What is Cosmolgy: Definition and 132 Discussions

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  1. Q

    Calculate Comoving distance as a function of parameters

    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...
  2. R

    B Exactly how quantum tunneling leads to a Big Bang?

    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.
  3. FelixH

    B What would a timeline for the Big Rip look like?

    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...
  4. G

    I'm thinking about 2nd Ph.D. for particle physics

    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...
  5. M

    Solving Redshift Confusion Homework Problem

    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...
  6. Barnak

    A Color of Deep Space: Distribution of Light Wavelengths

    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...
  7. Oganesson

    I Is Jupiter too big to orbit the Sun?

    I read the Jupiter is so big that it doesn't really orbit the sun. Is that true?
  8. Cosmology2015

    I How to measure time in the early universe?

    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...
  9. V

    Studying How much time it takes to know all physics concepts?

    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 ?
  10. A

    I Plotting number of halos per logarithmic bin

    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...
  11. kcookson251

    B Unraveling the Mystery of Dark Matter: Is it a Different Type of Gravity?

    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...
  12. thecourtholio

    Angular diameter distance to surface of last scattering

    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...
  13. Peter25samaha

    B Quantum gravity and cosmology

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

    Does mass slow the expansion of space?

    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...
  15. A

    Is Matter Created continuously?

    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...
  16. Living Tribunal

    Does a Gravity of a planet determine density?

    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?
  17. J

    Solve Lane-Emden Equation for n=0 | Mass, R, a

    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...
  18. S

    Astrophysics Career: 10th Grader Interested in Space

    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?
  19. U

    CMB Temperature - Will hydrogen be ionized?

    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##...
  20. SuperQYD

    What Are Potential Paths for a Physics Enthusiast with Varied Interests?

    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...
  21. U

    Lifetime of Universe: Limits & Expansion Explained

    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...
  22. U

    How do I find the scale factor of cosmological constant?

    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...
  23. U

    Redshift in Terms of k | General Relativity

    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 +...
  24. U

    How do I solve this cosmological model FRW?

    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...
  25. U

    General Relativity - FRW Metric

    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...
  26. Quarlep

    Does space-time have an energy itself?

    Is space time has a energy itself ? Thanks
  27. S

    How can you show the CMB shift parameter?

    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...
  28. T

    Greetings - Tommy From Australia

    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 :)
  29. slatts

    Scale of perturbations re entropy, in quantum bounce

    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...
  30. Quarlep

    Cosmological principles and their results

    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...
  31. varun atri

    From Mechanical Engineering to Cosmology: A Guide to Breaking into the Field

    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.
  32. E

    Cosmolgy- Density of the Universe

    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...
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