The cosmological constant is the energy density of space, or vacuum energy, that arises in Albert Einstein's field equations of general relativity. It is closely associated to the concept of dark energy, but, according to quantum field theory, it should also account for all the zero-point energies of quantum fields in space.
Questions tagged [cosmological-constant]
466 questions
87
votes
7 answers
Why isn't an infinite, flat, nonexpanding universe filled with a uniform matter distribution a solution to Einstein's equation?
In Newtonian gravity, an infinite volume filled with a uniform distribution of mass would be in perfect equilibrium. At every point, the gravitational forces contributed by masses in one direction would be exactly counterbalanced by those in the…
D. Halsey
- 2,253
56
votes
4 answers
Are modified theories of gravity credible?
I'm a statistician with a little training in physics and would just like to know the general consensus on a few things.
I'm reading a book by John Moffat which basically tries to state how GR makes failed predictions in certain situations. I know GR…
dcl
- 673
36
votes
8 answers
Do the laws of physics evolve?
Hubble's constant $a(t)$ appears to be changing over time. The fine stucture constant $\alpha$, like many others in QFT, is a running constant that varies, proportional to energy being used to measure it. Therefore, it could be agued that all…
qftme
- 1,870
33
votes
2 answers
Why are anti-de Sitter spaces so interesting when we believe the universe is expansionary?
Perhaps this is a naive question, but in my recent (admittedly limited) readings about AdS spaces, I keep wondering why they seem to be such a hotbed for theoretical research (AdS/CFT correspondence, etc.). To my understanding, an AdS space has…
JotThisDown
- 1,474
28
votes
2 answers
Why does dark energy produce positive space-time curvature?
My understanding is that dark energy, or equivalently a positive cosmological constant, is accelerating the expansion of the universe and I have read that this gives empty space-time positive curvature, ie de Sitter geometry. I also understand that…
Daniel Mahler
- 3,560
25
votes
2 answers
Lorentz invariance of the Minkowski metric
As far as I understand, one requires that in order for the scalar product between two vectors to be invariant under Lorentz transformations $x^{\mu}\rightarrow x^{\mu^{'}}=\Lambda^{\mu^{'}}_{\,\,\alpha}x^{\alpha}$, we require that the metric…
Will
- 3,163
20
votes
1 answer
Did Einstein really invent the cosmological constant to make the universe static in his 1917 paper?
The popular account of Einstein inventing the cosmological constant goes like this:
Einstein finds that the Einstein Field Equations predict an expanding universe
Unable to accept this, Einstein adds the cosmological constant to his field equations…
eigenchris
- 615
19
votes
2 answers
Why do we interpret the accelerated expansion of the universe as the proof for the existence of dark energy?
Why do we interpret the accelerated expansion of the universe as the proof for the existence of dark energy?
The accelerated expansion only tells us that the Einstein field equation must contain a cosmological constant, but I can put the constant…
RenatoRenatoRenato
- 2,602
16
votes
3 answers
Is the Cosmological Constant locally zero?
On earth and in our solar system we do not notice any effects of a non-zero cosmological constant. The accelerating expansion of the universe was only detected by observing the most distant supernovae.
There is no accelerated expansion of our solar…
jak
- 10,431
16
votes
1 answer
The cosmological constant as a Lagrange multiplier?
The cosmological constant $\Lambda$ can be introduced into the gravitational action like this :
\begin{equation}
S = \frac{1}{2 \kappa} \int_{\Omega} (R - 2 \Lambda) \sqrt{-g} \; d^4 x + \text{matter terms}.
\end{equation}
The spacetime region…
Cham
- 8,015
15
votes
4 answers
Why didn't Newton have a cosmological constant
Einstein initially added the Cosmological Constant because (if I get this right) it seemed to him that the universe should be static. I agree that back then this would have been an obvious assumption. I'm curious now, before Hubble, where there any…
user2550
14
votes
1 answer
On Flatness problem, Inflation etc
I have a couple of naive questions from the topic of the title.
We know
\begin{eqnarray}
\Omega-1=\frac{k}{a^2H^2}-\frac{\Lambda}{3H^2}
\end{eqnarray}
Now I read that from the standard big bang (SBB) model $\frac{1}{aH}$ increases with time and in…
user1349
- 2,167
13
votes
3 answers
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 spacetime causes spacetime to become curved and…
Aditya Malhotra
- 141
13
votes
1 answer
Newton's law of gravitation in de Sitter space
Given two masses $M$ and $m$ (with $M\gg m$) in a de Sitter background with cosmological constant $\Lambda>0$ and positive spatial curvature ($k=+1$). What is the corresponding (semiclassical "Newtonian") gravitational force between $M$ and…
user56224
12
votes
1 answer
Is broken supersymmetry compatible with a small cosmological constant?
I understand that we can find the energy of a bosonic field in its vacuum state via
$E_{vac}^{(B)} = \sum_{\vec{k},s} \frac{1}{2}\hbar\omega_{\vec{k},s}^{(B)}$
and a fermionic one similarly,
$E_{vac}^{(F)} = \sum_{\vec{k},s}…
Chay Paterson
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