1
vote
1answer
39 views

Is there an absolute center of mass exist in the universe? [duplicate]

By the "absolute center of mass" I mean the center of all the matter that exists in a given moment. My friend asserted that today and it intrigued us very much but since we only have a CS degree and ...
0
votes
2answers
58 views

What is entropy of the universe? [duplicate]

What is entropy of the universe? What is the change in entropy of our universe? Is this change increases or decreases? If the entropy of universe keeps on increasing then what are the consequences? Is ...
2
votes
2answers
375 views

Wouldn't the presence of dark matter slow the expansion of the universe?

If there is a huge element of dark matter in the universe, wouldn't this extra gravity prevent the accelerated expansion of the universe?
1
vote
1answer
67 views

The universe appears to have a lower bound in the time dimension, why not an upper bound?

The Big Bang looks like a lower bound to the "size" of the universe in the time dimension. Could it also have an upper bound, some furthest point in time from the Big Bang?
3
votes
1answer
110 views

How far can something travel in a straight line?

Suppose you have an object some distance from you and moving at a velocity different to the Hubble velocity you'd expect at that point. How does the motion of this object change with time? Does it ...
5
votes
4answers
480 views

Expansion of the Universe, will light from some galaxies never reach us?

Is it true that the light from some galaxies will never reach us? The explanation for that is that the Universe expanding faster than the speed of light. But, if the speed of light is constant in ...
1
vote
1answer
84 views

How did the universe get so big so fast? [duplicate]

The universe started at the big bang around 15 billion years ago. The universe is now at least 92 billion light-years in diameter. Together, don't these mean that the universe, at some time in the ...
1
vote
1answer
42 views

Number of Stars vs Value of Omega (Crtitical Density of the Universe)

I may be badly mixing things up here. If I am, please kindly correct me. As I understand it, if the universe was too dense at the start of the big bang, it would have collapsed back in on itself. Too ...
0
votes
2answers
92 views

Does the universe have an edge/boundary/barrier? If yes, what is at the edge? [duplicate]

My question related kind of to asking what the shape of the universe is. Say a hypothetical alien civilization built an faster-than-light spaceship. If they keep flying would they end up where they ...
0
votes
0answers
37 views

Cosmic Expansion - Why aren't we ripped off yet? [duplicate]

According to Hubble's law, the universe expands exponentially ever since the big bang. If the space-time expands, what effects does it have upon us, (1.Earth, 2.solar system and 3. Milky Way). ...
7
votes
2answers
480 views

What is “Energy” of a vacuum in the context of quantum theory?

I'm not a physicist or cosmologist, so I hope I am asking the right question with the right words here. My question regards the word "energy" as it pertains to quantum vacuum states, and to concepts ...
0
votes
1answer
56 views

How has the age of the Universe been derived from the observations made by the Planck mission?

The parameters of $\rm\Lambda CDM$ model have been determined to an amazing high precision from the measurements made by the Planck mission. In particular, the Hubble "constant" (the value of Hubble ...
-1
votes
0answers
51 views

Why only 4 spacetime dimensions? [duplicate]

What led the universe to expand only in 4 dimensions after the big bang? Why not in less than or greater than 4 dimensions? In other words, just before a moment of the big bang; the universe was just ...
2
votes
1answer
86 views

Why is an electric and magnetic field present in all universe?

the Earth has its fields due to the motion of molten metals in the core but how does this whole universe has its fields without any discontinuity? And we can say for sure that fields are present in ...
6
votes
2answers
111 views

When was the cosmic background radiation in the visible spectrum?

From what I understand about the Cosmic Microwave Background Radiation is that it was from the big bang, and since space has streched and become bigger since then the wavelength of the CMBR has ...
3
votes
1answer
75 views

Estimating age of the universe by Hubble's law?

Hubble's law states that $v=Hx$ Age of the universe is calculated by $T= \frac{x}{v} = \frac{1}{H}$ but the velocity is not constant; it changes with distance, so I think that this equation cannot ...
7
votes
1answer
160 views

Does everything orbit around some universal “center of mass”?

I have read many questions about the center of the Universe. I even have some favorite ones. I understand the fact that every point in the universe experiences inflation the same way. Also that it ...
26
votes
4answers
3k views

Why does a flat universe imply an infinite universe?

This article claims that because the universe appears to be flat, it must be infinite. I've heard this idea mentioned in a few other places, but they never explain the reasoning at all.
3
votes
4answers
100 views

Accelerating expansion of the universe: so?

Please help me out, I’m missing something. We know that, right now, space is expanding at roughly 73km/s/Mpc. This means: two points in space 1Mpc away from each other “move” 73 km farther away ...
2
votes
1answer
27 views

What is the current rate of change of the volume of the Universe?

Is it possible to know the current rate of change of the volume of the Universe? If we can't see past the cosmic horizon, can we still get a value for this rate of change, and if so, how would it be ...
8
votes
7answers
1k views

Mathematically possible vs physically probable outcomes

A good buddy of mine and I have had a friendly debate about the origins of the current state of our universe (namely; Earth and life on Earth) and have fundamentally disagreed in our stances with ...
1
vote
1answer
82 views

Reconciling “The Big Crunch” with the 2nd Law of Thermodynamics

Assume "The Big Crunch" scenario (the universe will collapse to a singularity). In this case, I think of the entire universe as an isolated system; in the "Big Crunch" scenario, it seems to me gravity ...
3
votes
3answers
100 views

If we say the universe is expanding, shouldn't it be expanding relative to something?

I don't understand, if everything in this world is relative to something else, then cannot we essentially say that nothing exists independently? We say that the universe is considered to be the ...
0
votes
1answer
95 views

Aside from Noether's theorem, what other concepts would explain energy conservation?

Energy is defined more in the mathematical sense, and tends to show true with observations in the physical world. But why is energy conserved aside from "Noether's theorem"? In a closed system that ...
4
votes
5answers
192 views

Is the universe expanding at a speed of almost $2c$?

I've been told nothing can travel faster than the speed of light. Therefore, from my vantage point the diameter of the universe is increasing at a rate of $2c$. Are there any flaws in my thinking?
7
votes
3answers
592 views

Dark Energy / Accelerating universe: naive question

Folks, I have a naive question regarding the subject of dark energy and an accelerating universe: From what I understand/read, it seems that the further we look out into deep space, the faster the ...
4
votes
1answer
80 views

Infinite number of galaxies?

I understand that the current estimate for the number of galaxies in the observable universe is about 100-200 billion. Is there anything in our understanding of physics and the evolution of the ...
0
votes
1answer
62 views

Is the universe expanding faster than we could catch up with it? [closed]

Like the title says, could we ever catch up with the expanding universe?
0
votes
0answers
20 views

Linear size of everything in the Universe is doubled overnight [duplicate]

Suppose the linear size of everything is doubled overnight. Can you test the statement by measuring sizes by a meter stick? Can you test it by using the fact that the speed of light is a universal ...
8
votes
2answers
678 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 ...
1
vote
1answer
137 views

If nothing can travel faster than speed of light then how the Universe is only 13.7 billion years old? [duplicate]

The light would take 93 billion years to reach the edge of universe but nothing can travel faster than the speed of light not even the big bang?
-1
votes
1answer
52 views

Reference frames and speed of light

If the speed of light is a constant, and the universe is expanding, wouldn't shining a light in the direction of the center of the universe have a different color (frequency and wave length) than ...
0
votes
1answer
57 views

does space-time expansion affect on fundamental particle? [duplicate]

does space-time expansion affect on fundamental particle or point particle?
0
votes
2answers
131 views

How does measuring redshift make us conclude that rate universe expansion is accelerating?

The universe is expanding in all directions. We can detect this by the redshift of electromagnetic radiation from other galaxies. We detect a larger redshift in galaxies which are further away, and ...
0
votes
0answers
34 views

Is Dark Energy Pushing Us Or Pulling Us? [duplicate]

This may seem silly, but how do they know that the effects we are seeing from dark energy, (which we only assume must be there due to observed acceleration), are not from gravity pulling us out from ...
5
votes
1answer
59 views

Open Big Bang-less universe?

This came up in discussion around a class I'm taking. For a Universe with $\Lambda$ and matter contributions to energy density (and implicitly curvature, but no radiation), can you have a universe ...
1
vote
3answers
145 views

Is the universe flat?

There are more than one way to view the description of the universe as flat. There is the description of an open, flat or closed universe in terms of it's fate, expansion forever away from gravity, or ...
2
votes
1answer
84 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
1answer
37 views

Does the rate of expansion of the universe exceed the rate at which the local group is being pulled toward the Great Attractor?

I understand that the expansion rate of the universe driven dark energy exceeds the rate at which the local group is being pulled toward The Great Attractor (Hydra-Centaurus Supercluster). Does this ...
0
votes
2answers
153 views

How does “space” expand? [duplicate]

According to Big Bang theory and The Red shift theory "space" is "expanding". Keeping this notion of "space" as physically something in and of itself(space -time did not exist before The Big Bang); ...
1
vote
1answer
95 views

Is the Universe Past-Eternal?

Does the Borde-Guth-Vilenkin theorem definitively demonstrate that the Universe cannot be past-eternal, whatsoever? Does it not assume a classical space-time while the real world requires Quantum ...
5
votes
2answers
328 views

Light takes too long to get here

When looking at the night sky, we see lots of stars. Several places tell you that the light of those stars has traveled to many light years to reach Earth and there may be others where light has not ...
0
votes
0answers
182 views

If nothing can travel faster than the speed of light, how can there be parts of the universe we can't see? [duplicate]

Assuming we originated from a single infinitely dense point in space time in the big bang, how can there be parts of the universe that we can't see as the light has not reached us yet, if nothing can ...
3
votes
1answer
127 views

Many times speed of light [duplicate]

http://www.huffingtonpost.com/2014/03/24/theory-of-everything-big-bang-discovery_n_5019126.html What does "many times speed of light" really mean in this context? For a layman it's easy to draw wrong ...
0
votes
1answer
120 views

What's the meaning of the age of the universe?

I'm not asking about how we worked backward from an expanding universe to the age of the big bang, but rather what is the meaning of time in a near infinitely dense point in the context of general ...
-3
votes
3answers
169 views

Is Space conserved [closed]

Can space be created or destroyed? Is space conserved? I am not asking for matter,energy and time. Its just a question about conservation of space PS: I am asking for what was there before big bang. ...
0
votes
2answers
280 views

If the universe didn't expand faster than light, would our nights brighter like day?

There's a common QnA which has amused and inspired many kids: There are billions of Stars in the sky. If we combine lights received from all stars, wouldn't it beat Sun? Why is night dark really? ...
0
votes
2answers
268 views

Did the singularity really existed in the begining of the universe?

I read in Hawking's brief history of time the following: The final result was a joint paper by Penrose and myself in 1970, which at last proved that there must have been a big bang ...
-4
votes
1answer
92 views

Is the universe a perpetual motion machine? [closed]

Is the universe a perpetual motion machine?
-1
votes
1answer
154 views

Can we have a static point in the universe? [closed]

Big bang theory states that the universe began from a single point (which we may consider as a central frame of reference for the objects in the Universe). In 1929, Edwin Hubble confirmed that the ...