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.

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Could the universe be a bubble in a larger mass?

I was reading this article which explains that Einstein originally thought about incorporating dark energy into relativity. It explains that dark energy is the thing that keeps pushing the universe ...
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1answer
320 views

Is there a “CGBR”?

The recent discovery by the LIGO made me wonder about this. We know that there exists a CMBR, Cosmic Microwave Background Radiation, a blanket of electromagnetic energy covering the universe, made by ...
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2answers
62 views

Is the expanding of the universe also a cause which can induce gravitational waves from mass? [duplicate]

Gravitational waves arises when mass is rotating in another mass'orbital, in explosions and of course in case of colliding black holes. But are they also created when mass is moving and speeding ...
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1answer
102 views

Is the cosmological time grosso modo isochrone?

Is the cosmological time grosso modo isochrone? by analogy with space isotropy. Or else do we have possibly great differences by analogy with great voids in the space. We know that it's not strictly ...
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1answer
133 views

How many galaxies could be the source of the recent LIGO detection?

The recent LIGO detection is pretty exciting, and a lot of people are asking whether there is a chance of optical detection of the black hole pair that created the signal. From a cursory reading of ...
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2answers
71 views

Does the speed of light change? [duplicate]

I know that there is a similar questions, but I think mine is a bit different. I wonder if with the expansion of the universe the speed of light changes. It seems that the speed of light is very ...
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64 views

Is it accurate to say that nothing can travel faster than $c$ in a GR context, where more space can be created?

Years ago, my brother and I had an argument where I was trying to convince him that nothing could travel faster than the speed of light. I was pursuing this in the context of Special Relativity. My ...
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1answer
76 views

Does a similar concept like centrifugal force exist for the whole universe? [duplicate]

Is it meaningful in the sense of falsificable to ask whether the whole universe (including everything known/observable: cosmic background radiation etc ..., excluding everything not directly ...
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1answer
51 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 ...
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36 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. ...
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1answer
104 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 ...
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39 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 ...
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1answer
43 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 ...
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1answer
74 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 ...
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1answer
145 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 ...
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1answer
57 views

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

Would it just wipe out everything, or would something else occur?
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1answer
109 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 ...
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1answer
60 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 ...
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1answer
63 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 ...
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1answer
86 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 ...
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41 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) ...
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1answer
96 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, ...
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1answer
144 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. ...
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32 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 ...
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3answers
546 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 ...
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1answer
39 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 ...
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3answers
388 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 $z=0.1$, ...
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3answers
109 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 ...
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1answer
97 views

Thought experiments about $c$ [closed]

Poincare had a brilliant thought experiment about what if everything in the universe doubled in size, would anybody notice any difference or even be able to measure anything that can be compared with ...
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0answers
49 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 ...
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0answers
62 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? ...
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1answer
55 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 ...
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1answer
95 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 ...
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1answer
47 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 ...
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1answer
44 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 ...
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86 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?
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27 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 ...
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0answers
37 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?
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1answer
69 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: ...
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2answers
152 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 ...
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1answer
49 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 ...
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0answers
71 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 ...
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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 ...
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0answers
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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: ...
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1answer
74 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), ...
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57 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 ...
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0answers
35 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 ...
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0answers
33 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 ...
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133 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 ...
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2answers
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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)?