Cosmological Definition and 433 Threads

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. D

    B Cosmological Redshift in Simulated Universe

    Suppose we have a simulated universe in which the observable portion (a collection of galaxies) is climbing out of a gravitational well at a very high fraction of the speed of light. The gravitational well is caused by a very large, accreting black hole outside of the observable portion. The...
  2. elcaro

    I Cosmological expansion of space - question

    I the lambda-CDM model, is the expansion of spacetime uniform around all of spacetime, is there a smooth transition between expanding parts of spacetime (the voids) and non-expanding parts of spacetime, or is there a sharp distinction between expanding and non-expanding parts of spacetime. Is...
  3. M

    I Expansion of the Universe and the cosmological principle

    Wikipedia states the following in their article about the expansion of the universe: If the cosmological principle was discovered to be false in our universe, i.e. our universe was discovered to be inhomogeneous or anisotropic or both on very large scales and the FLRW metric does not hold for...
  4. D

    I QFT vs GR Cosmological Constant

    I am sorry but I can't seem to find the actual estimated value of the cosmological constant that is predicted by quantum field theory. Can anyone help me and tell me the approximation of that value and/or the value of the approximate observed cosmological constant that physicists today think...
  5. S

    I Expansion-Collapse cycle in cosmological structures?

    Concerning cosmological structures (like galaxies, clusters of galaxies, gas bodies, superclusters...etc) if the elements that make them are close enough they will be attracted towards each other by gravity. Contrarily, if they are sufficiently far apart they will get further away following the...
  6. N

    I Einstein's General Relativity w/o Cosmological Constant

    I mean, what's "general relativity but without the cosmological constant term" (##G_{\mu \nu}=\kappa T_{\mu \nu}##) called?
  7. F

    A Coefficient correlation between 2 cosmological probes

    Hello, I have the demonstration below. A population represents the spectroscopic proble and B the photometric probe. I would like to know if, from the equation (13), the correlation coeffcient is closed to 0 or to 1 since I don't know if ##\mathcal{N}_{\ell}^{A}## Poisson noise of spectroscopic...
  8. AndreasC

    I Exploring the Cosmological Constant Problem & Zero-Point Energy

    Reading the Wikipedia page on it, one reads: But on the other hand, as far as I know and if I'm not mistaken, zero point energy is not a physical thing, and it is merely a mathematical artifact in QFT. Someone correct me if I'm wrong on that. So if that is the case, then why is it a "problem"...
  9. S

    I Deviations of conservation laws in cosmological evolution?

    If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an expanding accelerating spacetime (like it happens in our Universe), are there any observations of deviations from the strict conservation laws in the evolution and formation of...
  10. Buzz Bloom

    I How does the symbol Λ cosmological constant relate to Ω_Λ or ρ_Λ?

    My references are: https://en.wikipedia.org/wiki/Friedmann_equations#Detailed_derivation https://en.m.wikipedia.org/wiki/Cosmological_constant Ω_Λ is a term in the Friedmann equation along with terms for radiation, mass, and curvature. Λ is the coefficient of the term g_μν in the Einstein field...
  11. Safinaz

    I The Units of the Cosmological Constant: eV^2

    In natural units, it’s known that the unit of the cosmological constant is ##eV^2##. I don‘t get why in this paper : https://arxiv.org/pdf/2201.09016.pdf page (1), it says the value of ##\Lambda \sim meV^4##, this means ##\Lambda \sim (10^6 ~ eV)^4 \sim 10^{24} eV^4 ##, shoud not the unit ##eV...
  12. zrek

    B Experimental evidence on cosmological redshift

    The space expands due the dark energy, so the light wavelength also stretches during its journey between galaxies, causing a measurable redshift. How can I argue that this is the right reasoning for the measured redshift? What if someone states that the photon maybe simple loses its energy over...
  13. Alpha2021

    A Graceful exit of a cosmological inflation model

    How to determine whether a cosmological inflation model (say single-field slow-roll inflation) gracefully exit or not? Is it like showing that inflation is ending at some value of inflaton?
  14. Amaterasu21

    I Energy conservation in Doppler (NOT cosmological) redshifts?

    Hi all, My question is about Doppler redshifts, but I'm going to mention cosmological redshifts first because I'm a lay person as far as cosmology's concerned (I'm an amateur astronomer and did a few introductory astrophysics/cosmology courses at university, but my degree focus was planetary...
  15. K

    I Are two-body orbits with a cosmological constant unstable?

    For background, consider this paper, which describes circular orbits for the two-body problem in the presence of a cosmological constant: https://arxiv.org/abs/1906.05861 What they describe is a system with three regimes of behavior: stable circular orbits below a certain radius, unstable...
  16. Gary0509

    I Cosmological Positioning - How does one determine?

    Thought experiment I'm wondering if anyone has explored yet. Imagine by whatever means you like, that your spaceship plucks you out of our solar system and drops you at another random point in the observable universe. Due to light speed limitation, where ever you end up will be looking at our...
  17. Kwantumnaut

    Accurate depiction of cosmological redshift?

    Summary:: Accurate depiction of cosmological redshift? Hello. I'm thinking about getting a tattoo representing cosmological redshift, and just wanted to make sure my custom image is correct and accurate, and if you would recognize and be able to tell what it represents. If not then any...
  18. jordy1113

    I What are the Cosmological monopole and dipole?

    Hi there I'm currently studying cosmology but I'm having a hard time grasping that concept of the cosmological monopole and dipole (quadrupole etc) and was wondering if someone could explain what they are conceptually and physically. Thanks : )
  19. elcaro

    I Cosmological principle about space and time

    AFAIK there is no cosmological principle formulated about space and time. If it would be formulated, it would more or less state that spacetime is an interconnected whole, and has no gaps, edges or boundaries. It doesn't need to state wether spacetime is finite or infinite, that is an open...
  20. J

    I How well do cosmological models explain the observed µ vs. z data?

    The following figure shows observed distance modulus (µ) vs. redshift (z) data (references of data sources are available): How well do cosmological models, such as ΛCDM and models based on non-expanding universe, explain these observed data? For explanation of terms, please see, Type Ia...
  21. S

    I Does the CMB reference frame violate the Cosmological Principle?

    Studies of the Cosmic Microwave Background shows that the Earth is moving roughly 380 km/s with respect to it towards the constellation Leo I think. Yet (I think) the Cosmological Principle and the Michelson-Morely experiments suggest there is no preferred reference frame in the universe --...
  22. J O Linton

    B What is the distance at which gravity and the cosmological force are equal?

    In considering the excellent answers given to my previous query about a photon in a box, I was led to consider what force was needed to hold the walls of the box stationary (w.r.t. an inertial observer inside the box.). If you place a mass m on the end of a very long string of inextensible...
  23. N

    A Relationship between energy density and cosmological constant

    According to the wiki entry on Planck units, https://en.wikipedia.org/wiki/Planck_units, the energy density of the universe, 1.8 × 10−123, is 1/16th the cosmological constant, 2.9 × 10−122. Is there a theoretical reason for this precise relationship?
  24. mfb

    I New cosmological neutrino mass constraint: sum<0.09 eV at 95% CL

    arXiv: On the most constraining cosmological neutrino mass bounds From neutrino mixing we know that an inverted order (two "heavy" neutrinos, one light neutrino) needs a sum of masses of at least ~0.09 eV, while the normal order (two light, one "heavy") can have a sum as low as ~0.05 eV. The...
  25. J O Linton

    B Cosmological Red Shift in a Perfectly Reflecting Box

    When a photon travels from a distant galaxy to us it undergoes an increase in wavelength due to the expansion of the universe during the time of flight. On the other hand, physical objects such as atoms and galaxies do not undergo a similar expansion because they are bound together by...
  26. M

    A New string formulae for Higgs mass and cosmological constant

    https://arxiv.org/abs/2106.04622 Calculating the Higgs Mass in String Theory Steven Abel, Keith R. Dienes [Submitted on 8 Jun 2021] There are at least two properties of the Higgs mass one might hope to explain with such a fundamental calculation: its criticality, and its participation in...
  27. J

    B Cosmological constant for the Universe's expansion

    Astronomers1) tell us that a 'cosmological constant' can account for the universe's increasing expansion. Representing the universe by a symbolic expanding ring, Fig.a, at an instantaneous radius r the inward gravitational force varies as the inverse square of this radius, giving Fg ~ 1/r^2...
  28. E

    A Cosmological gravitational waves

    The exercise is to derive the form of the symmetric, trace-free and transverse gravitational wave perturbation ##\hat{E}_{ij}## to the FRW metric$$ds^2 = a^2(\tau) \left[ -d\tau^2 + (\delta_{ij} + 2\hat{E}_{ij})dx^i dx^j \right]$$First step is to figure out the connection coefficients, which are...
  29. A

    I Recession Velocity near Cosmological Boundary: Hubble's Law?

    I'm confused whether Hubble's Law applies to objects near the cosmological horizon (CH). I'm told that objects asymptotically approach the CH and freeze there (v -> 0) in the same way that occurs during in-fall towards a black hole. But Hubble's Law says that velocity is proportional to...
  30. Ranku

    I Spatial flatness and cosmological constant

    Was the universe always spatially flat due to the presence of the cosmological constant, or has it become flatter in the late-time universe?
  31. T

    B Request for an up to date list of cosmological theories

    Is there an up to date list of all cosmological theories resource which provides some or preferably all of the following information: Which theories are considered speculative and even highly speculative? (degree 1 to 4) Which theories are still actively being worked on and roughly how many...
  32. DuckAmuck

    I Einstein Field Eqns: East/West Coast Metrics

    My questions is: Depending on which metric you choose "east coast" or "west coast", do you have to also mind the sign on the cosmological constant in the Einstein field equations? R_{\mu\nu} - \frac{1}{2} R g_{\mu\nu} \pm \Lambda g_{\mu\nu} = \frac{8\pi G}{c^4} T_{\mu\nu} For example, if you...
  33. Cerenkov

    B How does the cosmological constant affect gravitational collapse?

    https://www.physicsforums.com/threads/what-are-the-best-parameters-for-lcdm.831858/ Hello. In the above linked thread from 2015 Science Advisor Chalnoth replies to Earnest Guest. First, the cosmological constant has been a component of General Relativity pretty much from the start. The way...
  34. S

    I What "space" is used in defining cosmological distributions?

    I assume 3-D cartesian space is not an adequate description for things at the cosmological scale. So what definition of "space" is used when people talk about things like the distribution of hydrogen atoms "in the universe"?
  35. Buzz Bloom

    I Contradictory Cosmological Values: Crisis for Cosmology?

    These two independent sources have cosmological values that seriously contradict each other. The article "Planck evidence for a closed Universe and a possible crisis for cosmology" https://www.nature.com/articles/s41550-019-0906-9 arXiv:1911.02087v1 [astro-ph.CO] 5 Nov 2019 gives as the...
  36. jk22

    I Exploring Cosmological Constants

    Can we explain the cosmological constant in this way ? The Einstein tensor is derived from the Ricci tensor and one property is that, like the stress-energy tensor, its covariant derivative shall vanish. Since the covariant derivative of the metric vanishes it can be added to the EFE as...
  37. C

    A The Cosmological Principle means infinite Observable Universes

    I am posting to ask for any comments about a couple things. I will post a link to a thread on another forum about this. and would love to hear any and all thoughts about it. the thread begins asking about 2 things. the first one is about how fast we are moving. I,402,00 mph relative to the CMB...
  38. P

    A How to see if a cosmological model is flat?

    The RW metric reads $$ds^2 = -dt^2 + a^2(t) \Big( \frac{dr^2}{1-kr^2} + r^2 d\theta^2 + r^2 sin(\theta)^2 d\phi^2 \Big)$$ The value of k determines the model is flat/open/closed. But say if we have a model on a completely different form, with no explicit k-dependence. How would I determine if...
  39. G

    I The Cosmological Principle and the Universe

    The cosmological principle seems to hold well, and would imply an infinite amount of matter in the universe if the universe is flat and unbounded
  40. Arman777

    Cosmology Book suggestion about Cosmological Density Perturbations

    I am trying to find some nice explanatory books about cosmological perturbation theory. I looked at Longair, Peacock, and Liddle. Even their level is nice, it seems to me that they are explaining things in a bit complicated way. Is there a nice textbook, articles, lecture notes that you guys...
  41. Arman777

    I Calculating the Maximum total neutrino mass by using cosmological boun

    In an article its written, $$\Omega_{\nu} = \frac{\rho_{\nu}}{\rho_{crit}}=\frac{\sum m_{i,\nu}n_{i,\nu}}{\rho_{crit}} = \frac{\sum m_{\nu}}{93.14h^2eV}$$ Now I am trying to derive this for myself but I could not. Can someone help me ? So the values are, ##\rho_{crit} = 1.053 75 \times...
  42. Arman777

    I Some questions related to the Cosmological Constant

    In Barbara Ryden's introduction to cosmology book its written that "Introducing ##\Lambda## into the Poisson's equation allows the universe to be static, if you set ##\Lambda = 4\pi G\rho##" Then later on, in the book energy density of the ##\Lambda## defined as ##\epsilon_{\Lambda} =...
  43. AshPowers

    I Cosmological scale and the pressure of light....

    One of the things I have yet to come across in the explanation for the expansion of the universe is the effect of light... Most all of the matter we observe out there are stars - fusing nuclei and radiating EM energy in incomprehensible quantities... And this has been happening since the dawn...
  44. George Keeling

    I Have I got the right picture for cosmological redshift?

    Summary: I have a question on cosmological redshift which I have just learned about from Sean Carroll. After calculating it for an expanding universe he does a thought experiment to show that it is different to Doppler redshift which would be detected if two galaxies were flying away from each...
  45. phyzguy

    A New paper on the cosmological constant

    I'd be interested to hear comments from the forum on this paper. Is it a significant step forward? I haven't been able to make up my mind.
  46. QuarkDecay

    A Friedmann-Robertson-Walker Models

    Can we say that a universe with a radiation density (only) exists only in near a Big Bang time, and not a Big Crunch? Since it gets much smaller as time passes. For example in here: http://www.nat.vu.nl/~wimu/Varying-Constants-Pictures/Time-Scale-Universe.jpg We have different cosmological...
  47. S

    A Is Seth Lloyd's cosmological model background independent?

    I have been interested in Seth Lloyd's cosmological model (which proposes that the universe is a some kind of quantum computer or at least similar to it: https://en.wikipedia.org/wiki/Programming_the_Universe, https://arxiv.org/abs/quant-ph/0501135) since long ago. I was wondering if his...
  48. Buzz Bloom

    I Question about the Cosmological Constant

    I am hoping someone can explain to me why the constant Λ has units 1/m2. In the article https://en.wikipedia.org/wiki/Cosmological_constant In the Equations section, the following equation is presented. Do tensors have dimensions? If so, can someone tell me what the dimensions are for these...
  49. Ranku

    I Cosmological constant and structure formation

    How much impact does the presence of the cosmological constant have on the formation of structures in the universe? On a larger scale, is there less structure formation because of the presence of the cosmological constant?
  50. F

    A Forecast with Fisher formalism : loss or gain of information

    In the context of a forecast, I am currently working on Fisher's formalism which is part of a more general theory, that of information. My problem applies to estimating cosmological parameters from input data with the Fisher formalism and recipes to build a Fisher matrix. The context is...
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