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.

learn more… | top users | synonyms (1)

-1
votes
1answer
93 views

If the universe can expand at a speed faster than that of light, why don't we feel the effect? [closed]

the universe, as I have read, is capable of inflating at a speed faster than that of light! How is that even possible if we don't feel the effect? or does it affect us?
1
vote
1answer
116 views

Metric expansion of space - past, present and future

Scientists say that out universe is expanding faster and faster. This was detected via the red-shift effect. Farther galaxies are moving from us faster than those that are more closely. But how can ...
5
votes
1answer
160 views

Age of the universe and age of stars

The age of the universe is 13.798±0.037 billion years, yet the age of HD 140283 is 14.46±0.8 billion years, how this can be the case?
5
votes
0answers
125 views

Does the radius of the Universe correspond to its total entropy?

I heard a claim that due to holographic principle, the surface area of the cosmic horizon corresponds to the universe's total entropy. As such the initial state had zero surface area and later ...
0
votes
0answers
32 views

What were the dimensions of the universe during Planck epoch?

Wikipedia says: It is believed that, due to the extraordinarily small scale of the universe at the time, quantum effects of gravity dominated physical interactions. But I wonder whether ...
1
vote
4answers
227 views

The universe is expanding but why the galaxies have no motion?

It is said that the universe is expanding and the galaxies are moving apart. I understand that the space between every two galaxies is increasing. Doesn't this seem to imply that the galaxies will ...
1
vote
1answer
69 views

are there any “known unknowns” that could affect the possibility of a false vacuum?

(Although Donald Rumsfeld was mocked for talking about "known unknowns" and "unknown unknowns", I think it's an truly important distinction.) Periodically, I hear about how the universe might be in a ...
0
votes
0answers
23 views

Hubble's law for the Kasner solution

I'm puzzled with the following question: find an analog of the Hubble's law for the Kasner solution. Kasner metric is a solution to the vacuum Einstein equations ...
11
votes
2answers
489 views

How is it possible the universe expanded faster than the speed of light during inflation?

In a documentary written in collaboration with Stephen Hawking, the narrator (supposedly Stephen Hawkings) says that by the time the cosmos was 10 minutes old, it had already expanded thousands of ...
0
votes
1answer
61 views

Temperatures at extreme densities

Cosmology (and astrophysics) talk about the "initial singularity" (IS, became the big bang) and "black hole singularities" (BS, inside black holes), and these appear to be quite different: The IS is ...
2
votes
1answer
36 views

Cosmological and gravitational redshift in physics

I am interested in knowing what are the differences between gravitational and cosmological redshifts?
0
votes
1answer
34 views

Distance to the galaxy which has velocity which is perpendicular to the point of view of the static observer

Let's have the galaxy which has velocity which is perpendicular to the point of view of the static observer in the FLRW universe. It emits the light. There is a given redshift $z_{0}$. It will be easy ...
8
votes
8answers
393 views

As the universe ages, will we see more stars or less?

After a very long time will we see more stars (due to the fact that more light is get to us) or less stars (as the universe expends and light have to pass larger distance)? In general, can stellar ...
2
votes
1answer
271 views

How to obtain the field equations in Brans-Dicke theory from the action?

The action for the Brans-Dicke-Jordan theory of gravity is $$ \\S =\int d^4x\sqrt{-g} \; \left(\frac{\phi R - \omega\frac{\partial_a\phi\partial^a\phi}{\phi}}{16\pi} + \mathcal{L}_\mathrm{M}\right). ...
0
votes
0answers
17 views

Method of determining peculiar speed of the galaxy which moves on celestial sphere and emits the light

This question is the continuation of this one. I came up with solution, but I'm not sure that it is correct. Can someone check it? Let's introduce transverse (to the observer) proper speed ...
0
votes
0answers
39 views

How to find proper speed (relate to homogeneous cosmic background) of the galaxy by given redshift z and observing angular velocity?

The galaxy moves of the celestial sphere. It is given that proper speed is transverse to the observer and it must to find this speed in the moment of light emission. The motion is in the FLRW ...
0
votes
0answers
39 views

Differential equation for speed relate to the homogeneous cosmological background in FLRW metric

How to derive DE for the speed (which relate to the homogeneous cosmological background) of the observer which moves with constant proper acceleration in spatially flat FLRW universe?
1
vote
1answer
41 views

Relation between red filter band and redshift?

I am interested in knowing what is the significance of red filter band in the study of redshift dependence of spatial orientation of galaxies?
0
votes
0answers
21 views

Redshift Dependence in the Spatial Orientation of SDSS Galaxies having Redshift 0.19 to 0.20

Does redshift depend on the spatial orientation of SDSS galaxies with redshift in the range 0.19 to 0.20 ?
0
votes
2answers
160 views

Goodwins “proof” and space time

I read about Goodwin's "proof" that $\pi = 3.20$, it's BS and I know that. What I am wondering is whether his technique may have stumbled on something ( a warped space) years before Einstein. So I ...
2
votes
2answers
288 views

Is Dark Matter evenly spread out in the universe?

Is Dark Matter evenly spread out? If no, could we ever find a correlation between the amount of dark matter and matter in a specific place?
6
votes
0answers
183 views

Equation of motion for cyclic model of the universe

I recently started to study about cyclic universe. I came across this article [1]. My question is about the action that used for describing the cyclic model: $$S = \int d^{4}x\sqrt{-g}(\frac{1}{16\pi ...
5
votes
1answer
113 views

Lower limit of the size of the Universe? (WMAP)

The measurement of the WMAP satellite resulted a planar geometry of the universe with a 0.4% uncertainity (http://en.wikipedia.org/wiki/Shape_of_the_universe). If there is a little deviation from the ...
0
votes
0answers
44 views

What will happen to matter if there is a Higgs metastability decay?

Previously, on Save us from swallowing baby universes, please!, I pointed out the dangers associated with false vacuum decay. I wish to be more specific here. Suppose the Standard Model remains a ...
0
votes
3answers
563 views

Whats left at the center of the Universe after Big bang?

If you consider big bang. According to that What's left at the center of universe where the Big bang occured?
3
votes
0answers
52 views

Are there any stable (not metastable) string theory compactifications with a positive cosmological constant?

Previously, on Save us from swallowing baby universes, please!, I asked how we can be saved from false vacuum decay assuming we are living in a false vacuum. What if we are living in a stable vacuum ...
2
votes
1answer
95 views

The universe being finite

I always thought we didn't know if the universe is finite or infinite. However is it true that the universe (not just the observable one) is finite with no boundaries? The articles arXiv:0901.3354 ...
2
votes
2answers
111 views

Could there have been two “Big Bangs”?

A couple of years ago, I remember seeing a documentary on the big bang theory. The theory presented was that to explain the cosmic microwave background radiation, there needed to have been two big ...
0
votes
0answers
143 views

Reference request: Hollow concave Earth hypothesis

Reference request concerning the Hollow concave Earth hypothesis. I am searching for this paper: A Geocosmos: Mapping Outer Space Into a Hollow Earth authored by M. Abdelkader and published in ...
5
votes
3answers
155 views

Is isotropy a fundamental/invariant feature of our universe, or is it merely a convenient, albeit arbitrary, feature of some reference frames?

This is related to a previous post. Assuming that the Cosmological Principle is correct, does this imply that the universe possess an empircially privileged reference frame? What I am trying to ...
7
votes
2answers
205 views

Assuming that the Cosmological Principle is correct, does this imply that the universe possess an empircially privileged reference frame?

OK...before everyone blasts this with references to the relativistic invariance of the physical laws, time dilation, etc let me add some context. Also, I am an amateur with an interest in physics, so ...
8
votes
1answer
189 views

Will entropy continue to increase even if the universe begins to contract?

If the universe is heading for a big crunch, when the universe starts to collapse will entropy decrease and the arrow of time consequently reverse or not? I'm interested in the explanations, not just ...
2
votes
1answer
109 views

Cosmological metric with off-diagonal terms?

In the context of Cosmology models, What are examples of metrics with off-diagonal terms?
6
votes
1answer
123 views

What are the different ways to measure the spatial curvature of the universe?

Just what the question asks. Assuming the Friedmann-Rovertson-Walker (FRW) metric, what measurements can be performed to determine the spatial curvature of the universe.
4
votes
1answer
156 views

How would one expect a massive graviton to behave?

Typically, adding a mass $m$ to a gauge boson causes the boson to only be able to travel over a finite distance, $L\sim m^{-1}$, limiting the range of the associated force. For example, photons ...
1
vote
2answers
203 views

Bathroom photons from the edge at the universe [duplicate]

I was looking through my bathroom window this night and I was wondering if any of the photons my retina is hit with are from 13 (40) billion light years away ?! I was looking through it a few ...
2
votes
0answers
61 views

What's the difference between eternal inflation and chaotic inflation?

Is there a real difference between eternal inflation and "chaotic inflation" theories?
4
votes
1answer
137 views

Can the total amount of energy in the entire universe be quantified?

Classical thermodynamics leads one to believe that if energy is transferred, and the universe is heading for maximum entropy, then back extrapolating to moments before the big bang, one could find a ...
5
votes
1answer
118 views

Charge neutrality of the Universe: evidences and theories

I've always wondered why the number of protons in the Universe exactly matches the number of electrons. They are such different particles with totally different cross sections. So, first of all, is ...
2
votes
1answer
51 views

Will the Hubble constant reach zero asymptotically in the far future?

In the current accelerated expansion universe model will the Hubble constant reach zero asymptotically in the far future?
0
votes
0answers
61 views

What's the timescale until the Medium Crunch?

The future of the universe seems to be: clusters of galaxies drift apart due to space expansion until they all pass out of each other's cosmic event horizon. Gravitationally bound clusters overcome ...
11
votes
0answers
571 views

Is the “Doctor Who” spacetime affected by Hawking's chronology protection mechanism?

Recently, there has been a paper1 (and an accompanying layman-ized white paper2) on "Traversable Achronal Retrograde Domains In Spacetime", TARDIS for short. It proposes a spacetime geometry that ...
1
vote
0answers
55 views

In bubble-multiverse theories, are the parameters values describing a given universe members of a countably infinite set?

I recently had the chance to read Brian Greene's "Hidden Reality" with all its talk of multiverses. He makes a case that there may be an infinite number of identical copies of our world "out there". ...
10
votes
1answer
88 views

Do primordial background neutrinos orbit in dark matter halos?

According to Wikipedia, neutrinos separated from other matter seconds after the Big Bang and formed a separate background radiation field which now fills space at a temperature ~2 K. Supposing ...
4
votes
1answer
115 views

Does space expansion imply light will *never* reach objects currently distant enough?

Let's say two objects are at about twice the Hubble Distance from each other. One of them emits light towards the other. When light emitted from one reaches the Hubble Distance from its origin ...
8
votes
1answer
124 views

Different age of universe

According to general relativity time runs slowly near a massive body. So, I have a question bothering me from some time, that if time for every body/object in universe runs at a different rate, then ...
0
votes
0answers
41 views

Calculate age of the Universe at 7 billion and 28 billion years old [duplicate]

If $1 / H_0 $ is about 14 billion years, then what happened when the universe was half its current age? Is the empirically determined $H_0$ supposed to have been twice its current value? And when ...
2
votes
1answer
242 views

How Does Cosmology Constrain the Number of Neutrino Species?

I know that based upon theories of structure formation cosmologists can constrain the sum of the masses of neutrinos - if neutrinos were too light or too heavy it would simply change the power ...
0
votes
2answers
231 views

Expansion of the Universe: Conversion of gravitational potential energy to kinetic energy?

Suppose there is an object floating in space which over time begins to fall toward the source of a gravitational field. As it falls, its motion happens to be such that it gets locked in orbit around ...
-2
votes
1answer
110 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, ...