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)

5
votes
1answer
83 views

How is $\Omega_0 = 1$ when the characteristic “teardrop” past light cone seems to admit curvature?

Introduction: The top graphic is just one I pulled from a page describing the process of detecting cosmic curvature. The second graphic is one I drew up to illustrate my misunderstanding. My ...
0
votes
2answers
189 views

Tired light red shift hypothesis

Have there been any recent attempts to falsify the tired light hypothesis alternative to the Doppler shift explanation for the red shift, or is it simply ignored like the pilot wave quantum mechanical ...
0
votes
2answers
70 views

If space is expanding, how can I see a galaxy 12 billion light years away where it is today?

Assuming space is expanding (and that seems plausible), photons from a galaxy that have been traveling for 12 billion years must have been traveling on a curve to get to us due to the fact that where ...
1
vote
0answers
41 views

Information loss from entanglement and cosmological horizons?

Suppose we have a qubit P in an unknown quantum state. Unknown as in we didn't prepare it, and don't know how it was prepared either. Without measuring the qubit in any way, we encode it into two ...
3
votes
0answers
51 views

What is the latest findings on the topology and size of the universe?

The paper G. Aslanyan & A.V. Manohar, The Topology and Size of the Universe from the Cosmic Microwave Background, JCAP 06 (2012) 003, arXiv:1104.0015, uses the 7-year WMAP data. Has any ...
0
votes
1answer
50 views

Proof of expression to combine different redshifts

I am trying to arrive to the following expression: $1+z = (1+z_C)(1+z_G)(1+z_D)$ so the total redshift is the product of the cosmological redshift, the gravitational redshift and the Doppler ...
1
vote
0answers
45 views

What does the temperature of the early universe tell me?

I am re-reading Weinberg's book "The First Three Minutes". In the Introduction he makes this statement: "At about one-hundreth of a second, the earliest time about which we can speak with any ...
3
votes
1answer
90 views

What physical processes can convert dark matter into dark energy?

In this news article, it is mentioned that it could be the case that some physical processes convert dark matter into dark energy ...
9
votes
2answers
397 views

Could I see the cosmic microwave background if it were Doppler shifted enough?

If I traveled fast enough, my current understanding is that visible light would be blueshifted to the blue/UV range, but also that microwaves and longer wavelength waves would be blueshifted into the ...
2
votes
2answers
237 views

Expansion of the Universe: is new space(time?) being created or does it just get stretched?

Is new space(time?) being created as the Universe expands, or does the existing spacetime just get stretched? If it just gets stretched, why do galaxies move along with the expansion instead of just ...
4
votes
2answers
106 views

Is entropy absolute (as in absolute temperature)?

Following this question on the Entropy at the Big Bang where I asked: Since Entropy always increases (in general); its expected that the entropy at the beginning of the universe should be the ...
0
votes
2answers
76 views

How could gravity affect the expansion of the universe?

I've read several books which talk about gravity slowing down, halting, or reversing the expansion of the universe. The expansion is often compared to a stretching of space at every point, so that the ...
6
votes
1answer
112 views

Angular Power Spectrum of CMB

I was wondering, if anyone could guide me through the different peaks of this spectrum (See below)? I've been reading and reading numerous pages about this, but I can't seem to get my head around ...
2
votes
3answers
179 views

Cosmic Background Radiation and redshift vs. temperature

I get that the CMB has gone from high energy photons, to low microwave photons today. And that is probably due to the redshift from the expanding Universe. But, since CMB is a black body it is ...
3
votes
4answers
295 views

Entropy of the whole universe

In "Thermal Physics", Charles Kittel proves that entropy always increases in systems when the degree of freedom are increased (adding particles, adding energy, expanding volume, etc ). I started to ...
0
votes
0answers
36 views

Does the holographic principle imply that objects exist twice?

The surface area that surrounds a volume of space contains the same information that the volume has. My question is if we have Alice in a 3D space the 2D boundary should have all of her information. ...
2
votes
1answer
139 views

The arrow of time and the cosmology of a black hole interior

When solving the Einstein field equations in Schwarzschild metric for an observer falling into a black hole the radial coordinate r of the black hole and time t switch roles in the equations when ...
-1
votes
1answer
39 views

Is this dark energy/matter?

Regarding dark energy and dark matter. It’s been a while but in my high school physics class I was taught that light energy was massless. However Einstein predicted and it has been proven that light ...
1
vote
1answer
134 views

Numerical solution for Friedmann equations

My problem today is to solve the Friedmann equations, for those who aren't familiar with them, here they are (in my specific case): $$ \left ( \frac{\dot{a}}{a^2} \right )^2 = \frac{\rho_1}{a^4} - ...
4
votes
2answers
268 views

Estimating the expansion of the universe using light from supernova

I understand that you can tell how far light has traveled by the measuring redshift but how accurate is this and could it be effected by anything like radiation from the sun it must be fairly accurate ...
-2
votes
1answer
89 views

How can we detect cosmic background microwave radiation? [closed]

From my understanding this stuff expands at or near the speed of light -- and it's origins are that of the creation of this universe (via big bang). Obviously, our planet does not expand from origin ...
0
votes
2answers
80 views

Can we solve most of the cosmological questions using the Illustris universe simulation?

The Illustris project (http://illustris-project.org) attempts to simulate the universe in its most accurate form according to their website. With the simulation, they were able to predict the neutral ...
1
vote
1answer
72 views

How fast am I moving? [duplicate]

Given the speed of light is 299,792,458 meters per second and that it is constant through out the universe, (i.e a person who measures the speed of light while standing still will get the same result ...
2
votes
4answers
602 views

Exploring beyond event horizons

In the expanding universe the velocity of separation between galaxies depends upon how far they are. If they are much far away will they have relative velocity of separation greater than speed of ...
15
votes
5answers
1k views

What was the entropy of the universe at the time of the Big Bang?

(I asked this question in Philosophy.SE; but I was advised to direct it here, despite it is, in my opinion, somewhat too speculative for physics.SE). High entropy generally means high disorder; and ...
11
votes
1answer
560 views

The status of the BICEP2 'discovery' after Planck 2014

The tumultous period after the original announcement that the BICEP2 experiment had supposedly detected strong evidence of cosmological inflation in the form of B-mode polarization in the cosmic ...
-7
votes
1answer
124 views

Could it be possible that the universe doesn't exist [closed]

Could it be possible that the universe doesn't exist? That nothing exists, not even you or me? And by not existing, I mean totally not existing, as in not even existing as a computer simulation, or a ...
33
votes
3answers
2k views

What are galactic speeds measured against?

The Earth moves through space at 67,000 MPH. The Milky Way travels through a local group at 2,237,000 MPH. Wouldn't you need a fixed point to be able to measure velocity against? After all, compared ...
14
votes
3answers
936 views

What is the most compelling evidence of General Relativity in the presence of matter and energy?

The most oft-cited triumphs of GR are things such as the shifting perihelion of Mercury, gravitational redshift experiments, and gravitational lensing. But, as far as I know, these are only ...
1
vote
0answers
38 views

How Do we Know How Old the Universe Is? [duplicate]

It is common knowledge that the universe is 13.8 ± 0.037 billion years - but how was this calculated?
7
votes
4answers
194 views

temperature of electroweak phase transition

How does one estimate the temperature at which electroweak phase transition (EWPT) occurred? Somewhere I have read it is around 100GeV but the reason was not explained.
1
vote
2answers
77 views

How can the universe be flat and have no center if universal mass-energy content is finite?

WMAP measurements confirm that the universe is flat within a 0.4% margin of error. If we assume the universe is flat and there is no 'center' then how could the mass energy content be finite since ...
-1
votes
1answer
102 views

Why did the big bang explode if there is no oxygen in space? [duplicate]

If there is no oxygen in space, where the super dense singular object was suspended, then why did it explode because this reaction needs oxygen?
0
votes
1answer
48 views

Universe from nothing [duplicate]

Does this video make sense? The Simple Math for a Universe from Nothing I mean, can I really explain a "universe from nothing" is this simple manner?
10
votes
2answers
1k views

How far away must a galaxy be for its light never to reach us due to the expansion of the universe?

My understanding is that at the present rate of expansion of the universe some galaxies are growing more distant from us at such a rate that light from them will never reach us. My question is how far ...
10
votes
3answers
362 views

Entire Universe's Momentum

I was thinking about the definition of the conservation of momentum, which says that momentum is conserved unless outside forces are acting on the system, and I was wondering that if the system is the ...
0
votes
2answers
117 views

Infinite Universe and Big Bang

A common view now in the physics community is that the Universe is infinite in extent (which makes Hubble sphere an infinitely small part of the Universe). On the other hand, there is the Big Bang ...
1
vote
2answers
82 views

Can Einstein's constant explain expansion?

I read somewhere that Einstein or Newton believed that the universe was completely static, where it neither expanded nor contracted, but simply remained fixed. It was concluded that due to attraction ...
0
votes
1answer
146 views

What happens to black holes if/when the universe “ends”

I've heard several ideas about what happens to the universe when it dies, and they range from infinite expansion and heat death, to a "big crunch". In the event that something like a "big crunch" ...
1
vote
1answer
63 views

Does the CMB signal get weaker over time?

If the universe is infinite or flat, then this isn't true (I guess). But if the universe is finite, then as it expands wouldn't the CMB signal weaker at any given point over time?
1
vote
2answers
60 views

Do things in the universe get farther apart or bigger? (Amateur)

To start off I would like to say I am a complete amateur and have no experience in physics! I am just a sophomore in high school with some questions. Now that that is out of the way. There are many ...
1
vote
3answers
110 views

How do you define a “universe” (in the context of multiverse)?

How do you define a universe (in the context of multiverse)? The traditional definition of universe is something like "The Universe is all of spacetime and everything that exists therein". But in ...
0
votes
1answer
49 views

Light speed after the Big Bang

We know that immediately after the Big Bang space was opaque to light. As space expanded, light could travel. However I would think that as space expanded at some de sites the light would be much ...
3
votes
1answer
80 views

Quantum Wavefunctions Without Space

A handful of physicists have a rather peculiar definition of 'nothing' in terms of cosmology. Their claim is that the Universe, assuming it has 0 total energy, could have arisen from nothing but ...
0
votes
2answers
30 views

entropy-infomartion correlation at preliminary universe?

according to the theory of cosmic inflation after Alan Guth, the information should have travelled 100 times the speed of light at the very beginning after the big bang. -when we talk about ...
0
votes
1answer
58 views

How much real and how much relative is our universe?

Apologies in advance if my question appears more philosophical than practical. It is indeed philosophy, but a philosophy relating to our scientific understanding of the universe as a whole. Special ...
4
votes
2answers
160 views

How can a black hole zap a galaxy into existence?

I am referring to this picture published here. Apparently super massive black holes emit radiation and matter in astrophysical jets. And these jets can form galaxies. I have some questions: Isn't ...
2
votes
2answers
88 views

Can the vacuum energy be made finite with quantized space

From what I know the reason we have infinite vacuum energy is because according to Quantum Field Theory at every point in space we have something analogous to a harmonic oscillator but since the Zero ...
7
votes
2answers
557 views

How would the universe be different if the electron mass was twice as large? [closed]

Would the universe even start? Would it collapse or act differently? What if, instead, the mass changed right now? Edit: Since this is too broad lets narrow it to two scenarios: What happens to ...
-2
votes
2answers
142 views

Is the big bang a fact? [duplicate]

I have watched many physics debated and in everyone of them, physicists take big bang for granted. But, is the big bang actually proven, or there are many evidence that indicate that it did happen?