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

learn more… | top users | synonyms

1
vote
2answers
321 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?
0
votes
3answers
231 views

Black hole accretion of dark energy

Dark energy physically can be interpreted as either a fluid with positive mass but pressure the negative of its density (pressure has units of energy/volume, and energy is mass), or a property of ...
2
votes
1answer
78 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
votes
1answer
86 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 ...
-1
votes
2answers
294 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 ...
2
votes
3answers
611 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
votes
2answers
602 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 ...
1
vote
2answers
265 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 ...
4
votes
1answer
153 views

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 ...
2
votes
2answers
332 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 ...
4
votes
2answers
281 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 ...
0
votes
1answer
118 views

Why the world is so deep and dark?

We live in a dark world, and the light is results of big bang. The world is really made mostly of dark matter and dark energy? Why the world is so deep and dark?
0
votes
1answer
162 views

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 ...
0
votes
4answers
333 views

What are the differences between dark energy and a cosmological constant?

My possibly mistaken understanding is that dark energy changes with time, whereas a cosmological constant is, well, constant. What about gravitational clumping? Detecting relative motion?
5
votes
2answers
292 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
votes
4answers
273 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 ...
2
votes
0answers
499 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 ...
1
vote
2answers
156 views

Cosmological constant of standard model of cosmology and observational data

I am curious whether the current Lambda-CDM model of cosmology matches well with observational data, especially expansion of the universe. How well does Lambda-CDM defend its established status from ...
1
vote
2answers
223 views

Possibility of making dark energy equivalent with dark matter

I was curious whether it is possible to make dark energy equivalent to dark matter. Can this unification be done? If it can, why do scientists prefer to separate dark energy from dark matter?
8
votes
2answers
1k 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 ...
3
votes
0answers
53 views

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 ...
1
vote
1answer
362 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 ...
4
votes
3answers
142 views

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)?
3
votes
3answers
493 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, ...
5
votes
2answers
822 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 ...
0
votes
1answer
152 views

Proportion of energy compared to mass in universe

In Wikipedia (http://en.wikipedia.org/wiki/Dark_matter), there is a picture that shows us the proportion of matter and energy in the current universe - CMB. It seems to suggest there is nothing that ...
1
vote
1answer
490 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 ...
5
votes
2answers
609 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 ...
8
votes
3answers
301 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 ...
2
votes
1answer
105 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 ...
5
votes
1answer
157 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 ...
2
votes
2answers
313 views

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 ...
0
votes
2answers
255 views

Is existence of cosmic dark energy falsifiable yet?

Is "existence of cosmic dark energy" falsifiable yet? And what about dark matters? Let me rephrase it again(pardon me for my previous poor expression)- Is there any condition discovered which can be ...
1
vote
0answers
64 views

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, ...
3
votes
1answer
496 views

Gravitational waves as dark energy?

Is the energy carried by gravitational radiation a viable candidate for $\Lambda$ / dark energy?
3
votes
2answers
133 views

“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 ...
5
votes
3answers
471 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), ...
2
votes
0answers
140 views

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 ...
8
votes
1answer
48 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 ...
2
votes
0answers
259 views

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 ...
-2
votes
2answers
243 views

Could dark matter be expanded atoms, and dark energy expanded radiation? [closed]

After watching Lawrence Krauss' lecture 'life, universe, and nothing', an interesting idea lighted up in my mind. Is it possible that dark matter is just spread out matter waves and dark energy ...
1
vote
1answer
35 views

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 ...
5
votes
2answers
828 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 ...
-2
votes
3answers
4k views

Is the Keppe Motor “real”?

Its makers say that it's a highly efficient motor because it resonates with (what they call) "Essential Energy", which is free energy that is everywhere in space. (I think that’s just a different name ...
4
votes
4answers
284 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, ...
15
votes
3answers
2k 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?
0
votes
1answer
687 views

Lawrence Krauss' Theory of Origin

I don't understand how a vacuum, the absence of matter, can hold energy. How can it hold energy when Einstein proved that matter is energy? And a second related question; how does the energy in a ...
30
votes
2answers
1k views

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 ...
8
votes
5answers
939 views

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 ...
3
votes
2answers
289 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 ...