Is the Universe's Energy Increasing Due to Dark Energy?

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Discussion Overview

The discussion revolves around the implications of dark energy on the universe's expansion and energy density. Participants explore whether the energy of the universe is increasing due to dark energy and the potential consequences of this increase, including concepts like the Big Rip and the conservation of energy in the context of general relativity.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants propose that dark energy's repulsive force contributes to an increase in the universe's energy and pressure per unit volume.
  • Others reference the Big Rip scenario as a potential outcome of increasing dark energy, questioning the nature of an "explosion" in this context.
  • A participant mentions that with a nonzero cosmological constant, the energy density approaches a final value, suggesting stability rather than instability.
  • There is a query about whether the increasing amount of dark energy implies a creation of energy, challenging the principle of conservation of energy.
  • Some argue that there is no global conservation of energy in the universe, noting that energy density can appear to increase as the universe expands.
  • A later reply discusses the implications of a constant dark energy density, stating that energy in a comoving volume increases over time, which raises questions about energy conservation in general relativity.

Areas of Agreement / Disagreement

Participants express differing views on whether dark energy leads to an increase in energy density and the implications for conservation laws. There is no consensus on the nature of energy conservation in the context of dark energy and general relativity.

Contextual Notes

Limitations include assumptions about the behavior of dark energy, the definition of energy conservation in cosmological contexts, and the implications of the cosmological constant on energy density over time.

edpell
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If "dark energy" is causing the Hubble expansion of the universe to increase due to its repulsive force does this mean the pressure and energy of the universe are increasing per unit volume (and as a whole). How far can this go before it explodes? That is how high can the energy per unit volume go before something(?) happens? It is hard to see where an explosion would go to.
 
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I think the Big Rip scenario describes what you are asking about. See here for more: http://en.wikipedia.org/wiki/Big_rip

I believe you are correct in thinking that it would be hard for an explosion to "go anywhere". I don't think the universe would "explode" in any sort of conventional way.
 
If there's a nonzero cosmological constant, then the energy density is decreasing toward a final value equivalent to the energy of about 30 hydrogen atoms/m3. This will not cause any 'instability' in the typical sense of the word.
Gotta be careful here though. The nonzero cosmological constant only acts equivalent to a final, constant density of hypothetical dark energy.
 
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Relevant (well, sort of - different question, sort of similar topic) inquiry I have...

Since the universe is by all observational data thought to be expanding, and that expansion accelerating, does that mean that the amount of dark energy is increasing to allow for this expansion? And if so, why is that not considered creation of energy? Energy/matter isn't thought to be able to be created or destroyed. I'm sure there is a very simple answer to this, but it still stumped me when I considered it earlier. Thanks
 
Tech, I am also interested in the question you ask. I think I have heard astrophysicists say yes more is created and yes it violates conservation of energy. Why they accept that I do not know.
 
There is no rule of global conservation of energy, which is only a local rule. That being said, the idea that 'dark energy density is constant over time' almost seems like energy conservation. It's not actually conservation because objects are getting farther apart. If there were global conservation we would expect the energy density to scale as the inverse cube of the expansion.
 
Consider the special case of constant dark energy density, i.e. the cosmological constant. Here we find that since the energy density is constant in time, that the amount of energy in a comoving volume is increasing in time. A local observer must then conclude that energy is not conserved within this volume. But that's OK, because there's no such requirement that energy be conserved in general relativity. Rather, it is the stress-energy tensor that satisfies a conservation requirement. For a nice description of this, see Baez:http://johanw.home.xs4all.nl/PhysFAQ/Relativity/GR/energy_gr.html
 

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