9 ms·

Will math answer the question: what releases energy, when two objects are attracted by gravitation, and what stores energy, when we pull them apart?

by drran 5y ago

rnhmjoj 5y ago
This is not something particular to gravity: you can ask the same in EM and any other classical field theory, I think. You can compute the amount of energy, but where is the energy stored is not well-defined: you can either think it's stored in the masses (or charges, currents, etc.) or in the fields without contradictions.
- radioactivist 5y ago
  This is true, though there is there is one strong philosophical reason to prefer accounting for the energy as being stored in the fields themselves: it makes the theory "local". I.e. for energy to go from A to B it's got to travel the distance between them (it does this through the fields). The idea locality is a central part of relativity and for this reason theories that are explicitly local (i.e. have fields to carry energy, momentum, etc) rather than implicitly local (have apparent action at a distance) are preferred.
  - drran 5y ago
    "Field" is mathematical terminology, a 3D array of values. What is represented by a mathematical field in the physical world? Is the gravitational field a gas, ideal fluid, solid, crystal, or plasma? (IMHO, it's ideal fluid). What causes it to release energy when two objects are attracted? Of course, it goes from higher energy state into lower energy state, but what state it is? What causes attraction? It's because there is a gradient in the ideal fluid around every object, or because it's a form of interaction between particles of objects, or it's a something global, e.g. shadow, which blocks background radiation causing imbalance? (Non-native speaker).
    - radioactivist 5y ago
      I think you're coming at this backwards: the field is the best representation of what's seen in electromagnetic/gravitation/etc phenomena and not the other way around. The fields (and their associated physical laws) accurately reproduce basically everything we've observed out there in the world in their respective domains. So regardless of some nebulous philosophical "ground truth", these mathematical laws provide a useful to way to think about these behaviors and make predictions of the future (and because these law are formulated mathematically, in many cases there are multiple entirely equivalent ways to work with them). Analogies of these fields to less fundamental things (like fluids) are just that: analogies, and don't hold any fundamental meaning. The physics of (e.g.) electromagnetism is a thing in itself and requires new primitives to talk about -- there isn't necessarily some more familiar thing hiding underneath -- the gravitational field isn't a fluid or solid or gas, it is it's own thing.
      - drran 5y ago
        Field is the best representation, but what thing it represents? We are not talking about an analogy. We are talking about representation. A physical thing X is represented in physics as a field (3D array, [x,y,z]) of values of Y, so, if we have a field of Y, what is the X? For example, height field represents the height of piles of rock and dirt about ocean average level, so, Y is height, and X is the rock. What is represented by EM field, by gravitational field, etc.? (Beware: non-native speaker).
        radioactivist 5y ago
        Two things: 1) The phenomena of electromagnetism and gravity are fundamental as far as we can tell -- there is no more familiar or more commonplace "thing" I can tell you that they are "made" of. In fact if you really pressed it, your concept of a "rock" or "water" as a solid, distinct object out in the world is probably better thought of as a manifestation of electromagnetic behavior. That's just the way the world seems to be. If you drill down into it, our best physical theories describe everything in terms of fields defined over space (including all matter, like quarks, electrons, etc). So if you've a got a philosophical problem with fields for gravity and electromagnetism you've actually got a philosophical problem with basically all of our modern understanding of physics. 2) Whether our mathematics represents something intrinsic to the world rather than just providing a description of what we observe is a philosophical question (it's "ontological") that has no bearing of how well that description works. So if you want to think of space being permeated by real fields like the electromagnetic and gravitational fields you're free to do so. It'll give a useful and extraordinary precise description of the bundle of phenomena we call electromagnetism and gravity. Conversely, if you want to think of these things as well built crutches that don't properly represent (some yet undiscovered) deeper reality, but nonetheless give a very accurate description of it -- you can do that to, it won't make any difference in the physics.
boublepop 5y ago
when the objects get closer the potential energy “releases” energy to the kinetic energy. When you pull them apart the potential energy “stores” the energy. It’s not really “math” answering that question, but it’s very basic Newtonian mechanics and you can set up the math for that and it’s often quite straight forward simple differential equations. I’d recommend khans academy if you want to learn more, as it’s really not that deep into the material at all. And if you dedicate a weekend to learning the subject matter you’ll not only get rid of the mystification you feel about the subject but have a really good understanding of it.
- drran 5y ago
  Yeah, I should create a course for the Khans Academy, to summarize 2 decades of research, but my English is too weak for that. So, kinetic energy is stored as potential energy, and then released as kinetic energy again? Yes, it's true, but the question is: what stores this energy and in which form? For example, when we use two electric magnets, when EM are attracted, energy for that is provided by grid, and when they are pulled apart, energy is returned back to grid. In case of gravitation, the "grid" is unknown yet, but we can try to find it by tracking the energy.

Will math answer the question: what releases energy, when two objects are attracted by gravitation, and what stores energy, when we pull them apart?

by drran 5y ago

Will math answer the question: what releases energy, when two objects are attracted by gravitation, and what stores energy, when we pull them apart?

rnhmjoj 5y ago

This is not something particular to gravity: you can ask the same in EM and any other classical field theory, I think. You can compute the amount of energy, but where is the energy stored is not well-defined: you can either think it's stored in the masses (or charges, currents, etc.) or in the fields without contradictions.

radioactivist 5y ago
This is true, though there is there is one strong philosophical reason to prefer accounting for the energy as being stored in the fields themselves: it makes the theory "local". I.e. for energy to go from A to B it's got to travel the distance between them (it does this through the fields). The idea locality is a central part of relativity and for this reason theories that are explicitly local (i.e. have fields to carry energy, momentum, etc) rather than implicitly local (have apparent action at a distance) are preferred.
- drran 5y ago
  "Field" is mathematical terminology, a 3D array of values. What is represented by a mathematical field in the physical world? Is the gravitational field a gas, ideal fluid, solid, crystal, or plasma? (IMHO, it's ideal fluid). What causes it to release energy when two objects are attracted? Of course, it goes from higher energy state into lower energy state, but what state it is? What causes attraction? It's because there is a gradient in the ideal fluid around every object, or because it's a form of interaction between particles of objects, or it's a something global, e.g. shadow, which blocks background radiation causing imbalance? (Non-native speaker).
  - radioactivist 5y ago
    I think you're coming at this backwards: the field is the best representation of what's seen in electromagnetic/gravitation/etc phenomena and not the other way around. The fields (and their associated physical laws) accurately reproduce basically everything we've observed out there in the world in their respective domains. So regardless of some nebulous philosophical "ground truth", these mathematical laws provide a useful to way to think about these behaviors and make predictions of the future (and because these law are formulated mathematically, in many cases there are multiple entirely equivalent ways to work with them). Analogies of these fields to less fundamental things (like fluids) are just that: analogies, and don't hold any fundamental meaning. The physics of (e.g.) electromagnetism is a thing in itself and requires new primitives to talk about -- there isn't necessarily some more familiar thing hiding underneath -- the gravitational field isn't a fluid or solid or gas, it is it's own thing.
    - drran 5y ago
      Field is the best representation, but what thing it represents? We are not talking about an analogy. We are talking about representation. A physical thing X is represented in physics as a field (3D array, [x,y,z]) of values of Y, so, if we have a field of Y, what is the X? For example, height field represents the height of piles of rock and dirt about ocean average level, so, Y is height, and X is the rock. What is represented by EM field, by gravitational field, etc.? (Beware: non-native speaker).
      - radioactivist 5y ago
        Two things: 1) The phenomena of electromagnetism and gravity are fundamental as far as we can tell -- there is no more familiar or more commonplace "thing" I can tell you that they are "made" of. In fact if you really pressed it, your concept of a "rock" or "water" as a solid, distinct object out in the world is probably better thought of as a manifestation of electromagnetic behavior. That's just the way the world seems to be. If you drill down into it, our best physical theories describe everything in terms of fields defined over space (including all matter, like quarks, electrons, etc). So if you've a got a philosophical problem with fields for gravity and electromagnetism you've actually got a philosophical problem with basically all of our modern understanding of physics. 2) Whether our mathematics represents something intrinsic to the world rather than just providing a description of what we observe is a philosophical question (it's "ontological") that has no bearing of how well that description works. So if you want to think of space being permeated by real fields like the electromagnetic and gravitational fields you're free to do so. It'll give a useful and extraordinary precise description of the bundle of phenomena we call electromagnetism and gravity. Conversely, if you want to think of these things as well built crutches that don't properly represent (some yet undiscovered) deeper reality, but nonetheless give a very accurate description of it -- you can do that to, it won't make any difference in the physics.

boublepop 5y ago

when the objects get closer the potential energy “releases” energy to the kinetic energy. When you pull them apart the potential energy “stores” the energy. It’s not really “math” answering that question, but it’s very basic Newtonian mechanics and you can set up the math for that and it’s often quite straight forward simple differential equations. I’d recommend khans academy if you want to learn more, as it’s really not that deep into the material at all. And if you dedicate a weekend to learning the subject matter you’ll not only get rid of the mystification you feel about the subject but have a really good understanding of it.

drran 5y ago
Yeah, I should create a course for the Khans Academy, to summarize 2 decades of research, but my English is too weak for that. So, kinetic energy is stored as potential energy, and then released as kinetic energy again? Yes, it's true, but the question is: what stores this energy and in which form? For example, when we use two electric magnets, when EM are attracted, energy for that is provided by grid, and when they are pulled apart, energy is returned back to grid. In case of gravitation, the "grid" is unknown yet, but we can try to find it by tracking the energy.