Timeline for Energy extraction from universe expansion?
Current License: CC BY-SA 4.0
16 events
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| Jun 16 at 13:07 | comment | added | A.V.S. | @vengaq Your #1 strongly depend on limitations of technology used, but I think that technology is fundamentally discrete and energy harvesting cannot persist for arbitrarily sparse resources, there must be some finite point beyond which it stops producing results. For #2 I meant that once we harvested energy from nearby galaxies, we cannot harvest from those anymore and must travel further. | |
| Jun 16 at 10:19 | comment | added | vengaq | I have a couple of questions on this: #1 You said that in an infinitely big universe without cosmological horizons "we must travel further and for a longer time with the gains per unit of our efforts (however we measure them) steadily decreasing". But would there be a time where the efforts and the gains result in a zero net gain? Or is the decrease between gains and efforts asymptotic and we wouldn't really get to a time point with zero net gain? #2 How would changes in non-local cosmological surroundings limit the extraction of energy? @A.V.S. | |
| Jun 14 at 15:14 | comment | added | A.V.S. | @FACald Re. FrankH proposal to “extract an infinite amount of energy from the expansion go the universe” It would not work, since for a cable to tether two bodies at distances larger than Hubble radius in a dark energy dominated universe, the matter of the cable would have to violate reasonable assumptions (such as energy conditions and absence of superluminal propagation of perturbations). | |
| Jun 14 at 7:57 | comment | added | A.V.S. | @FACald you are saying that local creation of energy is not possible right? but the cosmic cable introduces coupling between two cosmologically distant objects and thus makes this situation inherently non-local. Any local energy that appeared at the unwinding mechanism can be immediately traced to a flux of energy through the cable. But if we want to "backtrace" that flux to the other end of the cable we would have to include a lot of things: cosmological model, dynamics of the tethered galaxy, equation of state for the cable … If we forget something we can end up with non-conserved energy. | |
| Jun 13 at 19:38 | comment | added | FACald | My doubt is, if you take the view that carroll gives that energy is conserved if you take into account the gravitational energy, does for example this answer by FrankH physics.stackexchange.com/a/37584 where he says 2 heavy objects tied together can extract an infinite amount of energy from the expansion go the universe(basically the mining energy paper) invalidates what carroll says (I doubt when carroll wrote he was unaware of the argument) | |
| Jun 13 at 19:28 | comment | added | FACald | @A.V.S. this is a commonly shared whenever energy conservation in GR is discussed- preposterousuniverse.com/blog/2010/02/22/… in there he says that the increase in dark energy is compensated by the negative gravitational energy- just to be clear you are saying that local creation of energy is not possible right? because I head that the local conservation of the stress-energy tensor prevents that. | |
| Jun 13 at 19:23 | comment | added | A.V.S. | @FACald Sean Carroll said in his blog Link to blog (specific post), please? | |
| Jun 13 at 19:20 | comment | added | A.V.S. | @FACald I am saying that one should be careful with precise meaning of phrases like “create energy”: local creation of energy at the unwinding mechanism (as in the paper) would necessarily be accompanied by the change in non-local cosmological surroundings, and that change would place limits on further “energy creation”. | |
| Jun 13 at 17:46 | comment | added | FACald | Does what Sean Carroll said in his blog about the negative gravitational energy compensating an increase in energy due to the expansion of space apply here as well? | |
| Jun 13 at 17:05 | comment | added | FACald | @A.V.S. the paper you referenced “Mining energy in an expanding universe” says that the expansion of the universe can in fact be used to create energy, just to be sure you are saying this is not correct right? | |
| Mar 19 at 4:32 | comment | added | A.V.S. | @Yodo in purely de Sitter space cosmological horizon is static (see e.g. section “Static coordinates” in Wikipedia page ). Even in models where cosmic horizon is dynamic one cannot extract infinite energy by lowering a single mass on a tether. | |
| Mar 18 at 18:21 | comment | added | Yodo | In a de Sitter universe, won't the cosmological horizon expand over time? So we can extract infinite energy given infinite time (by keeping the tethered mass from moving too quickly). | |
| Apr 7, 2022 at 4:17 | comment | added | A.V.S. | @vengaq: If spacetime has a cosmological horizon then there is only a finite amount of matter with which we can interact (and thus finite reservoir of energy available). Moreover it is likely that one could write the laws of thermodynamics for cosmic horizons (similar to the laws of black hole thermodynamics) that would place limits not only on total energy but also on thermodynamic efficiencies. | |
| Apr 6, 2022 at 17:53 | comment | added | vengaq | How would the cosmological horizon limit the energy that we could theoretically extract? What does it mean to be limited in a fundamental level? @A.V.S. | |
| Sep 28, 2021 at 22:42 | vote | accept | Hermes | ||
| Sep 28, 2021 at 19:58 | history | answered | A.V.S. | CC BY-SA 4.0 |