Can Dark Energy be eventually infinite?

In summary, assuming the most common Dark Energy models, the density of dark energy remains constant even with the expansion of the universe. This means that as new space is created, it contains the same amount of dark energy as previously existing space. However, if the universe is expanding and accelerating, as currently believed, this would mean that the expansion will continue towards infinity, requiring an infinite amount of dark energy to be created. This raises questions about the source of this additional dark energy and whether it violates the principle of conservation of energy. However, energy is not a conserved quantity in General Relativity, and there is a model known as the big rip where the energy density of dark energy grows over time, leading to an increase in the rate of
  • #1
Gerinski
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15
Assuming the most common Dark Energy models, it's density remains constant even with the universe expansion. As new space volume is created, it contains the same amount of dark energy as the previously existing space for the same volume unit.

If we assume that at a certain epoch of cosmic time, say 13 billion years elapsed from the Big Bang, the universe is finite in volume and time (we opt to dismiss the block-time view), this means that the amount of dark energy contained in the universe at that epoch is finite.

But if the universe is expanding and accelerating as it is currently mostly believed, it should mean that the expansion will continue forever towards infinity, therefore also Dark Energy will need to be created in infinite quantity.

Where does the additional dark energy contained in newly created space come from? Doesn't this violate the principle of conservation of energy?

And eventually in case of infinite expansion, how can infinite energy become available to fill up all that space?
 
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  • #2
So far we have no evidence that what is called "dark energy" corresponds to an actual energy.
The simplest explanation is that there is a cosmological curvature constant Λ, which is a constant intrinsic curvature in spacetime (which could have various explanations or simply be a constant of nature).

this curvature Λ does not have to be caused by some mysterious "energy", it is reflected in the observations of how the Hubble expansion rate H(t) evolves over time. H(t) seems to be declining but not to zero, it seems to be leveling out at a longterm asymptotic rate we can call H ≈ 1/17.3 percent per million years.
The current expansion rate is H0 = H(now) = 1/14.3 percent per million years. But this has been declining and best fit to the accumulated data indicates H→H.

that is essentially what they mean by "acceleration". the rate is going to a positive rate as limit instead of zero.
growth at a constant positive rate is, of course, exponential, even if the rate is rather slow in percentage terms.

this does not require that space be full of some mysterious "energy" :oldbiggrin:
energy is not required for distances to increase, geometry is dynamic, that has been known for generations.
there is a lot of excited hype surrounding the discovery that the limiting longterm rate is not zero.
 
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  • #3
Gerinski said:
Assuming the most common Dark Energy models, it's density remains constant even with the universe expansion. As new space volume is created, it contains the same amount of dark energy as the previously existing space for the same volume unit.

If we assume that at a certain epoch of cosmic time, say 13 billion years elapsed from the Big Bang, the universe is finite in volume and time (we opt to dismiss the block-time view), this means that the amount of dark energy contained in the universe at that epoch is finite.

But if the universe is expanding and accelerating as it is currently mostly believed, it should mean that the expansion will continue forever towards infinity, therefore also Dark Energy will need to be created in infinite quantity.
The rate of expansion doesn't increase. That rate is decreasing and approaching a constant value. This is described as accelerated expansion because if you have a constant rate of expansion (speed per distance), then the distance between objects increases at an accelerating rate.

There is a (rather unphysical) model where precisely what you describe does happen. It's known as the big rip. This isn't normal dark energy, though: it's dark energy where the energy density grows over time. In such a universe, the rate of expansion increases, and yes, it becomes singular in a finite amount of time. This model is almost certainly impossible, however, as it violates all of General Relativity's energy conditions (if you're curious what that means, see the Wikipedia page here.

Gerinski said:
Where does the additional dark energy contained in newly created space come from? Doesn't this violate the principle of conservation of energy?
Energy is not a conserved quantity in General Relativity. Here is Sean Carroll's description of why this is:
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
 
  • #4
Chalnoth, why would you call phantom energy an "unphysical model"? It's perfectly physical.
 
  • #5
Space-Time Dude said:
Chalnoth, why would you call phantom energy an "unphysical model"? It's perfectly physical.
It violates all of the energy conditions of General Relativity. For example, it violates the weak energy condition which comes from the statement that matter density is non-negative for any observer. It also violates the more stringent dominant energy condition which states that mass-energy can never flow faster than light.

You can see more here:
https://en.wikipedia.org/wiki/Energy_condition

Note that dark energy in general violates the strong energy condition, but dark energy which grows in density over time violates them all.
 

1. Can dark energy be created or destroyed?

No, dark energy cannot be created or destroyed. It is a fundamental property of the universe and cannot be altered or changed.

2. Is dark energy the same as dark matter?

No, dark energy and dark matter are two separate concepts. Dark energy is a force that is causing the expansion of the universe to accelerate, while dark matter is matter that we cannot see but whose existence we can infer through its gravitational effects.

3. How do we know that dark energy exists?

Dark energy was first hypothesized based on observations of the expansion of the universe. In the late 1990s, astronomers discovered that the expansion of the universe was accelerating, which could not be explained by the known forces of gravity. This led to the theory of dark energy as a possible explanation.

4. Is dark energy the same as the cosmological constant?

Some scientists use the terms "dark energy" and "cosmological constant" interchangeably, but they are not exactly the same. A cosmological constant is one possible explanation for dark energy, but there are other theories as well.

5. Will dark energy eventually run out?

There is currently no evidence to suggest that dark energy will run out. In fact, some theories suggest that it may become stronger over time. However, our understanding of dark energy is still limited, and more research is needed to fully understand its properties and behavior.

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