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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Cosmological constant divergence

The cosmological constant is measured to be of the order of $10^{120} $ smaller than the value which has been calculated from quantum mechanics. As far as I know, usually this divergence is attributed ...
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Problems with negative pressure, imaginary speed or super-luminous speed?

Currently, dark energy is described as a being that exerts a negative pressure while having a positive energy density. However, there is a serious problem when considering a physical existence with ...
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What is the exact ratio of dark energy to mass?

I need to know the exact ratio between mass and dark energy (total dark energy in the universe / total mass in the universe). I could only find it to 2 decimal points (0.68). I need this to make this ...
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Could dark matter be just a gravitational effect of dark energy?

I'm wondering if we just looking at the two sides of the same coin and if there is actually a correlation of DM with DE? Is it possible that DM just to be a gravitational effect (or an effect that ...
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With how many Newtons of force is the universe expanding?

The universe is expanding at an accelerating rate. They key word here is "accelerating". Meaning that there is an equivalent "force" (in Newtons) that would cause that same ...
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Can dark energy expand the distance between the earth and the sun?

I remember that the expansion is 0. Is it exactly 0 or just really close?
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Is it a fact that vacuum energy exists?

I have always read that vacuum energy and zero point energy are established facts of physics supported by various observations of their effects both indirectly and even directly. But I have also read ...
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$Ω = ρ/ρ[c]$, so although near to 1, for an accelerating expansion $Ω$ must be below 1. What's its value?

$Ω$ is taken to have different components - ordinary matter, dark matter, dark energy. But because it is expressed in relation to the critical density for attractive gravity, it seems that omega is ...
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Dark energys energy density value

What mathematical property does dark energy have that causes the effect of an expansion? I have read that the energy density of dark energy is time invariant, which is the main cause of an accelerated ...
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Relationship between expanding space and dark energy [duplicate]

The excerpt below has been taken from a pop-science article. Dark energy is thought to be different, though. Rather than being a type of particle, it appears to behave as though it were a type of ...
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Does dark energy redshift over time?

In the expanding universe, light is subject to redshift. Does redshift also affect dark energy - and why?
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How is synthesized Vacuum different from the one in the Universe?

This question is with reference to Torricelli's Vacuum Barometer which was one of the first experiments involving vacuum creation in Laboratories. The Atmospheric pressure causes a rise in the mercury ...
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Why is FTL travel impossible if the universe expands FTL?

If the universe is expanding spacetime faster than light (FTL), is FTL travel no longer completely impossible? Do not care about energy requirements or needing new tech, just if it is NOT physically ...
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Experimental Evidences against Dark Energy

Subir Sarkar proposed that dark energy does not exist, i.e. the cosmological constant of our universe may not be positive (https://arxiv.org/abs/2106.03119). His stance was based on the 740 type Ia ...
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Does Normal matter also include anti-matter and engery?

We have studied approx 4.6% of normal/ordinary matter in the universe and everything till now we observed are a part of this 4.6% I always have doubt. this 4.6% include all the matters and energies ...
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Why is special relativity not enough to explain the seemingly accelerating expansion of the universe?

I have only recently studied Special Relativity, and have yet to learn anything regarding General Relativity, so I may be asking this due to a lack of knowledge - please educate me. I just read about ...
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Can dark energy dominate from the Big-Bang?

I'm studying the age of the universe for a universe dark energy dominated. Using Friedmann equation $$ \left( \frac{\dot{a}}{a} \right)^2 = H_0^2 \left[ \Omega_R \cdot a^{-4} + \Omega_{NR} \cdot a^{-3}...
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Why in the first Friedmann equation quantity $ρ$ is directly proportional to Hubble's constant despite the fact that gravity counteracts expansion?

Here is the first Friedmann equation: $$H^2 = \left(\frac{\dot a}{a}\right)^2 = \frac{8\pi G}{3}\rho - \frac{kc^2}{a^2} + \frac{\Lambda c^2}{3}$$ We know that matter and energy through gravity slow ...
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Why do some scientists believe that the zero point radiation of the vacuum is incredibly powerful?

I've been doing some research and i read about zero point energy. I've heard that a couple cubic cm of it can boil the earth's oceans. how does this work if the energy is only 2.7 kelvin? and what are ...
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Dark Energy & Thermodynamics

I'm not sure I'm understanding this correctly, but I recently read that the repulsive force of dark energy is responsible for the creation of new space as the universe expands - and since empty space ...
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Dark matter/dark energy in Einstein's equation as manifestations of entropy production

It is well known that pressure adds a contribution to the gravity sources in Einstein's equation. That contribution is unknown in Newton's theory. What about entropy itself, or more precisely the ...
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Why is the energy density of the dark energy component~magnitude as the density of matter now, when the two evolved in different time periods?

WMAP determined that the universe is flat, from which it follows that the mean energy density in the universe is equal to the critical density (within a 0.5% margin of error). This is equivalent to a ...
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Question about dark matter/energy and other dimensions

According to drummer and lyricist Henrik Ohlsson, the title Dark Matter Dimensions refers to the "appreciation and acknowledgement of the unseen worlds and dimensions, because without the ...
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About the spatial distribution of vacuum energy around strongly gravitating objects in the galaxy

We know that the distribution of vacuum energy is spatially uniform. But we also know that it couples to gravity. Anything with energy, such as a beam of light is affected by the gravitational field ...
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Can be the observed Universe expansion be explained by different speed of light in the past?

We see the redshift at spectres of all objects around us that was interpreted as space-time expansion. But could we see the same effect in case if speed of light was different in the past?
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Would the cosmological vacuum heat a hollow box?

The energy scale of the cosmological vacuum is about $10^{-3}\mbox{eV}\approx10\mbox{K}$. Imagine cooling an insulated hollow metal box with a vacuum inside it down to near $0\mbox{K}$ and then ...
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Could quantum gravity be explained via the use of a "gravitational charge"?

Could gravity be explained as the existence of a "gravitational charge", acting similarly to an electromagnetic charge but where like charges attract and opposite charges repel? A graviton ...
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Does dark energy violate causality?

Assume a perfect fluid with $p = w \rho$, approximately flat space-time and the existence of a hidrostatic equilibrium solution $\rho_0$ for $\rho$. With the definition of the speed of sound $c_s^2 = \...
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Could dark energy be a net repulsion from virtual colour-charged particles popping in and out of existence?

According to https://en.wikipedia.org/wiki/Dark_energy Dark Energy makes up 68% of "universal density" as the article expresses it. If there is a margin of error in that percentage which ...
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Newton's Law of Gravitation and dark matter [closed]

Before the days of Einstein the observation that light incident to the Earth's surface appears to be constant no matter whether the transmitter is travelling away from the earth or towards the earth ...
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Dark Matter/Energy & Space-Time [closed]

After searching for quite a while for a minimalist approach to explaining Dark Matter as well as Dark Energy, unfortunately without much good, I decided I may as well help fill the explored paths, or ...
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Is it possible that dark energy could be non-uniformly distributed?

Is it even possible that dark energy could be non-uniformly distributed? If it were the case at some points where creation is faster would some objects like for example stars move apart with a rate ...
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How do "chameleon particles" conserve energy and momentum?

I recently learned about the Chameleon particle model for dark energy, which involves bosonic particles whose mass changes depending on the nearby matter concentration, such that their mediated force ...
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What is the behaviour of massive particles traveling between tethered galaxies in the FLWR metric?

I was reading the following papers, arXiv:astro-ph/0104349 and arXiv:astro-ph/0511709. Both papers investigate the situation where two galaxies are held together by some sort of tether, such that the ...
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Is dark energy content related to the amount of the universe no longer causally connected to us?

As the universe expands, an increasing fraction of the universe passes behind the cosmological event horizon as space in that region recedes faster than the speed of light from us/our local, causally ...
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Shape of the universe as dark energy starts to dominate

We say that the universe has a particular shape (flat, sphere or saddle) depending on what the ratio between the average energy density and the critical energy density is, something we call $\Omega$. ...
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Could 'dark' energy just be ordinary photons?

I had this idea a while ago that dark energy might just be ordinary photons 'building up' in the recesses between galaxy clusters and giving rise to the expansion of the universe. I know that the ...
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About the "worst prediction in all of physics"

Physicist Sabine Hossenfelder on YouTube just recently posted a video about vacuum energy, the cosmological constant and the worst prediction in physics. The worst prediction in physics refers in this ...
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Why was more dark energy created during the creation of the Universe than normal energy?

I would like to know if there is an agreed upon explanation within the field of physics as to why more dark energy than normal energy was created during the creation of the Universe. More is unknown ...
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Could Dark Matter imply the existence of Dark energy? [closed]

This is admittedly a simple example, but it seems to check out. Consider the standard metric for the Schwarzschild solution in coordinates $(t, r,\theta,\phi)$: $$ g_{oo} = U, \ g_{11} = V, \ g_{22} = ...
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How could the universe be spatially flat on average, if all forms of energy have positive spatial curvature?

EDIT: I stated the current understanding wrong, thanks Koschi for the comment. In the $\Lambda$CDM model, it's said that the vacuum energy pretty much "balances" the baryonic matter, such ...
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Accelerated expansion of the universe caused by dark energy

Maybe I am misunderstanding this concept but my question is the following: would we state that the universe is accelerating its expansion if we measure the speed of an astrophysical object when it ...
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Dark energy and centrifugal forces [closed]

So looked it up when the thought occurred to me and ended up on this site where I read this: Does a similar concept like centrifugal force exist for the whole universe?, but now I want to ask to those ...
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What is the dark energy & dark matter? [duplicate]

Can anyone explain to me simply what is the dark energy or what is the dark matter. I have been trying to understand it deeply. but I somehow failed.
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Observational evidence for positive cosmological constant $\Lambda$ and need for cosmology beyond Standard Model

This is a continuation of Cosmological constant of standard model of cosmology and observational data asked in 2012. In 2016, Prof S. Sarkar, Nielsen and Guffanti published an article(see: https://...
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Is dark energy connected to a particle?

Normally, energy is a propery of particles. Both massless an massive particles can have an energy that is defined by $$E^2=m^2c^4+p^2$$ So both massless particles like photons as massive particles ...
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Given current densities of dark energy, dark matter and normal matter in universe currently, calculate ratio of density of dark matter at CMB to now? [closed]

I stumbled upon this question while preparing for the astronomy Olympiad. It is question #17 in this pdf. Given that dark energy is vacuum energy, and that the densities of dark energy, dark matter ...
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If gravity is attractive, why doesn't the Milky Way contract?

Einstein introduced the cosmological constant because without it, one cannot get a static universe - gravity would cause the universe to contract. Given that, why is the Milky Way not contracting? For ...
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How can we calculate formula for effective coupling constant in spin independent direct detection of dark matter?

At tree level, the spin independent (SI) direct-detection cross section includes effective coupling constant. How to calculate effective coupling constant? There is always a mandelstram variable in it....
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So Universe Expansion is accelerating, it already did with the Big Bang, so what came in-between?

So scientists are finding that the Universe is expanding at an accelerating rate. It is said 'Dark Energy' is the cause. Ok. But the Universe expanded at a reaally accelerated rate just after the Big ...
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