All Questions
Tagged with vacuum cosmological-constant
73 questions
2
votes
0
answers
81
views
On vacuum energy in a de Sitter universe?
I have a couple of questions about de Sitter cosmological horizons. Initially I made a single post containing the two questions, but after some suggestions, I asked them in two separate posts. This ...
- 2,878
3
votes
1
answer
554
views
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 ...
- 149
1
vote
1
answer
95
views
Cosmological Constant Problem calculations involving energy densities
I am following Timo Weigand lecutre notes on QFT, on page 28, he breifly touches on the Cosmological Constant Problem.
But I am a little confused.
He begins with a Lagrangian and include a nonzero $V_{...
- 501
1
vote
2
answers
169
views
Whether vacuum energy gravitate?
What is the relationship between vacuum energy and gravity, particularly in terms of gravitational effects and its contribution to the overall cosmological constant? Does vacuum energy possess ...
2
votes
2
answers
321
views
How to "naively" calculate the vacuum energy density in a $4 + d$ spacetime?
The "naive" calculation of the vacuum energy density in flat 4D spacetime is resumed by the following divergent integral (I'm considering only free massless fields):
$$\tag{1}
\rho_{\text{...
- 7,677
-3
votes
1
answer
88
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 ...
- 4,376
2
votes
2
answers
193
views
How the EM energy-momentum tensor of vacuum state could be proportional to the metric?
We read "everywhere" that, because of Lorentz invariance, the energy-momentum tensor of any field in the vacuum state should reduce to a constant multiplying the metric tensor (I'm using the ...
- 7,677
5
votes
1
answer
822
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
1
vote
1
answer
110
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 ...
- 4,376
2
votes
1
answer
144
views
Existence of any vacuum pressure
We know that there exists an underlying background energy in space throughout the entire Universe, called vacuum energy and this is a special case of zero-point energy that relates to the quantum ...
- 778
1
vote
0
answers
81
views
What IS the energy density of vacuum space (or spacetime)? [duplicate]
The question, even if similar to other questions here, pretends to clarify a subtle question: the identity of vacuum energy (or energy-density being more precise).
Should we be confident in the ...
- 6,727
0
votes
1
answer
128
views
Models in which the vacuum energy gravitates on small scales but not on large scales
Are there models in which the vacuum energy gravitates on small scales but the effect is diluted on large scales?
- 53
0
votes
0
answers
46
views
Why is the quantum vacuum space energy density not measurable?
I'm referring to the vacuum catastrophe unsolved problem where the Plank length quantum calculation of the vacuum space energy density:
$$
\rho_{\mathrm{P}}=\sqrt{\frac{c^{14}}{\hbar^2 G^4}} \approx 4....
- 4,376
-3
votes
1
answer
112
views
Is the speed of light $c$ invariant with the vacuum space energy density? [duplicate]
Vacuum space energy density is related to the speed of light in a vacuum $c$ as:
$$
\Lambda=8 \pi \rho_{v a c} G / c^4=\kappa \rho_{\text {vac }}
$$
where $\rho_{v a c}$ is the vacuum energy density ...
- 4,376
1
vote
1
answer
262
views
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 ...
- 2,878
0
votes
0
answers
85
views
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 ...
- 717
0
votes
2
answers
157
views
Does the Schrödinger equation take vacuum energy into account?
As I understand it (and excuse me if I get it wrong or partially wrong), the Schrödinger equation is an energy equation that states that the energy of a quantum system stays constant in time.
So how ...
- 85
-3
votes
1
answer
160
views
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 ...
user320481
5
votes
1
answer
396
views
Two cosmological Constants?
The cosmological constant $\Lambda$ can be written as part of the T-Tensor. It can then be considered as vacuum energy ($\rho_{vac}$) and vacuum pressure($p_{vac}$). $\rho_{vac}$ and $p_{vac}$ are the ...
- 255
13
votes
3
answers
2k
views
Does vacuum spacetime have an inherent curvature?
I am a complete novice in physics beyond the high school level, so please excuse anything wrong in my question.
So I have recently read that according to General Relativity, the presence of mass in ...
- 141
0
votes
1
answer
103
views
Would a 1022-keV vacuum contain real electron-positron pairs?
The cosmological vacuum energy scale is measured to be about $10^{-3}$ eV (see David Tong Quantum Field Theory Lectures, ch. 0, p. 5)
As I understand it this implies that the vacuum contains zero-...
- 5,991
2
votes
1
answer
65
views
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 ...
- 5,991
10
votes
8
answers
1k
views
About the "worst prediction in all of physics": the cosmological problem
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 ...
- 914
0
votes
1
answer
93
views
Equality for two expressions of vacuum energy density
I have sometimes seen two expressions for the vacuum energy density of a scalar field.
\begin{align}
\frac{E}{V} &= \int \frac{d^3 k}{(2 \pi)^3} \frac{1}{2} \sqrt{\vec{k}^2 + m^2} \\
&= \frac{...
- 11.8k
0
votes
0
answers
87
views
Vacuum Energy in QFT under the Light of Divergence Invariance of the Lagrangian
The divergence invariance of the Lagrangian has been exploited many times, eg., for the purposes of obtaining a symmetric energy-momentum tensor --Belinfante-like-- consistent with GR.
We know the ...
- 1,654
-2
votes
1
answer
78
views
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?
- 11
3
votes
1
answer
126
views
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 ...
- 45
3
votes
1
answer
518
views
Prove that the value of the cosmological constant equals the energy density of the vacuum
I know that Einstein introduced his cosmological constant assuming it as an independent parameter, something characteristic of the Universe, in itself, but the term of it in the field equations can be ...
- 53
1
vote
0
answers
850
views
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?
- 287
1
vote
0
answers
54
views
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?
- 143
3
votes
1
answer
594
views
Cut-off energy necessary to avoid vacuum catastrophe
My understanding is that to obtain a finite vacuum energy density prediction from QFT, one must choose a cut-off point for the maximum allowed energy of a photon. Two seemingly natural choices are the ...
- 152
2
votes
1
answer
333
views
Why does the cosmological constant problem use the expectation value of the QFT vacuum energy?
As I understand it, the famous 120 orders of magnitude discrepancy between the observed cosmological constant and the calculated QFT vacuum energy density relies on the vacuum Einstein field equations
...
- 21
1
vote
2
answers
450
views
What is the difference between the quantum fluctuation, the zero point energy and the cosmological constant?
I have difficulty to understand the real difference between those three concepts of the energy of the vacuum it's self.( Quantum fluctuation, the zero point energy and the cosmological constant.)
I ...
0
votes
1
answer
109
views
Vacuum energy and cosmic graviton background
What is the best way to show that vacuum energy (the cosmological constant) cannot be the same as a cosmic graviton background (or cosmic gravitational radiation background)?
- 684
0
votes
0
answers
66
views
Does this paper falsify the vacuum energy? [duplicate]
If Dark Energy is falsified by this paper, https://arxiv.org/abs/1808.04597, does that mean the vacuum energy is also falsified?
5
votes
2
answers
319
views
Is the cosmological constant problem real? [duplicate]
The cosmological constant problem assumes that the cosmological constant (determined experimentally) can be identified with the vacuum energy density. Theroretical arguments from quantum gravity ...
- 191
6
votes
1
answer
579
views
Negative temperature of the de-Sitter horizon?
I'm considering the $4D$ de-Sitter spacetime, in static coordinates (I'm using $c = 1$ and $k_{\text{B}} = 1$):
\begin{equation}\tag{1}
ds^2 = (1 - \frac{\Lambda}{3} \, r^2) \, dt^2 - \frac{1}{1 - \...
- 7,677
5
votes
2
answers
621
views
Entropy of de-Sitter spacetime and the $10^{120}$ vacuum discrepency
While doing some lazy calculations, I came across a curiosity that I'm unable to interpret. It is well known that the cosmological constant $\Lambda \sim 10^{-52}~\mathrm{m^{-2}}$ is usually ...
- 7,677
4
votes
1
answer
246
views
"Cosmological constant problem" and dark energy
Simply stated:
is the "cosmological constant problem" (the discrepancy of about 120 orders of magnitude between measured values of vacuum energy and the ones predicted by Quantum Field Theory) in any ...
0
votes
0
answers
97
views
How come the universe is considered flat if zero point energy is infinite?
If quantum field theory calculates that the vacuum energy is infinite and Einstein's theory of gravity implies this energy should produce a curvature of space-time then why shouldn't the universe be ...
0
votes
3
answers
3k
views
What's the difference between "dark energy" and "vacuum energy"?
Let's see if I understood well. "Dark energy" is a term that encapsulates everything that may be accelerating the expansion of Universe, and "vacuum energy" is a kind of energy that permeates the ...
0
votes
0
answers
193
views
Justification for "running" cosmological constant
I am looking for papers which seek out to justify that the cosmological "constant" could be time-dependent. I am aware that within the framework of GR the cosmological constants really has to be a ...
- 1,518
-1
votes
1
answer
97
views
Vacuum energy length scale detectable by Casimir effect?
According to Sean Carroll's The Cosmological constant (Eqn.20) cosmological observations imply that the magnitude of the vacuum energy density in natural units is given by
$$|\rho^{(obs)}_\Lambda|\le (...
- 5,991
12
votes
9
answers
3k
views
Strong empirical falsification of quantum mechanics based on vacuum energy density
It is well known that the observed energy density of the vacuum is many orders of magnitude less than the value calculated by quantum field theory. Published values range between 60 and 120 orders of ...
- 239
1
vote
2
answers
102
views
Could the cosmological constant be due to vacuum fluctuations in a box, i.e., in a finite universe?
Assumption: If the universe were a finite box whose boundary is the cosmological horizon, then there would be a zero-point energy inside that box.
Consequence 1: This zero-point energy would be given ...
- 684
2
votes
4
answers
1k
views
What does the 'cosmological constant' represent?
Newtons theory of gravity involves a gravitational constant $G$, however one does not refer to it directly, we speak instead of gravity or the force of gravity.
Now Einsteins introduced a ...
- 13.4k
1
vote
0
answers
105
views
What kind of average could give a Lorentz invariant energy-momentum tensor?
The electromagnetic (EM) radiation energy-momentum tensor is of the following shape, in the case of incoherent superposition of EM plane waves (I'm using $c = 1$ to simplify things, and metric ...
- 7,677
1
vote
0
answers
99
views
Natural classification of fundamental constants of Nature
I was wondering about the fundamental constants of Nature since several years, and still pondering on them. Of course, I have read a lot of papers on them, but never found any satisfying ...
- 7,677
3
votes
3
answers
1k
views
Absorbing the Cosmological "Constant" in the standard Energy-Stress Tensor
Recently I found some publications on Cosmologies with variable cosmological constant. The Bianchi Identity then implies that the divergence of the modified Energy Stress: Tensor $$\hat{T}_{ab}=T_{ab}...
- 1,518
1
vote
1
answer
301
views
Energy/mass of Quantum Vacuum
So far as we have measured the volume of the universe, has anyone calculated the virtual energy/mass of the Quantum Vacuum? If so, what? Or if not, a local volume such as 1 cubic meter?
This relates ...
- 31