Cosmological Definition and 421 Threads

In the Newtonian theory of cosmological perturbations, a density excess ##\delta\rho## in a localised region of spacetime leads to the equation of motion ##\ddot{\delta\rho} \sim G\delta\rho##. I can see that this follows directly from Newton's gravitational law. Why does this equation lead to...

Hello... Can the cosmological constant become so rigid as to resist the 120 magnitude quantum contribution? Where is the mathematical terms for it in GR EFEs? is the effect like contraction instead of expansion? Because the 120 magnitude quantum contribution should immediately warp spacetime...

Hi ive been googling but can't get the exact answer. quantum contributions give a calculated cosmological constant that is 120 magnitude more than observed.. what terms in the equation is supposed to cancel the 120 magnitude? in electrodynamics.. the bare mass cancels the virtual particles...

My professor wants to give me (and another kid) a problem in quantum cosmology. To that end, he asked me to read through his recent paper that appeared in the Physical Review Letters. He said that I should be able to go through it since all the paper employs is (quantum) scalar field theory...

I am currently creating a database of all the known cosmological objects, and need to know the percentage error in the following data: Diameter of the sun: 1.3914x108 metres Mass of sun: 1.989x1030 kilograms I have the orbital period of the sun to be: 2.75x107± 9.1% years

Hi, my question is if there exists a study systematically comparing different cosmological models in how well they fit the same standard cosmological data sets (CMB, luminosity, BOA, SNe, lensing,...). I can find very little besides LCDM. In the rare case of a comparison, it leads to...

Einstein's field equations, with cosmological constant, can be written as: G_{\mu \nu} + \Lambda g_{\mu \nu} = \kappa T_{\mu \nu} I understand that some physicists think that the cosmological constant, rather than being a free parameter, might instead be an effect of quantum field theory. Does...

hi, I have been watching some "world science festival" videos on youtube, also there were a conversation pertain to whether or not the cosmological constant should be a constant. As far as I know, our universe is expanding with a positive acceleration measuring the red shifts, and it implies...

I understand it's definition but i am unsure how it affects light. Does it slow light down? (is this even possible?) Does it stretch light's wavelength? Does it convert light into infrared? Does it make light brighter or dimmer? hmm. thank you for your kind help!

hello, My question will be quite naive for experts and reflects the fact that I'm new to the subject of varying the fine structure constant alpha and mainly need an introductory reference ... so if someone has a good one to advice ...thanks a lot i just don't understand the basics: how people...

Layman here, please excuse my ignorance. I believe to understand the basics of SR, GR, cosmic expansion, etc but questions come to mind now and then. As I understand, dark energy, the cosmological constant, vacuum energy, whatever you may call it, remains a constant per space volume unit. Empty...

This Invited Review article just came out: http://arxiv.org/abs/1603.08658 The Atoms Of Space, Gravity and the Cosmological Constant T. Padmanabhan (Submitted on 29 Mar 2016) I describe an approach which connects classical gravity with the quantum microstructure of spacetime. The field equations...

Homework Statement (Working with geometrised units) Consider the EFE ##G^{\alpha \beta }+\Lambda g^{\alpha \beta} = 8 \pi T^{\alpha \beta} ## work out (using weak-field considerations) an upper bound for the cosmological constant knowing that the radius of Pluto's orbit is 5.9 x 10^12 m...

When we measure the cosmological constant Λ what we are really doing is measuring the longterm value of the Hubble rate, namely H∞, the distance expansion rate that the present rate H(t) is seen to be declining towards and leveling out at. It's convenient to write distance expansion rates as...

Piran et al., "Cosmic explosions, life in the Universe and the Cosmological Constant," http://arxiv.org/abs/1508.01034 I thought this was interesting. If I'm understanding correctly, the idea is that satellite galaxies such as the Magellanic Clouds have low metallicity, which causes them to...

Could anyone please recommend a paper that accurately gives the value of the cosmological constant? Or else may you reply with values of the cosmological constant that you would you use in your research? Any help would be very much appreciated.

As a layman, I have come to understand basic expansion (meaning without dark energy) as objects which are not locally gravitationally bound are moving away from each other due to some inertia created from an initial period of inflation. This rate of recession is the Hubble constant and it...

How come that, in the context of discussing the search for gravitational waves, I never see the cosmological constant mentioned ? We know that ##\Lambda \neq 0##, so this seems strange to me; in the presence of a non-vanishing constant, the background is not Ricci flat in the vacuum case, so...

Hi, I'm doing a project on galaxy clustering and in a lot of papers where they list the cosmological parameters they've used, they list σ8 and ns. Can anyone quickly tell me what these parameters are referring to? Thanks

Are the cosmological constant and the universal constant essentially the same?

Firstly, I assume that I'm correct in assuming that since expansion is accelerating it will increase to any arbitrarily large value at some point in the future. If this is true, there must be some point at which particle/antiparticle pairs (due to uncertainty) are carried away from one another...

Firstly, I am just a very interested layman so please forgive my ignorance and non mathematical approach. As I understand it, the cosmological principle states that on larger scales the universe is homogeneous and isotropic. So could someone help me to understand the following: 1) Does this...

According to standard cosmology theory the physical momentum p of both massive and massless particles decay like: $$p \propto \frac{1}{a(t)}$$ where a(t) is the scale factor as function of cosmological time t (for a derivation see page 12 in the following lecture notes...

In the EFE, what does adding Λgμν mean and why is it not included in the Einstein tensor?

Hello! me and my friends were discussing a few ideas earlier this week and then we suddenly started talking about Einstein's biggest mistake. I was a bit lost because I am not all that familiar with the Cosmological constant and I was wondering how can probability be applied to that mistake?? I...

Good day all, A question that I haven't really found the answer for yet: "Whom did first come up with the idea of the cosmological principle?" I almost looked everywhere for the answer but still cannot find it. Was it Friedmann or Lemaitre? Or was it some other great physicist? But there...

bapowell submitted a new PF Insights post Inflationary Misconceptions and the Basics of Cosmological Horizons Continue reading the Original PF Insights Post.

Hello everyone, Can anyone assist me with the following; I have derived some very interesting cosmological quantities within regard to radiation as it moves through space. I am looking for someone trustworthy who can help me verify my work and point me in the right direction without claiming...

Hello everyone. I am having some problem with dark energy and the cosmological constant. The cosmological constant is a proposed form of dark energy. Alright, now the cosmological constant is is estimated by cosmologists to on the order of 10^-26 kilograms per cubic meters. But the density of...

In one book of Susskind I found the following claim and I wanted to ask for its basis. Susskind says that each kind of boson gives positive contribution to the cosmological constant (the lighter, the better). Each kind of fermion gives negative contribution to the cosmological constant. Thus...

Jorrie submitted a new PF Insights post The LCDM Cosmological Model in Simplified Math (Part 3) Continue reading the Original PF Insights Post.

I read a article now and It claims he found the cause of cosmological constant.Is that true ? The idea is actually good...

If we restrict ourselves to a homogeneous, spatially flat LCDM universe model, the Friedman equations can be written a very simple form. Marcus posted several threads in a collaborative effort to develop the simplified approach. Here is a summary of the parts that seem the most informative, to...

http://arxiv.org/abs/1409.4918 Abstract: We examine the cosmological consequences of an alternative to the standard expression for bulk viscosity, one which was proposed to avoid the propagation of superluminal signals without the necessity of extending the space of variables of the theory. The...

I want to know the sign of the cosmological term. It seems that in the left hand side of the Einsetein equation the cosmological term is -\Lambda g_{ik} for (+---) convetion or +\Lambda g_{ik} for (-+++) convetion. Right? Best

is there any limit to cosmological expansion?

Except the extreme case of Black Holes, all other objects in the Universe (say, Galaxies) are very far from the Bekenstein bound (BB). Any object saturating the BB tends to be BH. But we can try to saturate the BB increasing the radius of a sphere. In flat static Universe, sooner or later we...

This came up in the arxivs and had me thinking can this be true? arXiv:1506.05478 [pdf, ps, other] Is the baryon acoustic oscillation peak a cosmological standard ruler? Boudewijn F. Roukema, Thomas Buchert, Hirokazu Fujii, Jan J. Ostrowski Comments: 4 pages, 2 figures Subjects: Cosmology and...

I am trying to wrap my brain around the idea of the cosmological constant, and how it gives the result of an accelerating universe. I have read different explanations for it, and in some it gives me the impression that it is an actual physical force, pushing everything away from everything...

This is a physics question but since it is on a 'universal' scale, I will ask it here. Quantum entanglement. I was watching a panel discussion with Leonard Suskind and others leading theoretical physicists...also watched a Nova program presented by David Green, etc. In both there was a...

Hi. I was just curious about the current value of the cosmological constant. My astrophysics class lecture notes say on the order of 10^-122, but the Wikipedia article says 10^-35 s^-2. Could someone explain where the 10^-35 s^-2 value comes from? Thanks!

Why cosmological constant term ##\Lambda g_{uv}## in Einstein equation is proportional to ##g_{uv}##. Why it is even proportional to ##g_{uv}## in spacetime of MInkowski?

Hi all! I've got a question about the cosmological redshift. We're given the metric ds^2 = c^2\,dt^2 - a(t)^2 \left[ dr^2 + r^2\,d\theta^2 + r^2\sin^2 \theta\,d\varphi^2 \right] Now light moves on null geodesics, so c^2\,dt^2 - a(t)^2\,dr^2 for radially moving light. For a GR exercise, we are...

cosmological redshifts are caused by the metric expansion of space, whereas doppler shift is a result of relative velocities through space. So before the development of the modern cosmological models, how did astronomers originally distinguish these two causes of redshifts (e.g. when they tried...

Homework Statement (a)Sketch how the contributions change with time (b)For no cosmological constant, how long will this universe exist? (c)How far would a photon travel in this metric? (d)Find particular density ##\rho_E## and scale factor (e)How would this universe evolve?[/B] Homework...

Homework Statement (a)Find how ##\rho## varies with ##a##. (b) Show that ##p = \frac{2}{\lambda^2}##. Find ##B## and ##t_0##. (c) Find ##w## and ##q_0##. What values of ##\lambda## makes the particle horizon infinite? Find the event horizon and age of universe. (d) Find luminosity distance...

What is the cosmological constant for the Godel metric?

I reading book, part about gravity. It is Landau-Lifschiz, "Theory of field". And I trying to understand how to calculate cosmological constant. Re-read part with introduction of cosmological constant several times, still not understood. Let's imagine function of space curvature, without...

I was reading a book about cosmolgy.And there wrotes vacuum energy must be higher than cosmological constant 10100 times to satisfy (It may just the opposite ) observations. Is that true ?

Does anybody know a good read/primer that compares the observed cosmological redshift values to predictions made by the relativistic (gravitational) redshift? Thank you!