What is Cosmology: Definition and 925 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. J

    Courses Prerequisite to General Relativity/Cosmology Undergad course

    Hello, If anyone could help me with the prerequitisetes for an undergraduate General Relativity and Cosmology course I will enroll into, It will be much appreciated. The syllabus is the following(sorry for the rough translation): -Review of Special Relativity -Spacetime in GR -Geodesics...
  2. C

    A Do cosmologists take spontaneous symmetry breaking seriously?

    I suppose that my questions are pretty basic, but I've been trying to find out the answers and not succeeded. 1.- Do cosmologists really think that the vacuum state suddenly changed in the early Universe? If so, would it be like a phase transition? If so, first or second orther? 2.- Does the...
  3. D

    I Bose enhancement in early universe cosmology

    I have been reading through Mukhanov's book "Physical Foundations of Cosmology" and have reached the section where he discusses the process of reheating. In it he mentions that the decay of the inflaton into bosonic states can be "Bose enhanced", i.e. that if ##n## previously created particles...
  4. F

    I Hubble parameter in terms of the scale factor

    From Introduction to Cosmology by Matt Roos, he wanted to derive the Hubble parameter in terms of the scale factor. From the Friedmann's equation, ##\frac{R'^2 + kc^2}{R^2} = \frac{8πG}{3}ρ## The density parameter is ##~Ω(a) = \frac{8πG}{3H_o^2}ρ(a)~## and let ##~Ω_k = \frac{-kc^2}{H_o^2}##...
  5. ShayanJ

    Cosmology Relativistic Cosmology by Ellis, Maartens and MacCallum

    Authors: George F. R. Ellis, Roy Maartens, Malcolm A. H. MacCallum Title: Relativistic Cosmology Google Books Link: https://books.google.com/books?id=FPRFi3L0h9kC&printsec=frontcover#v=onepage&q&f=false
  6. F

    Cosmology Physical Foundations of Cosmology by Viatcheslav Mukhanov

    What are the prerequisites to read this book? In the book he stated that there are no GR and QFT knowledge assumed but some people said that it is not true. Can anyone comment on this book? Thanks.
  7. J

    Relativity General Relativity by Hobson, Lasenby and Efstathiou

    Hello, Is the book General Relativity by Hobson, Lasenby and Efstathiou good in the sense that is intuitive on the mathematics AND physics that it presents? Please vote and if you could also comment your opinion it would be much appreciated. Thanks!
  8. R

    I Absolute magnitude in cosmology

    When referring to the absolute magnitude ,for example, in the B filter of a distant galaxy(considered point source) what are we talking about? Are we talking about the observed redshifted flux density(luminosity density) hypothetically seen from 10 pc away (1) ; or are we talking about the...
  9. F

    I Difference between hubble sphere,particle horizon and event

    Based on my understanding, Hubble sphere is the region that contains GALAXIES receding subluminally while GALAXIES outside are receding superluminally (obviously on the border, GALAXIES recede at the speed of light). Particle horizon is the limit of what we have seen so far since the (big...
  10. F

    Cosmology What Are The Best Books To Study Cosmology?

    Hi, I'm currently in my last year of undergraduate degree, I have a basic knowledge of GR (A. Zee) but I have a very limited knowledge of cosmology, I did not cover the cosmology portion of Zee's book as it is too superficial and I don't want to waste my time reading that. I think my time will...
  11. W

    I Exploring Time in Physics and Cosmology: Insights from the Pi Conference

    The Pi just posted a bunch of videos from their conference on time http://pirsa.org A lot of the big names in cosmology were there: Sean Carroll, Lee Smolin, Abhay Ashtekar , Andy Albrecht, George Ellis etc I have to say though I'm a little surprised at some of the questions. How is it i (...
  12. Oganesson

    I Can someone please explain to me Leavitt's law?

    And how we use it to calculate distances from stars to the earth.Thank you
  13. JeJe

    What is the Connection Between Quantum Field Theory and Cosmology?

    I'm interested in all discussions but particularly those concerning the areas of QFT and cosmology. I've done much studying on the concept of quantum gravity over the past couple years and I want to learn more :)
  14. Multiple_Authors

    Insights Where Did the Big Bang Happen? - Comments

    multiple_authors submitted a new PF Insights post Where Did the Big Bang Happen? Continue reading the Original PF Insights Post.
  15. J

    A The equation of state of non-relativistic energy

    I just have a quick question about a concept I think I haven't fully grasped from my cosmology course. Why does non-relativistic energy have an equation of state with w=0? Also, is the concept of pressure different in general relativity than in thermodynamics or statistical mechanics?
  16. C

    In need of cool experiments for show called 'Quantum'

    Hello Everyone! My name's Christina and I work at the Everyman Theatre in Liverpool... We have a show coming up in the main space at the beginning of July that's going to be performed by YEP (Young Everyman and Playhouse)... and hopefully it's going to be a love story about all things Physics-y...
  17. L

    Cosmology Cosmology&particles astrophysics textbook

    Could you recommend me some good textbooks on cosmology, please? I'm looking for something that covers both general relativity topics and, which is more important for me, particles astrophysics stuff. I like the structure of Bergström&Goobar's book but it's a little bit sketchy. Something with...
  18. W

    I Is Information Conserved in the Universe?

    It's said that information is never destroyed ( I know there is some controversy here regarding black hole information loss but let's put that aside for the moment). But what about created? I information a conserved quantity for the universe as a whole? Is there a consensus on this issue? It...
  19. V

    I Understanding Etherington's reciprocity theorem

    Hi, Etherington't reciprocity theorem states that distances measured by angular separation and by luminosity differ. My question is which one (if any of them) is the actual distance. I can understand they might differ in an expanding universe, but there's still a physical distance in such one...
  20. W

    I Horizon Riddle (Infinite Horizon Problem)

    I'm reading Cosmology by Harrison and in Chapter 21 he discussed the horizon riddle, I understood the problem that he posed but his solution was confusing. "Consider two widely separated observers, A (for Albert) and B (for Bertha). We suppose they can see each other. Each has a horizon such...
  21. Bran

    B Book recommendations for Big Bang Model?

    A recent discussion at the Expanding from and eventually to a singularity thread has been both interesting and informative, and it has shown me very clearly that I would benefit from a few good books, rather than the piecemeal approach I've been taking to understanding singularities and the Big...
  22. K

    I Two numerical questions about inflation and the flatness problem

    Good day to you all I just started studying cosmology recently using several book and especially using TASI Lectures on Inflation(https://arxiv.org/abs/0907.5424) On page 25 the fine tuning problem of the flatness is introduced with conditions as |Ω(BBN)-1|≤ ο(10-16) |Ω(GUT)-1|≤ ο(10-55)...
  23. Einstein's Cat

    B What is the reason for galaxies fading in the distant future?

    Galaxies that are greater than a distance of c/H metres from Earth have recessional velocities exceeding the speed of light and begin to fade. Thus, theoretical astronomers 3 trillion years in the future will see only the Milky Way in the night sky. What is the reason for this fading of galaxies?
  24. Willfrid Somogyi

    I Flat vs Open Universe: CMBR & Type Ia Supernovae

    So CMBR points to a flat universe, and this seems to be the generally accepted model. But in a flat universe is expansion not supposed to slow exponentially, stopping after an infinite time? How does this fit with the observation that distant type Ia supernovae show the universe's expansion to...
  25. Matt atkinson

    Question about errors, Hubble's constant

    Homework Statement I am just looking through some old notes I have from for cosmology, and there's something cropped up that i can't seem to figure out: Say I have two (or more) values for H_o each with errors such as: H_{o_1}=70^{+a+b}_{-c-d} and H_{o_2}=69^{+e+f}_{-g-h} How would I go...
  26. Richo

    Exploring the Possibility of Discrete Spacetime in Cosmology and Cosmogony

    Would general relativity (axiom: spacetime is continuous) still work if we changed the axiom to: spacetime is discrete (but each individual chunk of it is so incredibly small* relative to a quark or gluon that it makes no difference)? *e.g. 3D's of Planck length, 1D of Planck time
  27. W

    Studying Maths, Physics, Astrophysics, Astronomy or Cosmology?

    Hi, I don't know where to begin, please forgive me for asking this if it's been answered before. I'm confused, I don't know what to study, can you help me out? I'm fascinated by the Universe, my only regret in life is that I don't live in space far away from humans. I've always liked...
  28. wolram

    I Is There a Preferred Axis in Cosmology and What Could Be Its Origin?

    Is there a preferred axis in cosmology, if there is what is the origin? arXiv:1604.05484 [pdf, other] Preferred axis in cosmology Wen Zhao, Larissa Santos Comments: 21 pages, 9 figures, 8 tables, invited review Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity...
  29. Gjmdp

    Do I need Astrophysics for a PhD in Cosmology?

    Another way to ask is if I can go to my PhD in Cosmology through Astrophysics. Many people will thought that obviously yes, but notice Cosmology isn't a branch of Astrophysics, but of Theoretical Physics. Now you'll think this is a completely nonsense, so that Astrophysics is very similar to...
  30. thecourtholio

    Distance to surface of last scattering in +, -, and flat uni's

    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...
  31. D

    A Instability of Cosmology with Quantum Corrections

    A good year ago, quantum corrections have been proposed to the very early Universe. It was concluded that these quantum corrections contain a precise estimation for the cosmological constant and the so-called radiation term. The authors even have interpreted the latter as evading the big-bang...
  32. Peter25samaha

    B Where Do Quantum Gravity and Cosomology Fit in Physics?

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

    I Cosmology Large Angular Scale Surveyor

    In the spring 2016 issue of the Johns Hopkins Magazine, there is a non-technical article (in graphic novel format) about a new instrument, dubbed CLASS, which is intended to detect "pinwheel patterns" caused by gravitational waves originating in the inflation era acting on the CBR. If these...
  34. wolram

    B Will super symmetry become part of cosmology

    AFAIK super symmetry as yet has no experimental evidence in cosmology, will it become part of cosmology in some useful application?
  35. wolram

    Is SUSY the next big step in cosmology

    https://www.sciencedaily.com/releases/2012/01/120111135928.htm When will SUSY detection be, 10yrs 30yrs what will SUSY tell us about cosmology. A better understanding of the universe will be the outgrowth of the discovery of the Higgs boson, according to a team of University of Oklahoma...
  36. sami_m

    A Expanding space or contracting matter?

    Expanding universe or contracting matter? this may look very weird question, but what if instead of that the universe is expanding, all matter is contracting as a function of its (proper) time? Δs' = Δs_0 /F(t) The contraction of matter would effect on the length unit what we use. I am...
  37. bcrowell

    Giancoli's Treatment of GR & Cosmology: Shockingly Inaccurate

    My daughter's high school physics class is using Giancoli (6th ed.) as their text. I'd previously looked at the treatment of SR, and it seemed OK, although old-fashioned. But this morning I started flipping through ch. 33, "Astrophysics and Cosmology," and I was pretty shocked. It reads like a...
  38. wolram

    B Can Cosmology Be Experimentally Verified?

    What parts of cosmology can be tested positively in the lab, and what parts can be tested for via electromagnetic radiation .
  39. C

    How did a 49-year-old electrical engineer become fascinated with QED and QFT?

    I am a 49 years old electrical engineer who lectures Optical Communications at the University of Seville. I learned QED because I wanted to understand the ground principles of my area of expertise. I was amazed and thrilled by the beauty of QFT, so I decided to keep on studying. Fearly recently...
  40. C

    Can electro-weak unification be tested at CERN?

    1.- Electroweak interaction broke its symmetry about 1ps after the Big Bang and two different types of interactions appeared: weak interactions and electrodynamics. 2.- The LHC at Geneva is routinely conducting experiments above the energy threshold of electroweak unification. Could these...
  41. K

    Loop quantum cosmology vs string cosmology

    which of the two is better supported by observational evidence and is more researched?
  42. T

    An article stating Cosmology is in crisis. Is it in crisis?

    An article stating Cosmology is in crisis because of our tendency to interpret data to fit our beliefs. Are we guilty of this? http://singularityhub.com/2016/01/09/cosmology-is-in-crisis-but-not-for-the-reason-you-may-think/
  43. A

    Schools Entrance in Princeton University for Post doct. in cosmology

    after having an integrated m.sc and p.hd from any institute of India qualified through JEST exam ,what i have to do to have an entrance in Princeton university for post doctorate in Cosmology?
  44. M

    Exploring the Depths of Astronomy and Astrophysics in Hawai'i

    Hello, all! My name is Marina and I currently live in Honolulu, HI. I'm an ocean engineering major, but my primary interests are in astronomy and astrophysics! I'm hoping to meet a lot of people here that can help me deepen my understanding of those subjects, and maybe even find some people...
  45. S

    Top 40 Physics Schools for Theoretical Cosmology in USA/Canada

    Hi guys, I am an italian student in the first year of Msc in physics. I'd like to make a good Physics Phd in USA/Canada in one of the top 30 cosmology schools(I know some good place in Europe, such as ETH, Scuola Normale di Pisa,...). I'd like to make theoretical cosmology. For now I'm...
  46. rmoh13

    Why is it that scientists think that dark matter annihilates

    Why do scientists think that dark matter annihilates just like antimatter? How is it that dark matter during annihilation can produce light when it cannot emit or absorb light itself?
  47. grauitate

    New valuation of ΛCDM Cosmology by 41 authors....

    P.Bull, Y. Akrami, et al. "Beyond ΛCDM: Problems, solutions, and the road ahead" 77 pages + 517 references arXiv:1512.05356 Written not without humour: e.g. pg. 67: "As Tom Shanks once said, there are only two things wrong with ΛCDM: Λ and CDM." " ΛCDM is like Hotel California: it is very...
  48. S

    Number density: Initial fluctuation strength and more....

    Dear all, I am trying to understand the physics behind the "number density" formula given by Weinberg. Is there anyone who can explain these parameters to me: 1- "Initial fluctuation strength": \begin{equation} \rho_1= \lim_{t \to 0}\frac{\Delta \rho_M^3}{\bar{\rho}^2_M}\end{equation} However...
  49. A

    Quantum Cosmology and Quantum Computing

    Hello All, I've just recently read David Deutsch and Michael Lockwood article about Time Travel of 1994 in Scientific American.They stated,that although among the physicists Everett's theory remains controversial,it has no alternatives in Quantum Cosmology and Quantum Computing.Is it really...
  50. R

    Exploring a Career in Astrophysics & Cosmology

    Hi, I am currently in the first of two years of the leaving cert course (A levels), and I am considering a degree with a view to having a career in Astrophysics or Cosmology. I study along with the compulsory subjects of Irish English and Maths Physics Chemistry Spanish and History. I do...
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