Dark energy is the unknown form of energy that drives the acceleration of the universe's expansion.

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Are modified theories of gravity credible?

I'm a statistician with a little training in physics and would just like to know the general consensus on a few things. I'm reading a book by John Moffat which basically tries to state how GR makes ...
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How do people calculate proportions of dark matter, dark energy and baryonic matter of the universe?

The Wikipedia page on dark matter mentions that the Planck mission had revealed that in our universe ordinary baryonic matter, dark matter and dark energy are present in the ratio: 4.9%, 26.8% and 68....
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How did the universe shift from “dark matter dominated” to “dark energy dominated”?

In order to get dark energy to dominate, wouldn't you first need another form of energy to push the expansion until dark energy could dominate? Otherwise I don't understand how the universe could ...
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Why does dark energy produce positive space-time curvature?

My understanding is that dark energy, or equivalently a positive cosmological constant, is accelerating the expansion of the universe and I have read that this gives empty space-time positive ...
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What experiments, other than Hubble Expansion, support the Dark Energy theory?

Dark energy is introduced as a constant inside Einstein's equations. Its primary purpose, from what I understand, is to make Einstein's equations compatible with the accelerating expansion of the ...
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1answer
958 views

What are the alternative theories of dark energy? ($w \neq -1$)

There has been a lot of related questions about dark energy around here but these are usually 2-4 years old and the closest question to mine hasn't really been answered, so I am going to proceed. ...
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What is Dark Energy, and how was it discovered?

I've heard a lot about Dark Energy, and how it's supposed to be one of the most powerful forces in the universe. What is it, and how was it discovered?
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Dark matter and dark energy references

I've been looking for questions about dark matter, and I've read some very interesting answers. However, I desire too look into it deeply. This is not actually a question. I'm asking the community ...
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578 views

Justification for new theories of Particle Physics and General Relativity

In reference to arxiv:1212.4893v3 and arxiv:1206.5078v2 papers of Ma and Wang, they have proposed new theories in particle physics, the weakton model where quarks and leptons are formed using these ...
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Does dark energy have gravity?

So I keep running into this idea on the Internet that only mass has gravity, but isn't mass simply contained energy? Energy bounces around, or travels at the speed of light, because it is not in the ...
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How do scientists calculate the percentage of dark energy in the universe?

I can understand how the percentage of dark matter compared to ordinary matter is calculated, because the amount of dark matter has a clear gravitational effect on the ordinary matter in a Galaxy. ...
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634 views

What current alternatives are there to the standard concordance model of cosmology?

The current "standard model" or concordance model of cosmology is Lambda CDM which includes late time acceleration due to a cosmological constant, cold dark matter as the missing matter component and ...
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How is dark energy consistent with conservation of mass and energy?

I initially thought that dark energy must in some way violate conservation of mass and energy since the component of the energy density of space that comes from dark energy is constant, and space is ...
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363 views

Why doesn't dark energy vary with time?

Trying to teach myself the basics of cosmology. I can see why, in an expanding universe, radiation and matter density, and radiation and matter pressure vary with time. But why is it assumed that dark ...
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1answer
60 views

New Type of Type Ia supernova. Implications to Dark Energy measurement?

As I understand it, we used Type Ia supernovas to determine that there is some sort of repulsive force (which we call dark energy) making things fly away from us at an accelerated rate. The reason we ...
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3answers
782 views

Dark Energy / Accelerating universe: naive question

Folks, I have a naive question regarding the subject of dark energy and an accelerating universe: From what I understand/read, it seems that the further we look out into deep space, the faster the ...
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154 views

Considering dark energy and other factors, what is the most distant object light could reach?

If we send a photon from Earth at this moment, what is the most distant object that it could reach? This question is partly inspired by this video which states we cannot ever travel beyond our local ...
7
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112 views

Was the matter-energy content of our universe always distributed in the same ratios?

Currently, Dark energy (68.3%) and Dark matter (26.8%) together constitute about 95.1% total matter-energy content of the universe while only 4.9% is ordinary baryonic matter. Was this always the case?...
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689 views

Could the acceleration of universe expansion be caused by gravity itself?

Dark energy is suggested to be a repulsive force in the universe causing an accelerated expansion. If the amount of mass outside our observable universe is greater than inside (higher mass density), ...
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4answers
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Negative pressure, tension, and energy conditions

We have lots of common everyday experience with positive pressure, the canonical example is a gas. But other examples of positive pressure are easy to imagine: for instance, a solid that gets ...
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2answers
189 views

Why are *high redshift* measurements of supernovae required to measure dark energy?

Why are high redshift measurements of supernovae required... in order to measure the equation of state parameter of dark energy? The luminosity distance can be written as \begin{equation} d_{L}(z) = ...
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4answers
684 views

Theory that gets rid of dark matter/energy

Is there any physics theory that either groups together gravity and dark energy/dark matter or eliminates dark energy/dark matter by modifying standard understanding of gravity or any force? If so, is ...
6
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3answers
858 views

If the universe is full of dark matter, why is it only 2.73 K cold?

people! I am just a physics layman, but I recently watched a documentary about the universe and it was told that the universe is full of dark matter and energy and the universe is empty, so that ...
6
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By what process did the era of inflation end, or has it just slowed down (a lot)?

Could someone please explain the current model regarding: a) how the era of inflation was turned off (the graceful exit idea or alternatives)? b) what the timeline is between the era of inflation ...
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1answer
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Can the inflaton be detected? Does it interact with the other fields?

In a recent article it is claimed that dark energy can actually be a new manifestation of the inflaton field at electroweak scales. This subject is pretty far from my area of expertise (if there is ...
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1answer
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Could observed accelerating expansion be an illusion based on distance?

The thought occurred to me that if we just happened to be born into a time when the the universe started slowing down, it would take some time for us to observe this - especially in more distant ...
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Is dark energy homogeneous and/or isotropic?

Shouldn't there be at least some fluctuations of dark energy in various regions, analogous to the fluctuations we observe in other forms of energy like matter?
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Can the cosmological constant change with time?

This post is a specialization of the post: Can the proportion of dark energy change? Can the cosmological constant change with time? If so, is there a measurement of this evolution up to now, and ...
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1answer
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How the CMB anisotropy is linked to the existence of cold dark matter and dark energy?

After the data from the cosmic microwave background has been collected by WMAP or Planck, what types of analysis is needed to conduct in order to deduce the cold dark matter density and the ...
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4answers
476 views

Do photons make the universe expand?

I have a problem understanding the ideas behind a basic assumption of cosmology. The Friedmann equations follow from Newtonian mechanics and conservation of Energy-momentum $(E_{kin}+E_{pot}=E_{tot})$ ...
6
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1answer
151 views

Could dark energy make a large black hole less black?

Theoretically, if a black hole grew to a huge scale such that the effect of dark energy was large, could the black hole become 'normal' space again (i.e. no horizon or singularity)? What I'm trying ...
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How much light is there in space and how heavy is it?

Our night sky is filled with stars. On a dark night a significant fraction of the sky is light. This light, we are told, has been in transit for many millions of years. There must therefore be quite a ...
5
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2answers
158 views

How does the inclusion of vacuum energy modify Newtonian gravity equation of motion?

The equation of motion (in the center of mass frame) due only to gravitational forces between two point masses is: $$\frac{d^2r}{dt^2} = -\frac{GM}{r^2}$$ How does the equation get modified when a ...
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396 views

How much does electromagnetic radiation contribute to dark matter?

EM radiation has a relativistic mass (see for instance, Does a photon exert a gravitational pull?), and therefore exerts a gravitational pull. Intuitively it makes sense to include EM radiation ...
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253 views

How does dark energy allow the universes expansion to accelerate?

I was wondering how dark energy is effecting the rate at which the universes expansion occurs.
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Why is it important that the equation of state parameter of dark energy is measured?

The equation of state for a perfect fluid is that $p=\omega \rho c^{2}$, where $p$ is the pressure, $\rho$ is the density, $c$ is the vacuum speed of light, and $\omega$ is called the equation of ...
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2answers
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'Negative pressure' counteracting gravity?

Dark energy may be described as a fluid with negative pressure. We say that this negative pressure counteracts gravity and accelerates the expansion of the Universe. Now consider, for example, a ...
5
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759 views

Is dark matter really matter?

Is dark matter really a form of matter? We know it has a gravitional attraction and we know that everything that has a gravitional force is made by matter. But maybe this is an exception? And if ...
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3answers
656 views

G4v Gravity Theory: Why does this get rid of Dark Energy?

Earlier this year, Carver Mead of CalTech published a paper which seems to be garnering a lot of attention: http://arxiv.org/abs/1503.04866 http://www.npl.washington.edu/AV/altvw180.html http://...
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2answers
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Are there experiments taking place right now that might show evidence for or falsify dark energy or dark matter?

What experiments at quantum or cosmic level might provide the strongest supporting evidence for or, conversely, potential for falsifying, the existence of dark matter or dark energy?
5
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1answer
178 views

Can dark matter and energy be formulated as local perturbations of the metric

Note, my formal physics education ended over ten years ago so I may be missing some obvious piece of understanding. The relationship between space-time and matter/energy distribution is described by ...
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2answers
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When will the Hubble volume coincide with the volume of the observable Universe?

The Hubble volume is the volume that corresponds to objects so far from the Earth that the space between us and them is expanding faster than the speed of light. (I.e. objects outside this volume ...
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1answer
281 views

What is the difference between the Big Bang Model and the Λ-CDM Model?

If I'm going to write about "The Consensus Model of Cosmology" should I include Big Bang Model or should I go with just the $\Lambda$-CDM Model?
4
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551 views

What type of energy is Dark Energy?

What type of energy is Dark Energy? Just as the title says. Is it kinetic/potential or some other type?
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3answers
850 views

Dark energy vs. gravity

If dark energy is everywhere around us, then why don't we get separated? For example why don't I get separated from the pen kept in front of me? Or take a similar example in free space. Is dark energy'...
4
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1answer
744 views

Gravitational waves as dark energy?

Is the energy carried by gravitational radiation a viable candidate for $\Lambda$ / dark energy?
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4answers
371 views

Could dark energy be powered by force particles that obey quantum mechanics?

From what (little) I know about physics, I understand that the universe is expanding due to dark energy, and I understand that no one quite understands it yet. I also understand that the cosmic ...
4
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1answer
320 views

What would happen to the universe if dark energy started “disappearing”?

Terribly naive question, I know. Obviously, not simply "disappearing", but if it could, theoretically, be absorbed or "used" somehow, what would happen to the universe? Would it stop expanding, would ...
4
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2answers
358 views

Dark Energy saving the world

Ok, my understanding of physics is still limited, hoping to change that in the following years, but I have a question. Dark energy is what provokes the expansion of the universe, so, in theory, it ...
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Proportion of dark matter/energy to other matters/energy at the beginning of the universe?

What was the proportion of dark matter/energy to other matters/energy at the moments after the beginning of the universe (standard Big Bang model)?