Questions tagged [cosmology]
Questions about the origin, history, evolution and fate of the Universe.
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In CMB data analysis, when calculating the signal-to-noise ratio for a binned power spectrum, do we use the bin centers in the SNR calculation?
The signal-to-noise ratio for angular power spectrum signal $C_l$ under theoretical noise $N_l$, where $C_l$ and $N_l$ are functions of multipole $l$, is given as
$$(S/N)^2= \sum (2l+1) (C_l/N_l)^2$$
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where are we in the universe as compared to the observable universe? [duplicate]
For distant galaxies to be accelerating away at equal speed in every direction, Earth would have to be at the centre of the universe. Since it is not, some region of the distant galaxies should appear ...
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Could inhomogeneities or topological defects break the fundamental symmetries of the Universe?
I have heard that some types of inhomogeneities and topological defects in cosmology have been proposed to be able to break fundamental symmetries of nature such as the Poincaré, Lorentz, ...
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Conditions in the Early Universe
I am interested in how the large-scale properties of the Universe change over time.
Does anyone know a trusted website which gives the temperature, density and radius (distance to the particle horizon)...
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What equation tells you how far in space you can go from a point and return?
We know that hubble expansion increases the distance between points in space, and that the cosmological event horizon represents the distance from the observer at which objects are receding faster ...
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Size of the whole universe if it were spherical
Suppose the universe is spherical and its density ratio is
$\Omega \leq 1.00125$
$\Omega = 1.00125$ is approximately the maximum possible value of the density ratio according to the Planck Mission ...
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Other Hubble spheres with no Lorentz symmetry?
Perhaps this may be a stupid question but anyways here it goes...
If the Lorentz symmetry is not global but rather local, wouldn't that mean that is possible that other Hubble spheres outside our ...
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Why is the latest Webb discovery of early-age universe considered so important?
The past week, news were flooding of an unexpected discovery of James Webb Space Telescope. In many articles it is mentioned that cosmologists cannot explain the formation of galaxies of this ...
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What does Dark Energy explain other than the accelerated expansion of the universe?
Dark energy is a vital part of standard cosmology and allows for an explanation of the accelerated expansion of the universe. Does it explain anything else?
Or put into other words:
If a different ...
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Can the curvature of a closed universe be measured?
Suppose we were in a closed universe likened with a spherical surface such as that of the Earth's surface.
Assume also that the limits, represented by the limits of the observable universe, ...
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Empirical Constraints on the Time Evolution of Cosmological Redshifts
The standard model of Cosmology predicts that the redshift of a single source at fixed comoving distance varies with observation time according to
$$ \dot z = \left( 1+z - \frac{H(z)}{H_0} \right) H_0....
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Coasting universe Hubble parameter behaviour
I’ve recently been trying to wrap my head around the potential behaviours of the Hubble parameter over time for various cosmological models but I’ve run into a little snag when it comes to a coasting ...
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In 2023, is space still thought to be "filled with a network of wormholes"?
The September 2009 YouTube music video Carl Sagan - 'A Glorious Dawn' ft Stephen Hawking (Symphony of Science) at about 00:30 depicts a clip from (what I think is) ...
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Gas heating due to high viscosity?
Has there been any observation where a gas or a fluid expands following the Hubble flow (the expansion of the universe) and gets heated because it has a large viscosity (transforming its kinetic ...
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Early Dark Energy [closed]
Early dark energy is one of the possible solutions for the Hubble tension. If it is correct then wouldn't the universe be somewhat larger than our current best estimates?
early dark energy:https://...
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How can a time-like trajectory be calculated using the Friedmann-Robertson-Walker metric?
Using the following FRW metric,
$$ds^2=-c^2dt^2+R^2(t)(d\chi^2+f(\chi)d\Omega)$$
and considering $d\Omega=0$ from now on, it is clear that for a light-like trajectory, the equation must read $ds^2=0$ ...
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When did the first cold dark matter halos begin to originate?
I know that these dark matter halos should have been created in an early universe because during the formation of galaxies, the baryonic matter was too hot to form gravitationally self-bound objects ...
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what does it mean to have momentum suppressed cross section
What does it mean to have momentum suppressed cross section and zero momentum transference in direct and indirect detection of dark matter
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What's the issue with Olbers' paradox?
I'm not quite grasping the reasoning behind Olbers' Paradox, or why an eternal, non-expanding and spatially infinite universe would be incompatible with a dark sky. For simplicity, let's suppose that ...
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3d distance between the Galaxies inside the galaxy cluster
I am currently working on the dynamics of the galaxy cluster, so i am trying to get the distance between the galaxies inside the galaxy cluster from its centre. As a input i have RA , DEC and Z (...
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Why is Earth 1/3 the age of the universe?
The Earth is 4.6 billion years old
The universe is 13.8 billion years old.
3 times the age of the Earth
Are there other planets with ages that are close to say 1/4 1/5 etc the age of the universe? Why ...
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Can LIGO distinguish rotating and non rotating black hole collisions?
I am assuming two rotating black holes create gravitational waves as they collide.
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Critical density and Hubble parameter
Is it possible for the Hubble parameter of an /expanding/ universe made of radiation, matter and cosmological constant to be increasing with time? I'm trying to figure out if any form of scale factor $...
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Can the Hubble expansion inject energy in AGN and quasar outflows?
I found this article about the behavior of quasar outflows in cosmology and how they can create a magnetic field.
In section 2.1.4., the authors say that when a quasar produces a "wave" or ...
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Limits of the universe
I am considering the limit in the expanding universe where the expansion matches the speed of light.
If we consider that the expansion is accelerating, how will the situation be after the next 14 ...
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Time and space travel as applied to expanding space and the ratio of/between time and distance
If a place is 500 light years away, then I set out to this place, then is it true to say that, the place which I set out from, will be 750 light years away from my destination, once I have reached it?
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Deviations of conservation laws in the context of cosmological evolution?
If energy is "not conserved" in General Relativity (or at least, it is difficult to define it) in the context of an accelerating expanding spacetime (like it happens in our Universe), are ...
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How do the abundances of heavy elements near the Solar System compare with the abundances at other places and times in the Universe?
We have measured the relative abundances of heavy elements (e.g. gold, lead, uranium) near the solar system and in cosmic rays. I'm interested in whether those abundances are particularly high (or low)...
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Is there any method that enables us to observe the 3D large-scale spatial distribution of the dark matter?
Can we get the three-dimensional spatial distribution of dark matter through gravitational lensing?
If not, is there any other way?
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Cosmic microwave background the same as the first visible light at 379,000 yrs after the Big Bang? How do these measure the age of the universe?
Was the CMB emitted at the same time as visible light at 379,000 yrs after the BB ? Was this a one time event ? If headed away from us, how does it measure the age of the universe?
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Redshift distance proportionality at high Z and need for "mighty mouse" galaxies?
Allegedly supported by some evidence from the new James Webb space telescope physicist Eric Lerner has written an article that have garnered some attention. He writes that:
"Put another way, the ...
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How much does foreground clumping affect the estimated sizes of high-redshift objects?
I've always converted angular to linear size by using the angular-diameter distance without really thinking about it. But in light of recent stories about high-$z$ galaxies observed by JWST being ...
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Distance of distant galaxies
Can two galaxies, one with a redshift of 7 and the other a redshift of 8 have the same angular distance (distance from the Earth during the emission of the observed photons)?
If not why ?
Example: ...
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RAMSES fine multigrid Poisson solver fails to converge?
I am working on setting up N-body simulations of galaxy mergers. The initial conditions are generated from the DICE code, and looking at them, they seem very realistic. Unfortunately, when I let ...
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Could the universe expand forever even if there is no force (e.g., dark energy or eternal inflation) pushing it apart?
Matthew O'Dowd specifically and repeatedly states in the PBS Space Time video called, "Why the Universe Needs Dark Energy", that even without taking an expansionary field into account an ...
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What happens if there were only ordinary matter in the universe? Would the universe expand constantly? or will it decelerate?
This question hit me when I was watching 'Cosmos by Neil deGrasse Tyson' explaining how the universe is expanding and how it accelerates because of dark energy and dark matter, then I asked myself ...
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What would be 1 hour equivalent on these moons of Jupiter and Saturn compared to earth? And their astrobiological implications
Considering the distance from and velocity of Sun, Saturn, Jupiter, thermal energy due to motion other than that adding/combining to velocity, and the individual mass and velocity of the particular ...
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Why is infrared the ideal band to detect the earliest and most-redshifted galaxies? [duplicate]
Was infrared chosen for the James Webb Space Telescope's mission to detect the most-redshifted galaxies and stars in the universe because most detectable galactic radiation emits most strongly in the ...
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What physical process can Metallicity(Z) of a galaxy tell us?
For example, if there is a galaxy and its metallicity increase or decrease from high redshift to present day (We can see it from simulation like TNG or EAGLE). What physical process we can know?
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What is Gravitational softening length?
I was reading the Aquarius simulation preprint (Springel et al. 2008) The Aquarius Project: the subhalos of galactic halos as a reference for my internship. I came across the term Gravitational ...
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Since the Hubble Constant changes over time (it's a variable parameter), why can't the conflicting values of 67.4 and 73 both be right?
Are the conflicting values from the 'early universe' (Planck) method and the 'late universe' (Distance ladder) method actually compatible? Since during the latter period of the universe 'dark energy' ...
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Why doesn't dark matter clump strongly in the center of galaxies, since it doesn't feel either radiation pressure or the Pauli exclusion effect?
Dark matter is described as being spread not only throughout a galaxy, but also around it in a halo of some sort that extends far beyond the visible parts of the galaxy...
In fact, dark matter haloes ...
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Using cosmological model GADGET - 4
I want to use GADGET-4 "a parallel cosmological N-body and SPH code meant for simulations of cosmic structure formation and calculations relevant for galaxy evolution and galactic dynamics" ...
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What is a 'square' Kelvin degree? μ$K^2$? In terms of the cosmic microwave background's (CMB's) temperature fluctuations?
From what I have read and seen, the minute temperature fluctuations in the CMB are measured in microKelvin, or μK.
However, many charts and graphs show μK2, or 'microKelvin-squared'.
Do they simply ...
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Planck epoch and time dilation
I guess this question can be broken down into three consecutive parts:
Does general relativity apply during the Planck Epoch?
If yes, does the gravitational time dilation prediction apply during the ...
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Why is the probability dP of finding an object (e.g. galaxy) in an infinitesmal volume dV equal to \overline{n}dV?
As pointed out by many cosmology lectures, such as Eq. (63) of Cosmology II-8 Structure Formation, and Eq. (3.1) of A Detailed Look at Estimators for the Two-Point Correlation Function, the ...
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Mass resolution in cosmological simulations [duplicate]
I've been reading papers about different cosmological simulations and they all talk about the "mass resolution" of those. Can someone please explain what does "mass resolution" ...
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following several unknown phenomena detected at the edge of the solar system, is there a 5th force which acts at the edge of the solar system?
following several unknown phenomena detected as the acceleration of Oumuamua and electrons and strange data sent by traveler 1 at the edge of the solar system, is there a 5th force which acts at the ...
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Why do most astrophysicists believe the cosmic microwave background (CMB) provides the best evidence for dark matter? What, exactly, IS that evidence?
I frequently read that the cosmic microwave background contains the best overall evidence for the existence of dark matter, and conversely against alternative gravity theories like MOND.
However, I ...
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How would a balloon structure of a universe look if we collected all mass together in a small region?
Imagine a universe with an inflating balloon structure of spacetime. Matter is distributed uniformly.
Now somehow we manage to collect all matter together within a small volume. What would happen to ...
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