- #1
Shovel
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Sorry if this has been covered before, but I couldn't find anything satisfactory with a quick search. I realize there is another thread on here regarding conservation of energy with respect to expansion, but my question sort of takes a different direction; can you create energy from this effect?
I'll start with explaining my understanding of cosmology, so if any of my assumptions are incorrect please feel free to point that out. It is my interpretation that cosmic expansion is caused by space being continuously "inserted" between any two objects, with the amount/rate of "new" space created being proportional to the proper distance between said objects. Naturally this would cause any two objects that are not bound by the fundamental forces to drift apart exponentially. It is my understanding that this effect is independent of GR and conservation of energy, which would explain how it is possible for distant galaxies to be receding from ours at speeds faster than c, how the radius of the OU is greater than c * T, and how energy lost from redshifted photons is not conserved. For my question I'm assuming that this expansion is constant with respect to time and roughly uniform with respect to space.
Consider a sizeable galaxy that has no gravitationally bound local group. After some eons, all nearby galaxies will have receded beyond the Hubble length and are thus forever unreachable. Some time after that, the last photon (or other fast particle) that will ever arrive from outside the galaxy strikes a space rock or something and the galaxy is now effectively its own universe from the point of view of anything in it. As the galaxy slowly suffers heat death, the local inhabitants decide they don't want to die a slow, painful death from corporate downsizing. They then attempt to engineer a device that extracts energy from the expansion of space so that they can do pod racing forever or slowly construct a whole new universe or whatever. Is this possible?
My guess is yes, but I'm not sure of the math of it. Imagine a cannon that is aimed away from the center of the galaxy (out into the void) and fired, with the cannonball leaving the barrel with less velocity than required to escape the galaxy forever. It should thus eventually fall back into the galaxy, and according to the conventional rules should arrive back with the same velocity that it left with. But if space is inserted between the moving cannonball and the galaxy, the apex of its flight should be further away than would normally be expected. Shouldn't this cause the ball to have increased potential energy at the apex, and thus when it arrives back in the galaxy, have more kinetic energy than it left with? The total mass-energy of the galaxy (which is well-defined and finite) will have been increased and the laws of thermodynamics will have been locally violated.
Now, I have to be mistaken somewhere, seeing as I have never read or heard about this possibility anywhere, just gloom-and-doom about inevitable heat death of local groups. What am I missing?
I'll start with explaining my understanding of cosmology, so if any of my assumptions are incorrect please feel free to point that out. It is my interpretation that cosmic expansion is caused by space being continuously "inserted" between any two objects, with the amount/rate of "new" space created being proportional to the proper distance between said objects. Naturally this would cause any two objects that are not bound by the fundamental forces to drift apart exponentially. It is my understanding that this effect is independent of GR and conservation of energy, which would explain how it is possible for distant galaxies to be receding from ours at speeds faster than c, how the radius of the OU is greater than c * T, and how energy lost from redshifted photons is not conserved. For my question I'm assuming that this expansion is constant with respect to time and roughly uniform with respect to space.
Consider a sizeable galaxy that has no gravitationally bound local group. After some eons, all nearby galaxies will have receded beyond the Hubble length and are thus forever unreachable. Some time after that, the last photon (or other fast particle) that will ever arrive from outside the galaxy strikes a space rock or something and the galaxy is now effectively its own universe from the point of view of anything in it. As the galaxy slowly suffers heat death, the local inhabitants decide they don't want to die a slow, painful death from corporate downsizing. They then attempt to engineer a device that extracts energy from the expansion of space so that they can do pod racing forever or slowly construct a whole new universe or whatever. Is this possible?
My guess is yes, but I'm not sure of the math of it. Imagine a cannon that is aimed away from the center of the galaxy (out into the void) and fired, with the cannonball leaving the barrel with less velocity than required to escape the galaxy forever. It should thus eventually fall back into the galaxy, and according to the conventional rules should arrive back with the same velocity that it left with. But if space is inserted between the moving cannonball and the galaxy, the apex of its flight should be further away than would normally be expected. Shouldn't this cause the ball to have increased potential energy at the apex, and thus when it arrives back in the galaxy, have more kinetic energy than it left with? The total mass-energy of the galaxy (which is well-defined and finite) will have been increased and the laws of thermodynamics will have been locally violated.
Now, I have to be mistaken somewhere, seeing as I have never read or heard about this possibility anywhere, just gloom-and-doom about inevitable heat death of local groups. What am I missing?