The tag has no usage guidance.

learn more… | top users | synonyms

1
vote
2answers
96 views

What is the most common photon wavelength in our observable universe (not including the Sun)?

Ignoring the Sun, what is the most common wavelength of a photon that is received by us on average? (I am not asking what is the average wavelength, but rather what is the most common wavelength ...
1
vote
3answers
71 views

Why do telescopes move synchronously?

Here's a very nice video (see it in HD) of timelapses captured at the atacama desert. In the beginning of the video you can see that 4 telescopes move synchronously. Could anyone explain why? I always ...
1
vote
2answers
82 views

What do we mean by the size of the universe? [duplicate]

Isn't it true that the concept of length exists only within the universe? Are we simply measuring the observable universe, that is to say, the spatial limits of our observation?
0
votes
1answer
53 views

Do we really need inflation for horizon problem?

This is a very fundamental doubt. I think i am missing something in inflation. The inflation theory solves the horizon problem by stating all of the universe started from a very small region in ...
2
votes
1answer
119 views

What kind of accuracy could one get with Pi to 40 decimal places? [closed]

I've come across the following YouTube video on the Numberphile channel: https://www.youtube.com/watch?v=FpyrF_Ci2TQ which mentioned that 38 decimal places of pi (i.e. 39 digits) is all you need to ...
4
votes
1answer
99 views

When they say the universe was the size of a baseball about a billion billion billion billionth of a second

after the big bang. Does that means the observable universe was the size of a baseball, or does it mean the entire universe? I'm guessing it means the observable universe - as we really don't ...
1
vote
1answer
61 views

Flat universe a torus?

As shown by cosmologists space is presumably a flat expanse. In his book the Fabric of the Cosmos, Brian Greene shows that one of the possible shapes of this flat universe is a Torus. My question is, ...
0
votes
2answers
61 views

Can I see stars in my light-cone that you can never see?

The light cone of our galaxy is a lot different to the light-cone of a galaxy 5 bly away. Our Hubble volumes are much different. Everyone is born in/at a different space/time. Can I see stars in my ...
0
votes
1answer
67 views

Is the center of the universe in another dimension?

If we live in a four dimensional world and when we try to find the center of the universe (where the big bang occured) we found that there is no apparent center, could that means that the big bang ...
0
votes
0answers
101 views

Can we really see new objects in future? [duplicate]

From Wikipedia: Some parts of the Universe are too far away for the light emitted since the Big Bang to have had enough time to reach Earth, so these portions of the Universe lie outside the ...
-1
votes
1answer
105 views

What lies at the very edge of the expanding universe? [duplicate]

We all know that the universe is expanding at an accelerated rate and it might appear much like a soap bubble. That is where the phrase dark energy whose essence is unknown and which is thought to ...
1
vote
1answer
45 views

Can invisible galaxies exist? [duplicate]

Is it possible that there are newly formed galaxies which are moving so fast that we will can't see them, even though they exist "inside" our visible universe? I've been wondering if this could be a ...
1
vote
1answer
70 views

Confusion with the meaning of CMB

We say that CMB is the radiation leftover from big bang. When we measure the radiations i.e., the flux of photons in a given microwave range (say 0.1cm to 70cm, for example), in deep sky, there are ...
1
vote
2answers
2k views

How can we know there is more than just the observable universe

If all we can observe are things inside the observable universe, how do we know that anything even exists outside this boundary? I can see four ways of solving this problem. 1) We wait a while, the ...
1
vote
1answer
127 views

Light emitted from galaxies receding faster than $c$

I'm wondering how it is possible that light cannot reach us, even all the way out there where metric expansion is making the distance between our galaxy and their galaxy increase at greater than $c$. ...
2
votes
0answers
21 views

Is the observable universe growing or shrinking? [duplicate]

For a lack of better word, I used growing and shrinking in the question, but what I really mean is: Are objects that are now in the observable universe passing getting out of range in the future, or ...
0
votes
1answer
99 views

How many galaxies in the observable universe have we counted and mapped?

I could find any sources. How many galaxies are counted, named and mapped? How many more there are to be mapped in the future(the total count)? Are there galaxies in the observable universe that ...
1
vote
1answer
98 views

Can we observe proton decay?

I know that the half life of a proton is more than $6.6\cdot 10^{33}$ years (antimuon decay). I have found this data on Wikipedia proton decay but I do not know the probability distribution that leads ...
1
vote
0answers
26 views

Will the background radiation get “dimmer”? If so when will it be “turned off” [duplicate]

This video http://youtu.be/_mZQ-5-KYHw talks about the background radiation which we can observe today. It's from the beginning of the universe and has traveled so long that the expansion of the ...
1
vote
1answer
44 views

Expansion of the universe [closed]

If matter cannot be created nor destroyed, I would assume that the universe expands only to the point that energy is expressed from the objects inside it until it collapses onto itself, given as the ...
17
votes
3answers
1k views

Why is the sky dark at night? [duplicate]

The question is the well-known Olbers' paradox: If there are so many/infinite stars, in every direction, why is it dark at night? Where goes all the light we don't see? Discussing with a friend ...
0
votes
2answers
79 views

A question concerning the act of observing distant galaxies

The comoving radius of the observable universe is currently put at $46$ to $47$ billion light years. Source wikipedia. When we observe galaxies at great distance, such as the Hubble Deep Field at ...
-1
votes
1answer
134 views

Leonard Susskind said that the small value of the cosmological constant could mean that the universe is much bigger than we thought. Why?

He said that near the beginning of this Youtube video that it could mean that the universe is much bigger than he had thought that it was, and that the cosmological constant wasn't even a constant. I ...
8
votes
2answers
1k views

Will the CMB ever stop shining?

Will we ever reach a point where all the light that was set free by recombination finally reaches us from our point of view and the CMB stops "shining" for observers on Earth?
1
vote
2answers
103 views

When we look in different directions in the universe how do we know we're not seeing the same thing?

For my question assume: 1: Big bang happened at a point (I know it happened everywhere) but after that explosion universe started to expand in all directions so it maybe considered to happened ...
8
votes
2answers
935 views

Can the coordinate of the big bang point be calculated via observed universe or it is impossible? [duplicate]

We know all galaxies spread out after Big Bang theory.The key idea is that the universe is expanding after that theory. Can we play back the scenes via observable universe (galaxies) and can we ...
2
votes
1answer
273 views

How come that an Infinite universe will collapse under gravity?

In this PSE post the issue is about the stability of an infinite universe under Newtonian gravity. Here I'will drop the Newtonian constraint because we know of the finite speed of interactions and I ...
1
vote
1answer
167 views

What's the total Cosmic Microwave Background energy?

This is a part of my wider attempts at accounting matter in the observable universe. The total light ever emitted by stars and other space objects is capped around 1% of baryonic mass (in energy ...
4
votes
2answers
453 views

How many states are there in the observable universe

If we took a single instant and considered all possible states of all energy and matter do we have any bounds on how much that would be? Would that number be related to information?
2
votes
1answer
138 views

Size of the Universe: Curved vs flat? Finite vs infinite?

I have recently heard the theory that the Universe may be smaller than observed but may be curved to the extent that light rays may have looped past us once already and hence appear to have originated ...
2
votes
2answers
361 views

Can we observe an edge of the universe? [duplicate]

Firstly, I apologise if my thinking is completely incorrect - I am by no means a physicist (yet!), I have included layman illustrations to hopefully assist in explaining my thinking. I am imagining ...
1
vote
2answers
158 views

How is the observable universe mapped?

As I was looking at how big earth was relative to everything else in the universe, this picture boggles my mind. http://en.wikipedia.org/wiki/Observable_Universe#Horizons We're like the size of an ...
0
votes
1answer
169 views

How is it possible for you to be at the centre of the universe wherever you are? [duplicate]

I saw on Richard Hammond Builds A Universe on BBC2 a few days ago that you are always at the center of the universe wherever you are. Surely this is illogical, because you could never get to the edge ...
10
votes
8answers
1k 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 ...
1
vote
1answer
561 views

How far away is Cosmic Background Radiation? [duplicate]

I've been reading about Cosmic Background Radiation (CMBR) lately. My understanding so far is that this is the "Noise"/"Flash" from the big bang. Assuming that information is correct, how far away ...
5
votes
2answers
735 views

Planck satellite 2013 results impact on cosmological models

I've recently watched a "Through the Wormhole" episode from 2010 named "What Happened Before the Beginning?", where cyclic and ekpyrotic cosmological models are explained. In this episode the creators ...
3
votes
1answer
492 views

Diameter of the universe [duplicate]

Should the diameter of our universe always be more than its age in light years? As if the distance between any two points in the universe is equal to 13.5 billion light years then the light from the ...
1
vote
1answer
2k views

Size of the Observable Universe [duplicate]

I wanted to know what the observable universe is so I was thinking and I thought, it must be age of the universe times 2. Well I was wrong. I found on one website that it is 46B LY across in each ...
2
votes
1answer
155 views

What are we all falling towards?

One meteorite fell on the ground in Russia, last week. In different circumstances, it could have orbited the earth, or perhaps pass close to the earth and then disappear into the space. It seems that ...
1
vote
1answer
122 views

Looking backwards in time at yourself

If a person on Earth today is looking at a star, say, 10 billion light years away, is it possible that some of the atoms he is looking at will eventually go on to make him?
2
votes
1answer
62 views

Observable universe does it account for farther away galaxies measure of the observable universe?

From our planet we can only see so far on any direction. If a galaxy farther out than ours had a planet would its view extend beyond our measurements?
0
votes
1answer
399 views

Large-Scale-Structure (LSS) and the Fingers-of-God

In the Large-Scale-Structure (LSS) artifacts named fingers-of-god are apparent in the redshift space and justified by "The large velocities that lead to this effect are associated with the ...
4
votes
3answers
128 views

How long would it take to scan the visible universe for unique signals?

The article Amazing rays as star succumbs to dark side talks about a very large black hole swallowing up a star. The report goes on to say that the only reason it was discovered was because it shot ...
18
votes
2answers
695 views

How would the night sky appear at the edge of the galaxy?

In Isaac Asimov's Foundation Series, there is a planet named Terminus which is believed to be the planet farthest from the galactic center. There are almost no visible stars in its sky, only the ...