Well, it goes away in the sense that “this particular theory of physics explains gravity without directly having a ‘force’ associated with it as such”
In GR, one doesn’t see any forces locally pulling on objects. One instead sees (if one zooms in closely) objects moving on straight (geodesic) paths through spacetime. It simply happens to be that spacetime is in some cases shaped in ways that alter the relationships between nearby geodesics.
I guess it’s an attraction, sort of, but once one starts taking locality seriously, that’s not that good, is it? “don’t tell me what’s going on way over there, tell me what’s happening right here!”
There may be alternate theories, but GR itself is a geometric theory and I wouldn’t even know how to interpret the central equations as force equations. Saying “there could be other explanations” or such is a separate issue. What I meant was “In GR, once one has the geometry, nothing more needs to be said, really.” (Well, I’m skipping subtleties, stuff gets tricky in that you have shape of space affecting motion of matter, and motion of matter affecting shape of space, but yeah...)
Actually, there’s really no way for Newtonian stuff to be reasonably extended to describe GR effects without going to geometry in some form. I mean, GR predicts stuff about measured distances not quite obeying the rules that they would in flat spacetime. Measured times too, for that matter. One would have to get really creatively messy to produce a theory that is more an extension of Newtonian gravity, isn’t at all based on geometry, curvature, etc… any more than regular Newtonian gravity, yet still produces the same predictions for experimental outcomes that GR does.
It would, at best, be rather complicated and messy, I’d expect. If it’s even possible. Actually, I don’t think it is. More or less no matter what, other stuff would have to be added on that doesn’t at all even resemble Newtonian stuff.
I think the Wikipedia page on Gravitomagnetism might be relevant; it seems to be an approximation to GR that looks an awful lot like classical electromagnetism.
Incidentally, what about electromagnetism and the other fundamental forces? Can they be described the same way as gravity? In classical mechanics they’re the same kind of thing as gravity, except they can be repulsive as well. And a lot of popsci versions of modern physics research seems to postulate the same kind of properties for gravity as we know from electromagnetism: like repulsive gravity, or gravitational shields, or effects due to gravitational waves propagating at speed of light, or artificial gravity. And all forces are related through inertial mass.
So is there a description of all these things, including gravity, in the same terms? Either all of them “forces” or fields with mediating particles, or all of them affecting some kind of geometry?
Scott Aaronson has a nice post about the differences between gravity and electromagnetism. It seems his thoughts were running along the same lines as yours when he wrote it; he asks almost all the same questions. http://www.scottaaronson.com/blog/?p=244
Gravity waves come straight out of GR. (Actually, weak gravity waves show up in the linearized theory (the linearized theory of GR being a certain approximation of it that’s easier to deal with, good for low energies and such))
And that was part of what I was asking about. Well, others have tried to find that sort of thing, but I was asking something like “in the standard model and such, are the forces really aspects of what would amount to the geometry (specifically the symmetries) of configuration space rather than additional dimensions in the config space?”
And, of course, one of the BIG questions for modern physics is how to get a quantum description of gravity or to otherwise find a model of reality which contains both QM and GR in a “natural” way.
So, basically, at this point, all I can say is “I don’t really know.” :)
(well, also, I guess depending on how you look at it, curvature either explains or explains away tidal force. It explains the effects/behaviors, but explains away any apparent “forces” being involved.)
Well, it goes away in the sense that “this particular theory of physics explains gravity without directly having a ‘force’ associated with it as such”
In GR, one doesn’t see any forces locally pulling on objects. One instead sees (if one zooms in closely) objects moving on straight (geodesic) paths through spacetime. It simply happens to be that spacetime is in some cases shaped in ways that alter the relationships between nearby geodesics.
I guess it’s an attraction, sort of, but once one starts taking locality seriously, that’s not that good, is it? “don’t tell me what’s going on way over there, tell me what’s happening right here!”
There may be alternate theories, but GR itself is a geometric theory and I wouldn’t even know how to interpret the central equations as force equations. Saying “there could be other explanations” or such is a separate issue. What I meant was “In GR, once one has the geometry, nothing more needs to be said, really.” (Well, I’m skipping subtleties, stuff gets tricky in that you have shape of space affecting motion of matter, and motion of matter affecting shape of space, but yeah...)
Actually, there’s really no way for Newtonian stuff to be reasonably extended to describe GR effects without going to geometry in some form. I mean, GR predicts stuff about measured distances not quite obeying the rules that they would in flat spacetime. Measured times too, for that matter. One would have to get really creatively messy to produce a theory that is more an extension of Newtonian gravity, isn’t at all based on geometry, curvature, etc… any more than regular Newtonian gravity, yet still produces the same predictions for experimental outcomes that GR does.
It would, at best, be rather complicated and messy, I’d expect. If it’s even possible. Actually, I don’t think it is. More or less no matter what, other stuff would have to be added on that doesn’t at all even resemble Newtonian stuff.
I think the Wikipedia page on Gravitomagnetism might be relevant; it seems to be an approximation to GR that looks an awful lot like classical electromagnetism.
OK, now I understand better, thanks :-)
Incidentally, what about electromagnetism and the other fundamental forces? Can they be described the same way as gravity? In classical mechanics they’re the same kind of thing as gravity, except they can be repulsive as well. And a lot of popsci versions of modern physics research seems to postulate the same kind of properties for gravity as we know from electromagnetism: like repulsive gravity, or gravitational shields, or effects due to gravitational waves propagating at speed of light, or artificial gravity. And all forces are related through inertial mass.
So is there a description of all these things, including gravity, in the same terms? Either all of them “forces” or fields with mediating particles, or all of them affecting some kind of geometry?
Scott Aaronson has a nice post about the differences between gravity and electromagnetism. It seems his thoughts were running along the same lines as yours when he wrote it; he asks almost all the same questions. http://www.scottaaronson.com/blog/?p=244
That was very interesting and relevant. Thanks.
Gravity waves come straight out of GR. (Actually, weak gravity waves show up in the linearized theory (the linearized theory of GR being a certain approximation of it that’s easier to deal with, good for low energies and such))
And that was part of what I was asking about. Well, others have tried to find that sort of thing, but I was asking something like “in the standard model and such, are the forces really aspects of what would amount to the geometry (specifically the symmetries) of configuration space rather than additional dimensions in the config space?”
And, of course, one of the BIG questions for modern physics is how to get a quantum description of gravity or to otherwise find a model of reality which contains both QM and GR in a “natural” way.
So, basically, at this point, all I can say is “I don’t really know.” :)
(well, also, I guess depending on how you look at it, curvature either explains or explains away tidal force. It explains the effects/behaviors, but explains away any apparent “forces” being involved.)