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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If energy is equivalent with mass, then how can an empty space or vacuum have energy? [closed]

If vacuum has no mass, and $E=mc^2$, then it follows that empty space or vacuum has 0 energy. How can anyone claim that a massless vacuum has energy, without rejecting this equation and special ...
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Question on linear perturbations in cosmology

I've been studying clustering dark energy when I came across a paper named "A Short Review on clustering dark energy" by Ronaldo Batista. there are 2 equations in this paper (eq.8 and eq.9) ...
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Is string theory really dead, given how it explains nearly everything? [closed]

Here, Sabine says that string theory has essentially been disproved and is dead. Is this true? I hope not. I think it's unlikely that a mathematically consistent TOE would just fall out of nowhere, ...
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Does dark energy get used up in the expansion of the universe?

Now, I am a beginner in Cosmology, so I am not sure if this makes sense. Since the universe is expanding at an accelerating rate, and thus distant objects are also accelerating away. In that sense, ...
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Sign of cosmological constant

I've heard that a cosmological constant can be used to model dark energy (e.g. $\Lambda$-CDM model), and that the constant $\Lambda$ should be positive. But my (quite small) understanding of dark ...
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Why are dark matter and dark energy favoured over changes to our physical models? [closed]

I am instinctively skeptical of the existence of "dark matter" and "dark energy". Together, they strike me as being analogous to luminiferous aether -- something that was invented ...
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Does dark energy increase tidal forces in cosmic voids...?

I would like to ask you some questions I have about some interesting work I was reading (https://arxiv.org/abs/1205.4238 & https://academic.oup.com/mnras/article/527/4/11962/7457744) where the ...
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Klein-Gordon equations in quintessence

I'm studying the quintessence model from a dynamical system point of view. I denoted the scalar field for the dark energy as $\phi$, so I have the following Klein-Gordon equation for the field $$\...
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Measurement of the Cosmological Constant

Is there some way to measure Lambda, the cosmological constant, independent of $H_o$, the Hubble constant and omega_lambda, the Dark Energy density? A standard equation for calculating Lambda, ...
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If the observable universe had only one galaxy, how would people know the expansion of the universe?

Hubble measured high redshifted galaxies to discover the cosmic expansion. In a hypothetical universe where only one galaxy exists, would there still be observational evidence for the Big Bang theory? ...
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Electromagnetic field pressure

Wikipedia gives that maxwell tensor components have minus in the electromagnetic stress energy tensor https://en.wikipedia.org/wiki/Electromagnetic_stress%E2%80%93energy_tensor. That mean the ...
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Will cosmic microwave background become invisible in the future?

If my understanding of CMB and Hubble's Law is correct, then CMB photons emitted from more than ~14.4 Glyr during Recombination Epoch would not reach us. The reason is this would correspond to Hubble'...
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Does the accelerated expansion of the universe have any effects in the orbital precession of galaxies? And in their eccentricity?

I found several papers (https://iopscience.iop.org/article/10.3847/2041-8213/ace90b; https://link.springer.com/article/10.1134/S1063772920100054; https://arxiv.org/abs/gr-qc/0301057; https://arxiv.org/...
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Does energy exist on its own? [closed]

So to my understanding as a layman is that energy transfers from one material to another (I guess that's why there's potential and kinetic energy), for example photons to solar panels. Now my question ...
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Cosmological constant, dynamical friction and structure formation?

I would like to ask a question about an interesting article that I found (https://repositorio.unesp.br/server/api/core/bitstreams/b8a5a5b8-4b3b-4198-9f5d-bf69431db1ae/content) In the context of ...
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Ejected bodies, dynamical friction and dark energy?

I have a question after reading a couple of papers (https://arxiv.org/abs/1707.06220 and https://www.arxiv-vanity.com/papers/1102.0007/). Here, the authors seem to indicate that when bodies like stars ...
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Does dark energy have mass?

For personal writing purposes, I’ve been researching dark energy, amongst other similar subjects. I’ve found it hard to discern whether or not we have any conclusive answers or generally accepted ...
Wasteland Vassal's user avatar
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Suppose the universe from our big bang is surrounded by many distant blackholes with each a mass of sextillions of suns. Could it explain dark energy?

Could dark energy "simply" be from multiple distant universe-scale mass black holes, that are there "all-around" the big bang? Scattered apparently randomly, throughout infinity (...
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Can a receding body due to the accelerated spacetime expansion be "rescued"?

Once a body "crosses" the limit where dark energy wins over gravitational forces (Is there a distance from a gravitational source where the influence of gravity and dark energy are balanced ...
vengaq's user avatar
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Is Dark Energy Taking Over?

First question, trying to keep it simple 😃 Because it's constant it grows in magnitude as the universe expands, whereas normal matter does not? Is this accurate as far as we know?
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Dark energy, bound systems and orbits...?

As far as I understand it, dark energy can affect bound systems at cosmological scales (How does dark energy affect the dynamics of galaxy clusters?) effectively modifying their orbits. This ...
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Does Dark Energy contribute to increase the isothermal temperature of plasma in galaxy clusters?

I have a question about this work called "Dark energy and key physical parameters of clusters of galaxies" There, towards the end, the authors talk about the isothermal velocities and ...
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Effects of dark energy in the kinetic energy of a body?

If I launch a ball into the sky it would reach a distance after which it would return into the ground transforming the potential energy into kinetic energy as it hits the ground This is similar to ...
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Tidal effects of galaxies orbiting one another in presence of dark energy?

I recently asked this question about whether there was a "distance" between two galaxies where both the gravitational force and the influence of dark energy would be balanced. The answers ...
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Theoretically, is it feasible for the dark matter density to be constant and homogeneous, as dark energy is, and the two to be related?

I know that currently dark matter and dark energy are separate things, not related and one not deriving from the other. But if both are included in a generalized gravitation theory, the picture can ...
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Is there a distance from a gravitational source where the influence of gravity and dark energy are balanced out?

While gravity is a force that attracts objects with mass, dark energy (or, alternatively, the accelerated expansion of the universe) is not. However, I have found numerous articles, forums, questions ...
vengaq's user avatar
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Dark energy contributing to, or modifying, mass estimates?

I have found some papers (like this one: https://www.aanda.org/articles/aa/full_html/2009/45/aa12762-09/aa12762-09.html) which say that dark energy increases the potential energy in a system of a ...
vengaq's user avatar
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Casimir Effect & Redshifting

The classic plate experiment highlights how omitted wavelengths of light create an energy differential and pressure. This pressure is dependent on the distance between the plates, including how this ...
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How does dark energy affect the dynamics of galaxy clusters?

Galaxies interact with each other gravitationally (just as every other celestial object) and in many cases they form groups or clusters. Does the expansion of the universe (or dark energy) affect the ...
vengaq's user avatar
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Is gravity just a repulsion coming from all directions? [closed]

Why not explain the apparent attraction of masses by a repulsion coming from all directions in space (perhaps the dark force)? I.e. there is no gravitational force, just a repulsive force. A point in ...
Leo's user avatar
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What is the formalism for calculating the vacuum energy density from the observed data of the expansion of the universe?

Wikipedia states here the calculated effective vacuum energy density value of free space from the observed and collected cosmological constant data of the 2015 Planck telescope satellite mission. But ...
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What is the evidence against a variable gravitational constant? [duplicate]

I understand that our main supporting evidence for dark matter is the anomalous speed of objects orbiting around the edges of distant galaxies. Is there a reason why dark matter solves this problem ...
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What if dark matter/energy did not exist?

What if dark matter and dark energy did not exist and were only due to a misinterpretation of the red shift of light or a measurement bias? What would be the implications/consequences?
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What is the correlation between the Hubble tension and Dark Energy?

When Dark Energy was first discovered it was because we noticed that distance type 1A supernovae were dimmer given their perspective redshifts. However, to determine the Hubble constant in the late ...
Python House's user avatar
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What causes a big rip?

If dark energy has $w<-1$ you get the Big rip scenario, where dark energy becomes more and more powerful until it eventually rips all matter apart. Why does this occur? Why does having $w<-1$ ...
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Does spacetime move? With respect to what?

Can spacetime itself rotate along a body, like a black hole? Would it move like a wave?
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Why would we correlate dark energy to the rate of universal expansion: $dS(x,y,z)/S(x,y,z)$ and not to the flow rate of cosmic time $dt/t$?

Cosmic time, which is the same from one place to another (at a given instant), is it also the same from one moment to the next? To compare the cosmic time at two different instants, we would need ...
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The acceleration of universal expansion in terms of volume

I've been trying to work out a formula for the second time-derivative of volume in a dark-energy dominated universe, in terms of the radius. But I'm not sure my intuition is correct. According to ...
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Questions about dark energy and negative pressure

The existence of dark energy leads negative pressure. Is the pressure can be anisotropic? What situation can cause anisotropy of pressure? Further, Is the pressure can be negative in some directions ...
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Can matter and light exist without the free space absolute vacuum?

According to the standard model of particle physics, is matter and light possible to exist without the existence of the omnipresent vacuum? By "vacuum" here I mean the ideal perfect vacuum ...
Markoul11's user avatar
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The speed of expansion of space in big freeze

In the case of big freeze, space expansion will be accelerating and there appears to be a lot of different phenomena occurring. However, in the case of big rip, the expansion is super-accelerating so ...
hi13's user avatar
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What exactly do astrophysicists mean when they say that the universe is expanding at an accelerated rate? [duplicate]

What exactly do astrophysicists mean when they say that the universe is expanding at an accelerated rate? Assuming that the universe is a sphere, do they mean that the radius of the universe increases ...
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How do different vacuum energies cancel out?

I've heard that the predicted vacuum energy by quantum mechanics is way far away from what we can actually calculate according to general relativity. The current patch is to include a cosmological ...
Antoniou's user avatar
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What is the longest detectable EM wavelength?

What is the longest detectable (by today's technology) EM wavelength? and is there a limit of the energy that those with longer wavelengths that we cannot detect can carry? can there be a galactic or &...
USER249's user avatar
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$w$CDM and quintessence

i was reading about alternative dark energy models and i stumbled across the concept of quintessence: a scalar field that should generate a dark energy component with a EoS parameter $w$ that varies ...
Alucard's user avatar
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In the $\Lambda$CDM model, is the cosmological constant always interpreted as the vacuum energy contribution?

As in the title, in the $\Lambda$CDM model, is the cosmological constant always interpreted as the vacuum energy contribution? Or is the origin left open? If I say that "it is usually ...
Alucard's user avatar
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Why the Hubble parameter that is proportional to dark energy is squared in the Friedmann's equation?

I'm studying Alexander Friedmann's equation about the Hubble parameter and, thus, the time dependence of the cosmic scale factor varies as the matter density, ρ, and as the dark energy, Λ as shown in ...
AliceX's user avatar
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Confusion regarding the cosmological constant

The value of the cosmological constant is:- $+2.036\times 10^{-35} ~\mathrm{Hz}^2$. What does it mean about the characteristics of our spacetime? What does the value of the cosmological constant tell ...
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The energy conditions and cosmological constant?

So I thought it didn't matter which side of the equation the cosmological constant was one (did it emerge from geometry or the stress energy tensor). However, then I remembered the weak , strong, null,...
More Anonymous's user avatar
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2 answers
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What does it mean that "relativistic material becomes cosmologically coupled to the expansion rate" in the recent dark-energy black-hole paper?

The recent paper "Observational Evidence for Cosmological Coupling of Black Holes and its Implications for an Astrophysical Source of Dark Energy" has made a splash in the popular press. ...
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