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Re: Why does gravity have to be transmitted through particles when gravity isn't a force in general relativity?

Subject	Re: Why does gravity have to be transmitted through particles when gravity isn't a force in general relativity?
Newsgroups	sci.physics.relativity
References	(16 earlier) <dd7c0e02-559b-4a8c-b121-6f8fc079947c@googlegroups.com> <ywPXC.623316$Hc3.377471@fx30.am4> <bad4cf0a-86c3-4b4d-85f0-c41a9ae12f67@googlegroups.com> <bx9YC.766381$nr7.569006@fx31.am4> <d97ed5e3-d083-4404-886e-aad672be48cc@googlegroups.com>
From	"Paul B. Andersen" <relativity@paulba.no>
Message-ID	<cGbYC.320405$463.265649@fx21.am4> (permalink)
Organization	Eweka Internet Services
Date	2018-06-25 21:48 +0200

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Den 25.06.2018 20.27, skrev kenseto:
> On Monday, June 25, 2018 at 1:22:17 PM UTC-4, Paul B. Andersen wrote:
>> Den 24.06.2018 21.09, skrev kenseto:
>>> On Sunday, June 24, 2018 at 12:19:44 PM UTC-4, Paul B. Andersen wrote:
>>>> Den 23.06.2018 13.52, skrev kenseto:
>>>>> On Friday, June 22, 2018 at 4:56:22 PM UTC-4, Paul B. Andersen wrote:
>>>>>> Den 22.06.2018 17.25, skrev kenseto:
>>>>>>> On Friday, June 22, 2018 at 4:50:43 AM UTC-4, Paul B. Andersen wrote:
>>>>>>>>
>>>>>>>> https://paulba.no/Spaceship.html
>>>>>>>
>>>>>>>> Ralph is travelling in his spaceship in interplanetary space on his way to Mars. The interior of the ship is cylindrical with  radius 10 metres. The ship is rotating with the angular velocity 1 radian per second, which >gives a centripetal acceleration of 10 m/s2 on the inner wall. So Ralph can walk around on the inner wall, always feeling that the gravitation is 1 g. Since there are no portholes in the ship, Ralph isn’t aware that the >spaceship is rotating; he thinks there is some form of artificial gravity made with Star Trek technology.
>>>>>>>
>>>>>>> Ralph is rotating with the ship and he is experiencing the CF force and this causes him to accelerate toward the wall and the wall is preventing him to accelerate further and that’s the artificial gravity he is experiencing.
>>>>>>
>>>>>> The only force that is acting on Ralph is the force
>>>>>> from the wall pushing him toward the centre.
>>>>>> The centripetal force.
>>>>>
>>>>> No, the wall is not moving so it can’t exert any CP force on Ralph. Ralph is in a state of CF accelerating motion toward the wall and the wall prevents him from going further and that’s the artificial gravity.  There is no CP force.
>>>>
>>>> Ken, Ken, Ken ... :-)
>>>>
>>>> In which direction did you say Ralph is accelerating?
>>>> Is he going through the wall? :-D
>>>>
>>>> https://paulba.no/div/CentripetalAcc.pdf
>>>
>>> Yes, Ralph’s CF motion is trying to make him going through the wall and the wall is preventing him to do so. That’s the artificial gravity Ralph is experiencing.
>>>
>>
>> An analogy:
>> Ken is standing on the floor in a spaceship
>> in interstellar space. A rocket engine
>> is giving the spaceship an upwards (on the drawing)
>> acceleration a.
>>
>>      / \
>>     /   \
>>    |  O  |
>>    | /|\ |
>>    |  |  |
>>    | / \ |
>>    -------
>>       ^
>>       |
>>       F
>>
>> Explanation #1:
>> The floor is exerting a real upwards force on Ken,
>> giving Ken an upwards acceleration a in
>> accordance with Newton’s second law.
> 
> In this case the floor of the rocket initiated the movement so it exerts a real upward force on Ken. And Ken feels heavier due to the upward force of the floor.
> 
>>
>> Explanation #2:
>> A real downwards force is acting on Ken, giving Ken
>> a downwards acceleration towards the floor.
>> This acceleration is trying to make him go through
>> the floor and the floor is preventing him from doing so.
>> That’s the artificial gravity Ken is experiencing.
> 
> No Ken is not exerting a downward force on the floor.....Ken has no way of generating a downward force.
> 
>>
>> Question #1:
>> Which explanation is correct?
> 
> Explanation #1 is correct.
>>
>> Question #2:
>> What would an accelerometer show the
>> direction of the acceleration to be?
>> Upwards or downwards?
> 
> Upwards.
>>
>> Question #3
>> What would an accelerometer on the wall
>> of the rotating spaceship show the
>> direction of the acceleration to be?
>> Towards the wall, or towards the centre?
> 
> Toward the wall....the accelerometer will have a CF acceleration against the wall and that’s why it direction of acceleration is point outside the wall.
> 

So tell me this, Ken:

Is there any way Ralph in the spaceship (without throwing
his ball) can tell whether he is in a rotating ship, or in
a non rotating ship which is accelerating linearly upwards
as seen by Ralph (from the wall where Ralph is standing towards
the centre).
Ralph would feel exactly the same artificial gravitation
in both cases, so why is explanation #2 correct in the former
case, while explanation #1 is correct in the latter case?

I suppose a physicist like you know that an accelerometer
stationary on the ground in the real gravitation of the Earth
shows that the acceleration is upwards.
So why does the accelerometer behave differently for
the two cases of artificial gravitation when Ralph
can't feel the difference?

-- 
Paul

https://paulba.no/

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