As space expands, is there work being done?
My understanding is that since there's no motion, in the traditional sense, involved, then no work is done, so no energy is involved. But then if your distance from a gravitational source increases, so does your potential energy. Is that a contradiction, or do the changing PEs from different sources all cancel out?
More generally, does expansion require energy?
Expansion is a property of space (space-time) itself, not of the objects within. Since our laws of motion apply to objects within but not space itself, it's hard to draw similar measurements such as work, force, etc.
dark energy basically
Can't you imagine it though
Mom: When are you gonna settle down into a nice theory like your big brother electromagnetism?
Dark energy: Shut up mom maybe I don't wanna be like him god.
Firstly, some models say that there is some kind of driving force responsible for the accelerated expansion. Depending on the model, this driving force is thought to be the vacuum energy of the universe resulting from QFT or a scalar field, called the quintessence. However, there is an energy behind the process, which from is thought to make up about 70% of the energy in the universe.
Secondly, energy conservation is not proven. While every experiment indicates that it is true in the local regime, including an underlying symmetry of nature, which leads to energy conservation, there is neither experimental data nor theoretical confirmation, that energy is conserved as a whole in the universe.
So yes, this might be a contradiction and we don't know if expansion requires energy, yet. This contradiction does neither mean that the theory of expansion is wrong nor that energy conservation does not hold anymore and one could build a perpetuum mobile.
Yeah, I was wondering if 'dark energy' actually meant energy that would still comply with conservation. If it's vacuum energy and conservation does still apply, then, what, space itself is becoming less active as it expands? In the sense that fewer random partcle/anti-particle pairs appear, maybe, or just the value of the scalar field may decrease?
Dark energy/matter COULD just be MACHOs (massive astrophysical compact halo object) or something else we can observe yet. I don't know if there is evidence yet for that theory or against is, but we only can observe the observable so why rule out the possibility that space is just full of a LOT more stuff than what we think it is?
Mom: I'm just saying he's doing very well in the standard model. And strong and weak nuclear force are there and your brother gravity might even join them I know how much you look up to him.
Emo energy: Shut up mom I wanna do my own thing!
Mom: Well could you at least stop accelerating the expansion of the universe you're gonna rip space apart one day you keep this up!
Emo energy: Yea well maybe that's what I want! *goes to room slams door and blasts "Crawling in my skinnnnnnn!!!"*
Interesting idea. I guess at the current stage of research, no one knows the answer. However, if energy conservation holds, a bigger universe should result in a smaller energy density, which would confirm your hypothesis.
Yet, from a cosmology course I slightly remember there are 3 contributions to the acceleration of the universe in the Friedmann equations: matter, radiation, and dark energy. And as far as I remember the ratio of dark energy increases with time. Maybe someone here can tell more about this.
That's an interesting idea, since it might mean that the dark energy in the universe is spent over time.
So, in the big bang, a large amount of dark energy is suddenly lost to overcome gravity, and then it keeps decaying to accelerate galaxies away from each other.
Which might mean the big crunch is still possible...