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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Dark energy from the cosmic boundary

So as I understand it, the Einstein-Hilbert action basically just says that, in the absence of matter, the spacetime manifold will try to minimize its total curvature. Which is super elegant and ...
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How are matter, dark matter and dark energy compared?

Matter, dark matter and dark energy "make up" 5%, 27% and 68% of the Universe. I can understand that matter and dark matter are comparable, but what does it mean that there is more than ...
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Is the commonly accepted Universe age of 13.8B years really accurate? [closed]

Hmm...challenging the error margin of a specific calculation result of a specific model based on confirmed inconsistencies is regarded as "opinion-based". Interesting. Just curious, is the ...
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What is the expected energy density of the vacuum for QED Planck cutoff?

I would like to know the value of the expected energy density of vacuum in QED with Planck's energy cutoff in the units of kg/m^3 (mass density). I only find rough estimations in erg/cm^3 or joules ...
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Cosmological constant, electron mass

I'm doing an essay on the cosmological constant problem. I understand that fluctuations in the vacuum have an energy of the order $(TeV)^4$, This is because it's proportional to $m^4 $where m is the ...
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How is Hubble constant measured by the method of observing BAO?

How is Hubble constant measured by the method of observing BAO?By just reading some articles it seems to me a more complex method than the astronomic scale.Can this method be explained in few words to ...
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Will spiral galaxies collapse when expansion of the universe isolates them from the rest of the universe? [closed]

If a galaxy gets isolated when the speed of the expansion of the universe exceeds the speed of light, will it collapse? The rotation of a spiral galaxy prevents it from collapsing due to gravity. So ...
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Einstein and his so-called biggest blunder

I was reading this article, https://earthsky.org/space/this-date-in-science-edwin-hubble-and-the-expanding-universe . Please note that my understanding is very basic. You could find my main question ...
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Is the present pressure in the universe negative?

I read from cosmological books that the pressure associated with the dark energy component, which is responsible for the accelerating expansion of the universe, is negative. Is the total pressure of ...
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Infinities of Mass, Energy, & Velocity

My layman's understanding is that photons are particles having 0 mass, which is why they are capable of moving at c (lightspeed). Does our current model of particle physics postulate the existence of ...
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Vacuum space has mass/energy?

It is said that vacuum spaces contain particles and antiparticles, my question is if so whether empty space has mass/energy?
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Might the Kaluza-Klein scalar provide a solution to the dark puzzles?

Kaluza-Klein theories of a five-dimensional spacetime yield not only the equations of general relativity and electromagnetism, but also a scalar field. This scalar field, sometimes quantised as the ...
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What is the equation that tells us that the universe is expanding?

Well I know that the universe is expanding, but is there any equation or letter or simply just an expression that tells us that the universe is expanding...
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Is Higgs cosmology a largely ignored theory, and if it is, why?

(I am not a cosmologist and instead currently working on a master thesis about Feynman integrals, so sorry if I'm missing something obvious. This question is merely out of interest.) I was wondering ...
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Does the Hubble constant measured for huge distances mean it is not the actual Hubble constant but a very old one?

I am citing Wikipedia about Hubble constant.... "Hubble constant is most frequently quoted in (km/s)/Mpc, thus giving the speed in km/s of a galaxy 1 megaparsec (3.09×1019 km) away, and its value ...
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Dark energy as negative matter for Alcubierre drive

Can dark energy be used for the Alcubierre drive as a substitute for negative mass? After all, to make the Alcubierre drive work, it is necessary to expand the universe behind it, and that is what ...
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What happens to the information content of the universe in the deSitter phase?

What happens to the information content of the universe when the accelerated expansion enters the empty deSitter phase in the distant future?
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To what extent is lambda-CDM a quantum model?

I understand that the $\Lambda$CDM cosmological model is mainly built over general relativity, however many of it's features invoke quantum field theory (such as inflation). I find this confusing ...
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If all that existed was a supermassive black hole and yourself would you ever have knowledge of its presence, how could you detect it?

So this question is a two-parter. To elaborate on the first question, let's say you are 10 light-years away from this black hole and it is the mass of the one in the center of our galaxy. 2nd question:...
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Negative mass as a property of space-time [closed]

What if negative mass is a property of space-time itself? We know that dark energy works against gravity and is currently expanding universe, while this expansion is increasing. Can this be because ...
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What does the value of the cosmological constant signify in layman's terms?

The value of the cosmological constant is $Λ = 1.10 \times 10^{-52}$ m$^2$. What is it saying or conveying in layman's terms other than the obvious that the universe is expanding?
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Relative speed of galaxies in deep space

Let say we observe two galaxies, one little bit closer to us than the other one. If we calculate the speed of the farther one does it mean that according to the Hubble law when the closer one reaches ...
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Cosmological constant (CC) vs vacuum energy density (VED)?

How are the two different? I know that CC has negative pressure and opposes gravity. But what about VED? Is VED supposed to have positive pressure and cause gravity too?
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Is the universe some sort of inflating bubble?

Let say we are measuring the Hubble parameter (HP) observing two galaxies:one 5 billion light years from us and the second one, 10 billion light years from us. We should get two different numbers of ...
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Why can't work be done by dark energy on cosmic scales?

My rudimentary understanding of dark energy as the cosmological constant is that the vacuum state of space has positive energy but negative/repulsive gravity/pressure. Given a system dominated by &...
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Friedmann equation and model universes

I was studying Barbara Ryden book on modern cosmology, on it's 5th chapter, she introduces the following image: This image summarises the general behaviour of the Hubble constant. I was wondering, ...
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What is the source of Dark Energy?

As the universe expands, wouldn't we need more dark energy pumped into the space to keep the universe expanding. If so, where does the new dark energy come from?
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Why is dark energy dominant between galaxies but not inside galaxies?

The ideas of dark matter and dark energy are mind blowing. Why is it said that dark matter overcomes dark energy in galaxies but it loses the battle in intergalactic space? In other words, why is dark ...
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Why isn't the 'Crisis in Cosmology' or 'Hubble Tension' explained by the Accelerating Universe?

The value of the Hubble parameter determined locally from the Type Ia supernovae is found to be greater than that determined from the Cosmic Microwave Background (CMB) radiation. This is known as the '...
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Negative energy density

There are some universe models where $\Lambda < 0$. In this case, the energy density of the dark-energy becomes negative. At this point, does it make sense to talk about "negative dark energy ...
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Relation between dark energy and universe expansion

I'm trying to understand the role of dark matter/energy in universal evolution. What I know is they occupy a large percentage of our unverse's energy density, and to observe them we use type Ia ...
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Instead of the universe accelerating its expansion, could non-constant constants also explain the phenomena?

The data gathered led physicists and astronomers to the conclusion that the universe is accelerating its expansion and therefore to theories about dark energy. My question is, could certian constants ...
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Cosmological consequences of the mass-energy content of gravitational waves

This paper published in 1969 indicates that a majority of the mass-energy of the universe may be contained in gravitational waves: "Turning next to phenomena on a galactic scale, we find it ...
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How are Dark Energy and the Inflaton Field related?

My understanding of Inflation Theory: Before $10^{-35}$ seconds the universe began to cool and the Inflaton Field approached a false vacuum. When it reached this false vacuum, there was a constant ...
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Is it possible to control dark energy in some models?

Dark energy seems like the explanation for the expansion of the universe. Are there any physics models where it is included? Is it possible to control it in those models? I was thinking because the ...
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Why is dark matter and dark energy needed to explain why there's more and less gravity respectively than there should be? [closed]

Why is dark matter needed to account for that there's more gravity than there should be, and dark energy for that there's less gravity than there should be? Obviously that can't be correct, but I'm ...
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Do dark matter and dark energy have different physical laws from ordinary matter and energy? [closed]

What are dark matter and dark energy? Do dark matter and dark energy have different physical laws from ordinary matter and energy? Can string theory explain their mechanisms?
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Could the cosmological constant $\Lambda$ decay with time and still have $w=-1$?

One of the larger puzzles (coincidences) of cosmology is that the cosmological constant $\Lambda$ has roughly the value given by the radius of the present universe. At the same time, cosmological ...
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Dark energy stars disproven by Event Horizon images?

I was reading about the hypothesis advanced by George Chapline and Robert Laughlin that black holes might actually be 'dark energy stars', regions where spacetime has undergone a phase transition (e.g....
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Assuming the big rip scenario is possible, what happens exactly at $t=t_{rip}$? Is spacetime really ripped?

I want to start by prefacing a scenario. Say equation of state is $w<-1$ and we live in a phantom dark energy dominated universe. This means in a finite time the cosmological scale factor reaches ...
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What exactly is the cosmological constant? [duplicate]

I know that the cosmological constant was developed as an addition to the Einstein Field Equation as an anti-gravity force: $$R_{\mu \nu} - \frac{1}{2} R g_{\mu \nu} + \Lambda g_{\mu \nu} = \frac{8 \...
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Equation of state for a perfect fluid $w=1$

In Cosmology matter is often descrived by the equation of state $$ P=w\rho $$ where $w=1/3$ for radiation and $0$ for non relativistic matter. Some more esotic forms are explored aswell, like for ...
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Energy density of a universe with inflation

What is the function discribing the energy density of the universe including inflation and a dark energy dominated phase?
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If everything in the universe is drifting away will We eventually be able to register things disappearing?

If everything in the universe is slowly drifting away how soon before we see signs of this?Maybe we’ve already registered things at the visible edge of the universe disappearing. If not will, it ever ...
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Is it possible for matter to occupy a singularity, which is the point of rupture of space time caused by a black hole?

Also, are singularities caused by blackholes reversible? May one do work to reverse the singularity or black hole? Do blackholes create permanent holes in space time, thereby shrinking space time, or ...
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What is the evidence that dark energy exists? (as of 2020)

Astrophysicists believe that dark energy exists and makes up ~70% of the universe's energy content. What is the evidence that dark energy exists? Wikipedia gives five lines of evidence: Supernovae. A ...
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Gravity against dark energy

If inflation of space makes stars and galaxies move apart from each other and gravity does the oposite, what happen to clusters of galaxies that aten't so close to get no effect of dark energy but ...
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Expansion of the relation between the cosmological growth factor and scale factor

Hello i'm studying large scale structure of the Universe (in $\Lambda$CDM Universe) using as time the growth factor defined by $$ \ddot{D}+2H\dot{D}-4\pi G\bar{\rho}_{DM}D=0$$ in my equations i have ...
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What is the largest gravitationally bound structure in the universe?

I understand the galaxy superclusters are not bound due to dark energy. I wonder what matter scale will remain gravitationally bound - galaxy clusters, galaxies, stars - if anything at all, as dark ...
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Does an alternative explanation exists for the observed structure of matter in the universe instead of the dark energy explanation? [closed]

I asked in this question if type Ia supernovae could be different in the past. According to me, this would imply that the existence of dark energy would not be so certain. After reading the answer ...

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