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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If nothing can travel faster than the speed of light… how come can there be parts of the universe we can't see? [on hold]

Thje question: "If nothing can travel faster than the speed of light, how can there be parts of the universe we can't see?" has been marked as duplicate. One of its duplicates, Can space expand with ...
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0answers
44 views

How does the Universe connect with other Dimensions? [duplicate]

I was wondering that if the Universe was expanding, what was it expanding into. I came up with a theory and I was wondering if there was any information to support my theory, if my theory is wrong ...
12
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3answers
810 views

How does the heat death looks like from inside the system?

As this answer points out, any human would first freeze rather than experience the heat death. However, assuming hypothetically that we could make some robot live at such low temperature (or even ...
0
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2answers
165 views

Origin of Universe [duplicate]

The universe is believed to have originated from absolutely nothing, and we know it is still expanding. Physics says "something can arise from nothing". I understand how mass and energy are related ...
6
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1answer
1k views

Correlation between speed, distance, mass, etc between a planet and a star (or moon and planet)?

While playing around with some little scripts, generating solar systems, I started to wonder about the correlation between the different objects. Up until now, distance, mass, size and speed are ...
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1answer
77 views

Why is universe expanding?

Okay, this question may sound silly: base on the observation Besides an expanding universe, would there be other possibilities? Would it be possible, say, there exists a fundamental repelling ...
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0answers
42 views

Matter originated out of space? [on hold]

Is it possible that matter has originated through space out of imbalance of space? If yes then is this event same as big bang? Also is it possible that there are multiple non-interfering big bangs? ...
0
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0answers
22 views

How redshift-space distortions affects baryonic acoustic oscillations

I have a question with BAO (baryonic acoustic oscillations) and RSD (redshift-space distortions). On large scales, Kaiser effect makes the observed radial separation of galaxies smaller then ...
0
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0answers
22 views

cosmology - Hubble parameter equation [duplicate]

I have a question. We know that the Hubble constant in the space is a constant, is the same everywhere, but it changes in time, so we don't talk of H0 but H(t). Is there a way, a formula to compute ...
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0answers
36 views

Cosmological Bulk Viscosity - is the universe a fluid?

I was trying to make heads of tails of both this paper and the press release about it. The scientists have used bulk viscosity (as opposed to shear viscosity) and popped it into a model and somehow ...
0
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0answers
37 views

Astronomy - Hubble Law and Universe age [closed]

We know that the approximated age of the Universe is calculated as 1/H0 where H0 is expressed like (km/s/Mpc). If I try to calculate the dimensional equation I obtain: (10^3 m/(s* 10^6*10^16 m))^-1, ...
2
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1answer
153 views

Obtaining a copy of Hawking's Ph.D thesis - Properties of Expanding Universes

Due to its popularity, I am interested to know the 4 chapter titles and topics covered in S.W. Hawking Ph.D, Properties of Expanding Universes. I also ask this because that thesis is hardly available. ...
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1answer
60 views

Does new energy creation exist?

I know that basic physics states that energy cannot be created or destroyed, but why is that true? For example, one theory called Quantum Fluctuation states that 'normal' and anti energy is constantly ...
4
votes
1answer
68 views

Dark Civilizations? [duplicate]

I just read that maybe the dark matter could have dark forces. Hence, I wonder: dark atoms, dark galaxies, dark intelligent beings. Basically a parallel, interpenetrating universe. Is this ...
0
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1answer
27 views

Why do elements on the Binding Energy per Nuclear Molecule after Iron (most stable) even form?

So I was reading about the stability of elements based on Nuclear Binding Energy, and I saw that the 'Iron group' of elements were most tightly bound and hence most stable, and that is why the graph ...
0
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0answers
38 views

Do The Diameters of Distant Objects Seem to Get Larger?

So I'm curious about the dynamics of an expanding universe, My question may stem from misunderstanding so i'll outline what I know. When we view distant objects in the observable universe we are not ...
22
votes
1answer
2k views

Why haven't we seen the big bang?

The Andromeda galaxy is 2,538,000 light years away, so if we view Andromeda from a telescope, we see Andromeda how it was 2,538,000 years ago. Now the diameter of the visible universe is 92 billion ...
1
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1answer
41 views

Can pre-inflationary gravitational attraction affect objects after inflation?

According to inflation theory, the inflation itself took place at some short yet finite time after Big Bang, so there should be some gravitational interactions present before inflation, some objects ...
0
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3answers
129 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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0answers
53 views

End of the universe [duplicate]

Is there hope that the universe does not die? How sure do the physicist know that the universe will die? What do you think: will the universe die?
2
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1answer
147 views

Question about universe expansion

In general relativity, we cannot determine the global structure of the universe (since it is not flat), therefore all measurements and observations are only meaningful locally. In particular, we can ...
0
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2answers
38 views

How the mass is conserved during continuous expansion?

If universe is continuously expanding doesn't it contradict the fact that mass is conserved? Because if mass is conserved so how is universe expanding?
2
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2answers
83 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 ...
16
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4answers
2k views

Shape of the universe?

What is the exact shape of the universe? I know of the balloon analogy, and the bread with raisins in it. These clarify some points, like how the universe can have no centre, and how it can expand ...
1
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4answers
2k views

Why is the singularity of the Big Bang not considered to be the center of the Universe? [duplicate]

If the universe is expanding, then at some time in the past, it must have started from a single point but why this point is not the center of the Universe. Just like the singularity of black holes is ...
0
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0answers
21 views

Expansion of universe faster then speed of light? [duplicate]

Watching one of the shows on discovery channel, I got to know that during the starting phase of universe its speed should have been faster then speed of light. But then didnt einstein say that nothing ...
1
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2answers
68 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?
5
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1answer
279 views

Can the total amount of energy in the entire universe be quantified?

Classical thermodynamics leads one to believe that if energy is transferred, and the universe is heading for maximum entropy, then back extrapolating to moments before the big bang, one could find a ...
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1answer
54 views

Is there any experimental setup to test if we are Boltzmann brains? [closed]

I am not sure if this subject belongs to mainstream physics. my question is motivated by the fact that I am not sure we could ever test if we are Boltzmann brains. The same happens with string theory, ...
0
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0answers
22 views

What's the difference between cosmic time and conformal time? [duplicate]

When they say that the age of the Universe is about 13.7 billion years, they are giving the age in cosmic time, is that right?. There's this other thing called conformal time which I don't understand. ...
0
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0answers
17 views

Why can't our universe be spherical? [duplicate]

if we happen to follow the bigbang singularity hypothesis, when he explosion occured shouldn't it expand in all directions. Seemingly our universe shouldn't have any boundaries. I searched for the ...
1
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1answer
141 views

How many electrons are there in the universe?

Someone on io9 estimated there were about 10^80 electrons in the universe, but I want to ask the Stack Exchange physics community.
12
votes
2answers
1k 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 expansion of space the same way. Also ...
0
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0answers
47 views
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2answers
54 views

What are the consequences of a non-computable universe?

I have seen that is is debated if the universe is digital, computable or non-computable. what specific consequence could this have in the format of the laws of physics? Or would that mean that we will ...
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1answer
500 views

Why does mass in the universe have no limit in large size, but has a limit in small size?

We found VY Canis Majoris, a star so big it can't even be seen in scaled illustratations with the sun itself. However, we stop at particle physics, or quantum mechanics, i.e. particles, subatomic, ...
2
votes
2answers
221 views

Is it possible to detect if everyting in the Universe is changing size? [duplicate]

This may be a trivial question, but I cannot find a good answer to it. What would happen if the size of everything in the Universe is multiplied by some constant factor at the same time, let's say ...
2
votes
4answers
781 views

If everything in the universe doubled in size overnight, would it be noticeable?

By my understanding, if everything doubled in size, such as the Sun and the Earth, and because the space in between them (which is nothing) can't expand, would the gravities greatly change and the ...
0
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1answer
55 views

Where is the universe expanding from? [duplicate]

It seems to be quite a common question to ask "what is the universe expanding into?" However I want to ask "where is the universe expanding from?" Is there a "centre of expansion" of our universe ...
1
vote
1answer
42 views

Cellular automata and time T

Reading around about various CA models I saw that there are even those who are following the track to provide a single mechanicist model of the universe. For example Gerard van 't Hooft claims that ...
1
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2answers
219 views

Is the universe 5 dimensional space-time or 4?

we've been told that in General Relativity (GR), matter tells space how to curve and space tells matter how to move. But my question is, if 3 dimensional space was curved by matter then it should be ...
3
votes
1answer
65 views

What are 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
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3answers
65 views

Why is the ratio dark matter / normal matter bigger today than in the past? Is it the dark matter that increased or the normal matter that decreased?

These two pie charts clearly show that the ratio dark matter / normal matter is bigger today than it was in the past. But why? How is it possible? And does it mean that the amount of dark matter ...
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votes
2answers
81 views

What's outside of the universe? [closed]

Assuming you found a way and managed to accelerate above light speed without disintegrating, and went to the edge of the universe, what would happen? Would you instantly explode due to the lack of ...
0
votes
2answers
472 views

Why does time exist? [closed]

So I have been thinking about some subjects and one of it involves time. And I tried writing a story/question on here to summarize the bigger picture but it's not going to happen it's too complicated ...
0
votes
0answers
13 views

Chemical potentials of SM particles at high temperatures

Recently I've heard the statement that chemical potentials of SM particles on $T > 1 \text{ GeV}$ are very small, so that Gibbs potential reduces to free energy. How to prove this statement? Does ...
3
votes
3answers
288 views

How do we know for certain that space is expanding?

How do we know for certain that space is expanding? Let's say that in the year 1950, we observe that galaxy 1 is 5 billion light years away from us and galaxy 2 is 10 billion light years away from ...
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votes
1answer
63 views

What proof do we have that space is expanding? [duplicate]

how can we really say that space is expanding when we cannot see the distant galaxies forming nor are the planets nearby newly formed, nor is anything expanding in size nor are we going far away? ...
0
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1answer
159 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" ...
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0answers
99 views

Calculating energy density in the early Universe

I've been told to calculate the energy density in the early Universe. It states that it is completely dominated by neutrinos (3 species), photons, electrons, and positrons. Now, I've found an ...