Since gravity is energy, and energy is related to mass, and all objects release gravity "waves", then shouldn't the mass of these objects decrease over time?
Guido:
The gravity that draws objects together can be viewed as energy but it must be kept in mind that in this view the gravitational energy is negative. The energy associated with gravity waves in this view is positive. Objects only emit gravitational waves when they accelerate. So an accelerating object may loose some of it apparent mass or not depending on what is causing the acceleration. For example a payload accelerated by a rocket will gain apparent mass even though it is loosing energy by emitting gravity waves.
If you limit the interactions to gravity then all the objects will be continuously loosing mass. The rate of loss for most observable objects is so low that it is unobservable. For any finite number of gravitationally interacting objects you will eventually reach a time where the mass loss comes arbitrarily close to zero. This is because the objects will have either coalesced or gotten so far separated that their interaction becomes arbitrarily small.
Guido:
The gravity that draws objects together can be viewed as energy but it must be kept in mind that in this view the gravitational energy is negative. The energy associated with gravity waves in this view is positive. Objects only emit gravitational waves when they accelerate.
So even if an object is stationary, it still "emits" the energy that draws together objects. Or not?
Here's what I don't get...
Say you have a large, stationary object in space, with nothing around it for millions of light years, and an astronaut goes near it and feels the gravity from the object. Maybe I'm wrong, but I look at this as a form of energy (although I don't know if it's positive or negative). If the only place this energy could have come from is the nearby object, then doesn't that mean the object is converting mass into energy? I understand humans may not be able to measure the rate of mass loss, but I wonder if it's a theory of where gravity comes from.
Good question, Guido, I don't know if this is helpful...
Does an electron loose something when it accelerates towards a proton? It's said that the electron and proton will exchange photons, and this exchange is the reason for the force of electromagnetic attraction between the two. When an electron emits a photon it is true that the measure of its energy changes, but the charge on the electron is always minus one. So if the charge doesn't change in the EM force, why should the mass change in the gravitational force?
The negative energy associated with gravitational attraction is not emitted by the body like a radio signal. It is intrinsic part of the body, the body and its gravitational attraction can not be separated. As your astronaut and the object approach each other they are in fact converting each others negative potential energies into kinetic (higher relative speed) or visa versa if they are moving apart. In the Newtonian theory the total of the potential energies and kinetic energies is constant.
In General Relativity some of the energy is emitted as gravitons which escape to infinity. So the pair of bodies appear to loose mass. But if you include the energy of the gravitons the total energy is still constant.
Quantum Field Theory allows for a lower level explanation of potential energy fields in terms of virtual particles and their differential absorption/creation close to a source. This is works well for electro-magnetic and weak particle interactions. It does not work at all for GR because GR and QFT are incompatible. Something similar is may be at work with GR but that is conjectural.
In General Relativity some of the energy is emitted as gravitons which escape to infinity. So the pair of bodies appear to loose mass. But if you include the energy of the gravitons the total energy is still constant.
If there was only one concentration of mass in the universe, it should have no cause move, hence no reason to emit gravitons, but if there's additional mass (even infinitely far away), won't gravitons be emitted back and forth, as with photons between an electron and a proton? A electron doesn't emit photons unless it moves, right? Why must some gravitons escape to infinity? Also, why would there be inspiral in a binary system if both objects are loosing mass in proportion to emission of GW radiation?
ChipperQ:
The theory of Quantum Electro-Dynamics uses the exchange of virtual photons to explain the Coulomb and Ampere forces between charges and currents. Virtual photons should not be confused with real photons such as light, radio signals etc. First off virtual photons can not be observed directly, real photons can. Second virtual photons can have different physical properties than real photons, such as traveling at less than the speed of light and a third degree of polarization freedom (real photons only have two). In fact QED predicts that fields of virtual electrons and positrons also exist through out space and time. The virtual electrons and positrons are also unobservable and have different physical properties than their real counterparts.
Quantum Field Theory has been successfully extended to cover weak forces and strong forces (somewhat less successfully). It has been shown that the current methods for converting a classical field theory into a quantum field theory do not work with General Relativity. Further when applied on a global scale the background sea of virtual particles predicted by QFT should result in a large vacuum mass which is not observed.
So while it seems reasonable (based on the successes of QFT) to expect that something similar to the ideas of the exchange of virtual gravitons is responsible the observed gravitational forces. IMHO great caution should be used when applying ideas from QFT to GR. Clearly important things going on that nobody understands. If you are going use this idea it should be kept in mind that like the other virtual particles the presumptive virtual gravitons will not be the same as real gravitons i.e. the virtual gravitons will be unobservable and have different physical properties than real gravitons.
won't gravitons be emitted back and forth, as with photons between an electron and a proton?
Possibly but such exchanges will not result in overall mutual attraction.
Quote:
Why must some gravitons escape to infinity?
The graviton need not escape to infinity if there are extra bodies present to absorb. The term 'escape to infinity' is a bit of jargon implying the objects ultimate fate no longer influences the outcome. If the graviton was reabsorbed by the system then the orbit would unchanged.
Quote:
why would there be inspiral in a binary system if both objects are loosing mass in proportion to emission of GW radiation?
If the bodies retained all of their energy and angular momentum then their orbits would forever retain their initial semi-major axis and eccentricity. It is the loss of energy (and again angular momentum) to the graviton that causes the contraction of the orbit. It would take a deeper dive into the details than I can give here but it is possible to show that the loss of energy and angular momentum in such a case implies loss of mass.
It is also possible to show a carbon 12 atom in either of the bodies would have the same mass if weighed locally as it would in isolation. Another one of those conundrums that arise when you compare local effects to global effects in general relativity.
... Further when applied on a global scale the background sea of virtual particles predicted by QFT should result in a large vacuum mass which is not observed.
Hmm. If this virtual sea is displaced to some extent, by normal mass and thermonuclear radiation pressure, might it form a dark matter halo?
If this virtual sea is displaced to some extent...
Intersting possibility but we are hijacking Guido's thread.
Aye, we are, a bit, although how many 'right paths' can there be? :) Sorry if I've been intruding, Guido.
Mark, many thanks again for your help. I've been meaning to get back to your recent 'Update on dark energy' thread, but need to do more homework first. When I do, I'll try to tie it in with your answers here. Cheers!
Am I on the right path here...
)
Guido:
The gravity that draws objects together can be viewed as energy but it must be kept in mind that in this view the gravitational energy is negative. The energy associated with gravity waves in this view is positive. Objects only emit gravitational waves when they accelerate. So an accelerating object may loose some of it apparent mass or not depending on what is causing the acceleration. For example a payload accelerated by a rocket will gain apparent mass even though it is loosing energy by emitting gravity waves.
If you limit the interactions to gravity then all the objects will be continuously loosing mass. The rate of loss for most observable objects is so low that it is unobservable. For any finite number of gravitationally interacting objects you will eventually reach a time where the mass loss comes arbitrarily close to zero. This is because the objects will have either coalesced or gotten so far separated that their interaction becomes arbitrarily small.
RE: Guido: The gravity that
)
So even if an object is stationary, it still "emits" the energy that draws together objects. Or not?
Here's what I don't get...
Say you have a large, stationary object in space, with nothing around it for millions of light years, and an astronaut goes near it and feels the gravity from the object. Maybe I'm wrong, but I look at this as a form of energy (although I don't know if it's positive or negative). If the only place this energy could have come from is the nearby object, then doesn't that mean the object is converting mass into energy? I understand humans may not be able to measure the rate of mass loss, but I wonder if it's a theory of where gravity comes from.
Good question, Guido, I don't
)
Good question, Guido, I don't know if this is helpful...
Does an electron loose something when it accelerates towards a proton? It's said that the electron and proton will exchange photons, and this exchange is the reason for the force of electromagnetic attraction between the two. When an electron emits a photon it is true that the measure of its energy changes, but the charge on the electron is always minus one. So if the charge doesn't change in the EM force, why should the mass change in the gravitational force?
The negative energy
)
The negative energy associated with gravitational attraction is not emitted by the body like a radio signal. It is intrinsic part of the body, the body and its gravitational attraction can not be separated. As your astronaut and the object approach each other they are in fact converting each others negative potential energies into kinetic (higher relative speed) or visa versa if they are moving apart. In the Newtonian theory the total of the potential energies and kinetic energies is constant.
In General Relativity some of the energy is emitted as gravitons which escape to infinity. So the pair of bodies appear to loose mass. But if you include the energy of the gravitons the total energy is still constant.
Quantum Field Theory allows for a lower level explanation of potential energy fields in terms of virtual particles and their differential absorption/creation close to a source. This is works well for electro-magnetic and weak particle interactions. It does not work at all for GR because GR and QFT are incompatible. Something similar is may be at work with GR but that is conjectural.
RE: In General Relativity
)
If there was only one concentration of mass in the universe, it should have no cause move, hence no reason to emit gravitons, but if there's additional mass (even infinitely far away), won't gravitons be emitted back and forth, as with photons between an electron and a proton? A electron doesn't emit photons unless it moves, right? Why must some gravitons escape to infinity? Also, why would there be inspiral in a binary system if both objects are loosing mass in proportion to emission of GW radiation?
ChipperQ: The theory of
)
ChipperQ:
The theory of Quantum Electro-Dynamics uses the exchange of virtual photons to explain the Coulomb and Ampere forces between charges and currents. Virtual photons should not be confused with real photons such as light, radio signals etc. First off virtual photons can not be observed directly, real photons can. Second virtual photons can have different physical properties than real photons, such as traveling at less than the speed of light and a third degree of polarization freedom (real photons only have two). In fact QED predicts that fields of virtual electrons and positrons also exist through out space and time. The virtual electrons and positrons are also unobservable and have different physical properties than their real counterparts.
Quantum Field Theory has been successfully extended to cover weak forces and strong forces (somewhat less successfully). It has been shown that the current methods for converting a classical field theory into a quantum field theory do not work with General Relativity. Further when applied on a global scale the background sea of virtual particles predicted by QFT should result in a large vacuum mass which is not observed.
So while it seems reasonable (based on the successes of QFT) to expect that something similar to the ideas of the exchange of virtual gravitons is responsible the observed gravitational forces. IMHO great caution should be used when applying ideas from QFT to GR. Clearly important things going on that nobody understands. If you are going use this idea it should be kept in mind that like the other virtual particles the presumptive virtual gravitons will not be the same as real gravitons i.e. the virtual gravitons will be unobservable and have different physical properties than real gravitons.
RE: won't gravitons be
)
Possibly but such exchanges will not result in overall mutual attraction.
The graviton need not escape to infinity if there are extra bodies present to absorb. The term 'escape to infinity' is a bit of jargon implying the objects ultimate fate no longer influences the outcome. If the graviton was reabsorbed by the system then the orbit would unchanged.
If the bodies retained all of their energy and angular momentum then their orbits would forever retain their initial semi-major axis and eccentricity. It is the loss of energy (and again angular momentum) to the graviton that causes the contraction of the orbit. It would take a deeper dive into the details than I can give here but it is possible to show that the loss of energy and angular momentum in such a case implies loss of mass.
It is also possible to show a carbon 12 atom in either of the bodies would have the same mass if weighed locally as it would in isolation. Another one of those conundrums that arise when you compare local effects to global effects in general relativity.
RE: ... Further when
)
Hmm. If this virtual sea is displaced to some extent, by normal mass and thermonuclear radiation pressure, might it form a dark matter halo?
RE: If this virtual sea is
)
Intersting possibility but we are hijacking Guido's thread.
RE: RE: If this virtual
)
Aye, we are, a bit, although how many 'right paths' can there be? :) Sorry if I've been intruding, Guido.
Mark, many thanks again for your help. I've been meaning to get back to your recent 'Update on dark energy' thread, but need to do more homework first. When I do, I'll try to tie it in with your answers here. Cheers!