The study of the large-scale structure, history, and future of the universe. Cosmology is about asking and answering questions about the "big picture" - the extent, origin, and fate of everything we know.

learn more… | top users | synonyms (1)

0
votes
1answer
29 views

Is there a limit to the size of black hole?

I have read answer by @John Rennie in regards to the size and density of black hole. In the last sentence he states that super supermassive black hole ...
0
votes
0answers
23 views

What is known about the physics of Planckbrane (another brane) in Randall–Sundrum model?

Randall–Sundrum model imagines that our universe is a five-dimensional anti-de Sitter space and the elementary particles except for the graviton are localized on a (3 + 1)-dimensional brane or branes. ...
1
vote
0answers
14 views

Density parameter (cosmology) as a function of redshift

Hopefully I'm missing some very basic algebra for this question. In essence, I need to derive the following: $$ \Omega=\Omega_{1}\frac{(1+z)}{1+\Omega_1{z}} $$ Now, I proceeded from the Friedmann ...
2
votes
0answers
28 views

Why do some stars actually produce “Gamma ray bursts”?

I looked it up but I haven't found any explanation as to why some stars produce them, I understand that collapsing and merging stars produce them, but my question is why is the energy concentrated in ...
0
votes
1answer
24 views

Number and energy density integrals in cosmological thermodynamics

I am working through Mukhanov's book "Physical Foundations of Cosmology" and something has me puzzled in the section on evaluating integrals for number density, energy density and pressure. The ...
4
votes
1answer
60 views

Importance of CP violation

To explain the matter-antimatter assymmetry, CP should be violated according to Sakharov conditions. Charge conjugation is required as matter and antimatter have opposite charges but why Parity ...
5
votes
1answer
123 views

The naive idea of the big bang

Many people think that according to big bang cosmology, first there was empty space, then there was an explosion in the middle of the emptiness, and now all the galaxies are flying away from that ...
0
votes
1answer
48 views

What would happen if you were to release the energies of the big bang in our universe a second time? [on hold]

Would it just wipe out everything, or would something else occur?
4
votes
1answer
52 views

Was the matter-energy content of our universe always distributed in the same ratios?

Currently, Dark energy (68.3%) and Dark matter (26.8%) together constitute about 95.1% total matter-energy content of the universe while only 4.9% is ordinary baryonic matter. Was this always the ...
2
votes
1answer
52 views

Would the Moon be able to take water from Earth?

I know that if you add mass to the moon, it would get closer to the Earth. We all know that the moon causes the tides because it's gravity pulls the water. So, my question is: If the moon gained more ...
3
votes
1answer
55 views

How could we know that the universe is homogeneous and isotropic at a moment?

Cosmologists say that the universe is homogeneous and isotropic within our Hubble volume based upon the astronomical observations. But how can we argue that the universe is homogeneous and isotropic ...
0
votes
1answer
51 views

Special Relativity problem - proper time interval

The supernova 1987A explosion in the Large Magellanic Cloud 170 000 light years from Earth produced a burst of anti-neutrinos ν ̄e which were observed in terrestrial detectors. If the anti-neutrinos ...
0
votes
0answers
34 views

(naive?) interpretation of Hubble's Law

From my understanding, the Hubble constant $H_0$ calculates from observed redshifts $z$ of distant galaxys against their proper distance $D$. The current value appears to be 67.80(77) ...
-3
votes
0answers
52 views

Proof that dark matter isn´t caused by a parallel universe? [closed]

Some time ago I read about a fortunate experiment unfolding in the heavens. Two ball-shaped stellar aggregates, by luck, bumped into each other. The collision was, for all practical proposes, head on. ...
3
votes
1answer
62 views

Universe vs Multiverse. Time and Space

Wikipedia defines a multiverse as a hypothetical set of finite and infinite possible universes. Similarly, it defines the Universe is as "all of time and space and its contents". On the surface, ...
0
votes
1answer
21 views

What is the meaning of the particle horizon in conformal diagrams?

I'm reading "Physical Foundations of Cosmology" (Mukhanov) and in Chapter 2.3 conformal diagrams get introduced. They seem to be a (graphical) tool to understand the causal structure of the universe. ...
0
votes
0answers
27 views

When did the strong force separate?

Given that Grand Unification may have happened, and inflation is accepted, which of these two scenarios is better accepted; 1) The strong force broke free before inflation, and is somehow causally ...
0
votes
0answers
120 views

The first Newton law is not globally valid? [closed]

How can space expansion drag galaxies in contradiction with the 1st Newton's law? The 1st Newton's law is equivalent to say that there is no bounds between space and matter, i.e. space is a perfect ...
10
votes
3answers
483 views

Age of the universe versus absolute time [duplicate]

In Wikipedia, the age of the universe is defined as the "time elapsed since the Big Bang" while "time" links to "the cosmological time parameter of comoving coordinates" which itself links to "the ...
1
vote
1answer
35 views

Why do we look at non-flat geometries in Cosmology?

In Cosmology we use the Robertson-Walker-Metric which follows from the cosmological principle & mathematics. This metric leaves three cases for a possible curvature (or geometry) of space (not ...
2
votes
3answers
374 views

What is the cosmological redshift of SN 1987A?

I haven't found any literature on SN 1987A, which provides me with its cosmological [not gravitational, wrong in inital question, thanks for the remark] redshift. Is it larger or smaller than $z=0.1$, ...
1
vote
3answers
101 views

Observing a point 13.82b ly away, 1b years ago

I understand that we can observe far away galaxies to get an idea how the universe looked like in the past. Assuming the universe is 13.82b years old, would it be correct to say that if we looked at ...
0
votes
0answers
30 views

Scalar field shift symmetry in early Universe

Suppose we have scalar field in FRLW spacetime: $$ S = \int d^4x\sqrt{-g}\left(\frac{1}{2}\partial_{\mu}\varphi \partial_{\nu}\varphi g^{\mu \nu} - \frac{m^2}{2}\varphi^2\right), $$ $$ g_{\mu\nu} = ...
0
votes
0answers
47 views

How come the cosmological constant supports the idea of dark energy existing? [duplicate]

According to an article I've read recently, the cosmological constant was used to support the theory of dark energy. But the cosmological constant already defines an inclination in the essence of ...
2
votes
0answers
53 views

Where does all the energy in the universe come from? [duplicate]

The principle of conservation of energy says that all energy in a system will remain the same. It can just be transformed. The universe contains a huge amount of energy, but where did it come from? ...
0
votes
1answer
52 views

Was decoupling actually detripling?

As I previously understood it, before recombination, high energy photons were bound up in interactions with excited electrons, meaning electrons couldn't settle into orbit with protons and other ...
0
votes
1answer
66 views

Protons, electrons and integers

From this calculation (https://uk.answers.yahoo.com/question/index?qid=20080724101956AA4zed1), two protons seperated by the distance of one atom feel the electromagnetic force repelling them ...
1
vote
1answer
79 views

What effects would a finding of Gravitational Repulsion Between Matter and Anti-Matter in the ALPHA Experiment have on Mainstream Theory? [closed]

The actual nature of the gravitational force between matter and anti-matter (attractive or repulsive) remains unsettled: See Are there experiments taking place right now that might show evidence for ...
1
vote
2answers
40 views

Large scale structure of the universe

I have read of two seemingly straightforward explanations that give reasons for the inhomogeneity of the large-scale structure of the universe (i.e. why stars / galaxies formed where they did) One is ...
1
vote
1answer
42 views

Hottest period in the history of the universe

Stack exchange's tagline is 'hot questions' - so here is one that will hopefully cause some heated debate. I remember hearing that the period immediately after inflation is theorized to be the ...
0
votes
2answers
80 views

Expansion of the Universe [duplicate]

At what speed is our solar system expanding, and if it is, why don't the positions of the sun and planets change, or grow farther apart? Why is the Big Dipper still where it is?
0
votes
0answers
25 views

Chaotic inflationary model - bubble inside bubble

I was reading a bit about Prof. Linde's chaotic inflationary model of expansion of universe. He has mentioned about 'bubbles' of space time expansion. But no one has spoke about bubbles inside ...
2
votes
2answers
70 views

What happens during mass-energy conversion

A mass is another form of energy. When a mass ceases to exist as 'matter', it exists as energy - in the forms of energy we generally know ( light,heat ). But is this so simple? When a mass exists in ...
1
vote
0answers
30 views

How did people think of the universe before Hubble? [closed]

Did they think the universe had always existed? And was there even any serious scientific inquiry into the question, or was it pure speculation?
1
vote
1answer
49 views

Is there a correlation between Brownian motion and cosmic microwave background radiation?

Is there any correlation between Brownian motion, the phenomenon of osmosis - compared to cosmic microwave background, the Noise we see in analog television? Brownian motion or pedesis (from Greek: ...
3
votes
2answers
118 views

Redshift due to a static gravitational field and the conservation of energy [duplicate]

I am standing on the surface of some planet. Gravity is described via General Relativity with some static metric (e.g. the Schwarzschild metric, so static means no time dependence, but the metric may ...
1
vote
1answer
36 views

Help with the Ricci tensor and Chistoffel Symbols [closed]

I really am confused with certain notations of the Ricci tensor and the Christoffel symbols. I'm looking to evaluate $R_{00}$ from my lecture notes, but I'm a little stuck at one point. The Ricci ...
1
vote
0answers
61 views

Intuitions for the simplest model in which the evolution of the laws of nature arises from the natural selection of structures [closed]

The problem I’m trying to solve can be described as To create the simplest model possible in which the evolution of the laws of nature arises from the natural selection of structures. This approach ...
5
votes
6answers
1k views

What came first, the Universe or the Physical laws that govern the Universe? [closed]

This sounds like the Egg and the Hen question but I am curious about this. If universe came first and created physical laws for itself, then what created the law or the principle as a consequence of ...
0
votes
0answers
46 views

Gravitational wave as a consequence of gravity being a field

I was reading an online article about gravitational wave detection and there is a sentence which says: The existence of gravitational wave is simply a consequence of the fact that gravity is a ...
2
votes
0answers
18 views

What do the $T, E, B$ in polarization spectra mean?

I was reading about CMB Polarization here. I know that $E$ and $B$ stand for E-mode and B-mode, but what does the $T$ mean? The author states that there are 3 observables: $T, E, B$ and six spectra: ...
1
vote
1answer
70 views

What is the limit of the deep field exploration?

The deep field exploration is quite fascinating, first the Hubble Deep Field (HDF) showing a small piece of the Univers one billion year after the Big-Bang, next the Hubble Ultra-Deep Field (HUDF), ...
1
vote
1answer
47 views

Is there inflationary solution in $R^2$ theory in Jordan frame?

In the Starobinsky $R^2$ inflation model, one usually uses a conformal transformation from Jordan frame to Einstein frame in which the action can be written just like Einstein action + scalar field ...
1
vote
0answers
21 views

Comoving and physical momentum in a Friedmann universe

It is most probably a very basic question, but I'm a bit stuck with it. Let us consider a spatially flat Friedmann universe with the usual metric ...
0
votes
0answers
29 views

Non-homogeneous expansion of the observable universe

This question may be more philosophical than cosmological, but here goes. Given that expansion of the observable universe is based on secondary data, i.e., we haven't actually measured the expansion ...
0
votes
2answers
92 views

Redshift of distant galaxies: why not a doppler effect?

How can I explain to my 17 year old pupils that the observed redshift of distant galaxies cannot be interpreted as a doppler effect and inescapably leads to the conclusion that space itself is ...
4
votes
2answers
77 views

Is space expanding equally in every direction?

Does space expand equally in every direction, so that it draws a perfect sphere or is expansion asymmetric, so it creates "bubbles" (when seen from the outside)?
4
votes
0answers
167 views

750 GeV diphoton resonance: KK graviton?

As everybody of you may know at LHC they found this probable resonance (https://cds.cern.ch/record/2114808, https://cds.cern.ch/record/2114853?ln=en). It may be a scalar or a KK graviton mode. Now, ...
3
votes
1answer
68 views

What is the average temperature of mass in the universe?

That is, ignoring speculative concepts like Dark Matter and just summing across stars and gas clouds etc
1
vote
1answer
32 views

About the ratio of the density of dark energy at the time of cosmic microwave background emission to the current density of dark energy [closed]

In a question, I am given the current densities of dark energy, dark matter and normal matter and am asked to find the ratio of density of dark energy at the time of CMB and now. The answer is 1. Is ...