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Questions tagged [dark-energy]

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

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57 views

Superposition of gravitational waves and the dark energy

Is it theoretically possible to create a superposition of gravitational waves that form a locally static negative curvature, something like the dark energy?
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0answers
48 views

Dark Energy and Black Holes

This question is similar but not quite the same as Could dark energy make a large black hole less black? My question deals with the evaporation or expansion of black holes. In trillions of years ...
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1answer
47 views

Where does negative pressure in dark energy arise?

In the 2nd friedmann equation, the pressure term of dark energy is what counteracts the energy density and cause acceleration of the expansion of universe. But normal pressure gradient arises from the ...
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1answer
55 views

Field equations with cosmological constant

Is it enough to add the cosmological constant in the einstein field equations to guarantee that the obtained solution describes an expanding universe?
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2answers
97 views

Is the acceleration of the expansion of the universe caused by expansion of space time itself?

When considering the accelerating expansion of the universe, it is often stated that dark energy is required to cause acceleration of expansion in order to overcome the pull of gravity. However, it ...
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2answers
90 views

What is really a negative energy particle (and why is it different from an anti-particle)?

I have read this question: What is negative Energy/Exotic Energy? This does not really give an answer. Why does a particle (charged) change sign passing the event horizon? Black holes and positive/...
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1answer
81 views

What theories purport to describe “physical-level understanding” of dark energy?

What theories propose to close the gap (as suggested by http://arXiv.org/abs/1210.6008) between 'phenomenological behavior of dark energy' and 'physical-level understanding of dark energy' and to what ...
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1answer
25 views

Volume of dark energy in space [duplicate]

As I understand it, Dark Energy is believed to reside in empty space. As the Universe exapnds, more empty space exists inside the Universe and so the small energy per unit of empty space adds up to a ...
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1answer
49 views

Correction to Newton's law of Gravity for dark energy

Is there any correction to Newtons law of Gravity that takes into account the expansion of the universe?
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1answer
53 views

How do they know the numbers of the energy pie chart of the universe?

They say that the total energy of the universe consists of 4.9\% ordinary matter, 26.8\% dark matter and 68.3\% dark energy. I hear this pie part in virtually every lecture in cosmology. How do we ...
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1answer
70 views

What are the units of dark energy?

Popular literature seems to equate dark energy with the cosmological constant of the Einstein field equations. We know however that the dimensions of any constituent of the field equations is ${\rm ...
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0answers
44 views

Could the source of dark energy be the universe rotating in a higher dimension?

As I understand it, the centrifugal force in a merry-go-round increases as we move further away from the center. Could the universe be spinning in a higher dimension (or even just spinning in a ...
2
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1answer
94 views

What's the definition of repulsive gravity?

After asking this question, I got confused. I always thought that repulsive gravity was a consequence of dark energy, the Nature of which is unknown. Many theories are flying around about its Nature. ...
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1answer
59 views

Is there a relationship between Black Holes and the Big Bang?

As the question mentions, is there a relationship between the Big Bang and Black Holes? It appears the Big Bang is a ‘tacked on’ theory that doesn’t align with current theories (since we don’t know or ...
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0answers
51 views

How accurate is the De Sitter solution of the Einstein field equations of general relativity?

The De sitter solution models the universe as spatially flat, neglecting ordinary matter, such that it is dominated by the cosmological constant. The cosmological constant notion arguably suggests the ...
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2answers
38 views

Does Higgs Boson influences with Gravity?

Does Higgs Boson influences with Gravity? Is there any way that if the universe is expanding Higgs particle has influence over it?
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7answers
181 views

Is there any opposition to gravity? [closed]

we have friction which opposes motion of moving body on another surface, resistance or reactance which opposes current, reluctance which opposes flux etc ,each and every physical phenomena there is ...
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1answer
82 views

Does string/M-theory provide a solution to the dark matter/energy problem?

Would string theory or any other propesed UFT help explain, at least in theory what the other 95 percent of matter and energy in the universe are about? It seems as thaugh there is a reacurring theme ...
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1answer
43 views

Gravity and dark energy in space

I've been studying astrophysics and I read that our universe is still expanding because the gravity is not enough compared to the dark energy present. And right now we are not sure whether are ...
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0answers
59 views

What is the co-moving distance to a point, at which the late-time acceleration of the universe began?

First of all sorry for my English - it is not my native language. According to the following wonderful diagram made by Pulsar, the late-time acceleration of the universe began at $t_{acc}=$ 7.7 ...
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1answer
45 views

Could a large amount of antimatter accelerate the universe instead of dark energy? [closed]

It is not known whether antimatter is repulsed by or attracted to matter. For the purpose of this question, I assume that antimatter is repulsive to regular matter (otherwise this question makes no ...
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1answer
2k views

Why do we interpret the accelerated expansion of the universe as the proof for the existence of dark energy?

Why do we interpret the accelerated expansion of the universe as the proof for the existence of dark energy? The accelerated expansion only tells us that the Einstein field equation must contain a ...
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1answer
73 views

Dark energy and dark matter difference

From the rotation curve of spiral galaxy it is found that for (>>r ) the total mass is not concentrated at the centre but varies as ~r for which the rotational velocities of the stars far from the ...
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3answers
273 views

Does string theory accommodate effects of dark energy?

String theory is arguably, among best candidates for a Theory of Everything. So, because every TOE is an attempt to bind together the big and very small effects and things, a TOE must be able to ...
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0answers
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Are deductions from CMB much less accurate than claimed, owing to approximations in the FLRW model?

My question concerns "timescape cosmology" and measurements of dark energy based on CMB radiation. The background to the question is Lawrence H. Dam, Asta Heinesen, David L. Wiltshire, "Apparent ...
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1answer
44 views

Can universe still expand without energy and matter?

I heard dark energy is the intrinsic property of space and it cannot be particle because particle's density dilute when volume increase, I do not know how nothingness can have property and Einstein ...
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1answer
157 views

Why are we trying to fit GR in QFT when there's a chance that GR is incomplete?

GR explains most phenomena in our universe, but not everything.. Dark matter and Dark energy still don't fit in explanation of GR. QFT, on other hand, is almost complete. Shouldn't physicists go for ...
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Why does dark energy make universe accelerate not slow down?

If mass=energy, then why doesn't dark energy not make the expansion slow down rather than accelerate seeing as gravity pulls masses together?
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0answers
21 views

What is the simple way to calculate the content of dark energy from CMB probe? Do i have to find out the power or anular spectrum

And which data should i use, after getting data which software can plot it. Here are software in this site but dont know which one to choose- https://lambda.gsfc.nasa.gov/toolbox/ , since i am ...
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1answer
49 views

Negative work done by dark energy

If I lift a book up, I applied a force opposite its weight so there's positive work done. Dark energy is said to be pushing galaxies apart and the energy is coming from this negative work done. ...
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2answers
214 views

Would a charge imbalance act like dark energy?

I realize that there are theoretical reasons to reject the idea that the charges on electrons and protons may not be exactly equal and opposite; and I am not suggesting that they're not. Edited 12/20/...
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2answers
174 views

Farnes, cosmology involving negative mass

I came across a paper recently which seems to be getting a lot of popular press, and a student also emailed me to ask about it: -- Farnes, "A Unifying Theory of Dark Energy and Dark Matter: Negative ...
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2answers
74 views

Is gravitational lensing affected by dark energy?

Is gravitational lensing affected by dark energy? I mean, despite the effect if cause on the expanding Universe, could dark energy cause gravitational or anti-gravitational lensing?
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1answer
37 views

How would we relate the cosmological constant to a dark energy distribution?

*Please excuse my lack of understanding of dark energy, the GR courses that I have taken so far haven't covered it How would we relate the cosmological constant to a dark energy density? Say we move ...
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1answer
42 views

Is dark energy just a cooling effect of CMB?

(1) Cosmic microwave background cooled down from about 3000K billions of years ago to a couple of Kelvin nowadays. (2) Adiabatic expansion causes gas (of photons in this case) to cool. (3) Dark energy ...
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0answers
28 views

$\rho-3P$ for ultra-relativistic regime in early universe

I am trying to read this paper, in which they try to get dark energy by modifying the EFEs to its unimodular form. As interesting as it may be for someone here, I'm struggling to understand the ...
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1answer
60 views

How can the effects of dark energy be distinguished from the effects of the acceleration of the universe from the big bang?

This is a conceptual question and has probably been asked before in many guises and forms. Mine has a little twist to it. I realize the Hubble Law tells us the farther back in time and space we look ...
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1answer
101 views

Is cosmological constant some kind of field that permeates all of space?

One simplest candidate for dark energy is a cosmological constant. Is cosmological constant some kind of field that permeates all of space, or is it just some kind of energy stored in space?
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2answers
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Is the astronomical magnitude identical to the distance? [closed]

Why do astrophysicists use Magnitude rather than the actual distance to calculate intergalactic parameters? The magnitude is the relative brightness and has no units, the typical distance requires the ...
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1answer
134 views

Is the expansion of the universe really accelerating? Or does it just look like it?

I pulled this quote from an article on the Hubble Constant: "...for example, if the Hubble Constant was determined to be 50 km/s/Mpc, a galaxy at 10 Mpc, would have a redshift corresponding to a ...
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0answers
56 views

If dark energy disappeared today, what would be the largest gravitationally bound structures in the universe?

In particular, what would be the largest gravitationally bound structure containing the milky way? As a bonus, how does this compare to the largest gravitationally bound structures assuming a ...
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1answer
37 views

Dark Energy and Newton's Gravity Formula

What would Newton's gravity formula look like if it accommodated the acceleration believed to be caused by dark energy (still assuming 2 masses)?
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0answers
80 views

Could alternate charges exist? [duplicate]

Currently there is 1 known type of electric field, it has positive(positrons and protons) and negative(electrons) charges. I would expect the charges of alternate electric fields to act the same ...
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1answer
108 views

The dimension of potential and kinetic energy of scalar field in Friedmann equation

From the Friedmann equation $$ H^2=\frac{8\pi G}{3}\rho_m - \frac{kc^2}{a^2} + \frac{\Lambda c^2}{3}. $$ The dimension of Hubble parameter $H$ is $\frac{1}{\text{time}}$ or $\frac{1}{[T]}$. Therefore, ...
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2answers
138 views

Can the fact that dark energy increases with volume be explained by classical thermodynamics?

Considering adiabatic process in classical thermodynamics, a normal substance with (positive) pressure must do work on its environment in order for the volume to increase by $ dV $(like pushing the ...
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1answer
140 views

What is meant by “Energy is exactly conserved locally in GR. Inflation and Dark Energy isn't an exception to this.”?

In Ben Crowell’s comments in these threads Attractive gravity has negative energy, what about repulsive gravity in the inflation phase? Does the fact that energy is not conserved in cosmology open ...
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1answer
246 views

Why are there a bunch of cosmological coincidences?

There are several cosmological parameters that are more or less of the same order $10^{-60}$ (in Planck unit), namely, inverse of the age of the universe $$ \frac{1}{t_0}, $$ Hubble constant $$ H_0, $...
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1answer
69 views

Could aliens harness stars to keep ahead of expanding universe?

In this paper, Dan Hooper of the Fermi National Accelerator Laboratory proposes that advanced aliens might gather stars from other galaxies as a hedge against the dark energy powered expansion of the ...
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1answer
133 views

Could dark energy and gravity be explained as same phenomenon?

I have watched VSouce video on gravity. The idea is that gravity pulling it is just lots of mass bending space-time, and natural direction of movement becomes moving towards the mass, and since we ...
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1answer
63 views

Does the expansion of the universe affect its shape?

This may be a very simple question, yet I cannot find an answer that satisfies me. I have read (and please correct me if I am wrong) that the shape of the universe depends on its density. If it has ...