A question regards Gravity

[Rucki]

One questions regards gravity, which bothers me already for a long time.

For my question we assume that the whole universe, the whole space, absolutely everything is empty, there exists nothing, no matter, no particel, nothing, besides 2 objects, which i wont describe further, besides: 

The Object A has the mass of an Car and the object B has the mass of an pencil. Both objects are 999kLy away away from each ( so more distance than between earth and Sagittarius A ).

Time is freezed and they have no speed and no rotation, they are standing still and now the time goes on, its the first second in my fantasy universe, what happens now ?
 

 

I would think that both objects would start to pull each other, but the object with the mass of an car would pull the pencil mass object much harder. So Gravity or better saying "curved space" never ever ends ? Am I right ?

I also think that if both objects wouldnt be perfect spheres, but look like a real car and pencil, they would start to rotate as they are pulling each other, because the central point of gravity from each object is not perfectly aligned with the mid, am I right ?

Edited August 22, 2016 by Rucki

[Bill Phil]

Not much. Light that is being emitted ( if any) would travel a bit further. The two masses would feel a tiny nudge towards each other, and that's it.

[peadar1987]

Gravitational waves move through space at the speed of light, so in the first second, absolutely nothing would happen at all (according to my understanding)

[Wraith977]

both objects would feel an equal force of attraction to the other after 999 thousand years once the gravitational waves from the one has reached the other, since the mass of the car is greater than that of the pencil the car will accelerate much slower (Force = Mass x Acceleration, since the force is equal for both, the greater the mass, the slower the acceleration). Nothing I know of in physics would suggest that they would begin to rotate, it is their respective centres of mass that are attracting each other, not their geometric centres.

Edited August 22, 2016 by Wraith977

[Rucki]

34 minutes ago, Wraith977 said:

Nothing I know of in physics would suggest that they would begin to rotate, it is their respective centres of mass that are attracting each other, not their geometric centres.

 

Hmm but f.e. if the car has most of his mass in front, where the engine is. Wouldnt that lead to a rotation of the car ? I dont know why i believe that, but somehow I do.

 

Edit: made a simple picture with paint, what I have in mind:

http://imgur.com/a/tbUL2

 

 

Edited August 22, 2016 by Rucki
added picture

[Nibb31]

No, the car would just move front first and the rest will follow behind. No rotation.

[Rucki]

17 minutes ago, Nibb31 said:

No, the car would just move front first and the rest will follow behind. No rotation.

But if the cars starting position, isnt with the "front in front". So the car would get a little rotation, because the front goes to the side where the pencil is. So there is nothing to stop the rotation, cause its in space, beside the gravity of the pencil. But I guess that this is enough to "balance" the starting rotation out ?

So if there are only 2 bodys in space, their rotation will always ( if we presume enough time until they will meet each other ) "balance out" until they dont rotate anymore ?

Edited August 22, 2016 by Rucki

[Wraith977]

7 minutes ago, Rucki said:

*snip*

No, objects in space pivot around their centre of mass

If a force is applied to the geometrical centre of an object with an offset COM the object will rotate->

If a force is applied to the centre of mass of an object with an offset COM the object will not rotate->

What will happen with the car and the pencil is the second scenario, since the force is applied to the centre of mass of both objects, it's the same principle as balancing birds.

[Green Baron]

Hypothesis: The gravity-induced force is actually uneven, point masses are just a simplification for game purposes. So the part with the engine of the car will pull harder at the pencil whose penball-tip is lighter than the button tip. That'll induce a turning moment in both parts, they'll start to swing back and forth like two pendulums while falling towards each other. Since the initial impulse then is not straight towards each other they start and end up in a highly elliptical/almost hyperbolical orbit, and if there is no other force then after one orbit they will end there again. Meanwhile the pencil will have had enough time to become tidally locked, facing it's heavier part towards the heavier part of the car.

-------------

If the tidal locking takes energy out of the system then each pencil's PE (and AE) will be a little lower than the one before, leading to a final impact. There is a slight chance that the impact leaves my signature on the body of the car. But probably it'll just become disarmed cause the button end hits first.

 

Cultural background: is the car a Ford Model T ? It might still work then ...

:-)

 

Edited August 22, 2016 by Green Baron

[PB666]

1 hour ago, Rucki said:

One questions regards gravity, which bothers me already for a long time.

For my question we assume that the whole universe, the whole space, absolutely everything is empty, there exists nothing, no matter, no particel, nothing, besides 2 objects, which i wont describe further, besides: 

The Object A has the mass of an Car and the object B has the mass of an pencil. Both objects are 999kLy away away from each ( so more distance than between earth and Sagittarius A ).

Time is freezed and they have no speed and no rotation, they are standing still and now the time goes on, its the first second in my fantasy universe, what happens now ?
 

 

I would think that both objects would start to pull each other, but the object with the mass of an car would pull the pencil mass object much harder. So Gravity or better saying "curved space" never ever ends ? Am I right ?

I also think that if both objects wouldnt be perfect spheres, but look like a real car and pencil, they would start to rotate as they are pulling each other, because the central point of gravity from each object is not perfectly aligned with the mid, am I right ?

Gravity in a sense does not exist. Or let me put it differently gravity is a metric for the aggregate effects of quantum space-time.

Look up articles on the Quantum foam, this will best explain as to what is going on.

I will give it a shot, 2 objects are composed of energy quanta in the form of mass and kinetic and other forms of energy. The mass-energy equivalents propogate feilds that give rise to space-time, which the other mass-energy equivalents propagate through. At any given moment (and I mean moment as the smallest division of time), the various sources of fields haggle it out to craft 'cells' in the quantum foam, this then 'copenhagen interpretation' realizes into relativistic space-time, by a process  not understood. The foam evolves at around 10⁴⁴/sec so it does not stay around long enough for anyone to see, and currently they are trying, in space, to see if far off black holes merging can momentarily produce a quanta in space-time. Bets are that they will only be able to see composite.

So here is a better example. A black hole is a singularity (effectively) because we cannot individualize the events inside of the hole, we can only see the collective effect, from the observer the black hole is singly warping space-warping space time, it is effectively a point mass with an event horizon. The idea here is that as one approaches a black hole, the space time begins to flatten in the radial direction. The quantum foam is thus cells that are flat until the point in which you are at the event horizon, at which point cells in the quantum foam is two dimension. This is a quirk behavior because quantum space is point-like, so when we talk about cells in the quantum foam, its more like we are defining the probability of finding a quantum event within a certain proximity, events will be much closer in one dimension than in the other two.

http://arxiv.org/pdf/1607.05410.pdf

Edited August 22, 2016 by PB666

[Bill Phil]

15 minutes ago, Green Baron said:

Hypothesis: The gravity-induced force is actually uneven, point masses are just a simplification for game purposes. So the part with the engine of the car will pull harder at the pencil whose penball-tip is lighter than the button tip. That'll induce a turning moment in both parts, they'll start to swing back and forth like two pendulums while falling towards each other. Since the initial impulse then is not straight towards each other they start and end up in a highly elliptical/almost hyperbolical orbit, and if there is no other force then after one orbit they will end there again. Meanwhile the pencil will have had enough time to become tidally locked, facing it's heavier part towards the heavier part of the car.

-------------

If the tidal locking takes energy out of the system then each pencil's PE (and AE) will be a little lower than the one before, leading to a final impact. There is a slight chance that the impact leaves my signature on the body of the car. But probably it'll just become disarmed cause the button end hits first.

 

Cultural background: is the car a Ford Model T ? It might still work then ...

:-)

 

It's not an actual car, though. It has a similar mass ( a few tonnes).

[Green Baron]

Ah, i see. So if these masses are just two perfect marble balls then my hypothesis is wrong .... :-)

Edited August 22, 2016 by Green Baron

[Rucki]

2 minutes ago, Green Baron said:

Ah, i see. So if these masses are just two perfect marble balls then my hypothesis is wrong .... :-)

And if we assume that we have a real pencil and a real car ? :=)

51 minutes ago, Wraith977 said:

No, objects in space pivot around their centre of mass

If a force is applied to the geometrical centre of an object with an offset COM the object will rotate->

If a force is applied to the centre of mass of an object with an offset COM the object will not rotate->

What will happen with the car and the pencil is the second scenario, since the force is applied to the centre of mass of both objects, it's the same principle as balancing birds.

Now I see, thanks for the good explanation. Now I even feel a little stupid that I thought they would start to rotate

But I guess if we would give the car a "starting rotation", that this rotation would never ever stop ?

18 minutes ago, PB666 said:

Gravity in a sense does not exist. Or let me put it differently gravity is a metric for the aggregate effects of quantum space-time.

Look up articles on the Quantum foam, this will best explain as to what is going on.

I will give it a shot, 2 objects are composed of energy quanta in the form of mass and kinetic and other forms of energy. The mass-energy equivalents propogate feilds that give rise to space-time, which the other mass-energy equivalents propagate through. At any given moment (and I mean moment as the smallest division of time), the various sources of fields haggle it out to craft 'cells' in the quantum foam, this then 'copenhagen interpretation' realizes into relativistic space-time, by a process  not understood. The foam evolves at around 10⁴⁴/sec so it does not stay around long enough for anyone to see, and currently they are trying, in space, to see if far off black holes merging can momentarily produce a quanta in space-time. Bets are that they will only be able to see composite.

So here is a better example. A black hole is a singularity (effectively) because we cannot individualize the events inside of the hole, we can only see the collective effect, from the observer the black hole is singly warping space-warping space time, it is effectively a point mass with an event horizon. The idea here is that as one approaches a black hole, the space time begins to flatten in the radial direction. The quantum foam is thus cells that are flat until the point in which you are at the event horizon, at which point cells in the quantum foam is two dimension. This is a quirk behavior because quantum space is point-like, so when we talk about cells in the quantum foam, its more like we are defining the probability of finding a quantum event within a certain proximity, events will be much closer in one dimension than in the other two.

http://arxiv.org/pdf/1607.05410.pdf

Thanks for the PDF ! Very interesting, but I will have to search that Black Hole topic in german language I think, as that topic is quite complicated  

I always wanted to understand quantum mechanics ( at least a little bit, what is it about ). I read dozens of articles about it and also watched nearly every episode of Harald Lesch ( a in germany very famous scientist ). 

Lesch has the wonderful ability to explain complicated things about physics and astronomy with simple words, so that everyone can understand, but even his explanations about quantum mechanics i could never understand. Looks for me that quantum mechanics might be to most complicated theory to understand.

[Bill Phil]

2 hours ago, peadar1987 said:

Gravitational waves move through space at the speed of light, so in the first second, absolutely nothing would happen at all (according to my understanding)

He didn't specify at what time index it's paused.

[Nibb31]

9 hours ago, Rucki said:

But if the cars starting position, isnt with the "front in front". So the car would get a little rotation, because the front goes to the side where the pencil is. So there is nothing to stop the rotation, cause its in space, beside the gravity of the pencil.

There will be more gravity pulling the front of the car than the back, so there is a force acting to stop the rotation.

Quote

So if there are only 2 bodys in space, their rotation will always ( if we presume enough time until they will meet each other ) "balance out" until they dont rotate anymore ?

They will eventually crash into each other and stop any relative movement. Unless a third object appears.

Edited August 23, 2016 by Nibb31

[KerikBalm]

the car won't rotate for the same reason a hammer and a feather fall at the same rate in a vaccuum.

sure a 10kg mass will have 10x the force of gravity than a 1 kg mass, but f=ma, and it 10x the force on 10x the mass will produce the same acceleration as 1x the force on 1x the mass... they both accelerate at the same speed.

The only rotational forces would be due to tidal effects, where the gravity on the part closer to the pencil is greater than the gravity on the part of the car farthest from the pencil

At 999 light years, that's irrelevant... orbiting a black hole right above the event horizon... very relevant

[Green Baron]

The Orbiter-game has a doc about a model to calculate gravitational forces between objects with uneven mass distribution.

:-)

Edited August 23, 2016 by Green Baron

[YNM]

First of all, gravity would pull both object with the same force.

Would there be rotation or anything ? Given that sometimes things would perturb themselves, then probably yes. Although the total of angular momentum would stay the same (in this case, zero) - so if the car rotates clockwise, the pencil has to rotate anticlockwise, but I'm not very sure. The key lies in the fact that both objects are not perfectly rigid.

Also, if light didn't have time to react before, each object will only know the others existence (and start to feel the pull) after 999,000 years. Good luck waiting that.

Edited August 23, 2016 by YNM