Questions tagged [dark-energy]
Dark energy is the unknown form of energy that drives the acceleration of the universe's expansion.
552
questions
9
votes
1
answer
768
views
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 the accelerated expansion of the universe) is not.
However, I have found numerous articles, forums, questions in the stack ...
- 1,880
1
vote
1
answer
81
views
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 ...
- 1,880
0
votes
0
answers
22
views
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 ...
2
votes
1
answer
89
views
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 ...
- 1,880
-4
votes
1
answer
56
views
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 ...
- 1
0
votes
0
answers
18
views
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 ...
- 3,728
0
votes
0
answers
34
views
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 ...
- 101
0
votes
1
answer
115
views
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?
2
votes
2
answers
88
views
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 ...
- 145
0
votes
0
answers
31
views
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 $w<-1$ ...
- 2,770
0
votes
0
answers
72
views
Does spacetime move? With respect to what?
Can spacetime itself rotate along a body, like a black hole? Would it move like a wave?
- 503
0
votes
0
answers
26
views
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 ...
0
votes
0
answers
17
views
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 ...
- 47
0
votes
0
answers
33
views
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 ...
- 73
-3
votes
1
answer
80
views
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 ...
- 3,728
-1
votes
2
answers
58
views
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 ...
- 13
0
votes
0
answers
37
views
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 ...
- 35
0
votes
0
answers
39
views
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 ...
- 503
3
votes
2
answers
163
views
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 &...
- 463
0
votes
1
answer
52
views
$w$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 ...
- 299
1
vote
0
answers
37
views
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 ...
- 299
0
votes
1
answer
45
views
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 ...
- 71
3
votes
1
answer
464
views
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 ...
- 836
4
votes
1
answer
152
views
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,...
- 1,221
7
votes
1
answer
339
views
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. ...
- 46.2k
3
votes
1
answer
36
views
Does rate of expansion of the universe affect perceived strength of gravitational pull?
As I understand expansion of the universe could be viewed as a constant negative pressure. So when we are looking at two bodies like Earth and Sun, from their perspective there should be a force ...
- 133
4
votes
1
answer
232
views
How can black holes possibly drive accelerating expansion of the universe?
(Potentially too broad, but all my questions are related to the paper in question.)
Recently there was an article published in Astrophysical Journal Letters that claims black holes "contribute ...
- 19.4k
5
votes
1
answer
621
views
What does it mean for a black hole to be "filled" with vacuum energy?
I've read the recent news about non-Kerr black holes coupling to the universe's expansion rate, and it looks like an excellent fit to the data. From the paper, I understand that these black holes grow ...
- 278
0
votes
2
answers
83
views
Mass matter, energy and "massless matter"
This is perhaps a rather silly question, or rather a matter of convention, but I would like to hear arguments about the appropriateness of certain definitions.
Traditionally, in chemistry and in pre-...
- 1,433
0
votes
0
answers
38
views
How can a cosmological constant exist in flat Minkowski Space?
The ground state energy of a standard scalar field in Minkowski space diverges so we need normal ordering to get it to zero. This divergence is normally interpreted as coming from the cosmological ...
0
votes
1
answer
57
views
Is it possible that humans have the capability to interact with Dark matter? [closed]
Recently, scientists and physicists have been making breakthroughs in dark matter detection. I'm wondering if it's possible for humans to potentially be able to travel deep enough into space to be ...
1
vote
1
answer
80
views
By what experiment is the vacuum energy density actually measured?
I have heard that the actual vacuum energy density which is up to 120 orders smaller than the predicted QED value can be measured in experiments or cosmological observations?
What are these ...
- 3,728
0
votes
0
answers
35
views
+ spin Photons inside a right hand circularly polarized field with -spin photons outside of that field…”dark matter/energy”
As I understand it, If I am inside of a rh, circularly polarized EM field, there are only +spin photons inside the field: no -spin photons are admitted inside. The field inside serves to “filter” out -...
- 11
3
votes
3
answers
341
views
Cosmological constant from the stress energy tensor or geometry?
Sabine does make some interesting points. Can a cosmological constant come from the stress energy tensor? If so, I don't see how one is suppose to distinguish this as an all permeating field in the ...
- 1,221
0
votes
1
answer
80
views
Inflation, dark energy and symmetry breaking
Aside as the inflaton has been hypothesized to have arisen from the breaking of the $SU(5)$ GUT symmetry, could dark energy have arisen as a weaker inflaton from electroweak symmetry breaking?
- 1
0
votes
0
answers
38
views
Dark energy, potential energy and energy conservation...?
The universe has an accelerated expansion (due to dark energy, according to the standard cosmology model).
There are some papers (like this one: https://arxiv.org/abs/astro-ph/0507195) that mention ...
- 1,880
1
vote
1
answer
24
views
Kinetic energy and collisions in cosmology? [duplicate]
Objects in space time can move due to the expansion of spacetime itself (where objects that are sufficiently far apart would recede from each other due to the Hubble flow) and peculiar motions (which ...
- 1,880
1
vote
1
answer
116
views
Does dark energy cause the creation of spacetime?
The universe is expanding, in theory because of 'dark energy'. Does this mean that this dark energy is causing an increase in the amount of spacetime? I.e., does dark energy cause the creation of ...
- 991
0
votes
1
answer
49
views
Blueshift caused by dark energy?
Galaxies that are sufficiently far away from our point of view are receding from us due to the accelerated expansion of the universe (supposedly caused by dark energy) and therefore their light is ...
- 1,880
1
vote
2
answers
83
views
The slowing of expansion in the matter dominated era
On all the graphs of the inflation of the universe, the era dominated by matter is slowing the rate of expansion. With an intuitive explanation (for all you science communicators out there) could you ...
0
votes
2
answers
53
views
What is the estimated velocity of expansion at the beginning of the Dark Energy era?
Approximately 7.5 billion year ago Dark energy began to accelerate the expansion of the universe. Data has shown us that up until that time the universe was decelerating in its expansion velocity. ...
0
votes
0
answers
46
views
$\Lambda$CDM's observations and the universe's matter content
It's known that the current value of the universe's total density parameter $\Omega_0=1$.
According to the $\Lambda$CDM model, the current density parameter of baryonic matter $\Omega_P \sim 0.04$, ...
- 321
1
vote
1
answer
78
views
Flat collapsing universe with dark energy (solution to Friedmann equation)
We always say due to the negative pressure of dark energy, the acceleration equation shows that dark energy will cause positive acceleration $\ddot a >0$.
For a flat universe with cosmological ...
- 161
2
votes
1
answer
76
views
Dark energy and neutrinos
Neutrinos are sometimes considered to contribute to dark matter, see e.g. E.Siegel.
Why not for dark energy?
There is a similar scale in energy density involved. If you use the current upper limit for ...
- 85
0
votes
0
answers
40
views
critical density and curvature
For a single component flat universe, the scale factor is $𝑎(𝑡)=(𝑡/𝑡_𝑜)^{2/(3+3𝑤)}$. Now if it's a dark energy that has w < -1 (that means dark energy density will increase with time), then ...
- 161
0
votes
1
answer
86
views
Could dark energy and dark matter be the elusive luminiferous aether that was being searched for over 100 years ago
Is it suggested that dark energy and dark matter is the luminiferous aether that Sir Isaac Newton was proposing might exist?
- 699
0
votes
1
answer
183
views
Am I wrong if I interpret dark matter just as a red herring to justify the shortcomings of the current theories? [duplicate]
Wikipedia defines
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe.
And continues with
Various astrophysical observations – ...
1
vote
0
answers
61
views
Dark energy/dark matter erodes confidence in origin theories [closed]
My layman's understanding is that we believe we have a good understanding of the development of the universe after the instant of the Big Bang.
Also, I understand that we believe that about 95% of the ...
- 21
1
vote
1
answer
118
views
The size of the universe and the scale factor of $\Lambda$CDM model
I wonder is there a relation between the size of the universe and the scale factor calculated by solving Friedmann equations.
I mean if the volume of the universe nowadays is a round $V= 10^{78} m^3$, ...
- 321
0
votes
3
answers
99
views
Question on gravity
Please excuse if my question seems very basic (I'm a lay person fascinated by physics and trying to learn more.) I'm trying to better understand gravity. I have read that "gravity is a natural ...
- 11