Timeline for What is gravitational energy in general relativity?
Current License: CC BY-SA 3.0
19 events
| when toggle format | what | by | license | comment | |
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| Jan 14, 2016 at 23:31 | comment | added | Tom Andersen | The r.h.s is often a 'how you look at it' thing - as I pointed out you can put a dust of black holes on the r.h.s quite easily. If you want to put gravitational waves on the r.h.s - say in a universe model, you would add them as some average noise term. As in any universe model you need to approximate matter and energy with dust and radiation on the right. So its not a problem - same r.h.s for e&m wave noise as gravity wave noise. Energy is a pretty simple concept. Something carries energy - as gravitational waves certainly do if you can extract that energy out and perform work. | |
| Jan 14, 2016 at 19:30 | comment | added | AccidentalFourierTransform | @igael see Redshifting of Light and the expansion of the universe | |
| Jan 14, 2016 at 14:54 | comment | added | user46925 | @AccidentalFourierTransform : what happens when space expands ? does the semi-classical work increase or remain constant ? | |
| Jan 14, 2016 at 12:10 | history | edited | AccidentalFourierTransform | CC BY-SA 3.0 |
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| Jan 14, 2016 at 11:57 | comment | added | AccidentalFourierTransform | @TomAndersen see my edit/uptade, which hopefully will make my answer more clear. [As a side note: "You could certainly put graviational waves on the r.h.s if it makes sense for the system you are looking at." how? what kind of tensor describes the energy of a G wave? I am unable to find a reference where they define a tensor for gravitational waves. Note that if you measure the energy of a G wave, e.g., through the amplitude of oscillating dipoles, that is a semi-classical analysis, and that energy is not the same as in my answer: see the edit where I define what I mean by energy.] | |
| Jan 14, 2016 at 11:47 | history | edited | AccidentalFourierTransform | CC BY-SA 3.0 |
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| Jan 14, 2016 at 2:22 | comment | added | Tom Andersen | Where do you get the notion that gravitational waves don't carry energy? Which authors say that gravitational waves don't carry energy? They certainly carry energy as you can use that energy to spin up a black hole or 'power' a gravitational wave detection. You could certainly put graviational waves on the r.h.s if it makes sense for the system you are looking at. | |
| Jan 14, 2016 at 2:19 | comment | added | Tom Andersen | You can build a universe made solely out of gravity and add items to the r.h.s. or the left hand side depending on how long you want to spend solving the equations, how much accuracy you need, etc. | |
| Jan 10, 2016 at 14:11 | comment | added | AccidentalFourierTransform | @TomAndersen Im not 100% sure I get your point, but if Im getting it right, youre example supports my answer: the rhs cant tell the difference between the type of matter that makes up the dust, so the only important thing about the black holes is their mass/charge/momentum. This means that in the rhs we have to write $\sim (\rho+p) u^\mu u^\nu+\cdots$, but not something like $\frac{GM}{r}$ nor any kind of gravitational energy. Only its kinetic energy+internal stresses+coulomb-like energy+angular momentum+etc. We cannot add the gravitational pseudotensor to the rhs, as its not a tensor! | |
| Jan 10, 2016 at 12:25 | comment | added | Tom Andersen | You can certainly put gravitational energy on the r.h.s. For example - think of a 'dust' of black holes in a model universe - the r.h.s can't tell the difference between the type of matter that makes up the dust. | |
| Jan 5, 2016 at 8:58 | vote | accept | Thomas Elliot | ||
| Jan 5, 2016 at 0:04 | history | edited | AccidentalFourierTransform | CC BY-SA 3.0 |
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| Jan 4, 2016 at 22:00 | comment | added | AccidentalFourierTransform | @PeterR thats a rather subtle issue, and in fact many authors disagree about it. To fit the question into my answer: gravitational waves don't carry the kind energy you would write in the r.h.s. of the Einstein Field Equations. Can we define other objects that reflect our intuition about what energy means? yes: but it is not a trivial task (and most of the time, it's a non-covariantly observer-dependent quantity). For more details, see Michael Seifert's comment above. | |
| Jan 4, 2016 at 21:36 | comment | added | Peter R | Do gravitational waves carry energy? | |
| Jan 4, 2016 at 21:18 | comment | added | Peter R | I know how curvature makes things move but there is still the issue of conservation of energy which has some tricky aspects when it comes to Generl Reltivity. GR is the last of the great Classical theories. | |
| Jan 4, 2016 at 21:03 | comment | added | AccidentalFourierTransform | @PeterR you are thinking classically. See, for example, this and this posts. They explain very clearly how "curvature makes things move". | |
| Jan 4, 2016 at 20:40 | comment | added | Peter R | So where does the kinetic energy of an accelerating body due to the "spacetime curvature" come from? | |
| Jan 4, 2016 at 20:29 | history | edited | AccidentalFourierTransform | CC BY-SA 3.0 |
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| Jan 4, 2016 at 20:15 | history | answered | AccidentalFourierTransform | CC BY-SA 3.0 |