All Questions
88
questions
0
votes
1
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67
views
If space has a positive curvature, is the expansion of the universe caused by time, not "dark energy"? [closed]
Ok, I will assume that space has a positive curvature, where space is the "surface" of this sphere, and time is the radius from the center, so the universe is a 4D hypersphere. Under these ...
- 403
0
votes
1
answer
70
views
Cosmological implications of String theory compactification?
Is the process of compactification of hidden dimensions in string theory equivalent to an increasing dilaton field?
Would one expect the compactification process to continue indefinitely?
Could the ...
- 5,925
0
votes
0
answers
94
views
Measurement of the Cosmological Constant
Is there some way to measure Lambda, the cosmological constant, independent of $H_o$,
the Hubble constant and omega_lambda, the Dark Energy density? A standard equation for calculating Lambda, ...
- 149
0
votes
0
answers
26
views
What is the change in vision and measurement between curved space and flat space, especially for measuring cosmic background radiation?
In a curved space, the light bends as it travels and acts like it is going through a lens. In a (positively) curved universe, a small object appears larger. If we know the actual size of an object, ...
0
votes
0
answers
48
views
Big Bang as stretching space time?
I am still new to researching the big bang so please be patient. I am having trouble envisioning the expansion. As I understand under current theory it is not to be thought of as a singularity ...
- 101
1
vote
1
answer
72
views
Cosmological constant, dynamical friction and structure formation?
I would like to ask a question about an interesting article that I found (https://repositorio.unesp.br/server/api/core/bitstreams/b8a5a5b8-4b3b-4198-9f5d-bf69431db1ae/content)
In the context of ...
- 2,462
0
votes
0
answers
40
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 ...
- 23
1
vote
1
answer
60
views
Reference: 1+1D paper-model representation of the Lambda-CDM cosmological model
I'm looking for a 1+1D (1 time + 1 space dimension) paper model of the current $\Lambda$CDM cosmological model; if possible, one which somehow respects the scales of geodesic spacelike distances at ...
1
vote
0
answers
52
views
Expansion of the Universe inside mattar [duplicate]
When talking about the expansion of the universe we usually refer to the Friedman equations so we assume homogeneous and isotropic solution to Einstein field equation which is true on cosmological ...
- 1,734
1
vote
0
answers
33
views
The General form of the Friedmann equation written in another way
Using the general form of the Friedmann equation:
$$H^2 =H_0^2(Ω_{m0}(1+z)^3+Ω_{r0}(1+z)^4+Ω_{k0}(1+z)^2+Ω_Λ)$$
and taking $a_0=1$, How can I derive that the Friedmann can be writing in the following ...
- 11
2
votes
0
answers
116
views
What's wrong with this thermodynamics argument on the cosmological constant?
I'm puzzled by the following thermodynamics argument on the cosmological constant interpreted as a perfect fluid of pressure $p = -\, \rho$. I start considering a simple fluid of local energy density ...
- 7,592
2
votes
1
answer
59
views
Deviations of conservation laws in the context of cosmological evolution?
If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an expanding accelerating spacetime (like it happens in our Universe), are ...
- 2,462
1
vote
1
answer
96
views
Complex Cosmological constant
Does a complex cosmological constant ($\Lambda = a + ib,\quad b\neq 0$) exist? If it does exist, what does it represent physically?
For example, we interpret $\Lambda > 0$ as dS space and $\Lambda ...
- 45
1
vote
1
answer
195
views
Dark energy from the large structure formation?
If I understand correctly, the expansion of space is like a law of motion: the space expands if there is no force to counter it. We also know that the Universe has evolved from the even 'quantum soup' ...
- 735
-1
votes
2
answers
43
views
Is this right that the fate of space expansion depends on matter density inside the universe?
Is it right think that a right amount of matter density inside the universe could eventually stop the expansion of the universe or the expansion of space is something intrinsic only to space so the ...
- 2,255