The dark-energy tag has no wiki summary.
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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 ...
12
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5answers
391 views
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 ...
10
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3answers
466 views
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?
8
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1answer
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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 ...
7
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2answers
206 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 ...
6
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2answers
74 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) = ...
6
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4answers
307 views
Dark matter 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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3answers
77 views
Could dark energy be the effect of gravity at great distances?
This may be a silly question, but is it possible that dark energy and gravity are related to each other?
Space-time is deformed everywhere in space by objects with mass. The more massive the object, ...
5
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4answers
285 views
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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3answers
147 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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2answers
319 views
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 ...
4
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1answer
298 views
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 ...
4
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3answers
302 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 ...
4
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1answer
153 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 ...
4
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2answers
262 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), ...
4
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2answers
68 views
Cosmological triangle with PLANCK results
Is there an updated version of the cosmological triangle with recent PLANCK results included?
4
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1answer
106 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 ...
4
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1answer
387 views
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 ...
4
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1answer
71 views
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 ...
4
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1answer
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Why is it desirable to have a symmetry to make cosmological constant zero?
It is sometimes stated that absence of a symmetry to make cosmological constant zero is a problem. But observed value of dark energy is very small and non-zero. So why is it desirable to have a ...
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1answer
298 views
Gravitational waves as dark energy?
Is the energy carried by gravitational radiation a viable candidate for $\Lambda$ / dark energy?
3
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2answers
224 views
asymptotic curvature of the universe and correlation with local curvature
There is not-so-rough evidence that at very large scale the universe is flat. However we
see everywhere that there are local lumps of matter with positive curvature. So i have several questions ...
3
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2answers
155 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 ...
3
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2answers
310 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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2answers
80 views
'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 ...
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2answers
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“Dark” quantities
I don't know much about the so-called dark matter, apart from what has been described in popular descriptions of the reasons for it being postulated.
My question is, is there dark momentum, dark ...
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0answers
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squeezed radiation astronomy
Squeezed electromagnetic vacuum does have a renormalized energy density smaller than the vacuum. So it makes it in my opinion a inconspicuous candidate for a dark energy carrier.
Are there ...
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2answers
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Why is it concluded that the cosmos is expanding when in fact the observations are for events further back in time?
Why is it concluded that the cosmos is expanding at an ever increasing rate when looking further out and therefore further back in time?
Surely, if the time were reversed to play forwards, the ...
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2answers
152 views
Could dark energy be heat? Could dark matter be stuff that is not seen because of its refraction limits?
Heat has to go somewhere. Would the light and heat of the stars in the universe amount up to being dark matter ...and dark energy ...
Dark matter would just be small pieces of stuff.
Dark energy ...
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3answers
300 views
Less than absolute zero possible? [duplicate]
Possible Duplicate:
Temperature below absolute zero?
According to this article
http://www.sciencemag.org/content/339/6115/52 (preprint: http://arxiv.org/abs/1211.0545)
it is. What do you ...
2
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1answer
36 views
Why do we need the concept of dark energy to explain the expansion of the universe?
Why can't the expansion of the universe be thought as the Big Bang itself still in progress? Why do we need to introduce dark energy? The Big Bang was powerful, and that explosion itself could still ...
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1answer
41 views
Dark Energy and Conservation of Momentum
IF dark energy was not perfectly evenly distributed(as some theories suggest), in other words if some cubic centimeter had a very small difference from another cubic centimeter, would that imply that ...
2
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1answer
64 views
Dark energy before radiation or after?
In the cosmic history of the universe, does the dark energy comes before the radiation epoch, or only now, in the 'matter' universe (matter dominated era)?
Because, we now know that like 75% of our ...
2
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0answers
83 views
Our Universe in collision with another one
This question is related to the possibility that there are many other universes in the UNIVERSE,the multiverse, that were created during collisions between membranes, according to string theories. The ...
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0answers
256 views
Is large-scale “time reversal” (Poincaré recurrence) possible given infinite time?
The following are some assumptions I'm basing my question on, from what (little) I understand of physics. I list them so an expert can (kindly) tell me where I'm going wrong.
There is a probability ...
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0answers
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Dark-energy sources and respective implications
Firstly, I want this to be a very layman/simple level. According to Sean Carroll, we have certain possibilities for where dark-energy comes from:
http://www.youtube.com/watch?v=v6o2bUPdxV0
...
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2answers
193 views
Dark matter and dark energy [duplicate]
Possible Duplicate:
Dark matter references
I have recently read about dark matter and dark energy, and why physicists think it must exist (dark matter: mass of galaxies are far bigger than ...
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2answers
217 views
Cosmology questions from a novice
These ideas/questions probably represent a lack of understanding on my part,
but here they are:
1) Cosmologists talk about the increasing speed of expansion of the universe and talk of dark energy as ...
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3answers
181 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, ...
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2answers
135 views
Is cosmic background radiation dark-matter and/or dark-energy?
Dumb question alert: Is it possible that the cosmic background radiation might be the source of dark-matter and/or dark-energy? What is the mass of the background radiation in the known universe?
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1answer
190 views
What allows us to infer the existence of dark energy?
A recent Indian examination asked: how do we infer dark energy is there? It gave as options: rotation curves of galaxies, accelerated expansion of the universe, existence of microwave background ...
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1answer
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Could dark energy be linked to dark flow?
I couldn't find any other questions regarding dark flow on Wikipedia, so I'm curious. As far as I can tell, dark energy's existence seems to be hard to explain. Since there may be a couple of ideas ...
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1answer
152 views
What exactly are super WIMPs?
I recently got confused (and slightly annoyed by the lack of technical details) when reading a popular article (authored by Jonathan Feng and Mark Trodden) introducing the concept of super WIMPs.
The ...
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1answer
42 views
Could there be a small-scale observation of dark energy?
The amount of dark energy in the universe is pinned down fairly precisely by fluctuations in the cosmic microwave background, if I understand correctly. So in that sense there's very good evidence of ...
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2answers
63 views
proportion of dark matter/energy to other matters/energy at the beginning of the universe
How will the proportion of dark matter/energy to other matters/energy be like at the momenets after the beginning of the universe (standard Big Bang model)?
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0answers
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How many times brighter could the stars shine without raising the temperature of space?
If my understanding is correct, the temperature of space (as defined by the temperature that a black-body will reach) has been decreasing since the big bang. It has never increased. Additionally, ...
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0answers
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Why do galaxies collide? Reconciling dark energy and an expanding universe with the fact that some galaxies are on a collision course
My layman understanding of cosmology is:
galaxies are uniformly (more or less) spread throughout the universe, per the Big Bang and the fact that in a central explosion, all dispersed points are ...
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3answers
113 views
Dark energy and dark matter
Our galaxies are speeding apart from each other and that is because of dark energy, but we don't know where it comes from right? If I'm not mistaken could dark matter have dark energy? (If they are ...
0
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1answer
118 views
Is Dark Energy converted to Gravitational Potential Energy?
Dark Energy is basically doing work against gravity to accelerate the expansion of universe. So, for time-translational symmetry to be hold, dark energy must be converted to gravitational potential ...
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1answer
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Is a new universe created when dark energy rips open a singularity?
Dark energy will tear everything apart, even black holes. Is a new universe created when dark energy rips open the singularity of a black hole ? And does the topology of the universe depend on the ...
