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.
I am interested in the topic of vacuum phase transitions in models of the universe. One popular instance of this is a vacuum decay from a metastable vacuum energy level to a "true" one (in which the vacuum would sit at the lowest possible energy level depending on the model)
I have 4...
So a bit of context, I've been trying to model a plot of energy density relation for radiation and Primordial BH, but it is not right. Would someone be able to help me out? This is what I have so far. I am assuming the PBHs decay into a Planck relic, and the decay is instantaneous. Does the...
I've been told that very energetic cosmic rays could cause a vacuum phase transition or vacuum decay (and even could cause a true vacuum level to go "uphill" to a false vacuum) due to their high energy levels.
I've found some references supporting this claim [1], [2], [3], [4]
But also one...
The cosmological redshift is generally assumed to be due to space expansion.
But if spacetime is locally flat Minkowskian then surely photon wavelength should not change?
I would love to hear from you if you have any suggestions, feedback, or criticism. The goal is to build better and more sophisticated software that would push the boundaries of research in astrophysics!
I know that cosmology usually deals with general relativity but what about QFT, is it modified depending on the cosmological model? Or is it not something that change with the model used.
Would it be possible to eventually have structures made from neutrinos somewhere in the universe, as it is indicated in this question (https://physics.stackexchange.com/questions/80390/are-neutrino-stars-theoretically-possible), like halos of neutrino gas surrounding the center of galaxies...
In the paper, the authors argue that a closed system can exhibit features of an open system one of the being the non-conservation of energy, my questions how can a closed system have non-conservation of energy. (I know in GR, conservation of energy is subtle issue but it doest seem like the...
In the context of cosmology, you can perturb around the FRW background, conventionally:$$g = a^2(\tau)[(1+2A)d\tau^2 - 2B_a dx^a d\tau -(\delta_{ab} + h_{ab}) dx^a dx^b]$$with ##a,b## being spatial indices only (1,2,3). You can do gauge transformations ##\tilde{x} = x + \xi## of the coordinates...
A very massive charged black hole could reach a near-extremal state in the right conditions supressing the rate of emission of Hawking radiation (https://physics.stackexchange.com/questions/490524/evaporation-of-large-charged-black-holes)
Meanwhile, the radiation emitted by a black hole can be...
I appreciate Sabine Hossenfelder's latest video, and thought I would assemble some references. There's a mix of particle physics and cosmology topics. In general, the coincidences mentioned are mainstream topics in cosmology, whereas the particle physics coincidences are not.
1) Proton/electron...
Dr. Smethurst summarizes the latest results of the DESI collaboration. What I found especially interesting is that the current value of the Hubble constant that they obtained from baryon acoustic oscillations is in good agreement with the value obtained from Lamda-CDM using Planck data.
I was thinking about this paper (https://arxiv.org/abs/1405.0298) where the authors argue that there wouldn't be dynamical quantum fluctuations in a De Sitter space as fluctuations would be static once all perturbative radiation escapes the horizon (in the case that the Universe has a finite...
I'm studying if there is some way to avoid black hole evaporation, even if it requires a very special set up of conditions...
Theoretically, extremal black holes (both for rotating Kerr and Reissner-Nordström ones) would avoid evaporation as they would not emit Hawking radiation. Since...
I'm trying to linearize (first order) the Euler's equation for a small perturbation ##\delta##
Starting with ##mna (\frac{\partial}{\partial t} + \frac{\vec{v}}{a} \cdot \nabla ) \vec{u} = - \nabla P - mn \nabla \phi## (1)
##\vec{u} = aH\vec{x(t)} + \vec{v(x,t)}##
Where a is the scale factor...
I was reading these papers by Sean Carroll (https://arxiv.org/abs/1405.0298; https://arxiv.org/abs/1505.02780) in which, among other things, he argues against vacuum up-tunneling occurring in the universe. He only acknowledged that it would be possible in the first moments of the universe while...
I've found this discussion (https://astronomy.stackexchange.com/questions/43525/is-there-an-equivalent-of-the-red-shift-effect-for-cosmic-rays) where it is said that there is an equivalent redshift of cosmic rays due to the cosmic expansion
However, how can this be? Cosmic rays are not EM...
I found this paper (https://arxiv.org/pdf/hep-th/0211160.pdf) which argues against the possibility of a decay from a metastable vacuum to a true vacuum state. However, this is the first time I've read this. Is it then impossible that a vacuum decay from a false vacuum may occur (even in...
Roy Kerr has recently written a preprint (https://arxiv.org/abs/2312.00841) in which he strongly argues against the possible existence of singularities inside Black Holes.
I've read that his arguments are really powerful and that he is most likely right.
But, does it mean that Kerr has...
According to some papers I've found [1], [2] expanding voids can be found inside clouds of denser materials that can cause them to eventually collapse. I have a question about this:
Overdensities generally expand up to a given turnaround radius and then collapse. However, as the elements in the...
CMB photons can be affected by the expansion of the universe through the linear integrated Sachs-Wolfe effect (ISW) [1] and the non-linear ISW effect or also called Rees-Sciama effect [1].
In particular, according to the ISW effect, the photons crossing superclusters would leave them having a...
Hi! I'm new here! Let me introduce myself!
I am Thomas and I have always been interested in science, cosmology and physics.
Anyway, I have an equally strong passion for arts and humanities, and after all I decided to form myself as a journalist, which is my daily job.
After years and years, I...
I would like to ask you some questions I have about some interesting work I was reading (https://arxiv.org/abs/1205.4238 & https://academic.oup.com/mnras/article/527/4/11962/7457744) where the authors analysed the effects of dark energy in the shape and evolution of voids
Apparently, they...
Hi,
I'm currently reading the introduction to cosmology second edition by Barbara Ryden and at the page 105, the author says we get ##t_0 - t_e = H_0^{-1}[z - (1 + \frac{q_0}{2})z^2]## by inverting ##z = H_0(t_0 - t_e) + (1 + \frac{q_0}{2}H_0^2(t_0 - t_e)^2)##.
However, I can't figure out how...
Quanta Magazine recently published "Clashing Cosmic Numbers Challenge Our Best Theory of the Universe"
I am no fan of Quanta and I am not a cosmologist but there is certainly the increasing buzz that something is wrong with ##\Lambda##-CDM and cosmological models thanks to the JWST. Is...
im reading through the sparc data and the accompanying scientific paper
SPARC: MASS MODELS FOR 175 DISK GALAXIES WITH
SPITZER PHOTOMETRY AND ACCURATE ROTATION CURVES
right now defining terms is my biggest problem
the reading through i come across the scale length' references are pg page, c...
New to the forum, hoping to study as much physics as I can understand. Atomic science interests me, and so does cosmology - but i'm still so new that I don't know enough maths for the latter, and havent got much knowledge on the former aside from gcse chemistry which was over 10 years ago
Please select up to 3 members who were most impactful in the Astronomy and Cosmology forums in 2023. This is a popular vote. Polls were created by weighing activity and measure of helpfulness. Everyone nominated should feel honored. Many more could be added to this poll, we can never...
Dark Energy puts a constrain on the size of overdensities (like clusters and superclusters of galaxies) and their growth.
A higher Dark Energy density would reduce the radius of the zone where matter would be gravitationally bound, because more Dark Energy density would mean that objects would...
I have a table of densities of galaxies :
Expected number density of galaxies for photometric survey per unit area and redshift intervals, ##\mathrm{d} N / \mathrm{d} \Omega \mathrm{d} z\left[\mathrm{sr}^{-1}\right]## and the corresponding density of galaxies per ##\operatorname{arcmin}^2## for...
I have a question about this work called "Dark energy and key physical parameters of clusters of galaxies"*There, towards the end, the authors talk about the isothermal velocities and tempreature parameters of the gas and particles circulating between galaxies in clusters. In particular they...
Hello, I have asked a similar question before, but this time I want to ask it a bit differently to be understood better.
I am a physics student at a university and this semester I am going to make a term project about Dark Matter Density Distribution by using rotation curves. However, I am a...
Is there a neat way to "not" run the internal Boltzmann solver (for perturbations) in CLASS code and rather just solve for the background quantities? This way I can save the time otherwise spent in evaluating the perturbations and transfer functions. I am only interested in the time evolution of...
I recently found a question in a physics discussion site [1] about whether there was a "distance" between two galaxies where both the gravitational force and the influence of dark energy would be balanced. The answers and comments seem to indicate that there is indeed such a "radius" around a...
Hi.
I'm not sure if this should be in Cosmology or Astronomy - a moderator can feel free to move it if required. Also the prefix (study level) may be an I or an A, you can change that, just thought I'd get a bigger audience with an I. I'm trying to read this paper:
"The Inner Structure...
I have found some papers (like this one: https://www.aanda.org/articles/aa/full_html/2009/45/aa12762-09/aa12762-09.html) which say that dark energy increases the potential energy in a system of a quasi-stationary gravitationally bound many-body system.
It also says that because of this, the...
1) In a cosmology context, when I add a centered Poisson noise on ##a_{\ell m}## and I take the definition of a ##C_{\ell}## this way :
##C_{\ell}=\dfrac{1}{2\ell+1} \sum_{m=-\ell}^{+\ell} \left(a_{\ell m}+\bar{a}_{\ell m}^{p}\right)\left(a_{\ell m}+\bar{a}_{\ell m}^{p}\right)^* ##
Is Poisson...
Suppose the universe were to eventually collapse in a Big Crunch [1]. How closely could the universe's final moments resemble those at the beginning of the universe? Could the universe return to its original state exactly in some kind of "Big Crunch" or "Big Bounce" model?
[1]...
Hi, I am new here so apologies if i am not using the right subforum. I don't have a physics background so i am not very technical but i do have a little bit of understanding. I was reading this paper by hawking/hertog and came across something that ended up confusing me.
Here is it:
"Pre-big...
If the universe keeps expanding at an accelerated rate (given by the cosmological constant) then the universe would approach a DeSitter spacetime where there would be a cosmological horizon that would radiate just as the event horizon of a black hole radiates Hawking radiation
I thought that...
In the far future there will be most likely a point where a maximal state of entropy will be reached in the universe and after the last black hole evaporates there could be no more structures and no more work could be done.
According to the Poincaré recurrence theorem for a closed universe...
Václav Vavryčuk has written two articles on replacing the standard FLRW metric in cosmology with what he calls a "conformal FLRW metric", which he claims explains astrophysical and cosmological phenomena traditionally attributed to dark energy and dark matter/MOND, such as the dimming of type 1a...
The article https://phys.org/news/2023-07-age-universe-billion-years-previously.html#:~:text=42-,New%20research%20puts%20age%20of%20universe%20at%2026.7%20billion%20years,as%20old%20as%20previously%20believed&text=Our%20universe%20could%20be%20twice,%22impossible%20early%20galaxy%20problem.%22...
Hi, I've recently developed an interest for the history of the development of cosmology and find it very interesting. The key events I have been reading up on are:
1915 - Einstein's theory of General Relativity was published.
1923 - Hubble discovered a Cepheid variable in the Andromeda...
Physicist Grigory Volovik has put forward some ideas about the universe undergoing a topological phase transition (especially in the early stages of the universe). He published a book called "*The Universe in a Helium Droplet*" where he explained his ideas. You can find a brief discussion here...