[Halc]

You’re not ignoring the laws of conservation of momentum are you, what’s your coefficients  of restitution for these collisions, gasses and solids ?

I carefully did not violate momentum conservation.  I simply computed the desired momentum and gave that to my small 'meteor'. It's small enough to have no gravitational effect on the experiment before the collision.

I think coefficient of restitution has more to do with collisions between two objects that remain reasonably distinct.  So we have two objects before, and a reasonably uniform moving blob of plasma afterwards. Coefficient of e=0 in the ideal case. It doesn't bounce back (e > 0) if that's what you're asking. More like a e<0 (like a human getting hit by a bullet that passes through), which is why I break it up just before collision. I want to move Earth, not shoot a hole through it.

Heck, the whole problem can be solved by having the major mass (sun say) be a black hole. That can't explode when you smack it with something. e=0 necessarily. Fire a small but very high momentum object at it and the black hole will acquire all that momentum without bits flying all over the place. Perfect for our experiment. How long before Earth deviates from its path when the sun abruptly changes velocity by .9c in some direction? GR can answer that because there's no violation of any laws in it, and we don't need to worry about the dynamics of a supernova-scale explosion.

[gem]

Hi all

You’re not ignoring the laws of conservation of momentum are you, what’s your coefficients  of restitution for these collisions, gasses and solids ?

I carefully did not violate momentum conservation.  I simply computed the desired momentum and gave that to my small 'meteor'. It's small enough to have no gravitational effect on the experiment before the collision.

I think coefficient of restitution has more to do with collisions between two objects that remain reasonably distinct.  So we have two objects before, and a reasonably uniform moving blob of plasma afterwards. Coefficient of e=0 in the ideal case. It doesn't bounce back (e > 0) if that's what you're asking. More like a e<0 (like a human getting hit by a bullet that passes through), which is why I break it up just before collision. I want to move Earth, not shoot a hole through it.

Heck, the whole problem can be solved by having the major mass (sun say) be a black hole. That can't explode when you smack it with something. e=0 necessarily. Fire a small but very high momentum object at it and the black hole will acquire all that momentum without bits flying all over the place. Perfect for our experiment. How long before Earth deviates from its path when the sun abruptly changes velocity by .9c in some direction? GR can answer that because there's no violation of any laws in it, and we don't need to worry about the dynamics of a supernova-scale explosion.

Very good 😌 can you please show your calculations 🧑‍🎓

Only joking
Wondering how ES is getting along given he said he was calling out the moderators, I feel for him.
I also am going to find the time to read the links Colin provided.

[Eternal Student (OP)]

Hi gem.

ES I don’t understand this:
  “More than that under Newtonian gravity we human beings would soon start to see and feel strange gravitational effects (like things falling upward on one side of the planet).

   Actually I don't think I can get objects to "fall upward" on one side of the planet.  The radius of the earth isn't big enough in comparison to the radius of the sun.  We'd have to adjust radii to get something quite that spectacular, sorry.  We'd have to settle for slightly less impressive effects at the surface of the earth.

   Acceleration of an object on the earth never was just toward the centre of the earth, there was always some gravitational force caused by the sun - but the sun is usually too far away to matter much.  Obviously this changes when the sun comes closer and people could observe a significant difference in acceleration while on earths surface just by using an accelerometer.  That's ok but it would have been nicer if the radius of earth was larger, then the centre of the earth wouldn't have been accelerated by the sun anything like as much as objects on the planet surface but nearer to the sun.  Those objects would have visibly started to float away from the surface of the earth unless they were tied down.  None of this is critical anyway.  The change in the trajectory of planet earth was the main consideration.

@alancalverd
   I think you mentioned on some other thread something about electric fields and aberration.  At a distance from a moving charge, a test charge still feels force directed to where the source charge is now and not where it was.   Well, more or less, it's a first order approximation so that the feld points to a linear extrapolation of where the particle is now  given where it was and the velocity it had at that time but ignoring any acceleration etc.  (I'm sure you know this and have stated it elsewhere).
    Anway, I think something similar happens with gravitational effects under GR.  If anyone is interested, see this paper -
Aberration and the Speed of Gravity,   S. Carlip
The Arxiv version is found at:  https://arxiv.org/abs/gr-qc/9909087
I haven't read all of it yet but it seems to imply similar things happen as for an electric field.  This could make it hard to detect phase lag in the swinging pendulum experiment you described.  I haven't really thought about it too much but I wonder if the gravimeter would point slightly infront of the pendulum on the upward swings (away from the centre) and slightly behind it on the downard swing back toward the centre.
   Anyway, this is mainly why I would have liked to keep the sun accelerating rather than just moving at constant velocity toward the earth.

Thanks again to absolutely everyone and best wishes.  I'm not planning on doing much more with this thread.

[alancalverd]

@alancalverd
   I think you mentioned on some other thread something about electric fields and aberration.  At a distance from a moving charge, a test charge still feels force directed to where the source charge is now and not where it was.   Well, more or less, it's a first order approximation so that the feld points to a linear extrapolation of where the particle is now  given where it was and the velocity it had at that time but ignoring any acceleration etc.  (I'm sure you know this and have stated it elsewhere).

I hope not. That would imply that information can travel at > c, which is contrary to the essential axioms of relativity.

[Eternal Student (OP)]

I hope not. That would imply that information can travel at > c, which is contrary to the essential axioms of relativity.

yes and no and wrong moderator, sorry.

    Yes, it does happen as previously described.   Electric fields from a moving charge point to where the charge is now not where it was (upto first order).

    No, it doesn't imply speed of information travel > c.    Why?   because it does not require the current position to be communicated to a remote location,  only the retarded position and the velocity at that time.
See, for example, The Feynman lectures   (Vol. II  chapter 26 ?).
https://www.feynmanlectures.caltech.edu/II_26.html

    Wrong moderator.  Sorry that's my mistake, it was Colin who said it:
A test +ve charge will be attracted to the electrons position. We know that the electric field propagates at light speed, but if the electron is moving the test charge will move towards the current position of the electron, not where it was. In this way the field behaves in a similar way to gravity.
              [Taken from reply #1,  https://www.thenakedscientists.com/forum/index.php?topic=82133.0  ]