What is Cosmology: Definition and 917 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. S

    Negative scale factor RW metric with scalar field

    Homework Statement The aim is to find a solution for the scale factor in a Robertson Walker Metric with a scalar field and a Lagrange multiplier. Homework Equations I have this action S=-\frac{1}{2}\int...
  2. J

    Particle horizon distance

    Homework Statement Numerically integrate and report the particle horizon distance today for the currently fa- vored model \Omega_M=1-\Omega_{DE}=0.25,\omega=-1. Assume the scaled Hubble constant to be h = 0.72, and report the particle horizon in billions of lyr (Gyr). Homework EquationsThe...
  3. J

    Onset of Universe acceleration

    Homework Statement Assume the cosmological model with H0=72,Omega_M=1-Omega_lamda=0.3,(so dark energy with w = − 1) and a flat universe.) a) Find the redshift z at which the universe starts accelerating (that is, when it transitions from decelerating to accelerating). b) How long ago did this...
  4. R

    Alternative hypotheses regarding dark energy?

    Currently, the favoured explanations for the accelerating expansion of the universe are the cosmological constant, and various scalar fields, most notably quintessence. All of these are mechanisms dependent on mathematical field properties. My question is: do any alternative hypotheses exist...
  5. J

    Link redshift with luminosity distance?

    Homework Statement Plot luminosity distance and redshift z Homework Equations $$d_L(z)=(1+z)r(z)$$ where d_L(z) is luminosity distance and r(z) is the comoving distance. and we have $$r(z)= \frac{H_0^{-1}}{\sqrt\Omega_K}*sinn[\sqrt{\Omega_K}\int_0^z\frac{dz'}{\sqrt{\Omega_M(1+z')^3}}]$$ where...
  6. J

    A circle in a non-euclidean geometry

    Homework Statement Consider a universe described by the Friedmann-Robertson-Walker metric which describes an open, closed, or at universe, depending on the value of k: $$ds^2=a^2(t)[\frac{dr^2}{1-kr^2}+r^2(d\theta^2+sin^2\theta d\phi^2)]$$ This problem will involve only the geometry of space at...
  7. P

    In a radiation dominated era, how do I show this?

    As above. In a radiation dominated how do I show this equation? http://i.imgur.com/nMwxvD5.png (It's easier for me to post the image to imgur than use latex. I know g is the relativistic degrees of freedom. I think that the scale factor a(t) is proportional to 1/t and that a(T) is proportional...
  8. S

    Difference between Astronomy and Cosmology

    What Is the difference between Cosmology and Astronomy..?
  9. J

    Why doesn't the vertical light beam get out of a black hole?

    For this we need a thought experiment: imagine you're on a gedanken planet manning a gedanken laser cannon, and it's pointing straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now let's keep you safe in a bubble of artistic licence, and...
  10. K

    Where to Start with Cosmology: Recommendations for Self-Study

    What are the essentials to starting on this topic from the very beginning? What are topics I should have covered before starting? Suggestions please? Thank you.
  11. wolram

    I Cosmology looks beyond the standard model

    http://phys.org/news/2015-07-cosmology-standard.html The most popular candidate for the elusive particles that give the Universe extra mass is Cold Dark Matter (CDM). CDM particles are thought to move slowly compared to the speed of light and interact very weakly with electromagnetic radiation...
  12. wolram

    Will a bouncing cosmology lose information

    I have been looking for literature on this question but can not find any, will a (bounce) retain all the information of the previous galaxy ?
  13. J

    Period of radial oscillations

    Assuming a neutron star is a uniformly dense sphere of radius 10km and mass =1.4 mass of sun, derive the period of radial oscillations.First use hydrostatic equilibrium to calculate p, then the velocity of sound is $$v= \sqrt{ \gamma p / \rho}$$, so the period of pulsation is time it takes from...
  14. C

    Good 1st year grad level texts in galaxies and cosmology

    I'm looking for some appropriate 1st year, or possibly 2nd year, level grad texts on galaxies and cosmology. The grad course at my university requires Cosmological Physics by Peacock and Galaxy Formation by Longair. I've noticed many old cosmology course websites require Weinberg or Dodelson or...
  15. wolram

    What is the matter in cosmology

    This paper states that gravity gravitates, to me that is mind boggling, i can not even understand how these additive effects may alter cosmology. arXiv:1509.06682 Let us start by recalling how interaction energies work in relativistic gravity. It is well known that gravity gravitates in...
  16. M

    Pre-Big Bang Environment & Rules: Insights on the Known Laws of the Universe

    The Big Bang process (with or without inflation) followed known rules which had to exist prior to time zero (start of big bang). For example, some of the obvious rules of the game included: mathematics, conservation laws (symmetry), thermodynamic laws (energy conserved, entropy increases)...
  17. T

    Stochastic Matrices in Cosmology

    Good afternoon all, I'm taking a linear algebra course this semester, and upon entering the topic of 'Applications of Matrix Operations', my professor has given our class the opportunity to earn some extra credit points by writing a paragraph or two on the application of stochastic matrices in...
  18. A

    Cosmology - Is it a smart choice?

    I am interested in studying cosmology or physics during university (as an Australian) and hope that this can lead on to a job further involving cosmology. What are the chances of actually succeeding with this endeavor and is there any chance of employment as an Australian?
  19. F

    Age of Universe in Planck normalized units

    Hello, I've a problem. I need to find the age of universe in normalized Planck units. In my case, I'm using Planck mass = 1 and: ##H = 1.18 × 10^{-61} \times t_P^{- 1}## With these values, how can I find the age of the universe? Thanks!
  20. S

    Difference between Cosmology and Astrophysics/Astronomy

    Well my question is what is exactly the difference between Astrophysics and Cosmology and Quantum mechanics ?
  21. Garth

    Exact Classical Correspondence in Quantum Cosmology?

    A paper published in 'Gravitation and Cosmology', [21, 208 (2015)] and on today's physics ArXiv claims to have found a solution to the Wheeler-DeWitt equation that exactly corresponds to the classical evolution of a Friedmann model with appropriate matter/energy density: Exact Classical...
  22. G

    The age of the Universe in a denser region of TimeSpace

    According to Einsteinian Relativity, is the Universe considerably younger if one was to view it from within a greater distortion of the gravitational field? Is the value we assign for flat or non-flat universal age dependant on our own point of reference for time?
  23. astralarcher

    I'm not sure where to start with very basic cosmology

    I understand that to make any sort of equations or mathematics I'll need some calculus and GR but beyond that I'm at a loss. What sort of books should I be picking up as a beginner before I can start touching on other things, such as GR? Is there something I should read before trying to attempt...
  24. ComaBerenices

    Virtual Particles & the Casimir Force: Exploring the Link to Universe Expansion

    This is just a short question, it might have been asked already but I couldn't find anything. I read that we have attempted to reconcile the Casimir force with the observed expansion of the universe, doing this, we get a number 10^120 times too big. This is obviously a bad number to say the...
  25. Steve Crow

    What's wrong with a flat, empty, and expanding universe?

    I'm new to this impressive forum and have a question that may have been addressed a thousand times, but here goes. A FLRW metric is happy with a time-varying scale factor a(t) and zero curvature parameter k and could care less about density. The combination of a FLRW metric and the Einstein...
  26. Steve Crow

    What sparked Steve Crow's interest in cosmology?

    I'm Steve Crow, presently retired in Boulder, Colorado. I attended Caltech as both an undergraduate and graduate and got my PhD in 1966. The degree is in "Aeronautics and Applied Mathematics", but I have always been interested in physics, especially cosmology. I spent my career in aerospace...
  27. Armando Valle

    How do we know galaxies are exactly where we see them?

    i have a doubt, how do we know far away (light years) galaxies and planets are on the right spot we see them? if light takes a lot of time to reach the Earth it means we are seeing the past of the galaxy/planet. Example: If Earth is becoming extinct and we need to find an exoplanet 30,000 light...
  28. Luminescent

    Other Cosmological Discoveries: Seeking Verification and Guidance

    Hello everyone, Can anyone assist me with the following; I have derived some very interesting cosmological quantities within regard to radiation as it moves through space. I am looking for someone trustworthy who can help me verify my work and point me in the right direction without claiming...
  29. E

    Where to start learning cosmology

    What are the prerequisites you need to have under your belt before you start studying cosmology? And frankly due to my naïveté, I'm not sure of any interdisciplinary fields in cosmology so I know my question is vague
  30. E

    Physical cosmology learning sites

    Hi all! Where are some good places on the Internet where I can learn about physical cosmology? Specifically any good websites that are devoted to physical cosmology that you know about?
  31. RyanH42

    Is dark matter distrubition always near galaxies?

    Is there any dark matter where no baryonic matter (which here the galaxies).I mean are we observe dark matter only around the matter ? Or dark matter can be anywhere (In empty space which there's no baryonic matter around)
  32. RyanH42

    Dark Matter density given specific location

    I am doing research and I need to find the dark matter density of Galaxies or dust clusters (It can be any type of thing) which the distance from Earth will be ≅4000 Mpc.Here the picture Think the radius of sphere.
  33. bcrowell

    Will all matter be converted to photons?

    bcrowell submitted a new PF Insights post Will All Matter Be Converted to Photons? Continue reading the Original PF Insights Post.
  34. S

    I'm an armchair Science nerd, links for Quantum Cosmology?

    I've retired but have interests in Quantum mech. and Cosmology.
  35. O

    Dark matter particle search at CERN vs cosmology simulations

    Dark matter particle candidates are being searched at CERN and the various dark matter models are being probed by cosmological simulations. The usual way to probe models via cosmology is to plug a candidate into a cosmological simulation and then compare the results with observations. Yet...
  36. S

    Derivation of non decaying mode in cosmology

    Homework Statement Derive the following result : \phi_k=-C_1(k)\frac{\dot{H}(t)}{H(t)} . Homework Equations \phi_k=C_1(k)\Bigg(1-\frac{H}{a}\int\limits^{t}a(t)dt\Bigg) a(t)= a(t_i)\exp\Bigg(H_i(t-t_i)+\dot{H}_i\frac{(t^2-t_i^2)}{2}\Bigg) The Attempt at a Solution So I stuck a(t) into...
  37. C

    High School Freshman Cosmology

    Hello all! I've been instructed to construct a week long Cosmology class for High School Freshman. The class will run from about 8am-3pm everyday (with breaks and lunch or course). My first step in constructing this class is just to ask you guys what you would want to learn about...
  38. N

    Jobs to gain useful experience in astronomy/astrophysics

    Hey guys & gals, a long time lurker here. For a variety of reasons I have failed to secure a PhD position that I wanted this year after finishing my MPhys degree in physics, so I decided to take a year away from studying, regroup, work towards publishing a paper and then come back with full...
  39. H

    Cosmology Diff between Ryden's two 'Introduction to Cosmology' books?

    Barbara Ryden seems to have two Cosmology books, her one https://www.amazon.com/dp/0805389121/?tag=pfamazon01-20 and one https://www.amazon.com/dp/129203971X/?tag=pfamazon01-20. I haven't been able to find any differences between the books online - the 2013 book doesn't seem to be a new edition...
  40. ComaBerenices

    Proportions and other Stuff about Expansion

    I'm not too well read in cosmology, but I know the universe is presumed to be homogeneous in space but not in time, therefore the curvature of the universe can essentially be calculated under one mean. I just have a few questions about how the universe expands and whether some proportions are...
  41. RyanH42

    Newtonian Friedmann Equation, Referance frame, Homogeneity

    Hi all I want to ask a question about NFE(Newtonian Friedmann Equation).I know that NFE is not usefull to describe universe.But we can have a general idea about universe to use that formula. I know that the only spatial coordinate system is CMB referance frame and NFE is derived from...
  42. TrickyDicky

    Coordinate conditions in cosmology

    The FRW cosmology is a solution of the FRW that can be foliated into 3D isotropic and homogeneous slices. This foliation is implemented mathematically first by the use of a not generally covariant coordinate condition https://en.wikipedia.org/wiki/Coordinate_conditions#Synchronous_coordinates ...
  43. Berenices

    Are Universal Oscillations Causing Changes in Cosmological Expansion?

    Hey all, I was reading up on some discoveries made in cosmology. http://iopscience.iop.org/1538-3881/149/4/137/ This could easily be due to observational error, but I was wondering whether something such as this is possible in our current models of expansion and dark energy without having to...
  44. Christian Grey

    Which theory or field can explain this?

    Suppose I am in a room and light(photons) from the light bulb reach my eyes, or I am outside light(photons) from the sun reach my eyes and I am able to see the objects around me. I want to know what factors affect the path of photons like temperature, gravity etc.I mean by knowing these factors...
  45. A

    Does universe expansion separate photons, traveling parallel?

    I understand that the force of gravity prevents galaxies from expanding, as space increases. However, I question if universal expansion separates photons (electromagnetism), as they are traveling along parallel paths (Would the normal distance between them increase over time)? Thank you.
  46. I

    Master Thesis Topic: GR & Statistical Mechanics

    Hello! I am a master student, and I am about to start working on my master thesis, which, in my counrty, is a substantial work of 6 months which usually involves original research. I will be supervised by two professors of Statistical Mechanics, who have many research interest. In these days...
  47. K

    The Entire Observable Universe

    The entire observable universe is contained rather graciously in this wonderful picture, for your admiration.
  48. A

    What Comes Next After Secondary Education? A Senior's Dilemma

    I do not know what to write here, so I just going to say hi! I am Aura a senior 2016 and in this point of my life the time has come to make in my opinion "the most decisive" decision of my life.
  49. P

    Exploring Nature: Joining Discussions on Software Testing and Astronomy

    I am looking forward to joining discussions here. My Backgroud is 2 years "applied physics", 5 years education for teaching in visual communication (art), 15 years experience as a database software developer. Now I am looking for a job as a software tester. Software Testing is similar to being...
  50. S

    Are there current efforts on ritz-type cosmology?

    What is the status of ritz-type cosmology?
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