What is Cosmological: Definition and 432 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. C

    B Can Cosmological Constant contract (negative)?

    Hello... Can the cosmological constant become so rigid as to resist the 120 magnitude quantum contribution? Where is the mathematical terms for it in GR EFEs? is the effect like contraction instead of expansion? Because the 120 magnitude quantum contribution should immediately warp spacetime...
  2. C

    B What cancel the quantum contributions in Cosmological Const?

    Hi ive been googling but can't get the exact answer. quantum contributions give a calculated cosmological constant that is 120 magnitude more than observed.. what terms in the equation is supposed to cancel the 120 magnitude? in electrodynamics.. the bare mass cancels the virtual particles...
  3. J

    I Cosmological Constant Problem: Pre-Req Knowledge for Paper

    My professor wants to give me (and another kid) a problem in quantum cosmology. To that end, he asked me to read through his recent paper that appeared in the Physical Review Letters. He said that I should be able to go through it since all the paper employs is (quantum) scalar field theory...
  4. Clever Penguin

    B Cosmological data margins of error

    I am currently creating a database of all the known cosmological objects, and need to know the percentage error in the following data: Diameter of the sun: 1.3914x108 metres Mass of sun: 1.989x1030 kilograms I have the orbital period of the sun to be: 2.75x107± 9.1% years
  5. V

    A Systematic study comparing cosmological models?

    Hi, my question is if there exists a study systematically comparing different cosmological models in how well they fit the same standard cosmological data sets (CMB, luminosity, BOA, SNe, lensing,...). I can find very little besides LCDM. In the rare case of a comparison, it leads to...
  6. stevendaryl

    I Question about cosmological constant

    Einstein's field equations, with cosmological constant, can be written as: G_{\mu \nu} + \Lambda g_{\mu \nu} = \kappa T_{\mu \nu} I understand that some physicists think that the cosmological constant, rather than being a free parameter, might instead be an effect of quantum field theory. Does...
  7. mertcan

    I Cosmological Constant: Expanding Universe & Data Contradiction

    hi, I have been watching some "world science festival" videos on youtube, also there were a conversation pertain to whether or not the cosmological constant should be a constant. As far as I know, our universe is expanding with a positive acceleration measuring the red shifts, and it implies...
  8. whatphysics

    I What does cosmological redshift do to light

    I understand it's definition but i am unsure how it affects light. Does it slow light down? (is this even possible?) Does it stretch light's wavelength? Does it convert light into infrared? Does it make light brighter or dimmer? hmm. thank you for your kind help!
  9. F

    A Alpha Variation vs Cosmological Expansion: Basics Explained

    hello, My question will be quite naive for experts and reflects the fact that I'm new to the subject of varying the fine structure constant alpha and mainly need an introductory reference ... so if someone has a good one to advice ...thanks a lot i just don't understand the basics: how people...
  10. G

    I Question about the cosmological constant

    Layman here, please excuse my ignorance. I believe to understand the basics of SR, GR, cosmic expansion, etc but questions come to mind now and then. As I understand, dark energy, the cosmological constant, vacuum energy, whatever you may call it, remains a constant per space volume unit. Empty...
  11. marcus

    A Atoms Of Space, Gravity and the Cosmological Constant

    This Invited Review article just came out: http://arxiv.org/abs/1603.08658 The Atoms Of Space, Gravity and the Cosmological Constant T. Padmanabhan (Submitted on 29 Mar 2016) I describe an approach which connects classical gravity with the quantum microstructure of spacetime. The field equations...
  12. davidbenari

    Finding an upper bound for the cosmological constant

    Homework Statement (Working with geometrised units) Consider the EFE ##G^{\alpha \beta }+\Lambda g^{\alpha \beta} = 8 \pi T^{\alpha \beta} ## work out (using weak-field considerations) an upper bound for the cosmological constant knowing that the radius of Pluto's orbit is 5.9 x 10^12 m...
  13. marcus

    A Could an entropic force help explain size of the cosmological constant?

    When we measure the cosmological constant Λ what we are really doing is measuring the longterm value of the Hubble rate, namely H∞, the distance expansion rate that the present rate H(t) is seen to be declining towards and leveling out at. It's convenient to write distance expansion rates as...
  14. bcrowell

    I Anthropic Lower Limit on Cosmological Constant

    Piran et al., "Cosmic explosions, life in the Universe and the Cosmological Constant," http://arxiv.org/abs/1508.01034 I thought this was interesting. If I'm understanding correctly, the idea is that satellite galaxies such as the Magellanic Clouds have low metallicity, which causes them to...
  15. Einstein's Cat

    Accurate Measurement of Cosmological Constant Value

    Could anyone please recommend a paper that accurately gives the value of the cosmological constant? Or else may you reply with values of the cosmological constant that you would you use in your research? Any help would be very much appreciated.
  16. R

    Clearing up my Cosmological Confusion - what is expanding?

    As a layman, I have come to understand basic expansion (meaning without dark energy) as objects which are not locally gravitationally bound are moving away from each other due to some inertia created from an initial period of inflation. This rate of recession is the Hubble constant and it...
  17. Markus Hanke

    Gravitational Radiation and Cosmological Constant

    How come that, in the context of discussing the search for gravitational waves, I never see the cosmological constant mentioned ? We know that ##\Lambda \neq 0##, so this seems strange to me; in the presence of a non-vanishing constant, the background is not Ricci flat in the vacuum case, so...
  18. S

    Sigma_8 and n_s Cosmological Parameters

    Hi, I'm doing a project on galaxy clustering and in a lot of papers where they list the cosmological parameters they've used, they list σ8 and ns. Can anyone quickly tell me what these parameters are referring to? Thanks
  19. S

    Are Cosmological & Universal Constants the Same?

    Are the cosmological constant and the universal constant essentially the same?
  20. T S Bailey

    Cosmological expansion and uncertainty

    Firstly, I assume that I'm correct in assuming that since expansion is accelerating it will increase to any arbitrarily large value at some point in the future. If this is true, there must be some point at which particle/antiparticle pairs (due to uncertainty) are carried away from one another...
  21. R

    Some questions on the Cosmological Principle

    Firstly, I am just a very interested layman so please forgive my ignorance and non mathematical approach. As I understand it, the cosmological principle states that on larger scales the universe is homogeneous and isotropic. So could someone help me to understand the following: 1) Does this...
  22. J

    Does a rigid box of gas cool over cosmological timescales?

    According to standard cosmology theory the physical momentum p of both massive and massless particles decay like: $$p \propto \frac{1}{a(t)}$$ where a(t) is the scale factor as function of cosmological time t (for a derivation see page 12 in the following lecture notes...
  23. Isaac0427

    Cosmological constant times the metric tensor

    In the EFE, what does adding Λgμν mean and why is it not included in the Einstein tensor?
  24. Shadowclan

    How can I apply probability to the cosmological constant?

    Hello! me and my friends were discussing a few ideas earlier this week and then we suddenly started talking about Einstein's biggest mistake. I was a bit lost because I am not all that familiar with the Cosmological constant and I was wondering how can probability be applied to that mistake?? I...
  25. yazanhomsi

    Who First Conceived the Idea of the Cosmological Principle?

    Good day all, A question that I haven't really found the answer for yet: "Whom did first come up with the idea of the cosmological principle?" I almost looked everywhere for the answer but still cannot find it. Was it Friedmann or Lemaitre? Or was it some other great physicist? But there...
  26. bapowell

    Comments - Inflationary Misconceptions and the Basics of Cosmological Horizons

    bapowell submitted a new PF Insights post Inflationary Misconceptions and the Basics of Cosmological Horizons Continue reading the Original PF Insights Post.
  27. 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...
  28. yazanhomsi

    Dark energy and cosmological constant

    Hello everyone. I am having some problem with dark energy and the cosmological constant. The cosmological constant is a proposed form of dark energy. Alright, now the cosmological constant is is estimated by cosmologists to on the order of 10^-26 kilograms per cubic meters. But the density of...
  29. haael

    Susskind on supersymmetry vs. cosmological constant?

    In one book of Susskind I found the following claim and I wanted to ask for its basis. Susskind says that each kind of boson gives positive contribution to the cosmological constant (the lighter, the better). Each kind of fermion gives negative contribution to the cosmological constant. Thus...
  30. Jorrie

    Insights LCDM Cosmological Model in Simplified Math (Part 3) - Comments

    Jorrie submitted a new PF Insights post The LCDM Cosmological Model in Simplified Math (Part 3) Continue reading the Original PF Insights Post.
  31. RyanH42

    Has the Cosmological Constant Mystery Been Solved?

    I read a article now and It claims he found the cause of cosmological constant.Is that true ? The idea is actually good...
  32. Jorrie

    The LCDM Cosmological Model in Simplified Math

    If we restrict ourselves to a homogeneous, spatially flat LCDM universe model, the Friedman equations can be written a very simple form. Marcus posted several threads in a collaborative effort to develop the simplified approach. Here is a summary of the parts that seem the most informative, to...
  33. craigi

    New approach to cosmological bulk viscosity

    http://arxiv.org/abs/1409.4918 Abstract: We examine the cosmological consequences of an alternative to the standard expression for bulk viscosity, one which was proposed to avoid the propagation of superluminal signals without the necessity of extending the space of variables of the theory. The...
  34. sweet springs

    The sign of the cosmological term

    I want to know the sign of the cosmological term. It seems that in the left hand side of the Einsetein equation the cosmological term is -\Lambda g_{ik} for (+---) convetion or +\Lambda g_{ik} for (-+++) convetion. Right? Best
  35. S

    Cosmological Expansion: Is There a Limit?

    is there any limit to cosmological expansion?
  36. T

    Bekenstein bound on cosmological scales

    Except the extreme case of Black Holes, all other objects in the Universe (say, Galaxies) are very far from the Bekenstein bound (BB). Any object saturating the BB tends to be BH. But we can try to saturate the BB increasing the radius of a sphere. In flat static Universe, sooner or later we...
  37. wolram

    Baryon oscillation peak a cosmological standard ruler

    This came up in the arxivs and had me thinking can this be true? arXiv:1506.05478 [pdf, ps, other] Is the baryon acoustic oscillation peak a cosmological standard ruler? Boudewijn F. Roukema, Thomas Buchert, Hirokazu Fujii, Jan J. Ostrowski Comments: 4 pages, 2 figures Subjects: Cosmology and...
  38. B

    Interpretting the cosmological constant

    I am trying to wrap my brain around the idea of the cosmological constant, and how it gives the result of an accelerating universe. I have read different explanations for it, and in some it gives me the impression that it is an actual physical force, pushing everything away from everything...
  39. T

    Quantum entanglement on a cosmological scale?

    This is a physics question but since it is on a 'universal' scale, I will ask it here. Quantum entanglement. I was watching a panel discussion with Leonard Suskind and others leading theoretical physicists...also watched a Nova program presented by David Green, etc. In both there was a...
  40. T

    Value of Cosmological Constant

    Hi. I was just curious about the current value of the cosmological constant. My astrophysics class lecture notes say on the order of 10^-122, but the Wikipedia article says 10^-35 s^-2. Could someone explain where the 10^-35 s^-2 value comes from? Thanks!
  41. E

    Cosmological constant term and metric tensor

    Why cosmological constant term ##\Lambda g_{uv}## in Einstein equation is proportional to ##g_{uv}##. Why it is even proportional to ##g_{uv}## in spacetime of MInkowski?
  42. F

    Cosmological Redshift: Calculating Wavelengths

    Hi all! I've got a question about the cosmological redshift. We're given the metric ds^2 = c^2\,dt^2 - a(t)^2 \left[ dr^2 + r^2\,d\theta^2 + r^2\sin^2 \theta\,d\varphi^2 \right] Now light moves on null geodesics, so c^2\,dt^2 - a(t)^2\,dr^2 for radially moving light. For a GR exercise, we are...
  43. throneoo

    Cosmological and doppler redshift

    cosmological redshifts are caused by the metric expansion of space, whereas doppler shift is a result of relative velocities through space. So before the development of the modern cosmological models, how did astronomers originally distinguish these two causes of redshifts (e.g. when they tried...
  44. U

    How do I find the scale factor of cosmological constant?

    Homework Statement (a)Sketch how the contributions change with time (b)For no cosmological constant, how long will this universe exist? (c)How far would a photon travel in this metric? (d)Find particular density ##\rho_E## and scale factor (e)How would this universe evolve?[/B] Homework...
  45. U

    What Are the Steps to Solve the FRW Cosmological Model?

    Homework Statement (a)Find how ##\rho## varies with ##a##. (b) Show that ##p = \frac{2}{\lambda^2}##. Find ##B## and ##t_0##. (c) Find ##w## and ##q_0##. What values of ##\lambda## makes the particle horizon infinite? Find the event horizon and age of universe. (d) Find luminosity distance...
  46. S

    Godel Metric Cosmological Constant

    What is the cosmological constant for the Godel metric?
  47. A

    How to calculate cosmological constant?

    I reading book, part about gravity. It is Landau-Lifschiz, "Theory of field". And I trying to understand how to calculate cosmological constant. Re-read part with introduction of cosmological constant several times, still not understood. Let's imagine function of space curvature, without...
  48. Quarlep

    Cosmological Constant and Vacuum Energy

    I was reading a book about cosmolgy.And there wrotes vacuum energy must be higher than cosmological constant 10100 times to satisfy (It may just the opposite ) observations. Is that true ?
  49. thrush

    Cosmological vs. Relativistic Doppler Shift

    Does anybody know a good read/primer that compares the observed cosmological redshift values to predictions made by the relativistic (gravitational) redshift? Thank you!
  50. Y

    Adiabatic vs. Isocurvature cosmological perturbations

    Dear everyone, Now, I'm reading some papers on the "Curvaton Mechanism"(eg.http://arxiv.org/abs/hep-ph/0110002v2 as the original literature.) Here I have some confusion on this topic. (1) Why the primordial perturbation of curvaton field is initially isocurvature-type? When the inflation driven...
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