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.
3
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1answer
10 views
Could asteroseismology have a significant potential to unravel the mechanisms of solar cycles that last thousands of years?
Could asteroseismology have a significant potential to unravel the mechanisms of solar cycles that last thousands of years?
And what about solar cycles 1 billion years ago and 2 billion years ago ...
4
votes
4answers
353 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 ...
1
vote
4answers
438 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 ...
9
votes
1answer
720 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 ...
15
votes
4answers
614 views
Why does every thing spin?
The origin of spin is some what a puzzle to me, every thing spin from galaxies to planets to weather to electrons.
Where has all the angular momentum come from? Why is it so natural?
I was also ...
5
votes
2answers
558 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 ...
5
votes
3answers
420 views
How can a quasar be 29 billion light-years away from Earth if Big Bang happened only 13.8 billion years ago?
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 ...
6
votes
1answer
14 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 ...
7
votes
3answers
212 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 ...
2
votes
5answers
332 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 ...
1
vote
0answers
225 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 ...
16
votes
3answers
2k views
Why is the universe so big?
The Universe is approximately 13.7 billion years old. But yet it is 80 billion light years across. Isn't this a contradiction?
14
votes
1answer
182 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) ...
1
vote
0answers
214 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 ...
3
votes
2answers
409 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?
8
votes
3answers
1k 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 ...
7
votes
1answer
197 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
votes
1answer
28 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 ...
6
votes
2answers
509 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 ...
7
votes
3answers
72 views
What's dark matter and who discovered it?
I have heard about dark matter that's called the Master Of The Universe. What's this and is the dark matter the reason galaxies exist?
10
votes
5answers
105 views
How large is the universe?
We know that the age of the universe (or, at least the time since the Big Bang) is roughly 13.75 billion years. I have heard that the size of the universe is much larger than what we can see, in other ...
12
votes
3answers
104 views
What is meant when it is said that the universe is homogeneous and isotropic?
It is sometimes said that the universe is homogeneous and isotropic. What is meant by each of these descriptions? Are they mutually exclusive, or does one require the other? And what implications rise ...
9
votes
3answers
50 views
Seeing cosmic activity now, really means it happens millions/billions of years ago?
A Recent report about a cosmic burst 3.8 billion light years away. It is written as though it is happening now. However, my question is, if the event is 3.8 billion light years away, doesn't that mean ...
9
votes
2answers
467 views
Why can we see the cosmic microwave background (CMB)?
I understand that we can never see much farther than the farthest galaxies we have observed. This is because, before the first galaxies formed, the universe was opaque--it was a soup of subatomic ...
11
votes
4answers
28 views
Can we observe changes in the fine-structure constant?
The fine structure constant is a number of constants rolled into one equation. Brian Cox mentioned in the April edition of Focus magazine that it is possible that the speed of light was once faster, ...
0
votes
1answer
183 views
If you removed every particle from space…? [closed]
I'm trying to find something Einstein (I think) said about time...It
was something like..
"If you removed every particle from space and were left with only one
pocket watch (clock, timepiece?), time ...
3
votes
3answers
383 views
If the multiverse and many-worlds don't exist, how should we interpret probabilities?
If the multiverse of eternal inflation and the many-worlds of quantum mechanics don't exist, how should we interpret the meaning of probabilities? If there is only one copy of the universe out there, ...
7
votes
3answers
597 views
Imaginary time in quantum and thermodynamics
The following question is about chapter 2 of Sakurai's Modern Quantum Mechanics. I wish I could link to the Google book, but it doesn't seem to have a satisfactory preview to be able to read the ...
3
votes
1answer
146 views
Can the entropy of a subsystem exceed the maximum entropy of the system in quantum mechanics?
Quantum mechanics has a peculiar feature, entanglement entropy, allowing the total entropy of a system to be less than the sum of the entropies of the individual subsystems comprising it. Can the ...
5
votes
6answers
670 views
Are many-worlds and the multiverse really the same thing?
Are many-worlds and the multiverse really the same thing?
Not too long ago, Susskind and Bousso uploaded the article "The Multiverse Interpretation of Quantum Mechanics" with the thesis that the ...
7
votes
1answer
490 views
Size of the universe
This is really a follow up to the Shape of the universe question.
In the first answer to the question, Ted Bunn says:
However, the best available data seem
to indicate that the Universe is very
...
1
vote
1answer
430 views
Has Cosmological Natural Selection been disproved?
I've been reading Lee Smolin's Life of the Cosmos.
Great book and it makes a lot of sense that the conditions in black holes are the same as conditions at the big bang.
Question is, has his theory ...
4
votes
2answers
777 views
Do the laws of physics evolve?
Hubble's constant $a(t)$ appears to be changing over time. The fine stucture constant $\alpha$, like many others in QFT, is a running constant that varies, proportional to energy being used to measure ...
0
votes
1answer
248 views
Inflation factor and doubling time
I get the general idea about cosmic inflation, but the numbers associated with it seem to be pulled out at random.
For example, in The Elegant Universe, Brian Greene says that the universe doubled ...
6
votes
1answer
131 views
What are the viable non-anthropic explanations for the tininess of the cosmological constant?
The cosmological constant is 10-120 times its natural value, but it is yet nonzero. Even TeV-scale supersymmetry breaking can't save it. The renormalization group would seem to imply it ought to be at ...
3
votes
2answers
207 views
If dark matter is a new type of particle, what does that imply?
My understanding is that dark matter cannot be (or is at least highly unlikely to be) an exotic form of any known particle. On the other hand, articles about particle accelerators seem to say that the ...
7
votes
3answers
273 views
Feedback on the paper, 'CCC-predicted low-variance circles in CMB sky and LCDM' by V. G. Gurzadyan and R. Penrose [closed]
Ref: CCC-predicted low-variance circles in CMB sky and LCDM
To all cosmology / theoretical physics / related or similar researchers and academics,
I humbly solicit your view/s on the above-mentioned ...
24
votes
3answers
845 views
The Pioneer anomaly finally explained?
Pioneer 10 & 11 are robotic space probes launched by the NASA in the early 1970's. After leaving our solar system, an unusual deceleration of both spacecrafts has been measured to be approximately ...
2
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1answer
189 views
5
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1answer
961 views
How can something finite become infinite?
How can the universe become infinite in spatial extent if it started as a singularity, wouldn't it take infinite time to expand into an infinite universe?
-1
votes
1answer
363 views
Lawrence Krauss' Theory of Origin
I don't understand how a vacuum, the absence of matter, can hold energy. How can it hold energy when Einstein proved that matter is energy?
And a second related question; how does the energy in a ...
7
votes
2answers
487 views
Is dark matter repulsive to dark matter? Why?
I think I saw in a video that if dark matter wasn't repulsive to dark matter, it would have formed dense massive objects or even black holes which we should have detected.
So, could dark matter be ...
1
vote
2answers
431 views
What is meant by positive and negative gravity/energy/spactimecurvature?
I have recently come across some cosmological assertions (based on empirical data) about the universe being self contained in the sense that it is entirely capable of coming into existence from a ...
12
votes
2answers
531 views
What exactly is meant by the “Gaussianity” of CMBR?
What does it mean when we say that the CMBR is mostly gaussian? What are non-gaussianities in CMBR? How does evaluation of 3-point correlation functions of the inflaton field tells us that there is ...
9
votes
7answers
1k views
How many bits are needed to simulate the universe?
This is not the same as: How many bytes can the observable universe store?
The Bekenstein bound tells us how many bits of data can be stored in a space. Using this value, we can determine the ...
0
votes
2answers
216 views
Have CMB photons “cooled” or been “stretched”?
Introductory texts and popular accounts of why we see the "once hot" CMB as microwaves nearly always say something about the photons "cooling" since the Big Bang. But isn't that misleading? Don't ...
2
votes
0answers
300 views
Calculation of the non-Gaussity parameter for primordial cosmological perturbations by the ADM Formalism
Maldacena has used the ADM Formalism in one of his papers (http://arxiv.org/abs/astro-ph/0210603) in computing the the three point correlation function (i.e the non-Gaussianity) parameter for ...
3
votes
1answer
565 views
Mathematical justification of Hartle-Hawking “no boundary” proposal
In Hartle-Hawking "no boundary" proposal it is proposed that Riemannian spacetimes rather than Lorentzian dominated the path integral near the big bang.
Moments after the big bang however spacetimes ...
10
votes
2answers
425 views
Can “big rip” rip apart an atomic nucleus?
Some scenarios describing the fate of the matter vs dark energy tug of war on the universe involve the acceleration of the universe increasing to the point that it ends up ripping apart even atoms. ...
5
votes
1answer
556 views
on causality and The Big Bang Theory
With the notion of causality, firmly fixed by GR, we derived the concept of a singular point from where space-time begun. Causality alone gives us the possibility to talk about a known past (i.e. ...
