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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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$\rho-3P$ 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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27 views

Is Time Cyclic? [closed]

Answering Unanswered questions about Physics, Universe and Time. Your comments are welcome with derivations please. By theory of relativity, if earth is orbiting sun for the last million years ...
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1answer
50 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
93 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
58 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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52 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
34 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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79 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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39 views

How does magnetar effect spacetime [duplicate]

I know that blackhole effect spacetime to a high extent and singlarity exists at their center . Do magnetar have any kind of effect on spacetime by their incredible magnetic feilds Can they interact ...
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1answer
40 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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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
109 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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223 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
60 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
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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 ...
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1answer
52 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 ...
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1answer
84 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 ...
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3answers
196 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 ...
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1answer
110 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 ...
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0answers
29 views

Can “dark energy” change a mass of a barionic object?

Energy may affect a mass of an object. Can dark energy have an impact on a mass of an object? This question (probably unusual) is prompted by observations of a change in mass (not weight) of large ...
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3answers
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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. ...
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1answer
72 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 $\...
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1answer
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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 ...
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1answer
54 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 ...
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59 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 ...
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1answer
48 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 ...
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2answers
55 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?
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1answer
66 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 ...
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0answers
52 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 ...
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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 ...
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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 ...
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1answer
44 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 ...
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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 ...
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1answer
68 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 ...
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0answers
23 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, ...
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21 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 ...
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1answer
44 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....
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3answers
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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 ...
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1answer
61 views

Solving analytic solution to 1st, 2nd and 3rd order

I'm currently reading a review paper on quintessence (https://arxiv.org/abs/1304.1961) and in §3.1 he plots the evolution of the equation of state parameter $w$ with the scale factor $a$. He produces ...
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1answer
83 views

Dark gravity; the result of gravitational pull from outside the observable universe?

Why can't I find anyone mention this online, what causes people to dismiss this theory instantly, so it's not even worth asking? So "dark gravity" is gravity that is pulling all planets away from ...
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36 views

Origin of dark energy [duplicate]

What is the origin of dark energy? What determines whether the space has positive or negative pressure?
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139 views

Inflation and dark energy have constant energy density - energy is created out of nothing without any source or mechanism?

I can understand that a photon in an expanding universe can be redshifted and lose its energy by its wavelength being stretched from space expansion. But in the case of inflation and dark energy, it ...
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1answer
112 views

Is it certain that accelerated space expansion is caused by negative pressure?

Pressure cause attractive gravity so we think that negative pressure should be repulsive. And I've read that negative pressure means constant energy density in an expanding universe which mean energy ...
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180 views

Cosmological constant problem and dark matter theory by Henke

Christian Henke has recently proposed one approach for the solution of the cosmological constant problem and of the dark matter dynamics: Quantum vacuum energy in general relativity Abstract: The ...
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2answers
67 views

What will happen if the universe expansion continues to accelerate?

From my understanding, dark energy is most likely causing the expansion of the universe and it is accelerating. For this thought experiment assume the rate that the universe is expanding is exactly c. ...
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53 views

Stress–energy pseudotensor of gravitation field for Dark energy

Suppose we have Einstein equation for Universe free of matter in form \begin{equation} G_{ik} = \chi T_{ik}, \end{equation} where the cosmological constant $\Lambda$ is transferred to the RHS of ...
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84 views

What is the theoretical relation between string theory and the multiverse theory?

I understand that the Nobel-winning discovery of the accelerated expansion of the universe 7 years ago started the speculation of dark matter and dark energy. I saw in a TED conference by Brian Greene ...
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Simplified definition of conformal coupling

I am trying to understand the very basics of what conformal and disformal coupling mean, and I found a really succint definition of disformally coupled scalars: "Scalars that couple to matter through ...
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36 views

Why a so strange shape on DES?

Why the selected area for the Dark Energy Survey was chosen to have such a shape? Are there any reasons? In the paper I found this The target footprint of the DES wide-area and supernova surveys ...