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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How Higgs Field is a constant in an Expanding Universe [on hold]

Going through information on Higgs Field in various forums, it seems that the mass of an object is due its interaction with the Higgs Field which is constant throughout the universe. However it ...
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2answers
69 views

Universe as a black hole - how did everything escape? [duplicate]

While listening to physics lectures, they glossed over things escaping from black holes insinuating it doesn't happen other than radiation... When talking about the period between Planck Epoch & ...
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Are we sure the universe expands uniformly in every direction? [on hold]

(Now I know this has been asked before and this question will be removed probably as a duplicate by John Rennie.) Doesn't information from the CMB radiation give us a clue as to whether the ...
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4answers
47 views

Does the universe expand in every direction evenly? [duplicate]

I've heard that the universe is expanding constantly and that galaxies are moving further and further away from each other because of this. However, does the universe expand in every direction evenly ...
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55 views

Solving the Friedmann Equation [on hold]

Through substituting for values of $\rho$ and $k$, I have: $$H^2=\left(\frac{\dot{a}}{a}\right)^2=\frac{8\pi G C}{3a^4} + \frac{\Lambda c^2}{3}$$ $a=a(t)$, and $a(t=0)=0$. Note that $C$ is a ...
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2answers
61 views

Why is the possibility of the universe having a centre around which everything orbits not considered feasible?

I'm sure there is some kind of reason as to why this isn't considered as a legitimate theory but upon giving it though it seemed to make sense to me. I figure if all gravitational orbits are ...
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Where does this data comparing the CMB with Eddington's 'temperature of space' come from?

Eddington estimated the temperature of space assuming that star light would be scattered by interstellar dust. He came pretty close to the temperature of the CMB. http://www.astro.ucla.edu/~wright/...
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Why is it said that photon-wavelengths have increased by a factor of 1000 since our universe became transparent to light?

After reading several explanations for the so-called "Hubble-radius", and still being confused, (as I reckon are some of the folks who tried to answer THAT question !!), I have a related question, ...
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63 views

How can the size of the universe change over time when time is part of the universe?

Bit of an awkward way to phrase it, but basically: Time in relativity is just one of four dimensions of space-time. Nothing really special about it. Yet the universe was once smaller than it is now ...
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44 views

Is there any primordial gravitational wave(form) that could explain dark energy?

First, I asked myself the question: Is there any gravitational waveform, however fantastical, that could explain dark energy. I suppose for a ubiquitous gravitational wave to be an explanation for ...
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Are the laws of physics and the properties of matter intrinisc to the universe? Could it have been different? [on hold]

Are the specific laws and properties of all that exists within this universe intrinsic to what makes up the universe (whether it was in the state it was in before the Big Bang, how it is now, or how ...
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The expansion of the universe and its edge

I have understood that the universe is expanding at an accelerated rate. I have also thought, perhaps mistakenly, that this expansion means not that the masses in the universe are moving away from ...
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13 views

Deceleration parameter in a Universe dominated by the cosmological constant

See Deriving the deceleration parameter of a universe whose density is dominated by matter for a derivation of $q_0 = \frac{\Omega_m}{2}-\Omega_\Lambda$ If the universe were $\Lambda$ dominated, ...
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1answer
63 views

Is the universe actually formed according to the big bang theory? [closed]

Big-Bang pretty much explain the origin of universe, but still many people don't believe it. Isn't it possible that our universe come out of a white hole which have been pulled out from a black hole ...
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58 views

Are all particles in the universe quantum-entangled on some level?

The CMB indicates the universe was in a thermal equilibrium early on, which I understand indicates causal connection. There appears to have been some rapid expansion, and the universe now appears to ...
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2answers
98 views

How does critical density affect the expansion of the universe if gravity is the curvature of space-time?

From what I know there are three scenarios about the end and expansion of the universe that all depend on the concept of critical density: If the matter of our universe is above critical density, ...
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1answer
84 views

What is the name of matter with $w = - \frac{1}{3}$?

What kind of "matter" is described by the following thermodynamic relation ? \begin{equation}\tag{1} p = -\, \frac{1}{3} \; \rho, \end{equation} Where $p$ and $\rho$ are the pressure and density ...
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3answers
497 views

How would cold neutrinos get trapped by stars?

Continuing on from the cool physics Q&A'd on the threads Where are all the slow neutrinos?, Is it possible that all "spontaneous nuclear decay" is actually "slow neutrino" ...
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1answer
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Estimation of Location of First Acoustic Peak

This question is inspired by the page at NED and references it throughout the question. On the linked page there is a method for calculating the location of the first acoustic peak of the CMB. It ...
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2answers
62 views

Source of Dark Energy.

In accelerated expansion dark energy play a crucial role because of negative pressure, but during expansion Dark Energy(DE) do not dilute. DE density is independent of scale factor unlike matter and ...
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1answer
22 views

Deriving the deceleration parameter of a universe whose density is dominated by matter

Assuming that the density of the universe is dominated by matter, so that $\rho = \rho_m$, how can the deceleration parameter today be shown to be $q_0 = \frac{\Omega_m}{2} - \Omega_{\Lambda}$ The ...
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2answers
54 views

Does the expanding universe prove the theory of relativity wrong? [duplicate]

I recently read an article which said the the universe is expanding with a very high velocity, which is even a lot faster than the speed of light. So, doesn't this prove Einstein's theory wrong which ...
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1answer
52 views

What does the Friedmann Equation imply for the cosmological constant?

The Friedmann equation is given by $$(\frac{\dot{a}}{a})^2 = \frac{8 \pi G \rho}{3} - \frac{kc^2}{a^2} + \frac{\lambda c^2}{3}.$$ Considering that the left hand side is analagous to the kinetic energy ...
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Correct expression for Suv = Tuv - 1/2*guv*T in Chapter 8.1 of Einstein Gravity in a Nutshell [closed]

In the textbook "Einstein Gravity in a Nutshell", Chapter 8 is called "The Dynamic Universe" and employs a well known expression for the stress energy tensor Tuv for a perfect fluid filling the ...
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1answer
68 views

Source of energy for infinite expansion

I read in several sources that matter, dark matter & dark energy contributes 5%, 26% and 69% of the known universe. Also, I read in a slide deck about Big Bang theory on nobelprize.org that total ...
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25 views

How do we know that the big bang happened everywhere, simultaneously? [duplicate]

If we can't see beyond the limits of the observable universe how do we know that the big bang happened everywhere, simultaneously?
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When was the first Earth-like planet formed?

By Earth-like planet I mean the formation of a planet near a Star analog to our Sun, almost the same size as Earth and all the parts needed to form cells. If we can pinpoint this Earth-like planet ...
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3answers
248 views

What does the cosmic neutrino background look like today, given that neutrinos possess mass?

This question is inspired by (or a follow-up to) the threads Where are all the slow neutrinos? and Is it possible that all “spontaneous nuclear decay” is actually “slow neutrino” induced? The cosmic ...
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1answer
68 views

Which theoretical models are there between quantum mechanics and cosmology? [closed]

I'm an enthusiast/hobbyist right now and I'm quite curious about the subject of understanding which scales come between the quantum scale (ab initio/first principles) and the macroscopic scale. After ...
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1answer
67 views

If the universe stopped expanding, when would we realize it?

Suppose in this moment the universe stopped expanding, how long would if take and how would we register the change? Since the bodies are still and it is space that is expanding in between, we wouldn'...
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0answers
15 views

Flat Universe and Evolving Geometry [duplicate]

I have heard in multiple locations that in the case of a flat universe, the universe is infinite. This seems to present multiple issues: a) If a flat universe were infinite, would would the space of ...
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2answers
38 views

A question on the redshift of photons due to cosmic expansion

Given that the universe is expanding over time, in the sense that the (spatial) metric is changing over time, corresponding to the physical distance between objects increasing, naïve intuition leads ...
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2answers
100 views

Is the universe actually expanding?

Up until recently I was fairly sure that the universe is expanding, i.e. the (spatial) metric is changing proportionally to the scale factor, such that the distance measured between objects is ...
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28 views

Scalar invariance and dimensions

I recently read an interesting article on scale in variance http://www.wired.com/2014/08/multiverse/ It discussed how modern physics is suggesting that scalar units really may not apply above the ...
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Resources on how to estimate the power density of gravity?

If a drop a ball from a height $h$, the work done by gravity (in this particular situation $i$) is $w_i=\int_0^h F_G \cdot dl \approx mgh$. What I would like, is to estimate the work done by gravity ...
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How do we know what happened during the Big Bang?

Any data that we have on the Big Bang comes from the cosmic microwave background (CMB) which was created about 380,000 years after the Big Bang. From there we have been able to calculate what the ...
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Quarks and pai-production [duplicate]

When Quark, antiuquark pair is created by high energy photons, they glue togheter as mésons or another pair is created to combine they, totalizing four particles? Following QCD both quarks would glue ...
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2answers
70 views

How can it be possible that the presently observable universe is much smaller than particle horizon?

We know that to solve the homogeneity and isotropy problem, we invite the inflation and the inflation at early universe can make the presently observable universe much smaller than the particle ...
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2answers
42 views

Reference frame for the Cosmic Neutrino Background

It is well known that there exists a reference frame where the total momentum of the Cosmic Microwave Background is zero (a basic fact of special relativity applied to a collection of massless ...
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1answer
40 views

Running Constant Values At Very Low Temperatures

From Wikipedia Coupling Constants, using QED as an example. I realise that the one-loop beta function in quantum chromodynamics is negative. If a beta function is positive, the corresponding ...
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67 views

How is the Universe expanding faster than the speed of light? [duplicate]

I was watching a youtube video about the expansion of the universe. So the video said that the universe is expanding at a speed faster than the speed of light. I have 2 questions about that. My first ...
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2answers
198 views

Are massive gravitons as the dark matter fluid more correct than the notion of WIMPs?

Accepted at APS Physical Review D: Massive gravitons as dark matter and gravitational waves Precursor: Bigravitons as dark matter and gravitational waves The massive graviton is a viable ...
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What is signifcance of density of the universe if it changes?

So theories of expansion of the universe (before dark matter and energy) said that the ultimate fate of the universe is based on the density of the universe and this being compared to the critical ...
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1answer
63 views

Before Dark Energy was discovered

I'm really confused on this topic. Pardon my French if my questions seem really stupid. Before Dark Energy was discovered in 1998 did scientists know that the cosmological constant calculated, I ...
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2answers
248 views

Is there any problem with the idea that gravity is repulsive at long distances?

If gravity is repulsive at long distances, would this suffice in explaining "dark energy"? Was there any reason why a new concept (dark energy) was introduced rather than just assuming that gravity ...
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1answer
32 views

Does the Bekenstein entropy bound present problems for unitarity in cosmological models that invovle a collapse or bounce?

If we expect the Bekenstein bound, or something like it, to hold in a collapsing universe, will that not eventually force us to accept some loss of information, or is there something I'm missing?
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Why is there a matter-dark matter asymmetry?

It is said generally that nature is symmetric. For example if light behaves as both a particle and a wave, then matter must also do so, which turns out to be true. But we find that the Universe ...
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complete local thermal equilibrium and conserved quantum numbers

I am reading Weinberg's Cosmology book and I am confused of the statement "complete local thermal equilibrium in which all conserved quantum numbers vanish". My question is: How is complete local ...
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3answers
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How can we look back at our Universe 13Billion years ago? [duplicate]

I read this article on Space.com and I quote "As far as we know, that's as far [back] as we can see — we get an image of the universe as it was when it was about 389,000 years old," So what I wanna ...
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Expansion Of Universe : On the Basis Of Aether Theory [duplicate]

I would like to ask that in the recent experiment of discovering Gravitational Waves scientists have also found or believe that they have found the evidence of Dark Matter. So if dark matter is made ...