Cosmological Definition and 433 Threads

A positive value for the cosmological constant was found by the studies of Adam G. Riess et al and Pearlmutter et al In terms of Planck units, and as a natural dimensionless value, the cosmological constant, λ, is on the order of 10−122 or 10−29 g/cm3 The cosmological constant has negative...

Padmanabhan is guilty of another interesting paper - Solution to the cosmological constant problem, http://arxiv.org/abs/1302.3226. Any thoughts?

Hi, I am recently reading Weinberg's Cosmology, and getting subtle on Ch5, small fluctuation. One of the subtle point is on P.225-226 (same as (F.11) -> (F.13) and (F.14) in appendix F). The equations of motion (5.1.24)-(5.1.26) are decomposed into many parts. For example, (5.1.24) is...

Perhaps I am missing something obvious, but here it is anyway. Observation of an astronomically distant object is essentially observation of a past condition of the object, due to the fixed speed of light. And IIRC, the Hubble constant seems to say that all sufficiently distant objects recede...

reading these new jacobsen papers, yesterday. a few questions came up Does Jacobsen tries to solve Cosmological constant problem with these papers ? http://arxiv.org/pdf/1212.6821.pdf

I can fairly well grasp the trace relationship between the Einstein tensor and the Ricci tensor, and see that Ricci tensor is a multiple of the metric. If the cosmological constant is included I don't get why the Einstein tensor shouldn't become a multiple of the metric (leaving out physical...

In the paper, http://arxiv.org/pdf/1205.3365v1.pdf, page 21, the author argues that if: t →∞(1-iϵ), all the terms in equation (193) goes to zero, except the first term. Can anyone explain this to me? Thanks

Homework Statement If Ω_0m=0.25 and Ω_0R=7.4*10^-5 calculate the redshift when the two densities Ω_m and Ω_R are equal. Relevant Equations 1+z=1/a \Omega = \frac{rho}{rho_{crit}} \rho_{0,crit} = \frac{3 H_{0}^{2}}{8 \pi G} The attempt at a solution convert matter density: \epsilon_{0,m} =...

Can the cosmological constant be derived from first principles? The answer appears to be - YES, according to this paper by Padmanabhan - 'The Physical Principle that determines the Value of the Cosmological Constant', http://arxiv.org/abs/1210.4174. This is, in part, an extension of...

Hi, I am trying to get a better understanding of the mass distribution as described by the LCDM cosmological model and data that might be more anchored in observation. What I mean by this is that the LCDM model appears to operate on the assumption of the large-scale homogeneity of the universe...

To quote cosmologist Ned Wright: If the Universe is the same at all times, it is argued that the value of the Hubble parameter must be a constant H_0, so H = \frac{\dot{a}}{a} = H_0 leading to an exponential cosmology a(t) = e^{H_0 (t - t_0)} where t_0 is the present age of the Universe...

We know stereographic projection is conformal but it isn't isometic and in general relativity it can not be used because in this theory general transformations must be isometric. But de sitter in his model (1917) used it (stereographic projection) to obtain metric in static coordinates. How...

Hello, I have read that `cosmological redshift` means a photon is being `stretched`by space dilation and thus gets to have `longer wavelength` I am unsure if this is true and if yes, why is it true Many thanks

The new A20 tabular calculator let's you look at changing geometry out to about 88 billion years according to the standard LCDM cosmic model (with usual estimates for the parameters.). http://www.einsteins-theory-of-relativity-4engineers.com/CosmoLean_A20.html It's pretty neat. Here is one...

hey everyone... i am working on an assignment of cosmological models and beginning and ending of the universe but unable to find something that is compact and describe it all.. can anyone help me in making of this assignment please

This paper dates to 1998: Cooperstock, Faraoni, and Vollick, "The influence of the cosmological expansion on local systems," http://arxiv.org/abs/astro-ph/9803097v1 They show that systems such as the solar system, galaxies, and clusters of galaxies experience nonzero effects from cosmological...

In Gravitation by MTW in section 17.3, they state (I assume it was a typo putting the cosmological constant in the center portion) Changing the symbol of the Einstein tensor and the cosmological constant to L and Ω so as not to confuse myself, I can see how with...

I'm considering writing a story in which we Earthlings have a few years to prepare for a cosmological catastrophe in which our planet will lose its energy source and be adrift in space. This would mean the end of life on Earth - but not right away. We could insulate giant underground chambers...

E=mc2 gives us the cosmological constant, which later was found to be the maximum speed at which light can travel. i also understand that when accelerating particles such as they do at CERN, it requires more and more energy the faster u want to go, the mass/speed issue. so i think i understand...

An interesting and well presented new paper by Kumar and Xu: "Observational constraints on a cosmological model with variable equation of state parameters for matter and dark energy" http://arxiv.org/abs/1207.5582 The idea of a variable equation of state for matter and dark energy is not...

I understand the beginning basics of what it represents but how exactly does it tie into the inflation of space and what sort of energy is in a perfect vacuum?

Cosmological expansion vs. "stretching" From a relativistic point of view, how can we tell the difference between a universe that’s expanding (outward) from a singularity versus one that is being sucked INTO a singularity? In the case of the latter, it seems that those objects closer (than us)...

Hello. I just added to my site a simple reasoning that quickly justifies the basic formulas of cosmology in General Relativity (Friedmann differential equations, assuming homogeneity and so on, including the role of the cosmological constant), without any heavy formalism (only assuming basic...

Hi, everyone~ I have a BS in EE, and I want to be a researcher in cosmology or astronomy. To accomplish that I have to get a PHD in such areas. But my major in college was mainly about signal processing and networks. So, I'm wondering if there is any PHD program in cosmology or astronomy that...

I was hoping somebody could point me towards a derivation of the following formula for cosmological redshift: z = R(t0)/R(te)-1. Wikipedia just presents the formula as a fait accompli and the only explanation is a vague reference to "stretched photons", which is not helpful. I was...

The equation for cosmological redshift where z << 1 is is commonly given as z = λobs / λemit -1 What is the equation for high-z, accounting for how light surpasses the spatial expansion it leaves behind, but abstracting from gravitational influences? I'm particularly interested in how CMB can...

I have read this new paper by Stephen Hawking and collegues. It is very interesting to see the use of wavefunctions to show the acceleration of a universe with lambda<0 which fits in the framework of string theory and quantum mechanics. This technique bridges quantum mechanics and general...

Why would we assume matter is spread homogeneously throughout the universe if its only 4.6% of universe :confused: The universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. BBT explains about CMBR, redshift, expansion and...

This is based on a side discussion in the balloon analogy thread, see #49 and #53. How is the definition of cosmological proper distance ("CPD" from now on) different from the usual definition of distance? Here, I want to discuss the respective defintions, what these definitions "really" mean...

We currently have a thread about logarithmic corrections to the basic black hole entropy formula. I was thinking about attempts to relate the magnitude of dark energy to the area of the cosmological horizon, and about the various analogies made between the cosmological horizon and the horizons...

I came across the following at Ned Wrights website and wondered [a] What does the boldface statement mean? [b] What is thought about the statement that "Cosmological expansion of the Earth orbit around the sun is negligible but not zero" instead of "its not been determined"...

Could the cosmological redshift be explained also as a change of the fundamental physical constants with distance? Say Planck's constant changing over billions of light years, instead of interpreting it as a Doppler effect due to a recession speed? Yes, I know, Occam's razor would favor the...

The Kalam cosmological argument as presented by William Lane Craig is as follows: 1. Whatever begins to exist has a cause of its existence. 2. The universe began to exist. (semi-intellectual nonsense involving infinity) 3. Therefore, the universe has a cause of its...

In General relativity: an introduction for physicists, the authors derive Newtonian gravity from the EFE, but then they also give a short statement that inserting in the cosmological constant derives down to: \vec{g}=-\nabla\Phi=-\frac{GM}{r^{2}}\hat{\vec{r}}+\frac{\Lambda...

While reading I came across this chart in Wikipedia http://en.wikipedia.org/wiki/Metric_expansion_of_space Anybody know the source or a similar plot with some explanations? What do you make of it?? What does it purport to show? Is it in the correct section [Theoretical basis and first...

Can someone, please, explain to me (in layman's terms, [ie no mathematics]) the theory behind early cosmological phase transitions and these supposed 'bubbles' ?

I see where someone listed a theory that they had https://www.physicsforums.com/showthread.php?t=49230 so going to attempt to do the same. I listed my theory at http://www.bautforum.com/showthread.php/129309-Negative-Mass-Interpretation-of-General-Relativity but they are very quiet and I would...

Homework Statement I'm working on a project to find evolution equations for a cosmological model, where the following propagations equations are known, \dot{\mu}=-\Theta\mu \dot{\Theta}=-\frac{1}{3}\Theta^{2}-2\sigma^{2}-\frac{1}{2}\mu...

What is the equation for the cosmological redshift as a function of the history of the universe? Basically as a function throughout all of time.

Hi Astro forum... I have got something to clarify which came across my mind as I was trying to answer few problems.So without any further delay , let's start : For simplicity we will assume that dark matter doesn't influence the center of mass of galaxy A. Now let's say galaxy A has mass 'M'...

I nearly referred to it as infamous in the title. Unfair? My question is this: why did they add up the combined energy of all the fields when only the Higgs field would be active in void space (I use this term to refer to the spaces between filaments, does it have its own name or is it...

Does the cosmological constant support MOND? The equation for critical density is as follows (in terms of mass rather than density): Critical density (90.4 x e54 gm) = matter (4.1 x e54 gm) + dark matter (20.6 x e54 gm) + dark energy/cosmological constant (65.7 x e54 gm). Most estimates...

If the vacuum contains all these Higgs bosons, at expectation of <246> GeV in vacuum, why isn't there a cosmological constant, given the vacuum an energy density of 246 GeV^4 , instead we see dark energy at a few meV^4. Could just say that the graviton doesn't couple to the Higgs at all, but...

I am no expert on cosmology. But from what I have heard, the big crunch is the scenario that will most likely happen to our universe in the (far) future. Yet the cosmological constant makes it so that our universe is currently expanding and acceleratingly so. So the question is (I know this...

Hello everyone. I was hoping that the theory of Cosmological relativity developed by Moshe Carmeli could be discussed in this forum. The theory is described as an extension of einsteins relativity on a cosmological scale. It is said to complement regular relativity and to get correct...

Does anybody know about a comprehensive list of cosmological models and their properties? E.g. FRW, dS, AdS, ... Goedelspacetime, ... with metrics g, Christoffel symbols, Riemann tensors, Ricci, Ricci scalar, Kretschmann scalar, ... Tom

I was just reading on wikipedia about the expansion of space. ( http://en.wikipedia.org/wiki/Metric_expansion_of_space ) It explains that the expansion of space can be treated as if it were a repulsive force between particles proportional to the distance between them, ie the further apart...

So I was watching the show "Curiosity" on the Discovery channel last night. In the show, Stephen Hawking describes the birth of the Universe, and why our theory of inflation leaves no place for God. I'm not going to comment on the God thing, but Hawking said something that got me thinking...

Wikipedia says: second paragraph here: http://en.wikipedia.org/wiki/Dark_energy Vaccum energy (density) can vary over time and space? Is that accurate? I've read the cosmological constant can vary, but not vacuum energy.

Can anyone please explain the physical reason of why is light losing energy as universe is expanding?