Cosmology Definition and 915 Threads

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...

If the space between any two objects is expanding at a rate faster than light itself can travel, how is it that we're observing light from things so far away? One would think that the expansion of space affects light too, such that the space between the emitted light and the destination of said...

I'm utterly confused by co-moving distance, transverse comoving distance and proper distance. Is comoving distance = proper distance? Then what is transverse comoving distance? Here's what I know so far: The FRW metric can either be expressed as ds^2 = c^2dt^2 - a^2(t) \left[ \frac{dr^2}{1-kr^2}...

Homework Statement [/B] (a) Find the value of A and ##\Omega(\eta)## and plot them. (b) Find ##a_{max}##, lifetime of universe and deceleration parameter ##q_0##. Homework Equations Unsolved problems: Finding lifetime of universe. The Attempt at a Solution Part(a)[/B] FRW equation is...

Hi everyone. Loving the forum, don't know how I haven't stmble upon it already. I'm studying Astronomy at the OU and finding a lot of the maths tough. Especially finding the chapters on Cosmology very difficult. I've seen another post regarding Scale Factor, so hope it's ok posting this too...

PF Insights Blog https://www.physicsforums.com/insights/postindex/ Was the early universe in a disordered state? Why is the radius of the observable universe in light-years greater than its age? Where did the Big Bang happen? Would that be the center of the universe? What is the total...

According to laplace,universe is totally deterministic.(one can tell position of object future position of object if he knows current position and velocity)but Heisenbergs's tells us that there is always uncertainty in position of particle and velocity.but Heisenberg's uncertainty only applies...

If a methane-filled planet or moon like Titan was pulled toward a star, as the methane warmed and became gaseous, would it be possible to ignite it, converting the methane oceans to H2O with a CO2 atmosphere, which could in turn cause photosynthesis to naturally occur? If it's possible, it...

You know friedmann equations derived from kinetic energy and potantial energy conservation.I found these shell model for universe.Here I am curious about something. This shell is like a surface of sphere isn't it.I mean it has only surface and that surface mass is m.And we made our equations...

I've got a homework question that I'm particularly stuck on: Suppose that the halo, assumed spherical, of non-baryonic dark matter surrounding our galaxy has mass ~ 5 x10^12 M solar and radius 0.1 Mpc. What it its average density in Kg m-3? I think that I need to use the formula...

I had a lot of trouble in my early undergraduate career and had received some really bad grades. I retook a lot of courses and after 6 years, I am finally graduating with good marks in my third and fourth year courses and I believe I have an overall good understanding of undergraduate physics. I...

Now that I have pretty much given up on Columbia, but still will have somewhere to go, I will try to make the best of what I have. Since Carnegie Mellon actually earmarks spots for waitlistees, rather than using it to fill up the class when too many No's have been recorded (like WUSTL, which I...

I am currently computer engineering student(second year). Well its not like I don't like computer engineering.but somtimes I think I should have chosen another path.I am pretty good at mathematics.I like to solve maths problems.I am also fascinated about cosmology.I like electronics as well.I...

To date AFAIK Dark matter and Dark energy are mathematical anomalies, What is the evidence for their existence and what is the latest thoughts as to what these hypothetical enteritis are?

I am reading some of "Planck 2013 results. XXII. Constraints on inflation." The paper is full of values for various inflationary parameters under various models, with their confidence intervals. For instance, in Table 5 on page 13, the authors report that — for a model including both running of...

Hello everyone, just a quick question: I have heard that it is impossible to do research in physics by yourself anymore. I heard that "The days of Einstein are gone" and that nowadays in physics, especially string and quantum relativity research, everyone publishes in groups. I feel like this is...

Before I say, I just want to mention that the Danish words for 15 and 18 are femten and atten Atten sounds a bit like the English word "eighteen". So that is where we get our metric prefixes femto- for 10-15 and atto- for 10-18. When you do cosmology the most common quantity, or one of the...

Hi guys, I recently started reading/working through Scott Dodelson's Modern Cosmology in preparation for a Masters course I'm taking next year and one of the exercises has stumped me and (arghhh!) its not one of the solved ones in the back! It is in Chapter 4 (The Boltzmann equations) and is...