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.
While studying the proper distance in cosmology I came across the thing as
The FRW metric
ds2=c2dt2-a(t)2[dr2+Sk(r)2dω2]
And Sk(r)=Rsin(r/R)
Where a(t) is the scale factor and dω2= dθ2+sin2θdΦ2,
While calculating the proper distance at the time of emmission of light the term ds and dω are...
Homework Statement
Show that the temperature of non-relativistic matter scales as ##a^{-2}## in the absence of interactions. Start from the zero-order part of Eq. (4.68) and assume a form ##f_{dm} \propto e^{-E/T}=e^{-p^2/2mT}##. Note that his argument does not apply to electrons and protons...
I am trying to estimate the distance of closest galaxy neighbor knowing the expression of number of neighbors into a volume ##\text{d}V##, the mean density ##n_\text{gal}## and the correlation function, i.e with this expression :
##\text{d}N=n_{\text{gal}}\,\text{d}V\,(1+\xi(r))##
with...
Hello,
I am asked to give the formal expression of the total number density of galaxies and explain why is this expression problematic in practice?
From what I saw from my research and into my lectures, I have found the follwing relation which gives the number of galaxies ##N## with mass ##(m...
Hi everyone,
On Page 72 of S. Weinberg's Cosmology book, it's mentioned, just after Equation 1.9.16, that, for the universe matter density ρ(r) to be an analytic function near the origin (spherical symmetry), it has to be given near r = 0 by a power series of r2. I'm not a math wizard, so can...
{Reference: Wikipedia's Friedmann-Lemaitre-Robertson-Walker (FLRW) Metric article)}
The FLRW (1935) mathematical model of the universe is the one most used by cosmologists. It is differentiable, which means it is based on sound, consistent, mathematical formulations. (The Lambda-CDM model is...
Hi Everyone,
One of Hawking's last publications studied the model of universe/multiverse and conjectured that the exit from eternal inflation is "finite and reasonably smooth" - in other words, the inflated boundaries of multiverses could be finite and smooth. Here is the paper link -...
Hi Everyone,
I'm interested in how to annihilate black holes (they are like blenders separating all the things apart and agglomerate like "tumors/cancers" in the universe). However, I'm new to this field and need some clarifications on some of the basic concepts like "annihilation" and...
I have been studying primordial black hole formation through inflation for a while and I was curious to know how the parameters in an inflation model are determined such that they are consistent with CMB constraints. In my literature reviews, there are quite a few models that exhibit an...
Homework Statement
Show that Eq. (6.33) follows from Eq. (6.32) by changing variables from t to ##\eta##.
Homework Equations
(6.32) $$\frac{d^2\phi^{(0)}}{dt^2}+3H\frac{d\phi^{(0)}}{dt}+V'=0$$
(6.33) $$\ddot{\phi^{(0)}}+2aH\dot{\phi}^{(0)}+a^2V'=0$$
The Attempt at a Solution
So...
Why should you prefer the view that cosmological expansion is due to distant galaxies moving apart according to the Hubble Law instead of cosmic space stretching, like stretching of space(-time) in the vicinity of black holes?
Hi,
I am trying to figure out how to solve the Mukhanov equation numerically in Mathematica, but have some problems dealing with it. In terms of the number of efolds, the Fourier modes satisfy the following ODE in terms of the Hubble slow roll parameters:
$$...
In 'Introduction to Cosmology' by Barbara Ryden, there is an argument made using the first law of thermodynamics to derive the relation T(t) ∝ a(t)-1 on pages 29 and 30.
MENTOR NOTE: removed copyrighted material.
I've been able to work out all the omitted details up to 2.37, which gives the...
Hello everybody,
I'm a undergraduate student in Physics at my first year, and we got a project in our course: Astrophysics and Relativity.
The topic is basically about how we can use the experiments at LHC in astrophysics/cosmology, (Which of course is trying understand the early universe etc)...
The Compton wavelength of a particle is given by
$$\lambda=\frac{h}{mc}.$$
One can construct an expression for the energy density ##\rho## of a particle of mass ##m## given by
$$\rho = \frac{mc^2}{\lambda^3}=\frac{m^4 c^5}{h^3}.$$
What is the physical significance of the mass scale ##m## in the...
Homework Statement
For a power spectrum density fluctuations ##P(k) \propto k^n##, I need to find the scaling (with respect to ##a##) of the horizon wavenumber ##\frac{2\pi}{\chi_H}## in a matter dominated universe in terms of ##n##. ##\chi_H(a)## is the evolving particle horizon, in a flat...
Conformal Cyclic Cosmology, or CCC, is a hypothesis put forward by Roger Penrose in the early 2000s. My understanding of physics is lacking so my explanation will not be that clear, but I will summarize it here.
Essentially, the existence of a previous spacetime, or "aeon," is postulated. This...
I'm beginning to study the Matt Roots book Introduction to Cosmology and in the section 1.3 Olbers' Paradox he writes:
"If the surface area of an average star is A, then its brightness is B=L/A. The sun may be taken to be such an average star, mainly because we know it so well.
The number of...
Homework Statement
Suppose (incorrectly) that H scales as temperature squared all the way back until the time when the temperature of the universe was 1019 GeV/kB (i.e., suppose the universe was radiation dominated all the way back to the Planck time).
Also suppose that today the dark energy...
Hello all,Next year, January I will start my PhD in Cosmology. Salary is fair and I don't have to pay the tuition fee.
I always loved the idea of doing a thesis about Cosmology.
My master's degree was about computational physics where I had to learn how to program in C/C++, Fortran, Matlab...
I'm trying to figure out how to arrive at the final expression, as given in the lecture notes. I tried to work this out by myself but getting different figure and units. I've considered the followings,
normalize the equation from its values e.g. spins and x parameter, as g~100, x~10(m/t~10)...
Considering one is taking all the required math courses for a typical physics degree, what math electives are most crucial to the field of cosmology/theoretical astrophysics?
Also, is it true that mathematical modeling courses(discrete and dynamical modeling across physics) are more important to...
I am looking for a way to get, by a simple numerical computation, the 3 curves on the following figure:
For this, I don't know what considering as abcissa (comoving distance ?, i.e
##D_{comoving} = R(t)r##
with ##R(t)## scale factor and ##r## the coordinate which appears into FLRW...
From this link https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations#Measured_observables_of_dark_energy , I can't get this relation :
##c\Delta z = H(z)\Delta \chi\quad\quad(1)##
with ##z## redshift, ##H(z)## Hubble constant at redshift = ##z## and ##\chi## radial coordinates.
One...
I found an article written by physicist George Ellis that confused me a little.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.498.4569&rep=rep1&type=pdf
At some part, he says:
3.2 Non-uniqueness:
Possibilities There is non-uniqueness at both steps. Stating “all that is possible...
I've been reading up on inflation, and have arrived at the so-called slow roll conditions $$\epsilon =-\frac{\dot{H}}{H^{2}}\ll 1\; ,\qquad\eta =-\frac{\ddot{\phi}}{H\dot{\phi}}\ll 1$$
I have to admit, I'm having trouble understanding a couple of points. First, how does ##\epsilon\ll 1##...
I am making this thread to discuss interesting open questions in Gravity and Cosmology with people working in these or even relevant area.
Anyone who is working in these (and relevant) areas, please identify yourself here and we will begin and hopefully people will catch on and contribute.
Hi,
I'm currently trying to wrap my head around how the Ly-α forest works. This is what I have so far;
A distant quasar produces these Ly-α photons, which occur when a hydrogen's electron drops from n=2 to n=1, and has a wavelength of around 121nm (depending on the exact transition). This...
Hi to whoever reads this,
Some back ground info: I am a current undergrad student halfway through their degree, and I'm starting to think about what I'd like to do after I receive my diploma. I know I want to continue studying, and possibly move to a different country to do that. I know I can...
I have completed post grad in Physics and in the transition phase between post grad and Ph.D. I am interested in cosmology and also completed a post grad course on Astrophysics and Cosmology. Can anyone enlighten me about what are the current debates and active topics of research going on in...
Take note of today's Obied-Ooguri-Spodyneiko-Vafa 18.
Curious situation: After it had influenced much the development of the string theory community’s attention and almost all of its public media perception since 2003, after what must be thousands of followup publications, the argument of KKLT...
If the uncertainty in the age of the Universe is ##\Delta t## then the Uncertainty Principle implies that it has an uncertainty in its energy ##\Delta E## given by
$$\Delta E \ \Delta t \sim h.\tag{1}$$
If this energy fluctuation excites the zero-point electromagnetic field of the vacuum then a...
There is an assumption in cosmology say that there is another universe Composed of antiparticles?
I mean that the atom composed of positron rather than an electron, anti-proton rather than a proton and anti-neutron rather than a neutron.
Hello all,
Can you tell me what is the best book to study QFT when you are thinking to follow a PhD in cosmology (Dark energy, scalar fields, extension to GR, string theory).
The Dynamical Casimir Effect is the production of real photons from the vacuum in a system where one has moving mirrors (see https://www.technologyreview.com/s/424111/first-observation-of-the-dynamical-casimir-effect/). The frequency of the photons is related to the ratio of the velocity v of...
I was just curious because if space can expand faster than light, doesn't that mean there will be a lot of space that we just can't see? Do objects just vanish because we can't see them?
For instance, if a hypothetical alien lived in MACS0647-JD galaxy which is 13.3 billion light years away...
we say everytime a couple of matter-antimatter particles get born near the edge of a black hole one of them falls into it and the other one escapes.
And we everytime mention that the antimatter particle kind of eats a bit of black holes mass out...and by time the black hole gets smaller and...
According to Source: They discover a mega cluster of 14 galaxies that originated only 1400 years after the Big Bang
This is the most active place in this universe
The question relates to the deterministic views of people like Descartes or Pierre de Laplace, the infamous "an omniscient intelligence who could know precisely the position and momentum of every single particle in the universe would be able to predict the future with total accuracy, past...
I've always loved physics, since my first science fiction novel in 1971. I won a scholarship to do a Math-Physics double honours program at University of Waterloo in 1977, but was immediately seduced into computer science by the promise of being paid big bucks to play with computers all day...
Homework Statement
Homework Equations
look up, look down, your pants fell down
The Attempt at a Solution
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Time-like killing vector is associated with energy.
## \frac{d}{ds} (\frac{\mu^2\dot{t}}{R^2})=0##
Let me denote this conserved quantity by the constant...
Hey!
I was reading some script and when it comes to the cosmological redshift, it says, that only relativistic particles are affected by cosmological redshift. This does feel quite natural, however, I haven't been able to come up with an explanation that shows it with proper physics and...
<< Mentor Note -- after a very long Mentor discussion, we acknowledge that this paper, while potentially controversial, has been published in a reputable peer-reviewed journal. We believe that a discussion of this paper can be useful and constructive. Thanks >>
This paper of mine was...
Hi! I just started high school and have developed a passion for cosmology and astrophysics. I would like to know if I really need to be very good at physics and mathematics (and if there is more that I need to be good at) and where do i find a job (spaces like N.A.S.A., SpaceX etc).
Thanks for help!
Is it possible for me to do cosmology and quantum mechanics as a joint degree at uni? If so where and does it cost extra? I’ve been wondering for a whole and I’m not sure where to look.
If the universe was in an energy eigenstate then d<A>/dt = 0 for any dynamic variable A. Stuff moves which implies that the Universe isn't in an eigenstate. What factors drive the energy spread?
NASA decided to stop *WFIRST and concentrate on Mars project (send humans to Mars).
What do you think about it?
In my opinion, since a lot of ventures have begun space developments such as SpaceX and this proves that rockets make money, NASA should tackle WFIRST. Generally, we cannot earn...
Homework Statement
Show that ##4\pi G(\dot \phi)^2=\epsilon a^2 H^2##
Homework Equations
Over dots mean derivative with respect to ##\eta##.
$$\frac{1}{a}\frac{d}{d\eta}=\frac{d}{dt}$$
$$H=\frac{\dot a}{a^2}$$
$$\epsilon=\frac{-\dot H}{aH^2}$$
$$(\frac{\dot...