Cosmological Definition and 433 Threads

okay, good. actually at another time i was staring at the more general equation and had a few questions regarding it. so 1/H is the Hubble Time and about the age of the universe (maybe a milli-smidgen longer). this has been measured independently (from astronomical observation), right? and...

Incredibly much has been written about the cosmological constant and all its implications on the evolution of the universe. I want to ask however a more basic question about it. The cosmological constant has the dimension of 1/R^2. So supposing this constant is non-zero, its value points to the...

How do we solve for it? I still don't know much about non linear equations. Unfortunately, this reduces to R=-4(cosmos constant) which is not a system thus making simplicfication difficult. I'm assuming that we can still use the previous arguments and assume that the metric coompontents Gtt and...

I have read that the current expansion of the universe could be due to a bare positive cosmological constant along with a negative cosmological constant due to the false vacuum of the higgs field. Currently this negative CC is not enough to cancel the positive cc but with time this can be...

this is a case where it could be very helpful if someone (Pervect? Wallace? hellfire?) who has the numbers handy could tell us how far away the CEH is at present according to the usual LCDM model I don't know the exact figure. I think it is somewhere around 16 Gly. that is, slightly further...

So there has been a few threads over the last few days where the whole issue of dark energy and/or the cosmological constant has been discussed in the context of whether it is a valid 'solution' to GR or if it violates some principle of relativity or even insults Einsteins 'legacy', whatever...

http://arxiv.org/PS_cache/gr-qc/pdf/0703/0703144.pdf Dynamical coherent states and physical solutions of quantum cosmological bounces Martin Bojowald_ 29 march 2007 I could ask a lot of question ... however, one for now What does he mean by "squeezing"? jal

One problem in the standard \LambdaCDM model is the near equality to an OOM of the densities of baryonic matter (4%), non-baryonic Dark Matter (23%) and Dark Energy (73%). The coincidence is more striking if it is realized that the proportion of DE, if due to the cosmological constant, will grow...

http://background.uchicago.edu/~whu/araa/node3.html I found this site, would it be a good reference?

lets say we have a ball with no air in it, so it is no bigger than a dot. now we attach a pump to it that pumps air into this very elastic ball at a relativistic speed. 1) there are an infinite number of 2-dimensional universes within the ball. all of them are of course at some radial...

I know that the variation of cosmological red shift with the distance is given by z= H_0 l (1+\frac{1}{2} (1+q_0) H_0 l) Where l is the luminosity distance, H_0 is the Hubble parameter at the corrent epoch and q_0 is the deceleration parameter. I would like to know how does z...

I'm currently looking into the values for the 'critical density' and 'cosmological constant', I managed to calculate a figure for the critical density which was close to the generally accepted figure, with lambda I came up with an astronomically small number which I later realized after...

Hi: The principle states that : the universe is homogeneous and isotropic. Then we have three solutions often depicted as i) Sphere ii) Plane iii) Hyperboloid I can understand that the sphere and plane is homogeneous and isotropic, but the iii) does not seems to be. There seems to be a...

Of closed, flat and open universes, which have the potential to act as a blackbody?

I'm told that the cosmological event horizon produces a temperature at every point of space similar to how a black hole event horizon produces a radiation near its surface. If there exists a temperature, then there must be particles to produce that temperature. They must be baryons since normal...

The status of cosmological natural selection Lee Smolin 25 pages "The problem of making predictions from theories that have landscapes of possible low energy parameters is reviewed. Conditions for such a theory to yield falsifiable predictions for doable experiments are given. It is shown...

From an https://www.physicsforums.com/showthread.php?t=140501", a new question comes to me. Is there a known generalisation of the Schwarzschild geometry when the cosmological constant is positive? Are there still black-holes in this case? Are there small modifications to the Newtonian...

How does one figure out the units of measure for the cosmological constant? In the Einstein Field Equation: \[Rab - \frac{1}{2}Rgab + \Lambda gab = 8\pi Tab\] Lambda is a constant but the units of measure for gab and Tab differ for each combination of indices. For example T00 is an...

Penrose: Before the Big Bang--Outrageous Solution to a Profound Cosmological Puzzle a video of a talk given at Perimeter Institute recently by Sir Roger Penrose Before the Big Bang: an Outrageous Solution to a Profound Cosmological Puzzle go here...

Hallo, perhaps you remind our last paper (gr-qc/0511089) about the local characteristics of differential structures. Meanwhile we examined the global characteristics and found a way to compute the cosmological constant. It would be nice to hear your opinion about it! See...

lee smolin claims that SUSY/string theory can account for negative (anti-DS) and zero cosmological constant, but not a positive de-sitter constant, which is what has been observed. he also claims the kodama state in LQG has a good semiclassical limit that is GR, and incorporates a small...

I hear that the calculated value of the vacuum energy using QFT is 120 orders of magnitude more than what is observed for the cosmological constant (or vacuum energy). But I wonder if this calculation was done in a very slow locally expanding spacetime. Or was it done with a strictly...

Has anyone got a reference to the entropy of the cosmological event horizon? Is this entropy an upper limit of the entropy inside (like a black hole) or a lower limit? I'm entertaining the idea that a shrinking cosmological event horizon puts a shrinking upper bound on the entropy inside it...

Like nested dolls, these black holes appear coexisting concentrically where the central stelactic (stellar-galactic) black hole mediates a symmetry between the other two. For instance, consider how stelactic Hawking radiation manifests under inversion of its event horizon. The events within...

are there theories in cosmology which do not incorporate/use the cosmological principle?

NOTE: Taken from another thread on a similar subject: https://www.physicsforums.com/showthread.php?t=125698 "An infinite amount of space with matter uniformly distributed throughout", is not a claim of infinite matter – at least it shouldn't be. If matter is assumed to be inside of a greater...

I recently came across this paper on arXiv.org http://arxiv.org/abs/astro-ph/0310808 Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe Authors: Tamara M. Davis, Charles H. Lineweaver Comments: To appear in Publications of...

Birkhoff's theorem says that any vacuum solution of Einstein's equations must be static, and asymptotically flat. One of the consequences of Birkhoff's theorem is that the gravitational field inside any spherical shell of matter is zero, even if the shell is expanding. But what happens if...

Birkhoff's theorem says that any vacuum solution of Einstein's equations must be static, and asymptotically flat. One of the consequences of Birkhoff's theorem is that the gravitational field inside any spherical shell of matter is zero, even if the shell is expanding. But what happens if...

In another thread, someone was talking about cosmological expansion effects on planetary orbits. (Actually it was about lunar orbits, but I think planetary orbits are more to the point). Through a somewhat round-about path, I eventually got to thinking about the following question. Suppose we...

How to understand that the cosmic microwave background (CMB) can define a cosmological frame? Cheers!

http://www.newscientistspace.com/article/dn9114-cyclic-universe-can-explain-cosmological-constant.html" I thought Einstein abondend the cosmological constant after they found out the uninverse is expanding. Why are they interestead in it again?

Einstein’s Cosmological Constant was inserted into his General Relativity equations to make the universe static, neither expanding nor contracting, as most physicists believed it was at that time, as his equations showed that the universe is unstable and would eventually contract into a single...

I thought this the right place to post this, from the little i can understand it seems interesting. http://arxiv.org/abs/astro-ph/0604265 Casimir Effect confronts Cosmological Constant Authors: Gaurang Mahajan, Sudipta Sarkar, T. Padmanabhan Comments: revtex4; four pages; 5 figs It has...

The newly release WMAP data supports the Inflation model that the universe expanded from subatomic scales to Astronomic scales in a fraction of a second. If so, then what would have been the distance from each point where space would have been expanding at the speed of light, approximately? Thanks.

I was thinking about posting this in the cosmology forum, but, concluded the more philosophically inclined souls would have more fun with it: http://www.arxiv.org/abs/astro-ph/0602280 Issues in the Philosophy of Cosmology A thought provoking paper, IMHO.

I have a few questions that have been piling up. 1. Einstein introduced the cosmoligical constant to demand a static universe like so, G + (Lambda * metric tensor) = T If you were to calculate the perihelion precession of mercury, bending of starlight etc. with this additional term would...

What is the difference between particle horizon and cosmological event horizon?

This is my first post here, so I appologise in advance if this is the wrong forum. Anyway, I was interested to see if this was a generally held opinion. My philosophy course didn't really go into much detail (alas, only Higher level (in Scotland)) I think that the cosmological argument goes as...

I was thinking about constraints on the stress-energy tensor of the vacuum, and came to an interesting conclusion that the vacuum itself should only be isotropic in one rest frame if there is a cosmological constant. If we start with a vacuum that is homogeneous and isotropic in some cartesian...

this just came out http://arxiv.org/abs/astro-ph/0601168 it is an update, as of year-end 2005, of the best estimates of the values of the main cosmological parameters like the Hubble parameter and the dark energy density (or cosm. const.) and the Omega number which is used to indicate how...

some examples: 1) inflation that turns on, then magically switches off simultaneously in causally-disconnected parts of the universe. 2) DM 3) DE 4) cosmological expansion that slowed nicely for billions of years, then accelerated (again, simultaneously in causally-disconnected parts of the...

What perspective can one take concerning the origin of the universe in the big bang model? Can a collapsed observer occupy the singularity itself, or is there a higher dimensional "superspace" (John Archibald Wheeler) one shares apart from it? Might an observer possesses properties beyond...

Einstein introduced the cosmological constant to keep a static universe But we know the universe is expanding due to dark matter? The exstistence of dark matter promotes the cosmoloigcal constant again. How does that make sense? Static universe: need cosmological constant...

Could entanglement arise from the continuity of the initial universal singularity?

what is cosmological constant?Why it is introduced by Enstien.?

Hi, I have been reading the paper "Quantum Gravity with a Positive Cosmological Constant" by Lee Smolin (http://arxiv.org/abs/hep-th/0209079), and am having some trouble making the constants in Part I, Sections 2, 3, and 4 match with what I would calculate them to be when I try to go through...

http://arxiv.org/PS_cache/astro-ph/pdf/0506/0506115.pdf Title: On quasar host galaxies as tests of non-cosmological redshifts Authors: E. Zackrisson Comments: 9 pages, 4 figures Journal-ref: MNRAS 359 (2005), 1193 Despite a general consensus in the astronomical community that all...

When we approach a calculation in relativity, do we have to change the cosmological constant in order to work with bigger dimensions? Because i know we are limited to seeing 1, 2 and 3 dimensions, i was just curious if you wanted to figure out an answer using an equation based on a bigger...

There are many examples of convergent evolution here on Earth, such as the separate development of wings on birds, bats and insects. I propose that the midpoint of evolution be marked by an equivalence between convergent and divergent adaptations. For the universe as a...