Cosmolgy Definition and 135 Threads

I'm opening this thread for discussion on the latest debate over inflationary cosmology as outlined over at scientific american the original article on inflation was Scientific American published an article by Ijjas, Steinhardt and Loeb https://www.cfa.harvard.edu/~loeb/sciam3.pdf then a...

Homework Statement Show that the time of matter-radiation equality, t_{eq} can be written: $$ t_{eq} =\frac{a_{eq}^{\frac{3}{2}}}{H_{0}\sqrt{\Omega_{m}}} \int_{0}^{1} \frac{x}{\sqrt{x+1}} dx $$ Homework Equations $$ t = \int_{0}^{t} dt = \int_{0}^{a} \frac{1}{H(a)} \frac{da}{a} $$ [Given]...

Given the metric of the gravitational field of a central gravitational body: ds2 = -ev(r)dt2 + eμ(r)dr2 + r2 (dθ2 + sin2θdΦ2) And the Chritofell connection components: Find the Riemannian curvature tensor component R0110 (which is non-zero). I believe the answer uses the Ricci tensor...

Homework Statement I'm doing research with a Professor and I'm constructing a likelihood function which has parameters the density parameters found in the Friedman equation found using Massive Gravity Action H Homework Equations H(z)^2=a + b (1 + z) + c (1 + z)^2 + d (1 + z)^3 + r (1 + z)^4...

In wikipedia says that in a big amount of time quantum tunneling can create a new Big Bang. EXACTLY, how this happens. https://en.wikipedia.org/wiki/Future_of_an_expanding_universe ("Beyond" part) *note: I'm in high school, but feel free to explain this with complicate process.

If the universe were to end with the Big Rip scenario, Would the milky way still exist up until the Big Rip? If so, how long would it take for the Milky Way, Earth and Humans to be ripped apart? (eg. How long from when we start feeling something to all atoms being separate) Would humans survive...

Hello. I'm actually taking Ph.D. course for plasma physics and I think I'll finish this course within this year. I took classes in quantum field theory and general relativity in last semester luckily and experience of these subject ignited a desire to study theoretical particle physics and...

Homework Statement I encountred a question that says : Assume that gravitational interactions between galaxies in groups lead to random galaxy velocities of 300 km/s At what distance would the redshift predicted by Hubble's law dominate over that produced by individual velocities? and what is...

I'm looking for the distribution of all wavelengths (or frequencies) of light that a stationary observer would receive at his location (at ##r = 0## and time ##t_0##), from all light sources emitting a single wavelength ##\lambda_{\text{e}}## (or angular frequency ##\omega_{\text{e}}##). The...

I read the Jupiter is so big that it doesn't really orbit the sun. Is that true?

I would like to study more about the notion of time in modern physics. In particular, I would like to understand better the following question: how does one measure the time in the early universe? To measure time one needs to have clocks. A natural choice to be used as clocks would be particles...

I have completed my engineering by now. I have decided to continue my further studies in Mathematics and to be aware of all physics concepts required for research. How can I study all physics concepts from home and what time would it take for me ?

Hello all,. I'm right now playing the publicly released data from the Illustris simulation. Im trying to plot the number of halos per logarithmic mass bin or the number of halos between mass M and M+dM I'm only familiar using theoretical models like Press-Schecter and I have no idea how do...

Dark Matter is every where and always passing threw us right? It apparently hold everything in place in our universe. We know it there but can't detect it. We see the results, but we don't really see who's responsible. What If dark matter was basically a different type of gravity? And the...

Homework Statement 1) Calculate the angular diameter distance to the last scattering surface in the following cosmological models: i) Open universe, ΩΛ= 0.65, Ωm = 0.30 ii) Closed universe, ΩΛ = 0.75, Ωm = 0.30 ii) Flat universe, ΩΛ = 0.75, Ωm = 0.25 Describe how the CMB power spectrum...

In which branch of physics we can put Quantum Gravity and Cosmology ? -astrophysics ? -relativity ? -quantum mechanics ? -classical mechanics? Or other ?

I read that the mass of the universe slows the expansion of the universe. I also heard that if the mass of the universe was above a critical value the universe would contract. I believe this is called the big crunch scenario. And that it is currently not considered a probable scenario. Is this...

I've studied in many books, from which I learned that a vacuum is not truly a vacuum, that is, virtual particles are created every time. And I had also learned that the universe is left handed, that is a small non obeying in parity symmetry(individually), resulted in production of around one in...

I always wondered this question i tried to ask my teachers but i keep forgetting so DOES the gravity of a planet determines its Density?

Homework Statement For n=0, compute the expressions forρ(r),T(r),p(r) in terms of the total mass M and radius R of the star.What is the the scale length a in terms of the radius R in this case? Homework Equations Lane-Emden Equation[/B] , where...

i am in 10th std. and i am very very interested in space.i want to choose astrophysics or cosmology as a career.but will it be perfect career for me in future?how much salary would i get, as an average?

Homework Statement Energy density of radiation ##\rho_r = 8 \times 10^{-14} J m^{-3}## and energy density of matter ##\rho_m = 2.63 \times 10^{-10} J m^{-3}##. Baryon density parameter is ##\Omega_b = 0.04##. Temperature of CMB today is ##2.73 K##. Ionization energy of Hydrogen is ##13.6 eV##...

So, I'm currently a sixteen year old sophomore who is really interested in Physics and I wanted to know what realm of Physics I could join that includes some of my interests. I enjoy soldering, programming, mathematics, circuits and electronics, mechanics, and computers. However, I do not want...

I am studying general relativity from Hobson and came across the term 'lifetime' of a closed (k>0) universe, ##t_{lifetime}##. I suppose at late times the curvature dominates and universe starts contracting? Are they simply referring to ##\int_0^{\infty} dt##? If so, would the bottom expression...

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...

Hi, I have been studying general relativity using Hobson's lately, particularly about the FRW universe. I know that for a matter universe with curvature, H^2 = \left( \frac{\dot a}{a} \right)^2 = \frac{8\pi G}{3} \rho_m -\frac{kc^2}{a^2} Another expression I came across is also 1 = \Omega_m +...

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...

Homework Statement (a) Find the FRW metric, equations and density parameter. Express the density parameter in terms of a and H. (b) Express density parameter as a function of a where density dominates and find values of w. (c) If curvature is negligible, what values must w be to prevent a...

Is space time has a energy itself ? Thanks

Dealing with CMB, people sometimes refer to the shift parameter; R = \sqrt{\frac{\Omega^0_m}{\Omega^0_k}}sinh(\sqrt{\Omega^0_k}\int^{z_{dec}}_{0}{\frac{dz}{E(z)}}) I know that it is related to the position of the first acoustic peak, however, the amount is around 1.7. What does this mean?! does...

Hey All, I'm Tommy, a 15 year old aspiring Astrophysicist living in Australia. I'd like to be an active community member so feel free to PM me. I have a good knowledge of Gravitation and Relativity. Tommy :)

In Bojowald's 2010 popularization of Loop Quantum Cosmology Once Before Time, there's a sketchy diagram (on his p.125) showing quantum perturbations in a transitional phase between contracting and expanding universes as widest at earlier times of decreasing volume, narrowing at the...

I am studying cosmolgy and when I thougt about cosmological princples and copernic principle I thougth something.We are observing things and we see the past of objects.From the cosmolgycal principles (isotropy and homogeneity) all observers must see the universe same ,so let's suppose we observe...

Hi guys, I am a mechanical engineer. and i am working as a naval officer.. but i want to get into the profession of cosmology can anyone suggest me how to get into that profession as i hv done mechanical engineering.

Assume the universe has an average galaxy density of p=0.9 Mpc^-3. Each galaxy has a diameter of 30 kpc. How far would you see on average in any direction before your line of sight would hit a galaxy? Assume a Eucledian spcae and infinitely large and infinitely old universe. Help get me...