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. M

    Fully relativistic, cosmological N-body simulations

    Hi, as you all know, current cosmological N-body simulations (like the Millenium run) are based on the Newtonian limit. Gravitational fields are supposed to be rather weak and therefore the force between dark matter particles reduces to Newtonian gravity. Other relativistic effects are...
  2. jfy4

    Is the Cosmological Constant Truly Constant?

    Hi, I am wondering if the cosmological constant is a constant in the sense that it can only have one value, ie some constant element of the reals, or if it can be a scalar function too dependent on the coordinate variables, eg \Lambda(r,t). Thanks in advance,
  3. A

    Does the first law of thermodynamics apply to the cosmological universe?

    How can the conservation of energy be applied to the entire universe? How can we define the energy of the universe? Is this definition unique for different observers? What is the difference between the thermodynamics universe (system+environment) and the cosmological universe?
  4. L

    What does homogeneity mean (in the cosmological context)?

    First, I must stress that I am not asking this question in relation to the proof, or disproof, of any form of rotating Universe. I am only asking in order to understand the meaning of “homogeneity” in the cosmological context. Secondly, I know that there are many threads that reference...
  5. TrickyDicky

    Cosmological principle and quasar distribution

    Our cosmology model follows the cosmological principle according to which we are not in a privileged place in the universe and there is homogeneity, but if you take a look at the distribution of quasars in the universe there seems to be a "quasar spherical void" roughly one billion lightyears...
  6. K

    Variation of cosmological constant with time

    Hello, in the paper from sean carroll "the cosmological constant" we can read this: Does this variation of the cosmological constant after symetry breaking is considered as real and accepted in standard cosmology? I find very few talks about a varying cosmological constant, and it is about...
  7. C

    Cosmological Models Predicting Heat Death of the Universe

    I have read that some cosmological models predict a heat death of the universe. Eventually all matter (beggining with superclusters, clusters, then galaxies, then stars) will lose all energy and separate (due to expansion which will eventually occur even on a galactically local level) so that...
  8. Chronos

    The Value of the Cosmological Constant

    I found this new paper by John Barrow to be quite interesting: http://arxiv.org/abs/1105.3105 The Value of the Cosmological Constant Authors: John D. Barrow, Douglas J. Shaw (Submitted on 16 May 2011) Abstract: We make the cosmological constant, {\Lambda}, into a field and restrict the...
  9. narrator

    Start Learning Cosmological Math Today

    Hi all.. As my appetite grows, so does the knowledge of my lack of knowledge.. lol 30 years ago as an engineering student I picked up calculus quicker than I did the more simpler math. I think that has to do with it being far more interesting. Mind you, with a side-step in career, I...
  10. C

    Cosmological Inflationary Models

    I am doing a project in school and am looking up different cosmological models to research. I have found Steinhardt Turok Model, Kaluza Klein. I know these are not the best models, so I was wondering if there are any more specific models that I can look into.
  11. S

    Is the inverse-square law valid for all cosmological distances?

    Among the three Friedmann models k=-1,0,+1, the only model in which the inverse-square law is valid at all distances is that for k=0. In other words, its validity depends on the flatness of space. It is easy to show using the R-W metric with k=+1 that objects get magnified and that effect...
  12. andrewkirk

    DIfferential equation for understanding cosmological expansion -

    I am trying to understand cosmological expansion and how it is possible to see objects that are receding from us faster than the speed of light. This is explained in words at http://www.mso.anu.edu.au/~charley/p...DavisSciAm.pdf" and I have tried to describe a simple mathematical model to...
  13. R

    Inflaton Field, Cosmological Constants and Spacetime

    I can accept that spacetime has no substantial aspect to it because for General Covariance (Diffeomorphism Invariance) to be true, spacetime "points" can't be real or else General Covariance won't work. Now question. How does Inflaton Field and the Cosmological Constants for example interact...
  14. P

    Is vacuum energy really identical to the cosmological constant?

    When Einstein proposed the cosmological constant, it was regarded as an arbitrary constant having no connection with flat-spacetime physics (e.g. QFT to be invented later). IMHO the effective cosmological constant, in principle, should be the sum of QFT vacuum energy and Einstein's arbitrary...
  15. M

    How is the observed redshift caused by a recessional velocity?

    I know that the issue of cosmological redshift has been discussed in this forum before, e.g. https://www.physicsforums.com/showthread.php?t=368958", but I would appreciate any knowledgeable insights regarding the model outlined below. This model is only considering light in terms of a stream of...
  16. M

    Calculating travel times on cosmological scales

    OK I'm still new to cosmology and this question is bugging me: if a photon is emitted toward me from a distant galaxy at a distance D, how do I calculate the time it takes to reach me? I assume the universe is expanding exponentially with a DeSitter scale factor a = exp(Ht), (H = Hubble...
  17. D

    AdS/CFT correspondence and the cosmological constant

    Hi all, From what I understand AdS/CFT correspondence has been one of the most researched areas in string theory. I'd like to know if there has been any work done to relate this duality to the cosmological constant. As unrelated as they may sound, the expansion of space will change the...
  18. J

    A new cosmological model (re are we living in a black hole)

    I think my argument is better this way round. 1/ Assume that space is flat and that there is no cosmological constant. 2/ Assume that the size of the universe R is bounded by the distance a light beam travels in the age of the Universe t. Therefore: R = c * t Putting this into the...
  19. L

    Cosmological Constant: Exploring Two Different Models

    Since the discovery of an accelerating expansion in the late 1990s, the cosmological constant has been included in cosmological models for dark energy. Einstein included the cosmological constant to make the universe static. Dark energy makes the universe expand accelerating. So in the 2...
  20. C

    Cosmological Constant Problem / Vacuum Catastrophe

    By my understanding, the cosmological constant problem is that the computed vacuum energy by quantum field theory (in the form of virtual particle pairs) is far larger than the measured vacuum energy density. Would it not seem to solve the problem with dropping the proposed mass of "virtual...
  21. A

    Einstein Equation with Cosmological Constant & Variable x^u

    with the action \int (k(R- 2 \Lambda)+L_m) \sqrt{g} the Einstein equation is: R_{uv}-\frac{1}{2}R g_{uv}- \Lambda g_{uv} = k' T_{uv} How is the Einstein equation if \Lambda=\Lambda(x^u)? with x^u a coordinate
  22. I

    Two dimensional anti de Sitter space without cosmological constant?

    I have a spacetime which is (I think) AdS_2. The metric is, I'm trying to find the Einstein tensor, defined as, and the result is zero! I thought that, for the AdS spacetimes I needed to have a nonzero Einstein tensor which is caused by the cosmological constant. What is wrong...
  23. S

    Unravelling the Mystery of "Faint Regime" in Cosmological Explosions

    What do they mean with "faint regime", when they talk about cosmological explosions?? (e.g X-ray flashes) thnx
  24. H

    Smolin's Cosmological Natural Selection: How does it help the problem?

    Alright, admittedly I'm a noob at LQG, but I have a basic question. The cosmological natural selection, as I understand it, is that universes are born from singularities (or something close) inside of black holes and 'bounce', inflate, and become universes like our own. But what spawned this...
  25. tom.stoer

    Questioning the cosmological principle

    The cosmological principle essentially says that there are no preferred locations and directions in the universe (homogenity and isotropy). We know that strictly speaking this principle is violated at the accessible scales (filaments, galaxy clusters and supercluster, voids, CMB). So one could...
  26. I

    Cosmological Constant: Dark Energy vs Gravity Ratio

    The cosmological constant has been a debated issue for a century... What if the constant is a ratio of the Force of dark energy to the force of gravity just like in a spring where the resistivity is the ratio of the force of gravity and the spring.
  27. bcrowell

    Post-2004 work on cosmological natural selection?

    I'm going to do a little popular-level talk for undergraduates (not necessarily science majors) on baby universes, cosmological natural selection, and Penrose's cyclical universe. The most recent substantive paper I have on CNS is this: Smolin, "Cosmological natural selection as the explanation...
  28. A

    Cosmological principle paradox?

    The cosmological principled as applied to modern cosmology and the standard model concerns only the spatial part of spacetime, this has been criticized based on Minkowski's predicated non-separability of spacetime, that led(among other things) to the "perfect cosmological principle" that...
  29. S

    How Do Objects Appear 14 Billion Light-Years Away in the Universe?

    Oops: Just discovered the Cosmology forum. Sorry for posting in the wrong area. (Can edit but don't see a way to move and delete.) I hope this isn't a really dumb question and that it is appropriate for this forum. Here goes: We look out in the night sky and see objects which are roughly 14B...
  30. J

    Cosmological Constant and Conservation of Energy

    The cosmological constant, or dark energy if you prefer, can be thought of as energy inherent in free space. This energy density is thought to be constant, and the volume which it occupies grows as space expands. The more this happens, the more dark energy comes to dominate the universe...
  31. B

    Light Speed & Expanding Galaxies: A Cosmological Mystery

    If galaxies aer expanding fast than the speed of light how are we able to see them. At the moment this expansion surpassed the speed of light shouldn't these galaxies dissappear or remain unchanged visually?
  32. heusdens

    Kalam cosmological argument & Refutation

    Anyone familiar with the Kalam cosmoligical argument, and has a valid refutation. [I have one, will post it later on] For Kalam cosmological argument, see Wikipedia
  33. nicksauce

    New Barrow paper - A New Solution of The Cosmological Constant Problems

    New Barrow paper - "A New Solution of The Cosmological Constant Problems" http://arxiv.org/abs/1007.3086 Anyone care to comment? I haven't taken too careful of a look yet, because it is late, but I'll try to write a response to it tomorrow.
  34. L

    Pioneer spacecraft - what cosmological direction are they travelling?

    Can anyone tell me how I could find out the exact direction that the Pioneer spacecraft are travelling? I need to figure out what direction they are traveling relative to the cosmic microwave background radiation. Thanks. ( http://en.wikipedia.org/wiki/Pioneer_anomaly )
  35. J

    Minimal mass from cosmological constant?

    I'm not sure in which forum this should go, but I hope this is close enough. I recently realized that the lightest neutrino could be close in mass to the fourth root of the cosmological constant and found out I'm (unsurprisingly) not the first one to think of this after some googling. The...
  36. P

    Cosmological Constant: QFT and Existence Explained

    How QFT might possibly explain existence of cosmological constant. Does it predict that vacuum stress energy tensor has on it's diagonal positive time component (density of energy) and negative spatial components (preasure=-density)?
  37. N

    Cosmological Redshift in FRW Coordinates – Energy Conservation & Time Dilation

    I want to discuss energy conservation and time dilation relative to the cosmological redshift. Because the elements of the redshift are coordinate specific, I’ll focus just on the FRW metric using proper distance coordinates (not comoving coordinates). As explained in Tamara Davis’s cover...
  38. S

    Is the Cosmological Principle a Product of Our Perceptions or a Universal Truth?

    How do we know that the universe is isotropic and homogeneous and why do we succumb to accepting that there is no special place in the universe that is the center? Since if everything is expanding from everywhere else at the same rate, there is still going to be a point center where everything...
  39. N

    Uncovering the Radiation of Cosmological and Black Hole Horizons

    Here I had been thinking the Unruh horizons and specifically black hole horizons were the only (thermal) radiators. Now I notice Leonard Susskind says in THE BLACK HOLE WAR that the cosmological horizon also radiates...but "inward" towards us. If a thermometer on a string were extended close...
  40. TrickyDicky

    Cosmological redshift and doppler redshift

    I am a bit confused here. Is cosmological redshift the same as doppler redshift? This is from wikipedia: "The redshift z often is described as a redshift velocity, which is the recessional velocity that would produce the same redshift if it were caused by a linear Doppler effect (which...
  41. N

    Cosmological argument in 1st order logic?

    So I've been discussing this alleged proof with another person, and I was wondering what are the issues with Dr. William S. Hatcher's proposal. His entire process can be found http://www.onecountry.org/e102/e10214xs.htm", but it can be summed up into three axioms 1) Principle of sufficient...
  42. A

    Cosmological redshift as a Doppler effect or metric evolution?

    In several threads where I've seen the redshift issue discussed there's been some confusion about this point, Must we treat cosmological redshift as a purely kinematic (relativistic)doppler effect or as the time dymamics of the metric space? Or both views can be made to converge?
  43. K

    Cosmological Models: Exploring Common Models

    Which of the common cosmological models do you prefer and why? Assume we don't know which if any of the models is the actual one that matches the universe.
  44. F

    Temperature of Cosmological Constant

    Is there a temperature related to the cosmological constant? As I understand it, the cosmological constant is produced by dark energy and is a form of zero point energy created by virtual particles and antiparticles being created and annihilated all the time. It seems to me that this process...
  45. I

    Cosmological expansion question

    I am working off the premise that: If Cosmological expansion is really occurring a redshift (as we currently observe) can only be obtained if (stars, planets, atoms) do not expand. See Misner, Thorne and Wheeler comment: "Only later does he realize that the atom does not expand, the...
  46. K

    Cosmological Redshift: Why Does k Remain the Same?

    condidering a photon in expanding cosmos, it 's said that the wavenumber k remains unchanged, the wavelength \lambda increases, proportional to the scale factor a(t) of the universe, and the frequency w decreases in the opposite way, that is the cosmic redshift. so, why does k...
  47. A

    The cosmological constant is always dimensional less?

    the cosmological constant is always dimensional less? in the randall sundrum models the tension of our brane is T=24M^3_5 \sqrt{\frac{-\Lambda}{24M^3_5}}...the sub index of M is the number of dimension of space time and the supercript is the power. ¿whats units have the Planck scales...
  48. J

    Is the cosmological constant constant?

    In a flat, matter-dominated universe the cosmological constant is zero and the scale parameter a increases according to a two-thirds power law. In such a universe, the expansion of the universe gradually slows down (but never stops). In recent years it has been discovered (?) that the rate of...
  49. V

    Cosmological redshift and photon energy loss in SR

    This might be a tired topic but please help me to understand. Assume a photon moving in vacuum, ignore potential interstellar medium absorption and re-emission since it is not relevant to discussion of space expansion in this context. Redshifted photons will undergo energy loss between *right...
  50. T

    Cosmological Constant: Why Lambda Units are 1/m^2

    Why are the units of the Cosmological constant Lambda 1/m^2? is this just convention to make the density parameter unitless?
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