What is Cosmology: Definition and 918 Discussions

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. D

    Baryon acoustic oscillations and sound horizon

    I'm having some trouble understand this correctly, so I was hoping someone could enlighten me a bit :) Okay, so in the early Universe most of the hydrogen and helium was formed, and then kept in equilibrium, and ionized via photons. So we have a plasma of baryonic matter, including dark matter...
  2. D

    Boltzmann equation for the early Universe

    I'm currently reading about the Boltzmann equation, used for the early Universe. The equation I end up with, after some simplifications is the following: \begin{equation} a^{-3}\frac{d}{dt}\left(n_1a^3\right) = n_1^{(0)}n_2^{(0)}\langle\sigma v\rangle\left[\frac{n_3 n_4}{n_3^{(0)}n_4^{(0)}} -...
  3. binbagsss

    Comoving Observers Concepts cosmology

    I have read 'comoving observers are a special set of freely-falling observers' . I have the following definitions: Comoving Frame: "defined at a time t is the inertial frame in which the accelerated observer is instantaneously at rest at t=t0. (Thus the term 'comoving frame' actually refers to...
  4. K

    What are the topological properties of the FLRW model?

    So, I was trying to do a derivation of my own for the FLRW metric, since I couldn't understand the one Wald had. The spatial slice M is a connected Riemannian manifold which is everywhere isotropic. That is, in every point p\in M and unit vectors in v_1,v_2\in T_p\left(M\right) there is an...
  5. twistor

    Is the Weyl Curvature Hypothesis a Viable Alternative to Inflation?

    Hello guys. I was thinking about alternatives to inflation, especially old ones (such as the hawking-hartle state and imaginary time) and I remebered a theory put foward by Penrose, in which his relatively new CCC is based. Called the Weyl Curvature Hypothesis. No idea of what it is. Could you...
  6. D

    Calculate the age of the Universe at a temperature

    Homework Statement I've been told to calculate the age of the Universe at T = 1 \, \text{MeV}, assuming that a(t=0)=0. Homework Equations Now, I've already calculated the value of H at that temperature, which was around H(1\,\text{MeV}) \approx 0.6 \,\text{s}^{-1}. I've also shown, that in a...
  7. V

    Big Bang: A True Singularity That is Coordinate Independent

    Consider a flat Robertson-Walker metric. When we say that there is a singularity at $$t=0$$ Clearly it is a coordinate dependent statement. So it is a "candidate" singularity. In principle there is "another coordinate system" in which the corresponding metric has no singularity as we...
  8. D

    Calculating energy density in the early Universe

    Homework Statement I've been told to calculate the energy density in the early Universe. It states that it is completely dominated by neutrinos (3 species), photons, electrons, and positrons. Homework EquationsThe Attempt at a Solution Now, I've found an equation to calculate the energy...
  9. WineRedPsy

    Cosmology or Theoretical Physics?

    I don't really have to look into this just yet but it bothers me. I quite like cosmology and stuff like such. Universal topology and relativity and sum of histories and stuff. Fun! I really would like to study any theoretical physics though, it just strikes my fancy particularly. I figure I'd...
  10. W

    Unranked/low ranked graduate programs in theoretical cosmology/hep-th or astro?

    I'm applying for graduate school but am from a basically unknown state school. My stats can be found here: http://www.physicsgre.com/viewtopic.php?f=21&t=5735. I am looking for a low ranked or unranked theoretical cosmology/hep-th school or a similarly ranked observational astronomy program...
  11. V

    Upper Energy Limit in Field Theory: Exploring Quantum Gravity

    I see that we use dimensional analysis involving constants of nature to obtain the Planck length and then apply the uncertainty principle to find the corresponding Planck mass-energy. But the energy and length scales were found by invoking a "particle" interpretation of fundamental entities of...
  12. T

    Proton-electron mass ratio; changed? how much?

    On the subject of our 'finely turned universe', I have read that the proton-electron mass ratio can not deviate more than 1:1037. In other readings, the allowable deviation was stated as 1% ("If the neutron were very slightly less massive, then it could not decay without energy input. If its...
  13. V

    Topology of Relativity: Implications of Niels Bohr's Arguments

    I have seen in the online Stanford Encyclopedia of Philosophy in the entry on Copenhagen Interpretation of Quantum Mechanics that Niels Bohr had argued that the theory of relativity is not a literal representation of the universe: "Neither does the theory of relativity, Bohr argued, provide us...
  14. m4r35n357

    Cosmology Chapter Mistake: Reflections on Relativity

    http://mathpages.com/rr/s7-01/7-01.htm I am completely unable to follow the following sequence of working between equations 2 and 3. AFAIK the final answer is correct, but the intermediate steps seem to be a "casserole of nonsense". I would appreciate feedback from anyone who can follow this...
  15. TumblingDice

    Alan Guth:Inflationary Cosmology live stream 10/31

    Just saw this. "Learn inflationary cosmology from the guy who invented it." Live stream Friday, 10/31, at 2pm EDT (11am PDT) here: http://new.livestream.com/accounts/4044190/AlanGuthLivestream
  16. R

    Number Density of Photons (Cosmology)

    Homework Statement Given the maximum possible number density of stars in the present universe, assume that they have been radiating light for 10 billion years at a solar rate of ##3.9 \times 10^{26} \ W##. Photons emitted all have a restframe wavelength of 500 nm. Find a crude upper bound for...
  17. R

    Cosmology Questions: Show Max Size in Expanding Universe w/o Quotes

    Homework Statement (a)[/B] From the continuity equation show that if ##P=\omega \rho## and ##\omega > -1/3##, show that an expanding universe will eventually reach a maximum size. Take ##k=1## (closed universe). (b) Show that if ##\omega <-1##, the energy density ##\rho## will increase as the...
  18. anorlunda

    Photon's History: Quantum Expression for Energy Loss with Scale Factor Increase

    I know that QM and GR have not net been combined, so perhaps this is a foolish question, but I'll try anyhow. A photon traveling in the vacuum, has energy h/λ. That energy is fixed. It never varies in any circumstances (true?) except one. That one is the expansion of space time; i.e. the...
  19. K

    Cosmological Expansion: Estimating Present Horizon Length

    Homework Statement If light traveled a distance L = H_{eq}^{-1} at M-R equality, how large does this distance expand to at present? (in Mpc) Homework Equations z_{eq} = 3500 \Omega_m = 0.32 at present \rho_c = 3.64 \times 10^{-47} GeV^4 present critical density The Attempt at a...
  20. C

    Ohio State vs. WUSTL vs. Notre Dame for particle cosmology theory?

    First off, my supervisor has connections at both, albeit under different forms: my supervisor postdocked at Ohio State, while he personally knows a professor at WUSTL and another research collaborator I worked with and that writes me a LOR knows another professor at WUSTL (connections at WUSTL...
  21. C

    Event Horizon Properties for Incoming Matter Explained

    Dear all, In one of his lectures,Prof. Susskind mentioned that the event horizon "bulges" forward to meet any incoming radiation or matter; and it is a property of Einstein field equations. I have not come across any such property, and if it exists, shouldn't it belong to the Schwarzschild(or...
  22. S

    Is the Big Bang replaced with a Big Bounce in String-Inspired Cosmology?

    We have made a third film in our "Before the Big Bang" series for youtube. Our first centred around an interview with Abhay Ashtekar and focused on LQC Our second Sir Roger Pernose on CCC This fetaures an interview with Gabrielle Veneziano (founder of string theory), Ali Nayeri ( who works...
  23. wolram

    Is Supersymmetry still viable in cosmology?

    Is Supersymmetry still viable in cosmology, given that so far no supersymmetric particles have been found. From Wiki. SUSY is often criticized in that its greatest strength and weakness is that it is not falsifiable, because its breaking mechanism and the minimum mass above which it is...
  24. julcab12

    Big Bang, Blowup, and Modular Curves: Algebraic Geometry in Cosmology

    http://arxiv.org/abs/1402.2158 Big Bang, Blowup, and Modular Curves: Algebraic Geometry in Cosmology Yuri I. Manin, Matilde Marcolli (Submitted on 10 Feb 2014 (v1), last revised 9 Jul 2014 (this version, v3)) We introduce some algebraic geometric models in cosmology related to the...
  25. ChrisVer

    Problem in Dodelson Modern Cosmology

    Could you please confirm my idea of how to deal with the problem question [b] in the attachment? In case of a non-relativistic neutrino, the energy density will be given by: \rho = m_{\nu} n And if we adopt a perturbation, then n \rightarrow n_{0} [1+ x ] So in general what he asks from...
  26. ChrisVer

    FRW cosmology [itex]Ω_{Λ}[/itex] domination

    Suppose you have a universe where Ω_{Λ}=1 and the rest are zero. Then the Friedmann equations are: (\frac{H}{H_{0}})^{2} + \frac{k}{(aH_{0})^2} = \Omega_{\Lambda}=1 since \Omega= \Omega_{\Lambda}=1 we have a flat universe and so k=0 This leaves us with: (\frac{H}{H_{0}})^{2}=1 or...
  27. K

    Cosmology, Quantum fluctuations,and entanglement

    I understand that 'roughness' in the universe is explained by inflation, because quantum fluctuations in density get separated farther than their Hubble sphere--far than any influence (distance greater than speed of light) between them. Some areas by quantum chance have higher density and can...
  28. B

    Studying pure physics or astrophysics for cosmology graduate study

    Hi there, I need to choose my major in a week and it's between physics or astrophysics. Most of the courses are the same except a few: The different courses: Physics: statistical mechanics, solid state physics, and nuclear and particle physics Astrophysics: Intro to astro...
  29. L

    Discover the Relationship Between CMB's Temperature and Redshift z in Cosmology

    I have a question about cosmos microwave background. Can we get a relationship between CMB's temperature and redshift z?? THX!
  30. I

    What mathematical backgrounds is needed for cosmology?

    Hi there! I would like to know, what kind of mathematical background is needed for cosmology? I'm about to reach 50% of undergraduate physics and I appreciate if you could point it out some interesting courses I can take to build a strong basis for a «future» cosmology masters or phd degree...
  31. Mueiz

    A paragraph about cosmology that made me laugh in the last 24 hrs

    The Florentine astronomer Francesco Sizi argued in this manner why there could not be any satelites around Jupiter. There are seven windows in the head , two nostrils , two ears , two eyes and a mouth ; so in the heavens there are two favorable stars , two unpropitious , two luminaries ...
  32. C

    How competitive is cosmology at the PhD level?

    I am a masters student at some Canadian school best known for astrophysics (and one of the premier schools in the world for white dwarves), dreaming to get into the likes of UPenn (a reach, but not a pipe dream-level reach à la Harvard and Princeton, which some over-ambitious recommender advised...
  33. Dr.Mobius

    Particle Physics vs. Cosmology

    I would like to study the fundamental aspects of the Universe (of course, assuming that I am capable of pursuing such a thing in the first place). Not necessarily on a large scale, but I am interested in space, time, the fundamental aspects of matter... Things like that. I know that there is...
  34. Q

    BransDicke Cosmology and Accelerated Exlansion

    I have just seen this paper on constructing a cosmology for the accelerated expansion of the universe through BransDicke theory http://arxiv.org/pdf/1402.4291v1.pdfBesides this approach What are the alternative or leading cosmological theories that can predict to some fairly strong confidence...
  35. Q

    Nth Quantisation and Cosmology

    This article on 4th Quantisation http://arxiv.org/pdf/1304.0259v3.pdf Takes the WDW equation to 3rd Quantisation to understand the spawning of universes from false vacua from a Multiverse And Furthermore goes to 4th Quantisation to investigate multiverse interactions Is this the best way to...
  36. C

    Big Rip Cosmology and Many-Worlds Quantum Mechanics

    My question is based on two theoretical assumptions. 1) The universe continues with its expansion resulting in an eventual "Big Rip". 2)The many-worlds interpretation of quantum mechanics is correct. In this scenario will all the "branches of reality" in the many-worlds undergo the "Big Rip"...
  37. twistor

    Does BICEP2 kill Conformal Cyclic Cosmology?

    Is CCC killed by BICEP2 or there is a way in which it survives?
  38. G

    Multiple universes in cosmology and quantum mechanics

    Hi, Are the multiverses that come up in some cosmological theories, e.g. inflation, in any way related to the worlds in the many-worlds interpretation?
  39. P

    Cosmology vs. Physical Cosmology

    Is there a difference between cosmology and physical cosmology? The two have separate wikipedia pages which seem to say essentially the same thing. Also, cosmology is obviously a branch of physics, so is "physical" redundant?
  40. Mordred

    Ideal gas laws in cosmology usage

    The ideal gas has the following requirements. 1) there are no intermolecular forces between the molecules. 2) the volume of the gas is negligible compared to the volume of the container they occupy. 3) the interactions between the particles and the container is perfectly elastic (total kinetic...
  41. N

    What is standard early inflationary cosmology?

    I am wondering whether discussions of inflationary cosmology in these forums generally includes or explicitly excludes prior Plank era and GUT era dynamics. I never gave it any thought until reading the following. The Wikipedia article provides a perspective I just don't remember from other...
  42. T

    Feedback and Control Theory applied to Cosmology and Particle Physics

    The radical Smolin thread left me wondering if other similar ideas could not be applied to other areas of Cosmology and even Particle Physics. Every complex system I can think of in our lives, and in nature, forms part of a complex multifaceted control system or process, with various feedback...
  43. F

    Is cosmology truly precise or is it just full of approximations and assumptions?

    I am quite a stranger to cosmology, so please go easy on me if what I say below is actually very stupid/ignorant! From the little exposure I've had to cosmology, it seems to me that in cosmology, a lot of approximations are taken, as well as a lot of huge assumptions made. For example, I've...
  44. Milan Nikolic

    Cosmology as quantum, ie. M-theory

    I wonder, whether cosmology come to an end as quantum, ie. M-theory?
  45. marcus

    Karami's Loop cosmology talk Tuesday at ILQGS,

    Karami's talk is scheduled for Tuesday 29 October in just a few days. http://relativity.phys.lsu.edu/ilqgs/ The title has not yet been posted. It is a good bet that it will be about one or more of the active topics in Loop cosmology of which there are quite a few. Karami's recent work...
  46. R

    Solve Cosmology Problem: Max Possible # of Stars in Universe

    Homework Statement Suppose the sun weighs ##2 \times 10^{30} kg##, calculate the maximum possible number density of stars in the present universe, if all the baryons in the universe were assembled into solar mass stars, and ##\Omega_b = 0.05## today. Homework Equations ##n=\frac{N}{(4/3) \pi...
  47. S

    What Do Canonical Quantum Gravity Models Tell Us About the Big Bang?

    Most people here I think will agree that in order to understand what happened at the big bang we most likely need a quantum theory of gravity. There do appear to be models of cosmology such as CCC or Baum/Frampton that seem to try and sidestep this requirement, but looking at quantum gravity...
  48. S

    Galileon Cosmology Explained: Summary & Overview

    This is a phrase I keep seeing dicussed in cosmology papers, can anyone give a summary of what "Galileon cosmology" is ?
  49. I

    Inflationary cosmology questions

    Hi all, first post, just a mechanical engineer with an interest in theoretical physics. I have a few questions about inflationary cosmology that I was hoping some people could help me with. First what exactly is the bowl that inflationary cosmology talks about, I read Brian Greene's Fabric of...
  50. J

    Are Quantum Mechanics and Cosmology Directly Linked?

    I recently read an article (http://vixra.org/abs/1308.0143) written by an acquaintance, Dr Dimitar Valev and wanted opinions on its relevance . Basically, dimensionless ratios are derived from equations based on both the Planck constant and the Hubble constant. Thus, Quantum Mechanics and...
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