The universe refers to the cosmos; all of space-time and that which exists as part of it. Alternatively, it can refer to the observable universe, which only contains the part we can see. Questions tagged with this should ask about physics at scales the size of the universe or specific properties of ...

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Universe as a black hole - how did everything escape? [duplicate]

While listening to physics lectures, they glossed over things escaping from black holes insinuating it doesn't happen other than radiation... When talking about the period between Planck Epoch & ...
0
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4answers
49 views

Does the universe expand in every direction evenly? [duplicate]

I've heard that the universe is expanding constantly and that galaxies are moving further and further away from each other because of this. However, does the universe expand in every direction evenly ...
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2answers
61 views

Why is the possibility of the universe having a centre around which everything orbits not considered feasible?

I'm sure there is some kind of reason as to why this isn't considered as a legitimate theory but upon giving it though it seemed to make sense to me. I figure if all gravitational orbits are ...
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0answers
46 views

The expansion of the universe and its edge

I have understood that the universe is expanding at an accelerated rate. I have also thought, perhaps mistakenly, that this expansion means not that the masses in the universe are moving away from ...
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1answer
64 views

Is the universe actually formed according to the big bang theory? [closed]

Big-Bang pretty much explain the origin of universe, but still many people don't believe it. Isn't it possible that our universe come out of a white hole which have been pulled out from a black hole ...
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0answers
13 views

Deceleration parameter in a Universe dominated by the cosmological constant

See Deriving the deceleration parameter of a universe whose density is dominated by matter for a derivation of $q_0 = \frac{\Omega_m}{2}-\Omega_\Lambda$ If the universe were $\Lambda$ dominated, ...
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1answer
222 views

Is the Universe infinite or it's just expanding to infinity?

According to the WMAP data in the past years we can say that our universe is considered flat or at least nearly flat and we also know that flat universe is allowed to be both infinite or finite in ...
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2answers
4k views

According to Hubble's Law, how can the expansion of the Universe be accelerating?

Scientists today think the expansion of the universe is accelerating. According to Hubble's law, objects further away are moving faster than objects closer to us. The further away an object is, the ...
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2answers
55 views

Does the expanding universe prove the theory of relativity wrong? [duplicate]

I recently read an article which said the the universe is expanding with a very high velocity, which is even a lot faster than the speed of light. So, doesn't this prove Einstein's theory wrong which ...
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1answer
69 views

Source of energy for infinite expansion

I read in several sources that matter, dark matter & dark energy contributes 5%, 26% and 69% of the known universe. Also, I read in a slide deck about Big Bang theory on nobelprize.org that total ...
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0answers
15 views

Flat Universe and Evolving Geometry [duplicate]

I have heard in multiple locations that in the case of a flat universe, the universe is infinite. This seems to present multiple issues: a) If a flat universe were infinite, would would the space of ...
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1answer
69 views

Why do we believe baryon asymmetry?

The question is that how can we make sure that our universe is baryon asymmetric? I mean, is it possible that there are antimatter domains beyond some very large scale. Yes, if that kind of domains ...
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1answer
240 views

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

Planet 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, can we say for sure that fields are present ...
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0answers
67 views

How is the Universe expanding faster than the speed of light? [duplicate]

I was watching a youtube video about the expansion of the universe. So the video said that the universe is expanding at a speed faster than the speed of light. I have 2 questions about that. My first ...
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0answers
18 views

What is signifcance of density of the universe if it changes?

So theories of expansion of the universe (before dark matter and energy) said that the ultimate fate of the universe is based on the density of the universe and this being compared to the critical ...
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0answers
101 views

Intuition behind deriving the FRW metric

I am studying the FRW metric and am looking at a motivation for it here. The motivation seems to use four spatial dimensions. Why do we need the fourth spatial dimension in this? This doesn't seem ...
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1answer
411 views

Can universal continuity be experimentally falsified?

It is an unresolved question whether the universe is discrete or continuous in its intricate quantum level structure. See for example: Is the universe finite and discrete? How could spacetime become ...
5
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3answers
63 views

Why is there a matter-dark matter asymmetry?

It is said generally that nature is symmetric. For example if light behaves as both a particle and a wave, then matter must also do so, which turns out to be true. But we find that the Universe ...
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3answers
62 views

How can we look back at our Universe 13Billion years ago? [duplicate]

I read this article on Space.com and I quote "As far as we know, that's as far [back] as we can see — we get an image of the universe as it was when it was about 389,000 years old," So what I wanna ...
3
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2answers
50 views

Could a pocket universe be birthed out of the negative pressure in our universe?

I have just recently started learning about inflationary cosmology so I don't know much about it. But from my understanding, the theory says the big bang was started by the expansion of a small region ...
2
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1answer
69 views

Is the age of the Universe relative to where you are within it? [duplicate]

The accepted age of the Universe is 13 billion years give or take. If you were a super space being and hypothetically had spent a large portion of this time sitting next to a black hole then your ...
0
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1answer
32 views

What is the fate of a hyper-sphere universe?

This PBS video postulates a positively curved universe which is in the shape of something the narrator calls a "hypersphere". http://youtu.be/AwwIFcdUFrE?t=6m33s Such a universe would have no edge, ...
3
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3answers
249 views

Big Freeze or Heat Death?

I can't seem to find this on the Internet.... Which is most likely to occur to "end" the universe, the big freeze scenario? Or the heat death scenario? P.s. When, if it does at all, will the ...
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1answer
39 views

Direction of travel in universe

When observe the universe we see that galaxies are much closer than they are at this very moment because of the time it takes for the light to reach us. However do we see this phenomenon in every ...
6
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2answers
3k views

If randomness doesn't exist, how come the universe isn't a perfect sphere with predictable distribution of matter?

I'm presuming that the scientific community pretty much agrees that randomness doesn't exits, and that everything has a cause. Please correct me if I'm wrong, I've heard of quantum mechanics, but as ...
5
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2answers
690 views

What is the equation for the scale factor of the universe, a(t), for the best fit of data to the $\Lambda CDM$ Model of Cosmology?

Ideally I like a single formula or multiple formulas for different time ranges that would cover the time from the end of inflation through 100+ billion years after the big bang using the $\Lambda CDM$...
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1answer
79 views

Why isn't mass still being created in the universe? [closed]

I was watching a lecture by Alan Guth and wished I was in the classroom to be able to ask a question. He explained that the total energy in the universe could be very close to zero since mass and ...
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5answers
3k views

Hubble's law and conservation of energy

If all distances are constantly increasing, as Hubble's law say, then lots of potential energies of form ~$\frac{1}{r}$ changes, so how is the total energy of the Universe conserved with Hubble's ...
5
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5answers
751 views

If the size of universe doubled

My question is silly formulated, but I want to know if there is some sensible physical question buried in it: Suppose an exact copy of our universe is made, but where spatial distances and sizes are ...
0
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0answers
38 views

Could dark matter annihilation prolong the stellar era?

I wonder, if we assume that dark matter actually exists, and it is WIMPs, and it's annihilate to fermions and W/Z bozons, which decay/combine into protons, neutrons and electrons and finally recombine ...
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1answer
65 views

Where does energy go in the death of the Universe?

So I thought that energy can't be destroyed or created but can only be transformed into another kind of energy. I read something about the Universe dying because all the stars will burn out and the ...
1
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2answers
74 views

In the classical inflation and big bang theory how can the universe grow to infinity?

Some astronomers make the conjecture that the universe is actually infinite in extent (which is a bad manner of expressing, I know). If so, how could it grow to this size in the classical theory of ...
0
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1answer
70 views

How to prepare mental skills to understand relativity theory? [closed]

Upto the high- school, I had to admit and write-on-exam the strange, counter-intuitive statements of relativity theory; those I could not believe. Now, I'm not a physics or math-student, (and indeed ...
6
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2answers
486 views

Does the current acceleration of universe imply that our universe is open?

Does the current acceleration of universe imply that our universe is open? If the universe is closed, from the Friedmann's equation, the acceleration of universe wouldn't be possible, would it be? (Of ...
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1answer
48 views

Compton wavelength And universe expansion

I'd like to ask stupid question. As I understand the wavelength of photons increase in time due to universe expansion. And it seems that Compton wavelength of particles does not changes in the same ...
0
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1answer
66 views

Space needed for expansion of the Universe [duplicate]

I realise that the universe is expanding, but doesn't it need more space to expand into? Is there some space outside our universe where the universe can expand? But if there is, doesn't it prove that ...
0
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1answer
58 views

What is Hawking's, “No Boundary Conditions”? [closed]

In his "No Boundary Conditions", is Hawking stating that time is eternal? And what is the difference between Real Time and Imaginary Time? Is he saying there are two different arrows of time, and ...
3
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2answers
2k views

Maximum Possible Information in the universe?

I remember hearing about this in one of the programs in discovery science. The physicist claimed that the maximum possible information in the universe is $10^{10^{123}}$ whereas the maximum possible ...
4
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4answers
371 views

Virtual Particles real? Virtual particles create a universe?

I am reading the book of Lawrence Krauss "A universe out of nothing", where he explained that the vacuum is not empty. It is a boiling brew of virtual particles that come out of their existence. And ...
3
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0answers
60 views

Which quantum gravity theories do predict a growing number of space dimensions?

In this 2013 Nature article there is a short presentation of the causal dynamical triangulations approach to quantum gravity, where it is said Intriguingly, the simulations also hint that soon ...
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3answers
1k views

What is space made of?

General Relativity posits that matter curves spacetime, such that geodesics point towards the object in question, hence, gravity. Now, how does matter do this? What is spacetime "made of", anyway, ...
2
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1answer
100 views

If the universe has no center, how it can collapse?

After reading Does the universe have a center? and trying to find a place in my mind for "There exists no center", I asked myself: If there is no center, in what direction our universe will collapse, ...
0
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0answers
36 views

Where is the origin of cosmic expansion? [duplicate]

Perhaps, a rudimentary or dumb question, but nevertheless am curious. There is the idea that space is expanding at an exponential rate. From where? If everywhere, why doesn't this rapid creation of ...
0
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1answer
51 views

In an infinite universe, would there be an infinite amount of matter as well?

Or would you eventually reach a point past which there is no matter? How would an infinite amount of matter work? Would it sort of "loop back" to the beginning, or would it be entirely unique the ...
1
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2answers
76 views

Trouble understanding spacetime and invariant interval

First, how is the invariant interval useful? How can it help us understand things around us in the universe? Second, I know that they changed time into space or better say SPACETIME in order to ...
3
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1answer
2k views

Is the universe linear? If so, why?

Simple question, I'm trying to build a quantum memory system that utilizes the superposition principle to model specific phenomenon I am trying to predict, anyways, my question is this. Is the ...
2
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3answers
468 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 ...
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0answers
43 views

Can we see the past view of our galaxy while observing in the sky because of the homogeneous structure of our universe?

As a sense, we think that simple speed addition should work ($V_1+V_2$) for all references but we know today that universe does not match our this sense. We cannot exceed the speed of light in any ...
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3answers
176 views

Is the Universe being dragged into a singularity rather than expanding?

Recently I've read that the expansion of the Universe as observed is not exactly uniform as proposed by Hubble. Therefore is it possible that instead of space expanding in all directions all matter is ...
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2answers
78 views

Universe Expanding

Quick question that I was just hoping to get some clarification on. Current theories state that the universe is expanding; with those planets farther away moving away from us at a faster rate. Is it ...