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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4
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2answers
213 views

Has neutrino redshift been observed?

I understand that neutrinos are emitted when supernova explode. I presume that there are quite accurate models that predict the energies of those neutrinos at the time of emission. Has the phenomenon ...
0
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0answers
20 views

de Sitter reviews?

I'm very interested in learning more about de Sitter and anti-de Sitter spaces and their applications in GR and cosmology. Can anyone recommend favorite review articles -- or, more likely, a series ...
1
vote
1answer
78 views

What's between the branes?

So I'm doing my best to explain M Theory to some friends... Mind you, I'm no expert... When we finally got past the obstacle of more than three dimensions... which can be difficult for folks who ...
1
vote
1answer
101 views

What is the temperature of the event horizon?

In a discussion with my son about absolute zero, we arrived at the conclusion that the event horizon might be the place to look, as it "absorbs?" all energy, including light. Found this in the ...
0
votes
1answer
38 views

Would those 'trapped' in a collapsing universe perceive space as expanding?

Let's say we have Uber Massif; a black hole so mindbogglingly huge, if you where to shrink the entire milkyway into a thimble Uber Massif would be the size of the milkyway. Those proportions need not ...
2
votes
2answers
84 views

Why can I always see a star? [duplicate]

Light moves along straight lines... Got it. So if the light from that faraway star is traveling in a straight line, and that beam is, considering the distaces involved, at best one or two photons ...
0
votes
1answer
58 views

Do sound waves travel before Big Bang?

So I was reading a Scientific American article about how the universe is spreading apart and how it is getting faster. But in the article there was something that baffled be and it was this "Sound ...
0
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0answers
51 views

Motion without matter

Suppose you have a vacuum spacetime with non zero cosmological constant then you can show that two test particles will move toward each other or apart depending on whether it is negative or positive ...
0
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1answer
36 views

Are the edges of a galaxy moving inwards?

Space is expanding, but as I understand it, galaxies are not since gravity keeps them together. If you think of space becoming bigger, your galaxies just become further apart. But taking the size of ...
-1
votes
1answer
51 views

Why is the expansion of universe continuously increasing? [closed]

If our universe is expanding and the concept of the multiverse is true, then why is the rate of the expansion of the universe increasing? Surely it must decrease?
1
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1answer
69 views

Does a rigid box of gas cool over cosmological timescales?

According to standard cosmology theory the physical momentum $p$ of both massive and massless particles decay like: $$p \propto \frac{1}{a(t)}$$ where $a(t)$ is the scale factor as function of ...
2
votes
2answers
81 views

Observer inside event horizon of an extremely large black hole [duplicate]

Imagine a very large black hole, with a mass equal to a large number of galaxies. Assume a space station is in orbit around the black hole some distance from the event horizon at a point A. An ...
0
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0answers
26 views

If a metric has off diagonal terms, how can I calculate the tetrads?

If a metric has off diagonal terms, how can I calculate the tetrads? I need to calculate the Dirac gamma matrices in BTZ blackhole spacetime... $e^\mu_{(a)} e^\nu_{(b)} \eta^{ab} = g^{\mu\nu}$ ...
0
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1answer
54 views

Evidence of possible tidal effects close to a gravitational wave emitting system

Currently we are attempting to detect gravitational wave emissions using the LIGO gravitational wave detection system (and similiar systems), by attempting to detect very weak gravitational waves ...
0
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0answers
54 views

Outer Space & Universe Expansion: [duplicate]

Experts agree that the stuff within the universe is moving farther apart from all the other stuff in the universe--much like the dots marked on the outside of a balloon that is being inflated. We ...
1
vote
1answer
48 views

Do observers at rest at different positions in a gravitational field see the Universe expand at different rates

If we consider observers at rest outside a Schwarzschild black hole, the amount of proper time elapsed in terms of coordinate time is given by $\Delta\tau=\sqrt\frac{r-1}{r}\Delta t$ (where r is ...
1
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1answer
22 views

Lifting an analogy of a pond to question signals at natural or artificial boundaries in space-time [closed]

I conjured up an idea to lift an analogy into the language of QFT and GR. I thought up the universe as a pond with a liquid. If we imagine a liquid poured into some pond (sort of bang and inflation ...
0
votes
2answers
87 views

If the Universe is going to last infinitely long, what is the type of this infinity?

Let's say we've built a machine, that prints a sequence of all natural numbers from 0 to $\infty$. We "could" do this in a Universe with an infinite amount time (if we also make many other assumptions ...
1
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0answers
32 views

Did the early universe violate the 2nd law of thermodynamics? [duplicate]

If the universe started out isotropic and homogenous and of all fundamental particles then how could there now be any concentration of energy anywhere? If you say that nothing is really homogenous ...
-3
votes
1answer
60 views

It's a Hypothesis about the Beginning of the universe [closed]

Let's take a piece of paper and plot a couple of dots in it. If we shrink the paper infinitely, at some point it would reach a state of infinite density, that is; a Singularity. But even at that ...
5
votes
3answers
283 views

If the expansion of the Universe accelerates, why its horizon does not shrink?

In de Sitter (expanding) universe to which our universe asymptotically approaches, the higher the rate of space expansion, the smaller the radius of the cosmic horizon. Why then our universe is ...
1
vote
1answer
55 views

How was there an extra particle in the early universe?

According to theories.. In the early universe.. There were particles and anti-particles in equal number.. But there seems to be one extra particle against the number of anti-particles.. As the ...
2
votes
2answers
80 views

Interpretation of cosmological redshift

I was trying to understand why we cannot explain the observed redshift of distant galaxies using special relativity and I came upon this article by Davis and Lineweaver. Unfortunately when I arrive ...
8
votes
4answers
947 views

Does an object's redshift actually decrease with time?

I am trying to determine how an object's redshift (specifically, redshift due just to the expansion of the universe) changes in time. Starting with a definition of the Hubble parameter, $$H \equiv ...
1
vote
0answers
28 views

Phase-space average equal to the quantum mechanical average in the early universe

I was reading Mukhanov's book of cosmology http://www.amazon.com/Physical-Foundations-Cosmology-Viatcheslav-Mukhanov/dp/0521563984 , specifically about symmetry restoration in the early universe ...
2
votes
1answer
69 views

What is the interpretation of a wave function of the Universe in Hawking's no boundary proposal?

In the path integral formalism we have an in state $\Psi_{in}[\phi]$ and and out state and we find the amplitude for going from one to the other: $$\Delta[\Psi_{in},\Psi_{out}] = \int ...
6
votes
1answer
69 views

What are the cosmological ramifications if we probabilise and continuify the order of differentiation in $F=\frac{d(mv)}{dt}$?

Newton's second law of motion states that $F=\frac{d(mv)}{dt}$. This is a first-order differential equation, in which the order of differentiation of momentum is 1. So we can write it ...
0
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0answers
35 views

Can the newly discovered mass of the neutrino explain in part, the missing matter [duplicate]

This question is related to the recent discovery of the neutrino mass 0.320 ± 0.081 eV/$c^2$. Could this account for at least some of the Dark Matter/Missing matter of the universe?
0
votes
1answer
39 views

How do Hubble Units work?

I'm reading through a document - Briel et al (1992) (pdf) - and I've come across Hubble units with which I'm not familiar. How do you interpret something like $$h^{1/2}_{50} \:\mathrm{cm}^{-3}$$ or ...
0
votes
1answer
57 views

Is entropy violated inside black holes and worm holes?

Do the laws of thermodynamics hold true everywhere in universe ? What about black holes and worm holes ?
1
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0answers
26 views

Primordial black hole mass [closed]

Use dimensional arguments to combine the fundamental constants $\hbar$, $c$ and $G$ to derive the least massive primordial black hole formed shortly after the big bang. I'm not sure how to combine ...
0
votes
0answers
27 views

Scale factor negative

Can the scale factor in a robertson-walker metric with k=0 (flat universe, with only matter, no cosmological constant or quintessence) depend on a polynomial function? For example: ...
0
votes
0answers
38 views

Could there be ways to form hypergiant stars, quasars or supermassive black holes at the beginning of the Dark Ages?

Original title: Heat loss in collapsing parcels of gas or weak plasma at the beginning (not the end) of the cosmological dark ages Star formation from collapsing parcels of primordial gas in the late ...
1
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2answers
24 views

What type of observational constraints are there for reionization?

What type of observational evidence is used to constrain reionization? At what redshift?
2
votes
2answers
114 views

How fast does space/time travel?

It is said that before the big bang there was no before, as space/time was created in the big bang. The big bang creates a rapid expansion of space/time... so how fast is rapid?
-4
votes
1answer
85 views

What is the value of the Universe's acceleration? [closed]

Please read this http://www.researchgate.net/publication/282157370_VALUE_OF_THE_UNIVERSE%27S_ACCELERATION Your ideas are welcome.
0
votes
0answers
40 views

Can an electron in empty space to create electromagnetic radiation?

Is it possible in the empty space to create electromagnetic radiation from oscillations of the charges only of one kind - positive or negative? This question stems from the fact that all man-made ...
3
votes
1answer
164 views

Can we regard dark matter as a special fluid rather than individual particles?

If we assume that dark matter is an $N$-body system of sizeless and collisionless particles which only interact via newtonian gravity, do these huge quantity of particles manifest some collective ...
0
votes
1answer
188 views

How fast are we moving when standing still? [duplicate]

The Earth rotates around itself and revolves around the Sun. Our solar system revolves around the center of our galaxy and our galaxy is moving in some way throughout the universe. If you took into ...
0
votes
1answer
51 views

What would antimatter planets look like?

Let's say – hypothetically – in the vastness of space, we found a planet made entirely out of antimatter and surrounded by barely any matter. If someone were to look at the planet, would they confuse ...
1
vote
2answers
119 views

Why does dark energy seem to push things apart? [duplicate]

Ordinary matter acts to slow down the expansion of the universe. That makes intuitive sense, because the matter is exerting a gravitational force, acting to pull things together. Moreover, dark ...
-3
votes
1answer
49 views

Explanation and quantum gravity [closed]

Is spacetime accelerating? Is it accelerating within an acceleration ?Or is it a constant? (are different objects or particles influenced by other rates in spacetime compared to one-another and if ...
7
votes
1answer
125 views

Did the initiation of the Higgs Field and the inflationary period occur simultaneously?

My question is: Both of these concepts involve a phase transition and they both started, as far as I know, early in time, so are the above two ideas linked in any way? My first source for this query ...
4
votes
2answers
83 views

What evidence is there for additional dark energy coming into existence when space increases?

As I understand since cosmological constant is a 'constant' - increasing the space must generate additional dark energy that fills that space This does sound counter-intuitive to me, but I am sure ...
0
votes
0answers
37 views

Bulk action - Can a brane velocity be defined?

a) If a brane action in a bulk is defined, in that case, that a brane is modelwise moving through a bulk, how is this ratio defined? Is this a regular "velocity" in that meaning, that space is being ...
6
votes
1answer
84 views

Could observed accelerating expansion be an illusion based on distance?

The thought occurred to me that if we just happened to be born into a time when the the universe started slowing down, it would take some time for us to observe this - especially in more distant ...
2
votes
2answers
69 views

During the “Dark Ages” of the Universe's evolution, how lumpy (anisotropic) and dynamic was the mass distribution?

In the dark ages between recombination (~0.4 Myr post-BB) and reionization (~300 Myr post-BB) of atoms, there was not any condensed-phase matter (except maybe some form of dark matter), nor radiation ...
2
votes
1answer
73 views

Convert from Relative Magnitude to Mass

I have data which gives me the magnitude density (${\rm mag}\,{\rm arcsec}^{-2}$) of M31 as a function of radius. How can I convert these data to the (enclosed) mass at a given radius (for velocity ...
2
votes
1answer
47 views

Why did formation of the first stars (population III) not happen earlier?

Was it the cooling of the universe? Naively, I would expect the lowering density to work against star formation.