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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Cosmic bubble collision

I'm reading this review right now. The claim seems to be that when you have an expanding "false vacuum", finite size bubbles form due to phase transition (cause by finite action instantons) (which, in ...
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3answers
296 views

What was so surprising about accelerating cosmological expansion?

The 2011 Nobel Prize in Physics, as far as I understand, concerns the expanding universe -- galaxies moving away from each other at ever increasing speed (that's what I think I read in newspapers). ...
2
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1answer
553 views

Does the heat death of the universe really imply a maximum entropy state *all* of the time? Or most of the time?

Statistically speaking, you're going to still encounter deviations from equilibrium, even though the expected value is equilibrium. But these rare deviations from equilibrium - which are inevitable - ...
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5answers
1k views

What is the extent of the universe?

Is there any realistic, understandable, provable (even in some extent) explanation/model for the extent of the universe? What is its shape? and Why? I mean physical explanations not philosophical ...
5
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2answers
1k views

Why do neutrino oscillations imply nonzero neutrino masses?

Neutrinos can pass from one family to another (that is, change in flavor) in a process known as neutrino oscillation. The oscillation between the different families occurs randomly, and the likelihood ...
2
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1answer
215 views

The relation between the speed of light and the Big Bang Theory

I would like to know how much of the Big Bang theory is dependent on the constancy of the speed of light. P.S.: It might be guessed that I am asking this because of the recent CERN news. Yes, of ...
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0answers
259 views

Why do galaxies collide? Reconciling dark energy and an expanding universe with the fact that some galaxies are on a collision course

My layman understanding of cosmology is: galaxies are uniformly (more or less) spread throughout the universe, per the Big Bang and the fact that in a central explosion, all dispersed points are ...
5
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1answer
362 views

How and why will the Milky way collide with the Andromeda?

Hubble's law says that the universe is expanding.How come the milky way and the andromeda are on a collision course?How will they end up colliding with each other?
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2answers
996 views

How long did inflation take to happen?

If inflation happened, it ended about 13.7 billion years ago. But how long was inflation going on before that? Was it just a short burst of time so that it's really okay to say that the age of the ...
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0answers
121 views

Confusion with infinity and time [closed]

I have some confusion between with resolving the following situation. I know that no measurable quantity can have a value of infinity. For example, I just wrote something out, but clearly this ...
2
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1answer
175 views

Does anisotropic expansion of the universe imply quintaessence?

a Recent paper establishes under solid grounds anisotropy in the expansion acceleration rate in the universe. My question is very simple: can this anomaly be explained entirely in terms of a ...
4
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4answers
728 views

Experimental evidence for parallel universes

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 ...
7
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1answer
244 views

Curvature of the Universe imaginary?

If the curvature of the universe is zero, then $$Ω = 1$$ and the Pythagorean Theorem is correct. If instead $$Ω> 1$$ there will be a positive curvature, and if $$Ω <1$$ there will be a negative ...
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2answers
250 views

Quantum Fluctuations as a model for the Big Bang?

I have quite often heard (and even used) the idea that quantum fluctuations are a way to explain the whole "something from nothing" intuitive leap. I am about to give a talk at a local school on ...
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11answers
2k views

How can it be that the beginning universe had a high temperature and a low entropy at the same time?

The Big Bang theory assumes that our universe started from a very/infinitely dense and extremely/infinitely hot state. But on the other side, it is often claimed that our universe must have been ...
5
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1answer
268 views

How did enough material from other dying stars accumulate to start our sun and planets?

How far apart do scientists estimate was/were the dying star(s) that supplied the elements that comprise our sun, planet, and us? With stars so far apart and expansion of space (as I understand it) ...
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3answers
2k views

photons in expanding space: how is energy conserved?

If a photon (wave package) redshifts (streches) traveling in our expanding universe, is it's energy reduced? If so, where does it go?
7
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3answers
119 views

Are there any Earth-Meteorites on Earth?

A follow-on from this question, if meteorites can come from Mars, it seems they could have come from Earth and ended up back here (though I'm guessing that to be less likely). Do we have any evidence ...
5
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6answers
325 views

Are there free data available online from cosmology (or astrophysics) experiments that anyone can analyse?

One can understand a subject better in physics by trying to solve as many problems as one can from a textbook say. When it comes to experimental physics and data analysis, no book on experimental ...
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4answers
942 views

At what speed does our universe expand?

Conceivably it expands with the speed of light. I do not know, but curious, if there is an answer. At what velocity, does our universe expand?
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2answers
430 views

Can the distance of a quasar be determined accurately?

As noted in A doubt about the age of the universe, the wiki about quasars still contains the following misleading sentence: "The highest redshift quasar known (as of June 2011) is ULAS_J1120+0641, ...
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1answer
322 views

evidence on the equation of state for dark energy?

If dark energy contributes mass-energy density $\rho$ and pressure $p$ to the stress-energy tensor, then you can define $w=p/\rho$, where $w=-1$ gives a cosmological constant, $w<-1$ gives a big ...
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1answer
179 views

Smoothed particle hydrodynamics in cosmological N-body simulations

What is the role of smoothed particle hydrodynamics (SPH) in cosmological N-body simulations like the Millenium Run (performed with Gadget-2)?
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2answers
242 views

Could dark matter be expanded atoms, and dark energy expanded radiation? [closed]

After watching Lawrence Krauss' lecture 'life, universe, and nothing', an interesting idea lighted up in my mind. Is it possible that dark matter is just spread out matter waves and dark energy ...
4
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1answer
423 views

Which Friedmann equation is redundant?

For flat FLRW cosmology, we can write down two Friedman equations and one matter equation: (1) $H^2=\frac{8 \pi G}{3} \rho$ (2) $\frac{\ddot{a}}{a} = -\frac{4 \pi G}{3} (\rho +3p)$ (3) $\dot{\rho} ...
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5answers
9k views

Stephen Hawking says universe can create itself from nothing, but how exactly?

Stephen Hawking says in his latest book The Grand Design that, Because there is a law such as gravity, the universe can and will create itself from nothing. Is it not circular logic? I mean, how ...
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0answers
56 views

Virtual particles contributing to universal expansion. [duplicate]

Possible Duplicate: Virtual particle production in space-time. Does virtual particle production contribute to observed universal expansion?
5
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2answers
826 views

When will the Hubble volume coincide with the volume of the observable Universe?

The Hubble volume is the volume that corresponds to objects so far from the Earth that the space between us and them is expanding faster than the speed of light. (I.e. objects outside this volume ...
11
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3answers
987 views

Is the observable region of the universe within the event horizon of a super-massive black hole?

Observations: I have read that for a free-falling observer within the event horizon of a black hole that all lines of sight will end at the singularity which is black. I also look up and see that ...
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1answer
484 views

Does the Big Bang need a cause? [duplicate]

Possible Duplicate: on causality and The Big Bang Theory Asking here in layman's terms.. When theoretical physicsists discuss the origin of our Universe, the wider consensus appears to be ...
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4answers
809 views

What does ionization of neutral Hydrogen have to do with “transparency”?

Most accounts of the early history of the Universe make some reference to (re)ionization as being the reason that the Universe becomes transparent after a period of opacity caused by the absence of ...
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4answers
519 views

Which cosmologies support Eternal Life? [closed]

Which cosmologies consistent with physics as we currently know it is consistent with Eternal Life lasting forever starting from here on Earth while preserving the memories of human life? With ...
23
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3answers
3k views

How would we tell antimatter galaxies apart?

Given that antimatter galaxies are theoretically possible, how would they be distinguishable from regular matter galaxies? That is, antimatter is equal in atomic weight and all properties, except for ...
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2answers
2k views

What is the cosmic “Axis of Evil” problem?

What is the cosmic "axis of evil" problem? Apparently it is a more modern version of the old cluster mass discrepancy problem, where masses determined by gravitational lensing are always higher than ...
9
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3answers
2k views

How can a quasar be 29 billion light-years away from Earth if Big Bang happened only 13.8 billion years ago? [duplicate]

I was reading through the Wikipedia article on Quasars and came across the fact that the most distant Quasar is 29 Billion Light years. This is what the article exactly says The highest redshift ...
7
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1answer
37 views

Temperature of WIMPs

As a dark matter candidate, what should be the temperature and kinetic energy (or also the speed) of the WIMPs (weakly interacting massive particles) to agree with the observed distribution of dark ...
3
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2answers
382 views

Cosmic Microwave Background (CMB) and its relation to Inertial Frames

We know that the CMB is isotropic when viewed outside of the spinning and revolving earth. Is it homogeneous? Can we relate the CMB to an inertial frame in the Newtonian sense (in which space and ...
8
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3answers
811 views

Is the “Great Attractor” an indicator of the “Multiverse”?

I have heard a bit about the Great Attractor (the gravitational anomaly that seems to be "sweeping" our universe in one direction). Someone (and forgive me, I do not recall the specifics) has ...
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5answers
452 views

Can computers survive bubble nucleations?

According to string landscape theory, our vacua with a cosmological constant of $10^{-123}$ is a metastable vacua which can decay to a supersymmetric vacua with either a zero or negative cosmological ...
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5answers
1k views

Given that matter cannot escape a black hole, how did the big bang produce the universe we see today?

Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. If the matter contained within our ...
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0answers
363 views

Is it possible for the universe to be infinite considering Zeno's and Hilbert's paradox? [closed]

I'm only in high school (junior) so goes easy on me. But, how do physicist refute these paradoxes? Considering there are a number of theories regarding the origin of the universe and some postulate ...
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2answers
246 views

Is there a consensus on the fate of our universe?

We all know that our universe is inflating from what is known as the Big Bang. However, will our universe continue to inflate at the current rate? Or after reaching a maximum size, will it collapse in ...
27
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7answers
5k views

Why is the observable universe so big?

The observable universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
18
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2answers
896 views

Why is the universe map shaped like an oval?

I understand that the Mollweide projection is used to show the map of the universe. Although I understand how this projection can be interesting for Earth where most populated (and of interest) ...
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0answers
219 views

Presence Of an Another Universe [duplicate]

Possible Duplicate: Experimental evidence for parallel universes Is there an universe similar to ours somewhere else, I mean I had heard from Einsteins theories that,actually when I am ...
4
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2answers
668 views

Is the entire Universe the same age?

Is all of the visible Universe exactly the same age everywhere? What about the Universe beyond what we can see?
10
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3answers
3k views

What has been proved about the big bang, and what has not?

Ok so the universe is in constant expansion, that has been proven, right? And that means that it was smaller in the past.. But what's the smallest size we can be sure the universe has ever had? I ...
8
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1answer
241 views

BCS wave function in Neutron stars

I've heard mentioned in various classes that neutron stars, like superconductors, are described by BCS theory. I know that in superconductors a key element in forming cooper pairs is a net attractive ...
4
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1answer
51 views

Why do astronomers say that there is not enough matter in Universe?

I was reading today about the birth of the Universe and the conjectures about the matter that was supposed to exist at the moment of the Big Bang and what can be measured now. There seems to be some ...
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2answers
1k views

Will the night sky eventually be bright?

I have read that the night sky should have been bright because every spot should end up pointing to a star in the infinite universe but this is not the case because the universe is expanding. I am ...