Cosmology Definition and 951 Threads

Good afternoon all, I'm taking a linear algebra course this semester, and upon entering the topic of 'Applications of Matrix Operations', my professor has given our class the opportunity to earn some extra credit points by writing a paragraph or two on the application of stochastic matrices in...

I am interested in studying cosmology or physics during university (as an Australian) and hope that this can lead on to a job further involving cosmology. What are the chances of actually succeeding with this endeavor and is there any chance of employment as an Australian?

Hello, I've a problem. I need to find the age of universe in normalized Planck units. In my case, I'm using Planck mass = 1 and: ##H = 1.18 × 10^{-61} \times t_P^{- 1}## With these values, how can I find the age of the universe? Thanks!

Well my question is what is exactly the difference between Astrophysics and Cosmology and Quantum mechanics ?

A paper published in 'Gravitation and Cosmology', [21, 208 (2015)] and on today's physics ArXiv claims to have found a solution to the Wheeler-DeWitt equation that exactly corresponds to the classical evolution of a Friedmann model with appropriate matter/energy density: Exact Classical...

According to Einsteinian Relativity, is the Universe considerably younger if one was to view it from within a greater distortion of the gravitational field? Is the value we assign for flat or non-flat universal age dependant on our own point of reference for time?

I understand that to make any sort of equations or mathematics I'll need some calculus and GR but beyond that I'm at a loss. What sort of books should I be picking up as a beginner before I can start touching on other things, such as GR? Is there something I should read before trying to attempt...

This is just a short question, it might have been asked already but I couldn't find anything. I read that we have attempted to reconcile the Casimir force with the observed expansion of the universe, doing this, we get a number 10^120 times too big. This is obviously a bad number to say the...

I'm new to this impressive forum and have a question that may have been addressed a thousand times, but here goes. A FLRW metric is happy with a time-varying scale factor a(t) and zero curvature parameter k and could care less about density. The combination of a FLRW metric and the Einstein...

I'm Steve Crow, presently retired in Boulder, Colorado. I attended Caltech as both an undergraduate and graduate and got my PhD in 1966. The degree is in "Aeronautics and Applied Mathematics", but I have always been interested in physics, especially cosmology. I spent my career in aerospace...

i have a doubt, how do we know far away (light years) galaxies and planets are on the right spot we see them? if light takes a lot of time to reach the Earth it means we are seeing the past of the galaxy/planet. Example: If Earth is becoming extinct and we need to find an exoplanet 30,000 light...

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...

What are the prerequisites you need to have under your belt before you start studying cosmology? And frankly due to my naïveté, I'm not sure of any interdisciplinary fields in cosmology so I know my question is vague

Hi all! Where are some good places on the Internet where I can learn about physical cosmology? Specifically any good websites that are devoted to physical cosmology that you know about?

Is there any dark matter where no baryonic matter (which here the galaxies).I mean are we observe dark matter only around the matter ? Or dark matter can be anywhere (In empty space which there's no baryonic matter around)

I am doing research and I need to find the dark matter density of Galaxies or dust clusters (It can be any type of thing) which the distance from Earth will be ≅4000 Mpc.Here the picture Think the radius of sphere.

bcrowell submitted a new PF Insights post Will All Matter Be Converted to Photons? Continue reading the Original PF Insights Post.

I've retired but have interests in Quantum mech. and Cosmology.

Dark matter particle candidates are being searched at CERN and the various dark matter models are being probed by cosmological simulations. The usual way to probe models via cosmology is to plug a candidate into a cosmological simulation and then compare the results with observations. Yet...

Homework Statement Derive the following result : \phi_k=-C_1(k)\frac{\dot{H}(t)}{H(t)} . Homework Equations \phi_k=C_1(k)\Bigg(1-\frac{H}{a}\int\limits^{t}a(t)dt\Bigg) a(t)= a(t_i)\exp\Bigg(H_i(t-t_i)+\dot{H}_i\frac{(t^2-t_i^2)}{2}\Bigg) The Attempt at a Solution So I stuck a(t) into...

Hello all! I've been instructed to construct a week long Cosmology class for High School Freshman. The class will run from about 8am-3pm everyday (with breaks and lunch or course). My first step in constructing this class is just to ask you guys what you would want to learn about...

Hey guys & gals, a long time lurker here. For a variety of reasons I have failed to secure a PhD position that I wanted this year after finishing my MPhys degree in physics, so I decided to take a year away from studying, regroup, work towards publishing a paper and then come back with full...

Barbara Ryden seems to have two Cosmology books, her one https://www.amazon.com/dp/0805389121/?tag=pfamazon01-20 and one https://www.amazon.com/dp/129203971X/?tag=pfamazon01-20. I haven't been able to find any differences between the books online - the 2013 book doesn't seem to be a new edition...

I'm not too well read in cosmology, but I know the universe is presumed to be homogeneous in space but not in time, therefore the curvature of the universe can essentially be calculated under one mean. I just have a few questions about how the universe expands and whether some proportions are...

Hi all I want to ask a question about NFE(Newtonian Friedmann Equation).I know that NFE is not usefull to describe universe.But we can have a general idea about universe to use that formula. I know that the only spatial coordinate system is CMB referance frame and NFE is derived from...

The FRW cosmology is a solution of the FRW that can be foliated into 3D isotropic and homogeneous slices. This foliation is implemented mathematically first by the use of a not generally covariant coordinate condition https://en.wikipedia.org/wiki/Coordinate_conditions#Synchronous_coordinates ...

Hey all, I was reading up on some discoveries made in cosmology. http://iopscience.iop.org/1538-3881/149/4/137/ This could easily be due to observational error, but I was wondering whether something such as this is possible in our current models of expansion and dark energy without having to...

Suppose I am in a room and light(photons) from the light bulb reach my eyes, or I am outside light(photons) from the sun reach my eyes and I am able to see the objects around me. I want to know what factors affect the path of photons like temperature, gravity etc.I mean by knowing these factors...

I understand that the force of gravity prevents galaxies from expanding, as space increases. However, I question if universal expansion separates photons (electromagnetism), as they are traveling along parallel paths (Would the normal distance between them increase over time)? Thank you.

Hello! I am a master student, and I am about to start working on my master thesis, which, in my counrty, is a substantial work of 6 months which usually involves original research. I will be supervised by two professors of Statistical Mechanics, who have many research interest. In these days...

The entire observable universe is contained rather graciously in this wonderful picture, for your admiration.

I do not know what to write here, so I just going to say hi! I am Aura a senior 2016 and in this point of my life the time has come to make in my opinion "the most decisive" decision of my life.

I am looking forward to joining discussions here. My Backgroud is 2 years "applied physics", 5 years education for teaching in visual communication (art), 15 years experience as a database software developer. Now I am looking for a job as a software tester. Software Testing is similar to being...

What is the status of ritz-type cosmology?

Hi,I am ihigh school 12 grade I will be in collage 3 months later.I know simple calculus (derivatives and integral ).I watched Leonard Susskind Cosmology and Classical Physics Lectures.I want to learn cosmology and GR.My first question is Did I have to learn Specai Relativity before GR. And Is...

In Dodelson's "Introduction to Modern Cosmology" at p. 61 he introduces a non- equilibrium number density $$n_i = g_i e^{\mu_i/T} \int \frac{d^3p}{(2\pi)^3} e^{-E_i/T}$$ and an equilibrium number density $$n_i^{(0)} = g_i \int \frac{d^3p}{(2\pi)^3} e^{-E_i/T},$$ from which it follows that the...

I am currently writing a funding essay for a (taught) postgraduate degree and I'd rather have a refresher on modern cosmology. As such, is anyone around aware of a recent early universe review article in the arxiv? I am not keen on learning the "basic stuff", just a review article of what has...

Hey there, i have a question regarding basic inflation and structure formation via linear first order perturbation theory in cosmology. I read through different material (Baumann lecture notes, wikipedia articles, Mukhanov, ...), but at this point i am just confused and find it hard to get an...

Are fundamental randomness and fundamental determinism inconsistent? Two such different mechanisms would imply a kind of dualism. (Does even the defeatist retreat into Many Worlds avoid this problem - if it is a problem.)

Hi, i am first year in physics graduation. At first I thought study of strings, but over time realize a large uncertainty in the area and my attention turned to the area of cosmology and gravity. I want to know any tips and books to start studying gravity and cosmology and because string theory...

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!

Homework Statement I am given this metric: ##ds^2 = - c^2dt^2 + a(t)^2 \left( dx^2 + dy^2 + dz^2 \right)##. The non-vanishing christoffel symbols are ##\Gamma^t_{xx} = \Gamma^t_{yy} = \Gamma^t_{zz} = \frac{a a'}{c^2}## and ##\Gamma^x_{xt} = \Gamma^x_{tx} = \Gamma^y_{yt} = \Gamma^y_{ty} =...

I want to know Universe density according to this equation( ##k=-1##) ? ##H^2(t)-8πρG/3=-k/a^2(t)## ##ρ_U=ρ_m+p_r## ##ρ_U##=Universe density ##ρ_m##=Matter density ##p_r##=Radiation density

A very fundamental doubt. Was inflation expansion of just space or the universe with whatever the state of matter it had?

I was watching a sixty symbols video on Stephen Hawking: , and it got me thinking. Is there any practical value for theoretical physicists, if what they are doing is simply speculation not backed by any data? I understand observing a physical phenomena, and from understanding it predicting new...

Space does not exist, so time can http://arxiv.org/abs/0909.1861 Can someone explain to me, what this article means by "space does not exist"?

Hi there, I'm in my final 2 years in high school studying mathematics, physics, further mathematics and chemistry. I'll be applying to universities next winter. But, here in the UK, there're courses for physics in the uni titled: Physics with Theoretical Physics or Physics with Astrophysics...

Hi. 4 years ago my child asked to me a question... What will be happen, if the light is stop? I tried to answer it ... But my knowledge is insufficient. (I had been educated at social science, specially labor laws) . So I searched, tried to learn something new... So I liked physics. Of course it...

My understanding: When we draw a triangle on a flat piece of paper and measure the angles using a protractor, the sum of the angles is ##180^\circ##. So we conclude that the universe is locally flat. Suppose we draw a very big triangle that spans across galaxies (say, using lasers and mirrors)...

Kolb&Turner in "the early universe" mentioned that for a scalar field ##\phi## at finite temperature, ##p=-V_T(\phi)## and ##\rho=-p+T\frac{d p(T)}{d T}## where ##V_T## is potential energy including temperature correction. My question is: when we consider the evolution of the universe using...