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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Total Mass in Universe [duplicate]

Currently (2015), what is the total mass of the universe? How can we say with mathematical certainty that 69% is dark energy; 25% is dark matter; 5% is atomic matter; and 1% is neutrino, photon, and ...
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83 views

Are physical constants determined by their observation?

In common interpretations of quantum mechanics, it can only be said that objects exist once I observe them - it is not legitimate to ask where an object was before I observed it. Does this point of ...
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1answer
105 views

Number $g(T)$ of relativistic degrees of freedom as a function of temperature $T$

Let us consider the total number of relativistic degrees of freedom $g(T)$ for particle species in our universe: $$g(T)=\left(\sum_Bg_B\right)+\frac{7}{8}\left(\sum_Fg_F\right)$$ Where the sums are ...
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2answers
72 views

What would happen after the big crunch?

What is the aftermath of the big crunch?
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3answers
223 views

Are electrons held together by vacuum energy?

If one models the electron as a hollow spherical conductor with charge $e$ and radius $a$ then its electrostatic energy is given by: $$E_{em}=\frac{1}{2}\frac{e^2}{4\pi\epsilon_0a}$$ However if one ...
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64 views

How do we get the power spectrum through the CMB?

How do we get the power spectrum through observing the CMB?
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5answers
342 views

Where does General Relativity (GR) fail experimentally? Experimental shortcomings of GR?

When speaking with researchers and professors at my physics department, I sometime catch this undertone in the conversation when speaking about GR: almost as if some are not entirely convinced about ...
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18 views

Olbers' paradox and singularity resolution

As Im sure many fo you there are many attempts at singularity resolution in quantum gravity approaches such in LQC and string theory. In the last few week there was a lot of press for a new approach ...
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62 views

Has the cosmic alignment of Earth and the Solar System been explained (CMB anisotropy)

The Cosmic Microwave Background anisotropy is currently aligning Earth and the Solar System with the largest and earliest structure of the universe. Has this been explained yet? Or are the theories ...
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43 views

Does Big Bang Cosmology imply/require infinite space?

The reason I am asking this question is because if all points in space observe recession of galaxies the same as we do from Earth, the universe would have to be infinite (or a closed sphere in 4D or ...
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3answers
393 views

How long ago did the Universe end? (Or, how much warning will we get when it does?)

Only partly kidding... Let's suppose that a thousand, or a million, years ago there was an explosion of some gigantic star (or other celestial object) that was strong enough to destroy Earth and Life ...
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65 views

Looking for more information about these two hypotheses

Big Lurch - This was one I read about in a special issue of Scientific American from 2014. It was explained as The Big Lurch is a theoretical scientific model suggested as one of the ...
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1answer
34 views

Power Density of Dark Energy (W/m³)

In cosmology empty space has an energy density $\rho_{\Lambda}$ of $$\rho_{\Lambda}=\rho_c \cdot \Omega_{\Lambda}\cdot c^2$$ with $\Omega_{\Lambda}$ beeing the dark energy fraction ($0.683$ ...
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35 views

Dark Energy EoS: which models ruled out, which remain?

Dark energy density is mostly assumed to be a constant, where the equation of state for w=-1 (for radiation it would be w=1/3, for matter w=0 and for curvature -1/3), so in the simplest model the ...
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1answer
43 views

What does inflationary theory explain which quantum entanglement cannot?

Introduction This is an honest question... I don't study inflationary theory extensively (This is an understatement) but I am lost as to why it was developed in the first place. Here is why: ...
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1answer
51 views

Are all galaxies we see really our Milky Way? Any possibility?

There is a possibility for our universe to be the surface volume of a (higher-dimensional) hyperspace. So if this possibility is true,then is there also a possibility that the other galaxies we see ...
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1answer
69 views

Does the strength of a beam of light determine how much distance it can travel?

If I point a light torch to a cloudless, crystal clear and an absolutely pristine sky, will the light beam exit the planet and travel forever in the vacuum of space? (assuming it doesn't get perturbed ...
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1answer
91 views

Why is space (almost) flat? Is it because masses are approximately homogeneously distributed? [duplicate]

The question I have is: Why is space (almost perfectly) flat in our neighbourhood? (I am disregarding the deviations due to the sun and the planets.) Is it correct to say that space is (almost) flat ...
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1answer
93 views

Can observations of cosmic super voids teach us anything about time, dark energy, or dark matter?

Can observations of cosmic super voids teach us anything about... Time - If gravity affects time is there a chance we could gain any further information from studying a region with lower than ...
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1answer
51 views

What was the significance of the ionization caused by the Population III stars?

I am reading that the ultraviolet light that radiated from the first stars would ionize the surrounding gas and apparently, all of the matter in the universe would eventually become ionized. So, ...
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128 views

What evidence is there of a universe older than 13.8 billion years

I've read an analogy that finding iron-rich galaxies just 900 years after the Big Bang is like finding an old man in a crib in a nursery. We just recently found a supermassive black hole 12 billion ...
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0answers
90 views

Can we really see new objects in future? [duplicate]

From Wikipedia: Some parts of the Universe are too far away for the light emitted since the Big Bang to have had enough time to reach Earth, so these portions of the Universe lie outside the ...
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0answers
66 views

Does Expanding Universe conflict with the Thermodynamics 3rd Law? [duplicate]

I know that thermodynamics 3rd law states that if a system in equilibrium is at zero temperature, its entropy is minimum. Expansion of the universe made a transition from radiation dominated era ...
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2answers
75 views

What is the process by which the density fluctuations that were detected in the CMB evolved into the first stars?

We can detect very slight fluctuations in the temperature (mass distribution) when the CMB was released (decoupling). It is believed that these fluctuations led to the first stars. However, these ...
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3answers
207 views

Is the accelerated expansion of the universe consistent with conservation of energy? [duplicate]

If energy can neither be created nor destroyed, how come the universe is expanding at an accelerating rate? Where does this energy come from?
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0answers
56 views

Assuming the universe is finite, at some point, CMB should go away, right?

I'm not talking about gradual red-shifting, that happens slowly anyway, but with a universe of finite size, we should actually see Cosmic Background Radiation turn off in a sense, first at a point, ...
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2answers
80 views

Negative energy of universe

According to a little I have understood whatever we see in the universe is its postive energy and there is so an equal negative energy. Is this Negative energy the Dark energy? which is responsible ...
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48 views

The “Big-Freeze”, laws of physics and empty space

We currently have data, that suggests the universe will end up in a Big-Freeze. My questions are: Will the laws of physics break down, when the last black hole disintegrates? If so, why? And how long, ...
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1answer
109 views

Is there any paper analyzing the validity of Relativity in expanding space? [duplicate]

Big Bang models result from applying Relativity equations to expanding space; however, as Einstein noted, Relativity was not established in expanding space. A basic question arises: is Relativity ...
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1answer
58 views

Long rod in an expanding universe

Suppose you have a metal rod, of vast length, floating in space. From it's center-of-mass reference frame it is assumed to be at rest with respect to the CMB. The rod will have some degree of ...
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2answers
267 views

Cosmic event horizon changes over time

The cosmic event horizon is the comoving distance beyond which the light signal from distant galaxy can never reach us. With dark matter, the event horizon converges to a finite value so does it mean ...
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1answer
36 views

Is the age of the universe different for different people located at different points in the Universe? [duplicate]

From Earth we say that the age of the universe is 14.5 billion years ago because that is how far we are able to see. But since we are probably not the center of the universe, wouldn't some one many ...
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67 views

CMB parameter, what's the meaning of the matter power spectrum normalization sigma_8?

Most CMB experiments like WMAP and Planck include a certain cosmological parameter called $\sigma_8$. My understanding is that normalization of the matter power spectrum is not a theoretical ...
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1answer
53 views

Even the universe is infinite, it could keep expanding? [closed]

the study showed Cantor, that there are infinite types, the universe would be expanding as well as the possibility of Stephen Hawking. http://phys.org/news/2015-02-big-quantum-equation-universe.html
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1answer
78 views

How do we know the expansion of the universe is “of space” and not “in space” or “into space” or another less intuitive arrangement?

How do we know the expansion of the universe is "of space" and not "in space" or "into space" or another less intuitive arrangement? For example, what implicit and explicit assumptions underlie the ...
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3answers
140 views

Is it valid to apply Einstein's Relativity to scenarios involving expansion of space?

IIs it valid to apply Einstein's Relativity to scenarios involving expansion of space? For a practical example of this: Is it legitimate to speak of distant red-shift galaxies as experiencing time ...
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1answer
225 views

Difference between Gunn Peterson trough and the Lyman Alpha Forest? Cosmological implications?

I'm having difficulty understanding the full implications of the Lyman alpha forest and its use in cosmology. My understanding is this: we detect features in the Intergalactic Medium (IGM) by very ...
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1answer
103 views

How can the universe by infinite when it has known start and finite time since? [duplicate]

Just watched the 'How Big is the Universe?' TV program and it indicated that the universe is believed to be infinite in size. They used an approach involving measuring the internal angles of ...
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1answer
68 views

Is the Big Bang instant considered a beginning of all the coordinates of our universe? [duplicate]

Is the Big Bang instant considered a beginning of all the coordinates of our universe? If we consider the BB to be the Beginning of of our universe, can we call this the Origin of all of the 3 ...
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3answers
61 views

Can we tell the difference types of recession? [duplicate]

Because of the the Hubble red shift pattern, Cosmologist generally assume that space is expanding. They assume this is a fact because of the observed redshifts and GR says it can be so. But how can we ...
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1answer
36 views

Power spectrum calculation in Weinberg's cosmology

In Weinberg's Cosmology, on page 412 eq. 8.1.42 he provides the power spectrum as; $$P(k)=\frac{4(2\pi)^3 N^2 C^2(\Omega_\Lambda / \Omega_M)}{25 \Omega_M^2H_0^4 ...
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2answers
57 views

How tall is the universe?

Let's suppose that I am on a spaceship in low-earth orbit, if I rise my spaceship higher and higher and hover it upwards forever, will there ever come a point where I just can't get up any further or ...
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1answer
84 views

What lies at the very edge of the expanding universe? [duplicate]

We all know that the universe is expanding at an accelerated rate and it might appear much like a soap bubble. That is where the phrase dark energy whose essence is unknown and which is thought to ...
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0answers
75 views

Big Freeze or Heat Death?

I can't seem to find this on the Internet.... Which is most likely to occur to "end" the universe, the big freeze scenario? Or the heat death scenario? P.s. When, if it does at all, will the ...
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29 views

About a *center of the universe* [duplicate]

I understand that the history of our universe began with an explosion - the Big Bang. Now, I saw a comment in some old post, that "the universe has no center". Is that true? If there was initially a ...
5
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1answer
166 views

Is inflation theory really dead?

I know the title is little bit challenging but maybe most of you heard about the last BICEP2 paper on February. As I have read about it here and here. My understanding is, BICEP2 results released on ...
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30 views

On the probability of the existence of a similar observable universe

Let's assume a standard ($\Lambda$CDM + some simple inflation model) cosmology in an infinite universe. Really it doesn't matter much what cosmology we take, just that we're considering an infinite ...
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2answers
96 views

Harvesting hydrogen from a star

I've been thinking about what highly technologically advanced civilisations would do once their energy requirements become comparable to the total output of a star, and how such activity could be ...
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1answer
43 views

Can accelerating universe avoid Big Bang?

Expansion of our universe is accelerating. This means that it was expanding less rapidly in the past. Is in accordance with the laws of physics a model of accelerating universe in which the rate of ...
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1answer
277 views

Is dark energy around a black hole locally curved?

The repartition of dark energy in the vacuum is homogeneous all over the universe. The diagram below represents space with a black hole in the middle. The square is divided in small unit squares. If ...