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How does it being a consequence of curved spacetime make it not a force? When we learn the more fundamental origins behind the other forces, will they also ceas

How does it being a consequence of curved spacetime make it not a force? When we learn the more fundamental origins behind the other forces, will they also cease to be forces? It's not helpful, IMO.

forgotpwd16 6y ago
A force is considered an interaction mediated by a carrier. When we learn, a force will be described in a way that adheres to the new/modified framework.
- DangitBobby 6y ago
  How long can that definition of a force have existed? 60 years? "Carriers" (carrying particles if I understand you correctly) only makes sense in the context of the standard model. It rubs me the wrong way when a field co-opts layperson definitions of something and redefines them to be something incompatible with the original definition, but I can understand that maybe physicists are not interested in helping people maintain what little physical intuition can be gleaned from the world around them. But I digress, are gravitons not a carrier of gravity?
  - forgotpwd16 6y ago
    There're no gravitons in the standard model and every attempt to introduce them has failed. That's the problem. Our current theoretical framework describes all fundamental forces but gravity.
nimish 6y ago
It's a pseudoforce in the same way centrifugal acceleration is "fictitious" It's a consequence of massive objects following geodesic motion on a curved space; e.g. To keep an ant on a sphere you would need "something" to ensure the ant's velocity doesn't lead the ant's position "off" the sphere. That something is interpreted as gravity. Here's a more technical explanation: https://physics.stackexchange.com/questions/212167/what-is-a-christoffel-symbol https://physics.stackexchange.com/questions/212167/what-is-a...
- DangitBobby 6y ago
  Interesting, thank you.
- lanstin 6y ago
  And massless. Light follows a geodesic in GR. Also i don’t think intrinsic curvature is well explained by the ant analogy. The apparent force isn’t to stay in the manifold but to stay on the geodesic thru space time (which is free fall).
  - nimish 6y ago
    Yep, though massless particles must follow null geodesics specifically. Yeah, the ant analogy isn't the best, though it does show off that movement on a curved surface needs "corrections" from the movement on a flat surface (and the degree to which that occurs happens to entirely characterize curvature itself). If you force the ant to always travel on a great circle, then it might be a little more precise :)
    - ars 6y ago
      It's neither massive nor massless object that follow geodesics, it's objects with energy (including the mc^2 kind).
      - nimish 6y ago
        Yes, and "massive" and "massless" exhaustively covers both, with the special highlighting of massless particles which are further constrained to follow null geodesics. Massive particles don't have that limitation but they only travel time-like geodesics (as far as we know).
        ars 6y ago
        > with the special highlighting of massless particles which are further constrained to follow null geodesics. Only to an approximation. Photons generate gravitational fields, and the planets they travel near are attracted to the photons (not much obviously). (See: Kugelblitz) Gravity does not treat photons specially, the rules are the same as for other particles. For extra credit imagine a Kugelblitz traveling by at light speed - it's moving so fast, it doesn't have time to add any mass. Yet, mass transited inside the event horizon of this object.
tsimionescu 6y ago
Gravity is sort of special compared to the 3 forces in the standard model because of its relation to inertia. For all 3 SM forces, there is a distinction between the charge of a particle and how easy it is to move that particle. For gravity no such distinction has ever been measured - the "gravity charge" of an object seems to be the same thing as its tendency to oppose movement (its inertial mass) in any experiment ever conducted, which has led to Einstein's observation that gravity seems to be a dual of acceleration in a curved space time. No similar explanation is required for the other forces, as they are not intimately tied to inertia in the same way. Now, unfortunately general relativity's curved space time has never been successfully meshed with QM's Uncertainty principle and/or wave function. Most physicists, at least particle physicists, do tend to believe that it is in fact GR that is limited in its description, since QM (in particular QFT) is the most precisely confirmed experimental theory ever devised, while GR is extremely difficult to work with for making precise experimental predictions (Einstein's equations are non-linear, and almost all predictions are actually based on linear approximations of the equations) - so there is much more "room" for GR to be modified at very low scales without contradicting the high scale results than the other way around.
cygx 6y ago
Acceleration being independent of the mass of the test particle being acted upon only holds true for two types of forces: Inertial forces, and the gravitational force. According to General Relativity, this is no coincidence: Free-fall spacetime trajectories ('worldlines') get modelled as straight lines ('autoparallels'/'geodesics'), indicating an absence of net forces. Apparent gravitational forces then arise the same way any of the other inertial forces do. Such an interpretation of gravity is natural insofar that it handily explains the measurements of accelerometers, which only will measure nonzero values if motion deviates from free-fall due to the presence of non-gravitational forces. But note that as is often the case, it boils down to a semantic argument about the definition of 'force'. The effects of 'fictitious' forces can certainly be as real as the effects of 'real' forces (in case of gravity, eg tidal heating, or the extreme example of spaghettification, ...); personally, I have no issue with calling gravity a force.

How does it being a consequence of curved spacetime make it not a force? When we learn the more fundamental origins behind the other forces, will they also cease to be forces? It's not helpful, IMO.

forgotpwd16 6y ago

A force is considered an interaction mediated by a carrier. When we learn, a force will be described in a way that adheres to the new/modified framework.

DangitBobby 6y ago
How long can that definition of a force have existed? 60 years? "Carriers" (carrying particles if I understand you correctly) only makes sense in the context of the standard model. It rubs me the wrong way when a field co-opts layperson definitions of something and redefines them to be something incompatible with the original definition, but I can understand that maybe physicists are not interested in helping people maintain what little physical intuition can be gleaned from the world around them. But I digress, are gravitons not a carrier of gravity?
- forgotpwd16 6y ago
  There're no gravitons in the standard model and every attempt to introduce them has failed. That's the problem. Our current theoretical framework describes all fundamental forces but gravity.

nimish 6y ago

It's a pseudoforce in the same way centrifugal acceleration is "fictitious" It's a consequence of massive objects following geodesic motion on a curved space; e.g. To keep an ant on a sphere you would need "something" to ensure the ant's velocity doesn't lead the ant's position "off" the sphere. That something is interpreted as gravity. Here's a more technical explanation: https://physics.stackexchange.com/questions/212167/what-is-a-christoffel-symbol https://physics.stackexchange.com/questions/212167/what-is-a...

DangitBobby 6y ago
Interesting, thank you.
lanstin 6y ago
And massless. Light follows a geodesic in GR. Also i don’t think intrinsic curvature is well explained by the ant analogy. The apparent force isn’t to stay in the manifold but to stay on the geodesic thru space time (which is free fall).
- nimish 6y ago
  Yep, though massless particles must follow null geodesics specifically. Yeah, the ant analogy isn't the best, though it does show off that movement on a curved surface needs "corrections" from the movement on a flat surface (and the degree to which that occurs happens to entirely characterize curvature itself). If you force the ant to always travel on a great circle, then it might be a little more precise :)
  - ars 6y ago
    It's neither massive nor massless object that follow geodesics, it's objects with energy (including the mc^2 kind).
    - nimish 6y ago
      Yes, and "massive" and "massless" exhaustively covers both, with the special highlighting of massless particles which are further constrained to follow null geodesics. Massive particles don't have that limitation but they only travel time-like geodesics (as far as we know).
      - ars 6y ago
        > with the special highlighting of massless particles which are further constrained to follow null geodesics. Only to an approximation. Photons generate gravitational fields, and the planets they travel near are attracted to the photons (not much obviously). (See: Kugelblitz) Gravity does not treat photons specially, the rules are the same as for other particles. For extra credit imagine a Kugelblitz traveling by at light speed - it's moving so fast, it doesn't have time to add any mass. Yet, mass transited inside the event horizon of this object.

tsimionescu 6y ago

Gravity is sort of special compared to the 3 forces in the standard model because of its relation to inertia. For all 3 SM forces, there is a distinction between the charge of a particle and how easy it is to move that particle. For gravity no such distinction has ever been measured - the "gravity charge" of an object seems to be the same thing as its tendency to oppose movement (its inertial mass) in any experiment ever conducted, which has led to Einstein's observation that gravity seems to be a dual of acceleration in a curved space time. No similar explanation is required for the other forces, as they are not intimately tied to inertia in the same way. Now, unfortunately general relativity's curved space time has never been successfully meshed with QM's Uncertainty principle and/or wave function. Most physicists, at least particle physicists, do tend to believe that it is in fact GR that is limited in its description, since QM (in particular QFT) is the most precisely confirmed experimental theory ever devised, while GR is extremely difficult to work with for making precise experimental predictions (Einstein's equations are non-linear, and almost all predictions are actually based on linear approximations of the equations) - so there is much more "room" for GR to be modified at very low scales without contradicting the high scale results than the other way around.

cygx 6y ago

Acceleration being independent of the mass of the test particle being acted upon only holds true for two types of forces: Inertial forces, and the gravitational force. According to General Relativity, this is no coincidence: Free-fall spacetime trajectories ('worldlines') get modelled as straight lines ('autoparallels'/'geodesics'), indicating an absence of net forces. Apparent gravitational forces then arise the same way any of the other inertial forces do. Such an interpretation of gravity is natural insofar that it handily explains the measurements of accelerometers, which only will measure nonzero values if motion deviates from free-fall due to the presence of non-gravitational forces. But note that as is often the case, it boils down to a semantic argument about the definition of 'force'. The effects of 'fictitious' forces can certainly be as real as the effects of 'real' forces (in case of gravity, eg tidal heating, or the extreme example of spaghettification, ...); personally, I have no issue with calling gravity a force.