# dark-energy's questions - English 1answer

314 dark-energy questions.

### 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 ...

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

1 answers, 31 views cosmology dark-energy
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, ...

### -1 Chaplygin gas as dark energy or dark energy plus dark matter, what is the issue?

0 answers, 21 views dark-matter dark-energy
One of the models of dark energy uses the Chaplygin gas (in the generalized version it can even provide a unified model of dark energy and dark matter). What is/are the issue/s with respect to the ...

### 2 Hawking Radiation and Dark Energy

Imagine you're inside a black hole event horizon. The curvature of spacetime is such that the direction towards the singularity becomes timelike, as reverse movement becomes literally impossible. How ...

### 7 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 ...

### 3 Is heat death observable?

0 answers, 178 views entropy event-horizon dark-energy
Dark energy is supposed to pull galaxies apart, their gravity not sufficient to escape or even slow the expansion of space. Notable scientists like Dr. Kaku all seem to agree that this results in ...

### 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 ...

### Dark energy and virtual particles

If space time is accelerating away from itself everywhere due to dark energy, could this acceleration be the cause of virtual particles, essentially Unruh radiation?

### 3 Could Dark Energy just be particles with negative mass?

Title speaks for itself. Dark matter: We see extra attractive force, and we posit that there are particles which create such a force, and use the measure of that force to guess their locations. Dark ...

### 7 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 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 ...

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

1 answers, 75 views gravity dark-energy
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 ...

### 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 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 Why do we need the concept of dark energy to explain the expansion of the universe?

2 answers, 143 views big-bang dark-energy
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 ...

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

0 answers, 43 views string-theory dark-matter dark-energy
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 ...

### 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 ...

### 3 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 ...

### 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 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 ...

### 1 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 Are dark energy and zero-point energy the same thing?

According to Quantum Mechanics is it possible that the famous "dark energy" and "zero-point energy" are the same thing that drives the accelerated expansion of the universe or maybe related to each ...

### 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 Anisotropy and the Planck results

If and when future probe discovers considerable anisotropy at large scales, and that the clustering of masses are aligned to an arbitrary axis, what consequences does it have for the age of the ...

### 2 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 ...

### 1 Quintessence: what are tracking and scaling models?

0 answers, 17 views cosmology space-expansion dark-energy
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, ...

### 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 ...

### 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 Meaning of slow-roll inflation and quintessence

0 answers, 20 views cosmological-inflation dark-energy
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....

### 4 Could M-Theory explain dark matter as well as dark energy?

1 answers, 3.385 views string-theory dark-matter dark-energy
Is it possible that M-Theory provides a solution to the mystery of dark matter and dark energy? The idea of dark matter and dark energy is that there is some inexplicable source affecting our ...

### 3 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 ...

### 25 How do people calculate proportions of dark matter, dark energy and baryonic matter of the universe?

The Wikipedia page on dark matter mentions that the Planck mission had revealed that in our universe ordinary baryonic matter, dark matter and dark energy are present in the ratio: 4.9%, 26.8% and 68....

### Origin of dark energy [duplicate]

0 answers, 36 views cosmology pressure dark-energy
What is the origin of dark energy? What determines whether the space has positive or negative pressure?

### 3 Is there 'gravitational force of repulsion'?

According to hubble's law of universal expansion, the velocity of a galaxy moving away from ours is directly proportional to the distance between the two. Now velocity is increasing in direction away ...

### 1 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 ...

### 2 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 ...