What is Cosmology: Definition and 926 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. 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...
  2. Milan Nikolic

    Cosmology as quantum, ie. M-theory

    I wonder, whether cosmology come to an end as quantum, ie. M-theory?
  3. 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...
  4. 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...
  5. 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...
  6. 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 ?
  7. 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...
  8. 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...
  9. Q

    Wald General Relativity: On the homogenous cosmology, Page 178

    Hi, everybody. I have some problem with Wald's statement shown in the picture. This is from the last paragraph in Page 178. He claimed that there are only solutions with two of the p_{\alpha} positive and one negative. But it's easy to find out that if two of the p_{\alpha} are negative while...
  10. C

    What is the definition of cosmology in a physics context?

    "Cosmology is the scientific study of the properties of the universe as a whole." That definition seemed concise and straight to the point for both scientist and the public. Everything else cosmology contains seems would be included within that definition. Does anyone here have a better one...
  11. jtbell

    Relativity Relativity, Gravity & Cosmology by Cheng

    Author: Ta-Pei Cheng Title: Relativity, Gravity & Cosmology: A Basic Introduction Amazon Link: https://www.amazon.com/dp/0199573646/?tag=pfamazon01-20 (submitted by serllus reuel)
  12. marcus

    Seriously gritty videojournalism applied to cosmology by Skydive

    This week Skydive Phil released an outstanding 40-minute special on quantum cosmology. It's different. What makes it different from, say, slick science cinematography you get on "Nova" and commercial channels is the Skydive team's "realness"---their intelligent probing interview style. Phil's...
  13. marcus

    Remaining problems w LQG (and cosmology application)

    Tom gave an honest assessment just now in another thread of the real situation with LQG which in effect includes the several roads from there to cosmology (eg. Agullo, Alesci, Barrau, Engle, Vidotto, Wilson-Ewing and others). He made a very good point which is that the problems are not...
  14. G

    Book suggestions for WKB approximation and Perturbations in Cosmology

    Hi everyone, I was wondering if you guys could suggest me some good books in cosmology with finely explained WKB method and Perturbations especially in Structure formation area. I have "The early universe" by Klob and Turner and "Cosmology" by Weinberg , but they seem unpalatable at first...
  15. T

    Is Conformal Cyclic Cosmology a Viable Explanation for the Big Bang?

    Hey everyone, I wanted to share this new interview I found with Roger Penrose wherein he discusses his theory of conformal cyclic cosmology: http://www.ideasroadshow.com/issues/roger-penrose-2013-07-12 I was wondering, are you convinced by his theory? I find it intriguing but I'm...
  16. C

    PhD in particle physics/ cosmology in US

    Hello folks, I am from Hong Kong studying in a university in HK, major in Physics. Next year will be my final year of undergrad (3 yr undergrad program) and I am considering applying for graduate schools in the US. My major research interests lie on particle physics and particle physics...
  17. marcus

    Higgs-driven cyclic conformal cosmology (Steinhardt Turok Bars)

    I approach this cautiously but with interest. (How often do ideas like this work out?) http://arxiv.org/pdf/1307.1848v1.pdf and suggest you jump immediately to page 24 where there is a suggestive graph, Figure 1. ==quote page 24 of Bars Steinhardt Turok 1307.1848== Fig.(1) is an...
  18. M

    Entropy in Cosmology: Exploring the Universe

    So we know that at the moment of the big bang the universe was relatively low in entropy; as the universe has expanded entropy has increased, but what about further down the line? What about when the universe is so cold that it's nothing more than a collection of black holes, and further more...
  19. C

    The Philosophy of Cosmology: a new field of study

    The Philosophy of Cosmology is a new field of study at Oxford and Cambridge in Europe, and Rutgers, Columbia, NYU, Yale and UC Santa Cruz in the United States. Apparently they got a million dollar grant from Templeton foundation to create this new field of study. I am asking if this...
  20. W

    Questions on Weinberg Cosmology Book

    I am following up Weinberg Cosmology book, but I have one question. In chapter 3.1, we have Eq (3.1.3) and (3.1.4) s(T) = \frac{\rho(T) + p(T)}{T} T\frac{dp(T)}{dT} = \rho(T) + p(T) In Eq (3.1.5), we have the Fermi-Dirac or Bose-Einstein distributions. n(p, T) = \frac{4 \pi g...
  21. G

    Is there a time paradox in Big Bang cosmology?

    In this post, I am going to assume the truth of the standard model of cosmology, which says that the universe is expanding as time progresses from some infinitely compressed state. The paradox Has anybody heard anything like this? Any thoughts on how to "solve" it?
  22. L

    The consistent histories approach to quantum cosmology

    I'm currently reading "Three roads to Quantum Gravity" by Lee Smolin. In the book he describes attending a presentation by Fay Dowker and James Hartle about the consistent histories approach to quantum cosmology. He describes that, "there were worlds that were classical now that were arbitrarily...
  23. A

    How can I contribute to the field of cosmology?

    A brief question: I am an armchair cosmologist - or maybe a "wannabe" cosmologist...it's a fine line. I am 47 years old with most of my career in software behind me but, without returning to college to become involved professionally in Astrophysics and Cosmology, I'd like to contribute to the...
  24. M

    Space engineering, astrophysics and cosmology

    I discovered that I have a very strong interest in cosmology and astrophysics but the field seems to be extremely competitive and jobs are very limited. I am thinking of doing aerospace engineering + science combined degree just because doing science alone seems like a gamble as I might end up...
  25. J

    What are the unanswered questions in Cosmology?

    What are the greatest mysteries in Cosmology? Please comment on my list. 1 Complete explanation of black holes, what happens to time and space (worm holes?). 2 Process of symmetry breaking during initial stages of the of the big bang (includes matter/antimatter unbalance). 3 Source and...
  26. A

    Boltzman equation on cosmology

    I need integrate "over heavy momenta" the following equation \sigma v>= <\sigma v>= \frac{1}{n^{(0)}_1n^{(0}}_2 \int \frac{d^3p_1}{(2Pi)^3 2 E_1} \int \frac{d^3p_2}{(2Pi)^3 2 E_2} \int \frac{d^3p_3 }{(2Pi)^3 2 E_3} \int \frac{d^3p_4}{(2Pi)^3 2 E_4} e^{-(E_1+E_2)/T} \\ \cdot (2 Pi)^4 \delta^3...
  27. marcus

    How would you teach quantitative cosmology? What examples to use?

    By quantitative cosmology I mean with real times, distances, expansion rates, horizons, CMB stationary observers etc , derived from the standard model fitted to data. I don't mean ideas about conditions shortly before or after the start of expansion, although that is very interesting too. The...
  28. N

    Brian Cox video Discusses Cosmology and CERN supercollider

    This is quite an entertaining 15 minute video that provides a high level discussion for a general public audience. [A physics teacher and childhood friend uses the video in her advanced placement HS physics classes in New York. Her students are one group of US kids that I know get a good...
  29. marcus

    Lightcone 1.0 tabular cosmology calculator

    New release of Jorrie's tabular calculator. http://www.einsteins-theory-of-relativity-4engineers.com/LightCone1.0/LightCone.html this is clearly the best on-line cosmology calculator for the general user on the web. Hands down. Lightcone rules. that's all there is to say. Check it out...
  30. C

    Cosmology questions, something that is puzzling me for days

    Hello folks My name is Mike. I am into Cosmology ever since I was a kid. Throughout the years I strayed away from Cosmology unfortunately but I am very very fond of Cosmology...and thus...call me an amateur Cosmologist :D Anyway... These days couple of questions puzzle me in the...
  31. M

    Can Tired Light Theory Explain Redshift Without Expansion of the Universe?

    Homework Statement The assignment is to find the energy loss constant for the theory of tired light. If redshift isn't caused by the expansion of the universe but from a loss of energy, how much of a photons energy is lost per unit distance(MegaParseC) for some set Hubble constant. Homework...
  32. S

    Schools Chosing College For Particle Physics And Cosmology

    I am an aspiring physicist. My main interests are Particle Physics, Cosmology and Black hole physics. I am going to join a college this year for the same. I applied to two colleges and got selected. University of Lancaster and University of Birmingham. I have applied for the course - Physics...
  33. Chronos

    Observational Cosmology & LCDM Model: What We Know

    This paper; 'What have we learned from observational cosmology ?', http://arxiv.org/abs/1304.4446, provides a good overview on the evidence supporting the LCDM model and why it is currently favored by mainstream scientists. It also offers considerable discussion on the motivation for Dark Matter...
  34. Garth

    Conspiratorial cosmology - the case against the Universe

    Conspiratorial cosmology - the case against the Universe Sounds pretty serious to me... Garth
  35. 4

    Looking for some good websites for Physics and Cosmology

    I've been looking for a few websites good for Cosmology and Physics, maybe you guys can help? I'm in 8thgrade, but I can comprehend a lot, just try to stay away from websites that have excessive technical math please. All posts are appreciated.
  36. M

    Ian Morisson's Introduction to Astronomy and Cosmology questions

    Hey there! I recently bought said book and would highly recommend it for any Astronomy and Cosmology undergrads. However, one little niggling thing about it (something that grinds my gears in general with textbooks) is that it features end of chapter questions yet no set of answers for the...
  37. P

    Solving Kolb & Turner's Reheating Problem with 1st Law of Thermodynamics

    Homework Statement i i am trying to derive \dot{\rho_{R}}+4H\rho_{R}-\Gamma_{\phi}\rho_{\phi}=0 as in Kolb an turner (Boltzmann describing reheating). Is the correct approach to, use the 1st law dU=dQ-pdV, but what would dQ be?
  38. P

    Questions on observational cosmology

    Can anyone explain: why COBE measured IR and microwave as opposed to visible light, when surely we are measuring photons that have decoupled? why Planck is measuring light polarisation?
  39. marcus

    Rethinking Cosmology (Steinhardt)

    http://www.perimeterinstitute.ca/seminar/rethinking-cosmology In five days Paul Steinhardt (Princeton) will give a colloquium talk at Perimeter. He has a 90 minute timeslot. Steinhardt has been a proponent of "brane-clash" cosmology. Sometimes called Cyclic or Ekpyrotic. Two spatial...
  40. L

    What is the difference between coasting and static cosmology?

    Is the key difference between coasting and static cosmology models the presence of a linear acceleration, or are there other major differences? Regards, Noel.
  41. K

    Questions arisen while reading Weinberg's Cosmology

    I was reading Weinberg's book Cosmology. When I went to chapter 2, under the subsection 2.1 "Expectations and discovery of the microwave background" I could not understand one statement. ---Quote--- The work done by pressure in an expanding fluid uses heat energy drawn from the fluid. The...
  42. atyy

    Interpretation of quantum mechanics in cosmology

    In Mukhanov's Physical Foundations of Cosmology p348, he writes "Decoherence is a necessary condition for the emergence of classical inhomogeneities and can easily be justified for amplified cosmological perturbations. However, decoherence is not sufficient to explain the breaking of...
  43. Greg Bernhardt

    Cosmology Spacetime, Geometry, Cosmology by William Lewis Burke

    Author: William Lewis Burke Title: Spacetime, Geometry, Cosmology Amazon Link: https://www.amazon.com/dp/0935702016/?tag=pfamazon01-20 Prerequisities: Level:
  44. marcus

    APS Physics view of pre-inflation cosmology article

    "APS Physics" view of pre-inflation cosmology article The APS has an online periodical that publishes "Viewpoints" on current research, for instance http://physics.aps.org/articles/v5/142 is an interpretive explanatory viewpoint, written for non-specialists, on the article by Agullo Ashtekar...
  45. K

    Brane cosmology and extra dimensions

    I have a few questions so I hope it is okay if I ask them all here in this thread. They are all related somewhat. According to brane cosmology, our 4-D universe is embedded inside a higher dimensional space, a hyperspace if you will, called the bulk. The reason we cannot perceive or interact...
  46. H

    Calculating the density parameter (Cosmology)

    Homework Statement Decide the density parameter from the following data: z=0.04, m= 17.38 and σ=0.19 Homework Equations Definition of the density parameter: Where p0 is the current density and pc is the critical density. The Attempt at a Solution I feel like I don't...
  47. H

    Calculating the scale factor (cosmology) for a universe starting at the Big Bang

    Homework Statement Show that by using the Friedmann-equation you can determine the scale factor for a Universe in it's early stages (starting with the Big Bang) to: Homework Equations The equation for the scale factor: Where r(t) is the distance from us to a given galaxy to the time t...
  48. N

    No Inflation in Brane Cosmology: Is Dark Energy the Driver?

    In brane cosmology how can there be no such thing as inflation. I was watching a lecture with Neil Turok and he said he made a bet with Hawking that says that the new Planck satellite will give us information that could prove against inflation. So, my question being, instead of inflation in the...
  49. D

    Cosmology - given omega_m and a static universe, find the range of values of q_0

    Hi there, the full question is as follows: Suppose omega_m = 0.2. If we observe cosmic acceleration at z=0, what is the possible range of values of q_0? What is the minimum value of lambda? What is omega_total? so I'm having trouble with the relationship between q_{0}, \Omega_{m,0}, \lambda...
  50. marcus

    Recent papers relevant to cosmology that seemed extra interesting

    The recent report from the South Pole Telescope seemed to several of us to be exceptionally interesting making one think we might have a thread that just lists recent papers, as they come out, which seem as if they might be important to cosmology. Here are a few. http://arxiv.org/abs/1210.7231 A...
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