Cosmology Definition and 948 Threads

Cosmology (from Greek κόσμος, kosmos "world" and -λογία, -logia "study of") is a branch of astronomy concerned with the studies of the origin and evolution of the universe, from the Big Bang to today and on into the future. It is the scientific study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the scientific study of the universe's origin, its large-scale structures and dynamics, and its ultimate fate, as well as the laws of science that govern these areas.The term cosmology was first used in English in 1656 in Thomas Blount's Glossographia, and in 1731 taken up in Latin by German philosopher Christian Wolff, in Cosmologia Generalis.Religious or mythological cosmology is a body of beliefs based on mythological, religious, and esoteric literature and traditions of creation myths and eschatology.
Physical cosmology is studied by scientists, such as astronomers and physicists, as well as philosophers, such as metaphysicians, philosophers of physics, and philosophers of space and time. Because of this shared scope with philosophy, theories in physical cosmology may include both scientific and non-scientific propositions, and may depend upon assumptions that cannot be tested. Cosmology differs from astronomy in that the former is concerned with the Universe as a whole while the latter deals with individual celestial objects. Modern physical cosmology is dominated by the Big Bang theory, which attempts to bring together observational astronomy and particle physics; more specifically, a standard parameterization of the Big Bang with dark matter and dark energy, known as the Lambda-CDM model.
Theoretical astrophysicist David N. Spergel has described cosmology as a "historical science" because "when we look out in space, we look back in time" due to the finite nature of the speed of light.

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  1. O

    B Age of the universe: observable or entire universe?

    I was wondering if we are only aware of the observable universe, and the actual universe could be infinite, what do we mean when we say the age of the universe is 14 billion years? Are we talking about the age of only the observable universe or the whole universe?
  2. J

    A Hawking and Unruh effects -- Differences and interpretations

    Hello, I am a bit confused on the relation between the Hawking effect(radiation) and the Unruh effect. What I understood with my little knowledge is that the Hawking temperature is the temperature that is emitted at the event horizon of a black hole as measured by an observer at infinite spatial...
  3. X

    Cosmology Modern Graduate Level Cosmology Textbook.

    I've been reading a lot of "Modern" Cosmology by Scott Dodelson and Introduction to Particle Cosmology by A. D. Dolgov and Cosimo Bambi. I like how rigorous and through Dodelson is but in 2017 it is quite dated. I love how modern and up to date Introduction to Particle Cosmology is but I wish it...
  4. X

    Courses Should I Take Graduate Level Cosmology?

    I'm a physics Ph.D student who just complete his first year of classes. I struggled a lot and found this year to be academically the hardest of my life. However in the end I did get excellent grades in all of my core classes. I would really like to take it easy next semester and only take 1...
  5. Riotto

    I Why do galaxy and galaxy clusters look so colorful?

    Why do galaxy and galaxy clusters look so colorful?
  6. D

    B How can anyone explain the universal equilibrium density problem

    With NASA defining this equilibrium density at 9.9 x 10<30 gm/cm3, how can an increasingly expanding universe maintain a steady density as it expands?
  7. S

    I Experimental bound on the scalar spectral index

    Based on the paper by Visinelli (https://arxiv.org/abs/1605.06449), He stated in page 6 that the scalar spectral index as given by the Planck 2013 data (https://arxiv.org/abs/1303.5076) is, ##n_s = 0.9655 \pm 0.0062~~## (##68\%## C.L.) but when I looked into the Planck 2013 paper, I did not...
  8. A

    B Wave-particle-duality and the evolution of the universe

    If I've understood correct, every particle in the universe exists in a waveform, which I've understood to mean propability where the particle does exist? Then which I've understood is, that the wave transforms into a particle only when observed, is this correct? Then if it is correct, how...
  9. L

    Filmmaker/Artist/Quantum Physics/Physics/Cosmology/Parent

    Hello folks. This thread is open for discussion among those who want to explore the similarities between the experiential principles found in art and physics.
  10. Beans56

    I Life permitting ranges for fine tuning constants

    Does anyone know What the life permitting ranges for the constants usually mentioned in the Fine Tuning argument are? i.e. h, G, e, rate of expansion, amount of dark matter ect... My thinking is that if they are just kind of randomly placed inside their respective ranges then that would indicate...
  11. L

    Other Quantum Information and General Relativity

    Last year I've finished the undergraduate course in Mathematical-Physics and Mathematics and this year I've started on graduate school on Physics in order to obtain a master's degree. What I'm really interested are two main topics: general relativity and quantum field theory. I also like...
  12. S

    A Calculating the power spectra of scalar perturbation

    I'd like to numerically calculate the power spectra of the scalar perturbation at the Hubble crossing in warm inflation, my problem is that I don't know how to do it. As I know, the Hubble crossing happens at the onset of warm inflation where the different modes become larger than the Hubble...
  13. J

    I Comoving mass density leads to linear cosmology?

    The Friedmann equation expressed in natural units (##\hbar=c=1##) is given by $$\left(\frac{\dot a}{a}\right)^2 = \frac{l_P^2}{3}\rho - \frac{k}{R^2}$$ where ##t## is the proper time measured by a comoving observer, ##a(t)## is the dimensionless scale factor, ##l_P=\sqrt{8\pi G\hbar/c^3}## is...
  14. F

    B Who is Lisa Randall and What Can We Learn from Her Interview?

    Lisa Randall (Harvard): https://www.physics.harvard.edu/people/facpages/randall Video: http://www.3sat.de/mediathek/?obj=62357 (41 minutes long, English, click the picture)
  15. T

    I Einstein Field Equations: PDEs or ODEs? - Thomas

    This past semester, I just took an introductory course on G.R., which translates to a lot of differential geometry and then concluding with Schwarzschild's solution. We really didn't do any cosmology. However, one of the themes that kept creeping up again and again is that in 4-dimensions...
  16. Gjmdp

    Studying What is better, Astrophysics or Cosmology?

    Even though Cosmology and astrophysics are pretty much the same thing, still there are some differences. Cosmology is like more mathematical, more theoretical. If you are a cosmologist you can apply ideas from String Theory or so. But if Astrophysics is more "experimental". I mean, obviously...
  17. D

    Schools How good is the cosmology program at OSU? (Ohio State University)

    I might be accepted to the OSU physics PhD program and I have mainly an interest in cosmology / early universe stuff. How is OSU's program in cosmology? I hear their astronomy program is very good, but how is their cosmology especially?
  18. R

    How can thermal fluctuations decrease entropy?

    https://en.wikipedia.org/wiki/Future_of_an_expanding_universe "Over an infinite time there could be a spontaneous entropy decrease, by a Poincaré recurrence or through thermal fluctuations (see also fluctuation theorem)"
  19. F

    A End of Inflation: Definition, Meaning & Models

    From cosmology, the end of inflation is usually defined as when the Hubble slow roll parameter is equal to one, ##\epsilon_{H} = -\frac{\dot H}{H^2} = -\frac{d\ln H}{dN} = 1## Is this really the definition of the end of inflation? Or is it for the standard cold inflation only? How about the...
  20. CassiopeiaA

    I Curvature and the size of the Universe

    I always have trouble understanding this concept. Please correct me if I am wrong somewhere in my line of thought. Is the universe finite or infinite? Using the famous balloon analogy, we can think of it as a finite expanding universe. But in that analogy the balloon has a curvature. Does the...
  21. phyzguy

    A Is Dark Energy an Illusion? A Closer Look at Concordance Cosmology

    What do people think of this paper? If I understand correctly, they are saying that the need for Λ disappears if we do N-body simulations that properly take account of GR. I think they are saying that past simulations have used Newtonian approximations that don't properly account for density...
  22. R

    Other A module choice between Cosmology and Fluid Mechanics....

    Hi all, I study Mathematics and Theoretical Physics at university. Next year, I'll have a choice between three modules; Thermodynamics and Statistical Physics Cosmology Fluid Mechanics My main interest is Condensed Matter Physics; therefore, thermodynamics and statistical physics is a given...
  23. J

    Cosmology - determining if a model universe would recollapse

    Homework Statement Show mathematically that a model with: Ω_M0 = 3 Ω_Λ0 = 0.01 Ω_R0 = 0 Ω_T0 = 3.01 is a model that re-collapses in the future. Be certain to indicate at what value of the scale factor 'a' the expansion reverses and becomes contraction. Homework Equations It's hinted pretty...
  24. binbagsss

    Schwarzschild spacetime proper time to fall radially inward

    Homework Statement Question attached My method was going to be: set ##r=R## and solve for ##n(R)## set ##r=2GM## and solve for ##n(2GM)## I was then going to integrate proper time ##s## over these values of ##r##: ##\int\limits^{n=cos^{-1}(\frac{4GM}{R}-1)}_{n=cos^{-1}(1)=0} s(n) dn ###...
  25. durant35

    I Many worlds and cosmological evolution

    Hello guys, I have a question that came up to my mind while thinking about the evolution of our universe and quantum mechanics. It involves cosmology so maybe that was the right spot to post it, and of course the moderators can do it if they feel it's more adequate for the thread, but my...
  26. R

    I Big Freeze and Law of convervation of energy

    (Kurzgesagt- In a Nutshell) says that in the Big Freeze scenario all the matter will decay in the end, how is this possible without breaking the law of convervation of energy?
  27. R

    I How does nucleation work in cosmology?

    In this article https://en.wikipedia.org/wiki/False_vacuum#Bubble_nucleation it says that "In the theoretical physics of the false vacuum, the system moves to a lower energy state – either the true vacuum, or another, lower energy vacuum – through a process known as bubble nucleation." What is...
  28. R

    How does Nucleation work? Relationship with vacuums?

    What is nucleation and how it works? In cosmology, which is the relationship that nucleation have with quantum tunneling, vacuums and Big Bang?
  29. L

    I Exploring Evidence and Data Pre-CMB in the Early Universe

    I have been looking online and in other resources for some answers to no avail. Thought I would sign up on astrophysics forums to find the answer.What is the evidence and data for the period before the cosmic microwave background (CMB) in the early universe? In other words, is the idea of energy...
  30. arnazkh

    Python How Can I Plot Multiple Alpha Values in Cosmology Using Python?

    Hello! I've been working on a code that solves the Friedmann equation with quintessence using a scalar field potential of the form x^(-alpha) where alpha is a free parameter. I would like to plot different values of alpha in the same plot with annotations for each. For now, my code has initial...
  31. Andy_K

    Cosmology Review of Hidden In Plain Sight Series

    Has anyone read the 7-book series http://amzn.to/2lwgn66 by Andrew Thomas? Just wondering what you think of his conjectures / speculations at the final sections of each book, i.e. on the link between relativity and quantum mechanics, equation of the universe, etc... I like that he...
  32. W

    I Exact expression for the tensor-to-scalar ratio

    Based on the vast cosmology texts, I have seen that the expression for the tensor-to-scalar ratio ##r## in cold inflation is, ##r=16\epsilon_H = -16\frac{\dot H}{H^2}\qquad## where, ##~~~\epsilon_H = -\frac{\dot H}{H^2}## ##H## is the Hubble parameter, and ##\epsilon_H## is the Hubble slow...
  33. Arman777

    Studying Learn Cosmology: Beginners Guide to Friedmann Equations

    I want to learn cosmolgy very much,Like from the begining,Proper distance comoving distance how can we measure them then friedmann equations etc. I know leonard susskind lectures but he is describing too general,I want more detail. Is there any other good video lectures...(I couldn't find) a...
  34. M

    I How Would Future Species Understand a Dynamic Universe?

    OK, let's imagine that in a few billion years time, when our local group of galaxies have merged, our Sun has reached and surpassed it's giant red phase stage and has become a White Dwarf, and we as a species are extinct. At the same time the distant galaxies will have moved beyond our...
  35. S

    I Solve Nonlinear DE: Friedmann Eqns for H 0-10^7

    From cosmology, the friedmann equations are given by, ##H^2 = (\frac{\dot a}{a})^2 = \frac{8\pi G}{3} \rho \, , \quad \frac{\ddot a}{a} = -\frac{4\pi G}{3}(\rho+3p) \, , \quad## where ##\rho = \frac{1}{2}(\dot \phi^2 + \phi^2)## and ##p = \frac{1}{2}(\dot \phi^2 - \phi^2)## To get ##\dot H##...
  36. Arman777

    I Time & Cosmology: Observing Past Quantities & Effects on Equations

    I know that If we look further we seethe past...So we are measuring some quantities like a mass of a far galaxy or dark matter mass of a galaxy...All in general does this mean we are observing past quantities ? These time dependent quantities can change with time so How this affect our...
  37. T

    Help Ted Decide on a Career Path: Seeking Advice from Experienced Professionals

    Hi guys I'm ted. I'm posting this thread because I'm not sure what career to follow and I could really use some help. First of all let me give you some info for me.I'm16-17 y.o and going to high school. At 15 I came 2nd to my countrie's astrophysics Olympiad.Read apostol's calculus and since...
  38. S

    I Friedmann Equation Analysis, expansion of the universe?

    Friedmann's Eq can be viewed here https://ned.ipac.caltech.edu/level5/March08/Frieman/Equations/paper1x.gif What I don't get is that all the texts/analyses of Friedmann's equation say that if the right hand side is negative it means that the universe will expand reach a critical point and then...
  39. smodak

    Particle The Standard Model in a Nutshell - Goldberg

    Just found this new book on amazon. Looks interesting. I purchased. https://www.amazon.com/dp/0691167591/?tag=pfamazon01-20 The TOC, Preface, and intro could be found here http://press.princeton.edu/titles/11050.html I wish they included a sample chapter as well (the book in not cheap), but I...
  40. Jorrie

    I Evolution of the Energy Density Parameters

    I am busy with an effort to show how the energy density parameters evolve over time in an update of the LightCone7 calculator. See the posts on the thread Steps on the way to Lightcone cosmological calculator. As part of this effort, I ran into some difficulties with deciding how to find and...
  41. S

    I Rescaling the equation of motion of inflation

    From the equation of motion of inflation, $$\frac{d^2\phi}{dt^2} + 3H\frac{d\phi}{dt} + \frac{dV}{d\phi} = 0$$ Example: ##V= \frac{1}{2}m^2\phi^2## $$\frac{d^2\phi}{dt^2} + 3H\frac{d\phi}{dt} + m^2\phi = 0$$ If I want to make the DE dimensionless then I let ##~t = \frac{1}{H_o} \tilde t~## and...
  42. Bolhuso

    I Where did the Dark Energy (or similar mechanism) come from?

    Hi all! I'm new to this forum and, as a matter of fact I only recently rediscovered my interest for physics. I am starting to catch up, yet I find that Wikipedia sometimes falls sort for some basic questions, and I was hopping that this community could gently help me understand some concepts...
  43. A

    I Expanding universe and the Boltzmann brain problem

    Hello I have been reading Sean Carroll's book "From eternity to here" where he mentioned the concept of functioning brains emerging from random fluctuations on a quantum level due to the expansion of universe. They have been called Boltzmann brains https://en.wikipedia.org/wiki/Boltzmann_brain...
  44. S

    I Different forms of energy density in inflation

    From the second Friedmann equation, $$H^2 = \frac{1}{3M_p^2} \rho \quad (k=0, flat)$$ In warm inflation, radiation is present all the way therefore not requiring proper reheating process, so $$\rho = \rho_\phi + \rho_r \, ; \quad \rho_\phi = inflaton, \, \rho_r = radiation$$ But, $$\rho =...
  45. S

    I How Can I Graph Hubble Term vs. Inflaton Using Mathematica?

    From cosmology, ##H^2 = \frac{ρ}{3M_p^2} = \frac{1}{3M_p^2}(½\dot φ^2 + ½m^2φ^2)## Suppose ##V(φ) = ½m^2φ^2## where ##ρ## = density ##M_p## = Planck mass I want to graph ##H## vs. ##φ## but there is a ##\dot φ## and I know this is a differential equation, can somebody help me what to do here?
  46. C

    I Cosmological electroweak phase transition

    There is a question that has been bugging and puzzling me for a long time and I wondered if somebody could help me to figure out what the answer is or where I am not thinking straight. Let us assume that the standard model of particle physics is more "right" than "wrong" and there is no such a...
  47. C

    I Scaling and the renormalization (sub)group

    I am aware of only two fields where the renormalization (sub)group ideas can be systematically and unambiguously applied: particle physics and equilibrium critical behaviour. 1.- Are there any others? 2.- What are these ideas used for in fluid mechanics? 3.- When cosmologists speak about...
  48. S

    A Gravitational waves in warm inflation

    https://arxiv.org/pdf/astro-ph/0006077v2.pdf page 5. Tensor Perturbations "Tensor perturbations do not couple strongly to the thermal background and so gravitational waves are only generated by quantum fluctuations, as in standard supercooled inflation". Why? Tensor perturbations are created...
  49. Jules Winnfield

    B Galaxy Clusters, Masses and Radius

    This is a request for a good reference. I'm doing a report on dark matter and am wondering if there's any recent references that collects a bunch of galaxy clusters, their dark masses and the radius of the cluster. Preferably in a table that I can shred or download but I'll copy if I have to...
  50. G

    A Flatness Problem Differential Equation

    Hello to everybody, Since 3 days, I've been trying to obtain Eq. (173) from https://ned.ipac.caltech.edu/level5/Sept03/Trodden/Trodden5.html I know I need to derivate with respect to a, but it is being impossible to obtain the final answer. Can anybody help me with a detailed derivation...
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