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
103 views

The 3rd derivative of the size of the universe?

We know the size of observable universe, that it is expanding, that expansion is accelerating. Does sufficiently precise data exist to determine at least the SIGN of the next (the 3rd) derivative? ...
0
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1answer
43 views

Size of the Hubble volume in 4 billion years

What will the size of the observable universe be in 4 billion years? At present day, light would only reach us if it came from a galaxy within 13.5 billion1 light years, with anything outside that ...
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0answers
70 views

Center of mass & Big Bang Theory

I have read in my text books about the Big Bang theory and quote "the entire matter in the universe was once concentrated in a single very dense and hot fire ball; it exploded some 20 billion years ...
1
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1answer
30 views

Quasars with differing emission / absorption redshifts

I was reading this (perhaps offbeat) "anti-big-bang" article, http://www.newtonphysics.on.ca/hubble/ and the author comments "a recent catalog of objects having very large redshifts shows that among ...
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2answers
78 views

Newtonian potential defines size of Universe?

As I understand it the Newtonian potential $\Phi$ at the position of an observer in space is approximately given by: $$\Phi \sim \frac{G M}{R},$$ where $R$ is the radius of a sphere centered at the ...
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3answers
64 views

source of energy for expansion of the universe

I know in order for something to expand or grow it has to be fueled by something? So, if the universe is expanding their must be something that's keeping the universe at a temperature high enough for ...
3
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0answers
31 views

C and CP violation in Baryogenesis

Why both C and CP are needed for baryogenesis? Isn't CP violation enough?
0
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1answer
77 views

dark energy and expansion definition [closed]

I am trying to get a few key points correct regarding expansion and dark energy... Expansion: the Universe has been expanding continuously at different rates since the singularity that caused the ...
0
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0answers
25 views

Need advice for self study in physics [duplicate]

I need advice for self study in Physics. I have a good theoretical and practical background in math & statistics, but virtually no physics. My ultimate interest is cosmology / relativity / ...
4
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2answers
146 views

FRW metric and its validity througout the age of the universe

Why do we think that the FRW metric should be valid throughout the entire history of the universe?
0
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1answer
51 views

TEO: raise of a System [closed]

I think this question is settled somewhere betweeen physics and philosophy and we surely can not find a answer that fits 100%, but lets talk about it. While thinking about how the universe and its ...
2
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1answer
83 views

How can the Big Bang singularity exist in spacetime if it has zero volume? [closed]

How can the Big Bang singularity exist if it has zero volume? I tried googling to find the answer - no help. Can someone give a general idea how can the big bang singularity exist even if it has zero ...
3
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2answers
113 views

Could Dust Equation of State have some negative pressure?

Traditionally the cosmological equation of state of cold matter (so-called dust) is simply: $$p = 0.$$ But, in Newtonian terms, each particle is gravitationally attracting every other particle. ...
2
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1answer
57 views

Why is the graph of CMB/black-body radiation asymptotic?

Speaking of this graph of blackbody radiation, I see that the graph goes to 0 asymptotically: As we go to higher and higher frequencies, the energy of a single photon becomes increasingly high. ...
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0answers
69 views

How strong is the force of space expansion?

There are many questions about space expansion, its cause, or its effects. But I have the feeling we never get straight and simple answers. I do not expect answers to be simple in general, but I ...
17
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3answers
788 views

Why is the sky dark at night? [duplicate]

The question is the well-known Olbers' paradox: If there are so many/infinite stars, in every direction, why is it dark at night? Where goes all the light we don't see? Discussing with a friend ...
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1answer
42 views

Are there other places to look for the gravitational wave, other than space?

The recent BICEP2 announcements about the existence of gravity waves made the news, and made a big pitch for cosmic inflation, in the process they also claimed to detect the existence of gravitational ...
0
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1answer
54 views

Spiral Galaxies and Gravity Lenses

Spiral Galaxies must have a great deal more mass than elliptical galaxies of the same size in order to account for the flat velocity curve. I've seen references of eight to ten times the visible ...
49
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3answers
5k 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?
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1answer
75 views

A universe from nothing [duplicate]

The more time you spending in measuring your experiment (thus standard deviation will become smaller) the more precisely you will measure energy of this system.... energy time uncertainly principle ...
2
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3answers
121 views

Has the universe we live in started as a black hole that is imploding?

As discussed in this question, as far back as the 1960s it was suggested that the Schwarzschild metric can be smoothly joined to a de Sitter metric. For example the idea has been used by Lee Smolin in ...
2
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1answer
67 views

Can a lone black hole in a closed Universe evaporate?

If there is a closed Universe which only has a black hole in it, can that black hole evaporate? As the black hole evaporates, it gives off energy, which will eventually come back and be re-absorbed ...
4
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1answer
700 views

Why do we only talk about three options when it comes to the Shape of Spacetime?

The shape of spacetime is a hotly debated topic which can determine how we understand the ultimate fate of the universe and many more things. Despite this I only ever see factions supporting three ...
9
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1answer
276 views

How does the Hubble parameter change with the age of the universe?

How does the Hubble parameter change with the age of the universe? This question was posted recently, and I had almost finished writing an answer when the question was deleted. Since it's a shame to ...
3
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0answers
48 views

When Did Structures Begin to Orbit in the Universe?

In Big Bang Cosmology, I am familiar with the radiation era, and the moment of last scattering, but I am just not familiar with the physics of orbits, or of the “falling outward,“ if you will, that ...
0
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1answer
48 views

Simplifying Friedmann's Equation

So we have one of Friedmann's equation: $$\rho_c = \frac{3H^2}{8\pi G}$$ Using This website, resources where gathered for specific times in the universe. The resources being the Hubble constant at ...
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0answers
24 views

A physical understanding of the 2/3 in the Sachs-Wolfe effect

I am trying to develop an intuitive but quantitative understanding of the factor of 2/3 in the Sachs-Wolfe effect. I believe I have a picture that makes sense but it relies on one assumption I don't ...
0
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1answer
49 views

Friedmann equations question

Friedmann equations for critical density is: $$\rho_c = \frac{3H^2}{8\pi G}$$ Is there any other way to write this equation? For example: $$\rho_c = \frac{3}{8\pi GH^2}$$ I saw the above form on ...
2
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1answer
138 views

Is there an alternative to dark matter?

I've been reading about dark matter. I understood that its existence is inferred by the discrepancy between the gravity exerted by a galaxy (total mass) and the movement of the stars that compose it. ...
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2answers
55 views

Searching for Big Bang Neutrinos

How is it possible to discover neutrinos from the big bang? Were the neutrinos emitted just before the big bang? Or at the same moment? If they moved outward in all directions, basically unhindered ...
9
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1answer
88 views

Is it possible to determine whether distant galaxies are gravitationally bound

In a previous question, one issue was related to the potential energy of cosmic structures. This raised in particular the question of whether these structures are gravitationally bound. If you ...
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1answer
48 views

Degrees of freedom in the early Universe

I am reading Dodelson's textbook on cosmology. On page 66 we find equation 3.26: $$\rho = \frac{\pi^2}{30}T^4\biggl[\sum_{i=\text{bosons}}g_i+\frac{7}{8}\sum_{i=\text{fermions}}g_i\biggr]\equiv ...
7
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2answers
65 views

What is the composition of the universe's population of neutrinos?

I believe earth-based detectors measure mainly solar neutrinos, which have energies on the MeV scale of nuclear physics, are directed from the sun, and have flavors determined by the sun's nuclear ...
1
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1answer
49 views

Data/signal from a black hole to observe a singularity

I wonder if a situation is possible where, we measure some signal/property concerning a black hole. Supposing the measurement we make with some telescope, gets us the Fourier transform coefficients of ...
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0answers
37 views

Sharpness of starlight

I am interested in argument that the observed lack of blurriness in starlight refutes the "tired light" theories. I have not been able to find this argument expanded in detail. There are two ways ...
2
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1answer
61 views

Expanding universe space through matter or matter through space? [duplicate]

So the universe is expanding, rather space is expanding. By expanding we mean space is coming into existence at all points.  Is that an equal rate of expansion everywhere? Now the expansion does not ...
1
vote
1answer
94 views

Expanding metre sticks [duplicate]

Given the Universe is expanding. Therefore everything within the U is expanding, in all dimensions, subatomic to cosmic. Then all metre sticks are expanding. The question: How can we measure U ...
27
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3answers
4k views

How can interstellar space have a temperature of 2-3K?

Several different sources online state that the average temperature of interstellar space (or the universe in general) is around 2-3K. I learned that temperature is basically the wiggling of matter, ...
7
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2answers
79 views

What did recombination look like?

I recently remembered that someone worked out what the big bang sounded like and that got me thinking... About 377,000 years after the Big Bang, electrons became bound to nuclei to form neutral ...
3
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3answers
111 views

The Universe as a four-dimensional sphere?

I was chatting with my 12yo cousin yesterday and we got to the Universe, its size and stuff like that. Then he came up with the idea (I'll rephrase it), that the Universe could basically be a 4d ...
2
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2answers
68 views

How do we observe the expansion of the universe?

This is my first question. So I was reading about expansion of the universe and from what I've seen, the only way that we know that universe is expanding is by measuring redshift. Also, here it says ...
3
votes
1answer
699 views

Does dark energy annihilate energy?

Antimatter and matter particles annihilate. But does dark energy annihilate energy? We consider energy to be photons, and such, correct? So when we say energy, we're actually talking about some ...
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2answers
65 views

Tachyonic field

i'm working on a paper about symmetron cosmology. symmetron is a scalar field that by its symmetry breaking can explain the dark energy. the action is: ans A , V are assumed to be: where M ...
7
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2answers
279 views

If we could build a telescope to view the cosmic neutrino background, what would we see?

If we could build a neutrino telescope capable of viewing relic neutrinos that decoupled after the big bang, with a similar angular and spectral resolution that is possible now for the CMB (e.g. with ...
2
votes
2answers
87 views

Why did the big bang need to produce equal amounts of matter and antimatter? [duplicate]

I've tried to find an answer for this but couldn't find one. Whats the problem with matter being created with little or no antimatter
13
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1answer
257 views

As the universe expands, the wavelengths of photons are stretched, and energy is lost. What about electrons?

Will electrons, and other particles, also loose energy as they travel through the cosmos? They have wavelengths. Do they get "stretched"? My guess is that the EM force, somehow, counteracts this ...
2
votes
2answers
110 views

Expanding universe and the speed of light [duplicate]

When physicists talk about the expanding universe they often say that the distant galaxies are not really "moving" away but instead the space itself between us and them is expanding. If this is true ...
1
vote
1answer
116 views

Why is everything colder nowadays? [duplicate]

I know that when the universe began it was incredibly hot. Ever since, it is been cooling, and nowadays the average temperature of the universe is quite close to 0 K. Is this a consequence of having ...
1
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2answers
80 views

Best Research Documentation Habit for Computational Physics Research [closed]

I am currently doing research in a subset of the field of gravitational lensing called weak lensing. I am simulating blended galaxy profiles and creating an algorithm to extract the true parameters I ...
12
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4answers
246 views

Is the Big Bang defined as before or after Inflation?

Is the Big Bang defined as before or after Inflation? Seems like a simple enough question to answer right? And if just yesterday I were to encounter this, I'd have given a definite answer. But I've ...