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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1answer
43 views

What is the difference between the Big Bang Model and the Λ-CDM Model?

If I'm going to write about "The Consensus Model of Cosmology" should I include Big Bang Model or should I go with just the $\Lambda$-CDM Model?
0
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1answer
161 views

Is the Universe infinite or it's just expanding to infinity?

According to the WMAP data in the past years we can say that our universe is considered flat or at least nearly flat and we also know that flat universe is allowed to be both infinite or finite in ...
4
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5answers
514 views

What is the significance of Planck force?

I have been curious to find what could be the significance of Planck force? It is calculated by the formula $c^4/G = 1.21031359\times 10^{44} \, \mathrm{N}$, where $c$ is the speed of light and $G$ is ...
0
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2answers
42 views

Cosmic Scale Factor $R$ and redshift

I'm slightly confused by an idea of redshift: If we assume the distance between two points is given by: $$d = R Δx$$ we can assume that $$λ_0 = R_0 Δx$$ And when we receive the emission it will ...
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0answers
31 views

Could dark energy and Hawking radiation be the same thing?

Specifically, could black holes effectively emit some kind of negative mass or other form of dark energy, so that the mass of the black hole itself would actually increase rather than decrease ...
1
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2answers
362 views

Hamiltonian constraint in spherical Friedmann cosmology

I'm taking a GR course, in which the instructor discussed the 'Hamiltonian constraint' of spherical Friedmann cosmology action. I'm not quite clear about the definition of 'Hamiltonian constraint' ...
0
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1answer
82 views

How can Big Bang happen without time?

I had recently watched a video and he says big bang could have happen by the slow collision rather than a fast collision. But I know that there was no time before the big bang and fast and slow are ...
1
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1answer
43 views

Cosmic inflation and space flatness

I am new here, an avid Physics reader, but have lots of questions and doubts on which I'd like to get the help of a pro physicist. Here goes some about the theory of Inflation: a) after the first ...
20
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2answers
855 views

Do intergalactic magnetic fields imply an Open Universe?

According to a paper on the arXiv (now published in Phys Rev D), they do. How credible is this result? The abstract says: The detection of magnetic fields at high redshifts, and in empty ...
105
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4answers
13k views

Did the Big Bang happen at a point?

TV documentaries invariably show the Big Bang as an exploding ball of fire expanding outwards. Did the Big Bang really explode outwards from a point like this? If not, what did happen?
0
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0answers
22 views

Weinberg Cosmology book Ch 5.2

I am working on Weinberg Cosmology book, and have one question about what contained in Ch 5.2 (page 229). Basically, this chapter is dealing with stochastic initial conditions. What he wrote is that ...
7
votes
4answers
813 views

Experimental evidence for parallel universes/multiverses

My idea of physics is that it is a collection of mathematical laws relating observables. And that one can perform alot of mathematical derivations on these laws to produce new laws between ...
1
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1answer
51 views

Many questions about expanding of the space

Sorry if my grammar is a bit off. But I have few questions about space and its expansion. If space expands faster and faster all the time, will there be a time when we cannot see further than "hubble ...
7
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2answers
739 views

How does universal inflation fit with the Planck length?

If the universe is undergoing inflation, and there is a minimum scale that things can exist at (the Planck length), does that mean that new Planck-sized domains have to be continuously popping into ...
9
votes
1answer
390 views

Pressure and density using a general Lagrangian

Given a lagrangian of a form: \begin{equation}\mathcal{L}=f(\phi,\partial_{\mu}\phi\partial^{\mu}\phi)\end{equation} where $f$ is a function, I need to derive pressure and density in a FLRW universe ...
0
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1answer
50 views

Big Bang not really the beginning of a completely new universe? [on hold]

From what I know about the origins of the universe and the big bang, it is stated that it all started from an intensely hot and dense mass. This sounds like a singularity to me, which means a black ...
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0answers
27 views

What are the effects of relativity on the universe itself? [on hold]

I'm obviously not anything like an expert on the subject, but it occurs to me that the relativity of objects or lack thereof would affect the environment around it. Time moves fastest when there is ...
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0answers
23 views

Question about errors, Hubble's constant

I am just looking through some old notes I have from for cosmology, and theres something cropped up that i can't seem to figure out: Say I have two (or more) values for $H_o$ each with errors such ...
3
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1answer
39 views

Will stars disappear from the sky when their particle horizon is outside the event horizon

Given that the universe is expanding at an accelerated rate, will there be a point where stars visible in the night sky will simply disappear from view when their particle horizon is outside the event ...
3
votes
1answer
56 views

How could the universe be hyperbolic if hyperbolic space isn't symmetrical?

In the 2-D projections of the shape of the universe shown here, we see that the flat universe and the spherical universe are perfectly symmetrical, so any triangle drawn anywhere on them will be the ...
2
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2answers
39 views

Is the metric expansion of space relatively uniform on different length scales?

Is the Metric expansion of space relatively uniform in space? In other words, loosely speaking, does expansion happens everywhere, and over a wide range of length scales. For example, the Hubble ...
0
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1answer
35 views

Expansion of the Universe and Conservation of Energy [duplicate]

How the expansion of the universe doesn't violate the principle of the conservation of energy? If we would put a spring between two objects, the distance would get bigger between them, so would the ...
4
votes
1answer
49 views

What is a slow-roll field?

I am studying inflation reading this article http://lanl.arxiv.org/abs/hep-ph/0406191 and in section 3 it states: This inflaton field may evolve slowly down its effective potential, or not. While ...
0
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2answers
193 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 ...
0
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0answers
6 views

What is the relationship between the E mode polarisation of the CMB and the velocity of the primordial plasma precisely?

I understand that the CMB is polarised into E and B modes due to Thompson scattering in the primordial plasma of the early universe. Also, I understand that this polarisation is directly related to ...
0
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1answer
60 views

In a static bounded universe, what happens to particles that hit the edge?

Consider a flat universe. The metric tensor is $$g_{\mu\nu}=\left(\begin{array}{cccc}-1 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 0 & 0 & ...
3
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2answers
209 views

How do we know that the galaxies the farthest away from us are actually speeding up?

What i mean is Hubble proved that the galaxies the farthest away from us were moving away faster than the galaxies closer to us. I have a basic understanding of red shift. I've always wondered (and ...
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0answers
20 views

What is Phase Transition in Cosmology and where does the energy of it comes from?

There are different theories on how our universe will end. The Big Crunch, The Big Rip, The Big Freeze but I also heard about Phase Transition on a space science program on a science channel, what ...
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3answers
460 views

What is the speed of acceleration of the inflation of the universe?

Is the inflation speed of the universe accelerating or is it a constant speed of expansion proportional to distance between objects.
5
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1answer
65 views

What's the evidence, if any, for some local concentration(s) of dark matter in some region(s) smaller than a galaxy?

What's the evidence, if any, for some local concentration(s) of dark matter in some region(s) smaller than a galaxy? Galactic-sized - or larger - gravitating halos seem to get all the attention. I'm ...
-3
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0answers
37 views

General theory of relativity proves beginning of the universe? [duplicate]

As I'm not a physics student, i only have some basic idea about how the theory works. As Hawking quoted in his book - "A brief history of time " Roger Penrose and I showed that Einstein’s ...
-1
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1answer
65 views

What is a simple explanation to the fact that the universe is expanding? [closed]

How can we prove that the expansion of the universe is actually occurring to highschool children?
3
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1answer
126 views

Distance between two galaxies of different redshift

Let $Q_1$ and $Q_2$ two different objects in the Universe (we can think to two galaxies or quasars), that we observe from the Earth at different angular position $(\alpha_1,\delta_1)$, ...
0
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1answer
358 views

Does the Casimir effect give the correct value for Dark Energy?

My understanding is that the Casimir Effect is caused by vacuum energy. Quantum mechanics (QED) predicts vacuum energy, but gets the value grossly wrong, by a factor of $10^{120}$. On the other hand, ...
2
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1answer
326 views

In the big crunch theory, when the big crunch singularity forms, can the resulting black hole decay through hawking's radiation?

I've been pondering about this and I couldn't really find the answer for this. The big crunch theory postulates that the universe will eventually stop expanding and reverse back in on its self into a ...
1
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1answer
130 views

The CMB and the Hubble comoving radius

I have been thinking on this for a while and i don't get it. My point is, the comoving Hubble radius $(aH)^{-1}$ is the distance at wich the universe expansion begins to be superluminical. In an ...
3
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1answer
22 views

What is a quasar flux ratio anomaly?

In the context of strongly lensed, multiply-imaged quasar observations, I sometimes hear about "flux ratio anomalies". What are these? Why are they important?
5
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4answers
648 views

Before the Big Bang

I've heard this saying before I don't know about anyone else. It says, "What ever was before the Big Bang is something physics can't explain..! Is this saying true (accurate)?
0
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1answer
48 views

Did time also began from big bang?

Did time began from big bang? If not then what existed before big bang? If time had a beginning, then does it have a end, or pause because if time had a pause then we would not have known about it, ...
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1answer
45 views

Can the curvature of the Universe be a function of time?

Apologies for the repetition here, but can our Universe experience (either physically or mathematically) non-constant curvature that is a function of time?
5
votes
2answers
193 views

Is entropy absolute (as in absolute temperature)?

Following this question on the Entropy at the Big Bang where I asked: Since Entropy always increases (in general); its expected that the entropy at the beginning of the universe should be the ...
-1
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0answers
48 views

Can the energy released from a black hole be calculated at the time of birth?

this might be a stupid question but when a black hole is formed it releases a lot of energy our satellites just catch the gamma rays and X rays released by the black hole. can we estimate the amount ...
1
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1answer
77 views

What would happen if there was a fifth fundamental force? [closed]

Preceding this question, as a student of physics, my knowledge of theoretical physics is somewhat limited. So I came across this article, which posited what the universe would be like if three ...
1
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0answers
32 views

Doppler shift of light from stars and galaxies [duplicate]

I was reading about how we can ascertain whether a cosmic object is receding from or approaching us by studying the doppler shift of its spectrum- I mean the redshift and blue-shift. But we have no ...
1
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3answers
60 views

What evidence is there that universe will not shrink again?

There are theory that universe eternally expanding and shrinking, so that every event and our lives will repeated again. At the other hand some scientists thinks that it will not shrink again because ...
1
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0answers
32 views

Curisioty about universe [duplicate]

I am a bachelor student and I have a question going round my mind about the universe. Every one says that the universe is ever expanding and it is also said that the vast possible space is also the ...
1
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0answers
28 views

Is there a direct/indirect detection for the homogeneity of the Universe?

I know that for mathematical simplicity the Universe is assumed to be isotropic and homogeneous (the cosmological principle). The isotropy of the universe, and correct me if I'm wrong, is confirmed ...
-1
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0answers
26 views

In the end, will all the matter of the universe end up where it began?

Toward the end of everything, when all the matter in the universe comes back together, will it be in about the same position in space as the matter that instigated the big bang?
11
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2answers
724 views

Could I see the cosmic microwave background if it were Doppler shifted enough?

If I traveled fast enough, my current understanding is that visible light would be blueshifted to the blue/UV range, but also that microwaves and longer wavelength waves would be blueshifted into the ...
2
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2answers
268 views

How does a particular galaxy's apparent recessional velocity CHANGE as the universe expands?

By this I mean will the light from distant galaxies continue to show red shift (i.e. if you look at light from a particular galaxy now and in 10000 years time, the spectra will have been shifted ...