.

You must realize that a flat spacetime (or absolute space and time, as 
Newton thought) requires an attractive force – gravity – and acceleration, 
to have orbits; while a curved spacetime requires force and acceleration to 
be *absent* to have the same orbits.  In a curved mathematical space, the 
projection of the shortest path connecting two points is _not_ a line.  Try 
city-to-city flights on Terra for a start.

It also turns out that Newton’s idea of the gravitational force is only a 
good approximation as long as masses are small; IOW, the greater the masses, 
and speeds the greater the error in calculations based on Newtonian gravity:

The precession of the perihelion of Mercury cannot be explained using 
Newtonian gravity.  It can be explained with great precision using general 
relativity.

According to Newton, the stars’ light should have been deflected half as 
much by Sol than it was measured during the 1919 solar eclipse and later; 
put simply, they should have appeared somewhere else than observed.  They 
were observed almost exactly where general relativity predicted them to be.

<https://en.wikipedia.org/wiki/Tests_of_general_relativity>

Finally, according to Newton, those gravitational waves could never have 
been detected by LIGO as they have been, because in his view gravity 
propagated instantaneously.  They (GW150914) were detected exactly as 
general relativity predicted.  And again the second (GW151226) and third 
time (GW170104).

<https://en.wikipedia.org/wiki/List_of_gravitational_wave_observations>

If you do not want to discuss about the theories of relativity, you should 
not post here, in sci.physics.*relativity*.
 
-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

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Thread

Meditations about the force Luigi Fortunati <fortunati.luigi@gmail.com> - 2017-08-15 17:50 +0200
  Re: Meditations about the force Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-16 01:34 +0200
    Re: Meditations about the force mlwozniak@wp.pl - 2017-08-15 23:34 -0700
      Re: Meditations about the force Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-19 12:52 +0200
        Re: Meditations about the force Séverin Thibault <ruud@bwiu.ei> - 2017-08-19 11:04 +0000
        Re: Meditations about the force mlwozniak@wp.pl - 2017-08-19 10:43 -0700
    Re: Meditations about the force Luigi Fortunati <fortunati.luigi@gmail.com> - 2017-08-18 10:10 +0200
      Re: Meditations about the force mlwozniak@wp.pl - 2017-08-18 01:32 -0700
      Re: Meditations about the force Dirk Van de moortel <dirkvandemoortel@hotspam.not> - 2017-08-18 15:06 +0200
      Re: Meditations about the force Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-18 15:56 +0200
        Re: Meditations about the force mlwozniak@wp.pl - 2017-08-18 07:06 -0700
      Re: Meditations about the force "Paul B. Andersen" <relativity@paulba.no> - 2017-08-19 14:00 +0200
        Re: Meditations about the force Luigi Fortunati <fortunati.luigi@gmail.com> - 2017-08-19 17:45 +0200
          Re: Meditations about the force Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-08-19 21:28 +0200
        Re: Meditations about the force mlwozniak@wp.pl - 2017-08-19 10:44 -0700
        Re: Meditations about the force Thomas Heger <ttt_heg@web.de> - 2017-08-19 20:19 +0200
          Re: Meditations about the force Séverin Thibault <ruud@bwiu.ei> - 2017-08-19 19:56 +0000
            Re: Meditations about the force Séverin Thibault <ruud@bwiu.ei> - 2017-08-19 20:00 +0000

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