Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [dark-energy]

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

16
votes
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 ...
-3
votes
1answer
67 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 ...
7
votes
3answers
244 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 ...
2
votes
0answers
68 views

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 ...
-1
votes
1answer
40 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 ...
2
votes
1answer
130 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 ...
1
vote
1answer
64 views

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?
0
votes
0answers
18 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 ...
1
vote
1answer
46 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. ...
7
votes
2answers
204 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/...
1
vote
2answers
149 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 ...
4
votes
2answers
67 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?
0
votes
1answer
36 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 ...
1
vote
1answer
39 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 ...
1
vote
0answers
23 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 ...
3
votes
1answer
57 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 ...
1
vote
1answer
96 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?
-1
votes
2answers
101 views

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 ...
0
votes
1answer
86 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 ...
1
vote
0answers
54 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 ...
0
votes
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)?
2
votes
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 ...
2
votes
1answer
72 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, ...
7
votes
2answers
135 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 ...
0
votes
1answer
114 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 ...
1
vote
1answer
241 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, $...
1
vote
1answer
66 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 ...
-2
votes
1answer
110 views

Could dark energy and gravity be explained as same phenomenon? [duplicate]

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 ...
2
votes
1answer
57 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 ...
0
votes
1answer
89 views

Why can't the Higgs vacuum energy clump to galaxies and act as dark matter (instead of dark energy)? [closed]

The Higgs field has a nonzero vacuum expectation value which contributes to the energy density of the Universe. Energies contribute to the curvature of spacetime and affected by gravitational ...
3
votes
3answers
217 views

How can cosmological constant serve two opposite purposes?

Einstein used the cosmological constant to prevent expansion which he regarded as his greatest blunder. On the other hand, we are saying that the cosmological constant can cause the space expansion to ...
2
votes
1answer
147 views

Was the expansion of the universe ever decelerating?

The Universe has always been expanding since the big bang. Today the expansion is accelerating. Has there been any point in time when the expansion of the universe was decelerating? How do we know ...
4
votes
3answers
128 views

Will a closed universe with dark energy still collapse into a big crunch or will it expand forever?

In a closed universe without dark energy, it departs rapidly from flatness and become more curved over time. The expansion of the universe eventually stops and starts to collapses into a big crunch. ...
2
votes
1answer
81 views

Flatness puzzle in a $\Lambda$-dominated Universe

Friedmann equation together with the acceleration equation yield $\dot{\Omega} = (1+3w) H \Omega (\Omega-1)$. The Flatness puzzle lies in the fact that $1+3w>0$, but how is this possible in a $\...
7
votes
1answer
137 views

Can a closed universe become open?

My feeling is that no a closed universe can't become open. Under normal evolution according to the Friedman equation the curvature would be more exagerated as time goes on (i.e. a a closed universe ...
1
vote
1answer
84 views

How did cosmologists calculate the small density of dark energy in our universe?

I've seen the number a few times (138 x10 to the power of -123) but i haven´t found how scientists calculated it. Max Tegmark mentions it in his research paper about multiverse types as representing ...
0
votes
0answers
62 views

The universe is speeding up?

I just watched a show on spacetime. In the show they said that the universe's expansion is speeding up instead of slowing down. They said it had to do with dark energy. I was wondering if you could ...
1
vote
1answer
65 views

Why does the current age of the universe increase when dark energy is included? (open universe)

When numerically solving the Friedmann equations for varying cases of an open universe (i.e. $\Omega_0 < 1$) I get the following evolution plots, where the left plot is for an open universe ...
2
votes
2answers
62 views

Is cosmological expansion caused by dark energy?

People hear about dark energy, conceptualize it as a kind of universal repulsion of space itself, and then tend to say that cosmological expansion must be caused by dark energy. Is this correct?
2
votes
1answer
69 views

Isn't A Singularity Inevitable Given Infinite Time?

I am not a physicist but this is a question I've been trying to find the answer to for years and no answer I've been given has satisfied me. It's my understanding that gravity affects all matter all ...
1
vote
0answers
60 views

Can “Dark Strings” give rise to “Dark Matter”? [closed]

If dark matter consists of some kind of particles that can be described by String Theory, could we be able to describe this kind of strings ("dark strings", i.e, the strings which give rises to dark ...
0
votes
0answers
15 views

What makes a force fundamental, how does dark energy fit? [duplicate]

The 4 generally accepted fundamental forces are the gravitational, electromagnetic, strong nuclear, and weak nuclear forces. How did we come to define these 4 forces as fundamental? I am interested ...
0
votes
0answers
19 views

The Space Between Us [duplicate]

We are told the universe is expanding at anything between 68 and 73km per second, per megaparsec (depending on the places you look) - so by association, the space between us and anything else out ...
-1
votes
1answer
46 views

Is Dark Energy a particle? [duplicate]

Is Dark Energy a particle due to the mass-energy equivalence ($E=mc^2$)? I mean surely something cannot have energy without mass. Hence my question, I've been trying to figure this question out, but ...
0
votes
0answers
16 views

Can we set experiments measuring expansion of space fabric?

I was thinking about the nature of "dark energy" and the exponential expansion of space. There must be a mechanism for converting energy into space, causing the overall amount of space to grow. This ...
1
vote
1answer
75 views

Flat universe and changing energy/matter ratios

Of what I understand, current observations indicate the universe curvature is closely a flat one. This is made possible since adding up the energy densities of regular matter, dark matter and dark ...
1
vote
0answers
35 views

Quintessence: what are tracking and scaling models?

I'm currently reading around the topic of dark energy, in particular quintessence, and I understand the idea of freezing and thawing models. In freezing models the potential is shallow at late times, ...
0
votes
0answers
22 views

Alternative to the explanation of large scales phenomena [duplicate]

I've been reading a lot trough different articles about dark-matter and dark-energy and how they could explain observations such as the acceleration of the expansion of the universe or the ...
1
vote
1answer
69 views

Meaning of slow-roll inflation and quintessence

I'm currently reading around the topic of quintessence and other models for dark energy and was hoping someone could explain to me what is meant by slow-roll in terms of quintessence and inflation etc....
0
votes
3answers
75 views

Does the changes to gravitational time dilation caused by the observable universe expanding explain the observed redshift from distant objects?

My thought process, where have I gone wrong? Question 1: There is no gravitational force at the center of the earth is there still gravitational time dilation. Answer: Yes, there is a potential ...