Cosmology Definition and 915 Threads

The usual calculations for gravitational waves linearize the GR equations around the background solution of flat space time ( g = Minkowski metric matrix ) empty of matter and energy ( T = 0 ) What happens in cosmology, when one must linearize the GR equations about the FRW metric matrix with...

Hello every body. I want to learn about quantum cosmology but I always find lot of difficulties :confused:. I have a very usual background :frown: on Quantum Mechanics and General Relativity. What are the required specific topics of QM or GR that i should learn before I can learn about Quantum...

Homework Statement (a) Show that the equations satisfy FRW equations. (b) Show the metric when ##\eta## is taken as time Homework EquationsThe Attempt at a Solution [/B] The FRW equation is: 3 \left( \frac{\dot a}{a} \right)^2 = 8\pi G \rho Using ##\frac{da}{dt} = \frac{da}{d\eta}...

Is there any book, on cosmology, or anything related (Not too deep) recommended for a high school students interest basis. Thank you.

I am not sure where to find people who may understand the following paper but I figured someone here might be interested and or educated enough to weigh in on this subject. I tried with my local astronomical society and haven't heard anything back from them. This idea is interesting to me but I...

I have always considered cosmologists to be physicists because I noticed that cosmologists usually apply (Correct me if I'm wrong) general relativity. They seem to take approaches similar to those of physicists. Astronomy is the study of celestial objects, while cosmology is the study of the...

Ahoy there. I am twenty years old, and have (as a result of my interest in cosmology and astronomy, and the natural sciences) developed a keen appreciation for mathematics (in physics, primarily). I have always had an interest in the sciences, but lackluster teachers and personal disinterest...

Hello, I am currently studying astrophysics in my undergrad. I am concerned with the fact that I do not know what field I want to explore during grad school yet. I am in my junior year and will probably finish my undergrad in five years due to double majoring in math as well. I realize I have...

What are the important numbers in cosmology that dictates the very fate of the universe? I searched through Google and one site states that they are 13 constants; http://www.popularmechanics.com/flight/g163/13-most-important-numbers-in-the-universe/ What could be the possible consequences if...

Hello, this is my first post. I am a 15 year old from India just finishing my 1st year in high school. One of my friends recommended to me the world science U website - http://www.worldscienceu.com/courses/master_class I watched Max Tegmarks' History of the universe -...

Series of Lectures on Astrophysics and Cosmology This is part 1 of 12 in the series. Click the youtube link to select another video in the series.

...of physics on both quantum and cosmic scales. I am a chemical engineer and avid programmer who has always had an interest in fundamental physics, but this will be my first effort to truly pursue that passion. And I make beer for a living. :)

I understand that the first cosmological computer simulations Did not have DM Only gas dynamics on expanding grids And, that those sims produced no structure of any kind No LSS Only vast expanses of nearly uniform space plasma Devoid of any clumps Essentially reminiscent of the real...

Hi, as an engineer i don't have much formal training in theoretical physics so bare with me. As most of you know, we can only understand 4% of our universe with the current models we have. The rest of the 96% is dark matter and dark energy (23% and 73%, respectively). Could these unexplained...

I just finished reading a book called Three Roads to Quantum Gravity, and in it the author mentioned a few arguments surrounding quantum cosmology. He did not seem too fond of it, but to me (relatively inexperienced) combining the two makes a lot of sense. What are your thoughts on it?

I'm having some trouble understand this correctly, so I was hoping someone could enlighten me a bit :) Okay, so in the early Universe most of the hydrogen and helium was formed, and then kept in equilibrium, and ionized via photons. So we have a plasma of baryonic matter, including dark matter...

I'm currently reading about the Boltzmann equation, used for the early Universe. The equation I end up with, after some simplifications is the following: \begin{equation} a^{-3}\frac{d}{dt}\left(n_1a^3\right) = n_1^{(0)}n_2^{(0)}\langle\sigma v\rangle\left[\frac{n_3 n_4}{n_3^{(0)}n_4^{(0)}} -...

I have read 'comoving observers are a special set of freely-falling observers' . I have the following definitions: Comoving Frame: "defined at a time t is the inertial frame in which the accelerated observer is instantaneously at rest at t=t0. (Thus the term 'comoving frame' actually refers to...

So, I was trying to do a derivation of my own for the FLRW metric, since I couldn't understand the one Wald had. The spatial slice M is a connected Riemannian manifold which is everywhere isotropic. That is, in every point p\in M and unit vectors in v_1,v_2\in T_p\left(M\right) there is an...

Hello guys. I was thinking about alternatives to inflation, especially old ones (such as the hawking-hartle state and imaginary time) and I remebered a theory put foward by Penrose, in which his relatively new CCC is based. Called the Weyl Curvature Hypothesis. No idea of what it is. Could you...

Homework Statement I've been told to calculate the age of the Universe at T = 1 \, \text{MeV}, assuming that a(t=0)=0. Homework Equations Now, I've already calculated the value of H at that temperature, which was around H(1\,\text{MeV}) \approx 0.6 \,\text{s}^{-1}. I've also shown, that in a...

Consider a flat Robertson-Walker metric. When we say that there is a singularity at $$t=0$$ Clearly it is a coordinate dependent statement. So it is a "candidate" singularity. In principle there is "another coordinate system" in which the corresponding metric has no singularity as we...

Homework Statement I've been told to calculate the energy density in the early Universe. It states that it is completely dominated by neutrinos (3 species), photons, electrons, and positrons. Homework EquationsThe Attempt at a Solution Now, I've found an equation to calculate the energy...

I don't really have to look into this just yet but it bothers me. I quite like cosmology and stuff like such. Universal topology and relativity and sum of histories and stuff. Fun! I really would like to study any theoretical physics though, it just strikes my fancy particularly. I figure I'd...

I'm applying for graduate school but am from a basically unknown state school. My stats can be found here: http://www.physicsgre.com/viewtopic.php?f=21&t=5735. I am looking for a low ranked or unranked theoretical cosmology/hep-th school or a similarly ranked observational astronomy program...

I see that we use dimensional analysis involving constants of nature to obtain the Planck length and then apply the uncertainty principle to find the corresponding Planck mass-energy. But the energy and length scales were found by invoking a "particle" interpretation of fundamental entities of...

On the subject of our 'finely turned universe', I have read that the proton-electron mass ratio can not deviate more than 1:1037. In other readings, the allowable deviation was stated as 1% ("If the neutron were very slightly less massive, then it could not decay without energy input. If its...

I have seen in the online Stanford Encyclopedia of Philosophy in the entry on Copenhagen Interpretation of Quantum Mechanics that Niels Bohr had argued that the theory of relativity is not a literal representation of the universe: "Neither does the theory of relativity, Bohr argued, provide us...

http://mathpages.com/rr/s7-01/7-01.htm I am completely unable to follow the following sequence of working between equations 2 and 3. AFAIK the final answer is correct, but the intermediate steps seem to be a "casserole of nonsense". I would appreciate feedback from anyone who can follow this...

Just saw this. "Learn inflationary cosmology from the guy who invented it." Live stream Friday, 10/31, at 2pm EDT (11am PDT) here: http://new.livestream.com/accounts/4044190/AlanGuthLivestream

Homework Statement Given the maximum possible number density of stars in the present universe, assume that they have been radiating light for 10 billion years at a solar rate of ##3.9 \times 10^{26} \ W##. Photons emitted all have a restframe wavelength of 500 nm. Find a crude upper bound for...

Homework Statement (a)[/B] From the continuity equation show that if ##P=\omega \rho## and ##\omega > -1/3##, show that an expanding universe will eventually reach a maximum size. Take ##k=1## (closed universe). (b) Show that if ##\omega <-1##, the energy density ##\rho## will increase as the...

I know that QM and GR have not net been combined, so perhaps this is a foolish question, but I'll try anyhow. A photon traveling in the vacuum, has energy h/λ. That energy is fixed. It never varies in any circumstances (true?) except one. That one is the expansion of space time; i.e. the...

Homework Statement If light traveled a distance L = H_{eq}^{-1} at M-R equality, how large does this distance expand to at present? (in Mpc) Homework Equations z_{eq} = 3500 \Omega_m = 0.32 at present \rho_c = 3.64 \times 10^{-47} GeV^4 present critical density The Attempt at a...

First off, my supervisor has connections at both, albeit under different forms: my supervisor postdocked at Ohio State, while he personally knows a professor at WUSTL and another research collaborator I worked with and that writes me a LOR knows another professor at WUSTL (connections at WUSTL...

Dear all, In one of his lectures,Prof. Susskind mentioned that the event horizon "bulges" forward to meet any incoming radiation or matter; and it is a property of Einstein field equations. I have not come across any such property, and if it exists, shouldn't it belong to the Schwarzschild(or...

Is Supersymmetry still viable in cosmology, given that so far no supersymmetric particles have been found. From Wiki. SUSY is often criticized in that its greatest strength and weakness is that it is not falsifiable, because its breaking mechanism and the minimum mass above which it is...

http://arxiv.org/abs/1402.2158 Big Bang, Blowup, and Modular Curves: Algebraic Geometry in Cosmology Yuri I. Manin, Matilde Marcolli (Submitted on 10 Feb 2014 (v1), last revised 9 Jul 2014 (this version, v3)) We introduce some algebraic geometric models in cosmology related to the...

Could you please confirm my idea of how to deal with the problem question [b] in the attachment? In case of a non-relativistic neutrino, the energy density will be given by: \rho = m_{\nu} n And if we adopt a perturbation, then n \rightarrow n_{0} [1+ x ] So in general what he asks from...

Suppose you have a universe where Ω_{Λ}=1 and the rest are zero. Then the Friedmann equations are: (\frac{H}{H_{0}})^{2} + \frac{k}{(aH_{0})^2} = \Omega_{\Lambda}=1 since \Omega= \Omega_{\Lambda}=1 we have a flat universe and so k=0 This leaves us with: (\frac{H}{H_{0}})^{2}=1 or...

I understand that 'roughness' in the universe is explained by inflation, because quantum fluctuations in density get separated farther than their Hubble sphere--far than any influence (distance greater than speed of light) between them. Some areas by quantum chance have higher density and can...

Hi there, I need to choose my major in a week and it's between physics or astrophysics. Most of the courses are the same except a few: The different courses: Physics: statistical mechanics, solid state physics, and nuclear and particle physics Astrophysics: Intro to astro...

I have a question about cosmos microwave background. Can we get a relationship between CMB's temperature and redshift z?? THX!

Hi there! I would like to know, what kind of mathematical background is needed for cosmology? I'm about to reach 50% of undergraduate physics and I appreciate if you could point it out some interesting courses I can take to build a strong basis for a «future» cosmology masters or phd degree...

The Florentine astronomer Francesco Sizi argued in this manner why there could not be any satelites around Jupiter. There are seven windows in the head , two nostrils , two ears , two eyes and a mouth ; so in the heavens there are two favorable stars , two unpropitious , two luminaries ...

I am a masters student at some Canadian school best known for astrophysics (and one of the premier schools in the world for white dwarves), dreaming to get into the likes of UPenn (a reach, but not a pipe dream-level reach à la Harvard and Princeton, which some over-ambitious recommender advised...

I would like to study the fundamental aspects of the Universe (of course, assuming that I am capable of pursuing such a thing in the first place). Not necessarily on a large scale, but I am interested in space, time, the fundamental aspects of matter... Things like that. I know that there is...

I have just seen this paper on constructing a cosmology for the accelerated expansion of the universe through BransDicke theory http://arxiv.org/pdf/1402.4291v1.pdfBesides this approach What are the alternative or leading cosmological theories that can predict to some fairly strong confidence...

This article on 4th Quantisation http://arxiv.org/pdf/1304.0259v3.pdf Takes the WDW equation to 3rd Quantisation to understand the spawning of universes from false vacua from a Multiverse And Furthermore goes to 4th Quantisation to investigate multiverse interactions Is this the best way to...

My question is based on two theoretical assumptions. 1) The universe continues with its expansion resulting in an eventual "Big Rip". 2)The many-worlds interpretation of quantum mechanics is correct. In this scenario will all the "branches of reality" in the many-worlds undergo the "Big Rip"...