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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Questions about the Jeans length

I have a couple of questions about the Jeans length. Suppose the universe has a homogeneous energy density, except there's a spherical region that is overdense. I understand that if the region is ...
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1answer
183 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 ...
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1answer
136 views

What arguments are in favour of an atomic structure to space-time?

The atomic theory as first theorised by Democritus has been successfully applied to matter and to energy (quanta). Space-time is still generally seen as a continuum. What arguments are there (if any) ...
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1answer
130 views

How would it be to live in a very small universe, let´s say 20x20 square meters?

Let´s consider a curved universe that is very small, say 20 square meters and not expanding. If you stood at the middle of this tiny universe and looked forward, you wouldn´t see any walls, since it ...
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1answer
86 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 ...
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1answer
527 views

parallel universe- are there an infinite amount of universes?

Parallel universe: in every universe, you are presented with a different decision. Does that mean there are an infinite amount of parallel universes? I.e., if in one universe I choose to go left, I am ...
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1answer
272 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, ...
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1answer
124 views

Finite amount of matter and space

(Please bear with me.) If the universe included multi-universes, and black holes transferred matter between them, AND yet there was a large, but FINITE amount of matter and space, How would that ...
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0answers
176 views

Poincare recurrence and the multiverse

In this paper Susskind claims that a stable de Sitter universe is problematic (among other things) due to the existence of Poincare recurrence, which happen because of finite entropy. I disagree that ...
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0answers
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What coordinate system is used to describe planets positions in the universe?

How are planets positions described in the space and in respect to what? For example is Sun the origo and right now at this moment Earth has [coord_X, coord_Y, coord_Z]? or maybe [lng, lat]? ...
3
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0answers
104 views

What is the theoretical geometry of bubble universes?

My research has led me to look into the idea of bubble universes which I don't know very much about. The first thing that I am looking for is understanding or visualising how could many bubbles ...
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0answers
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In the αβγ cosmology paper, how do the authors assume the integral of density over time in the early universe?

In the famous Alpher-Bethe-Gamow paper, the authors say: "it is necessary to assume the integral of $\sigma_n dt$ during the building-up period is equal to $5 \times 10^4 \frac{\text{g ...
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According to Penrose, Weyl Tensor=0 is the start/end of the Universe. Must it =0?

If I understand Roger Penrose's theory, as the Universe expands and cools, matter is consumed by black holes. Eventually the black holes collide and evaporate so that there is only energy and the Weyl ...
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0answers
75 views

Modelling a matter dominated universe collapsing into a black hole

With the FLRW equations we can get solutions for a matter dominated closed universe in which the finale is an ultimate collapse, but this is only in terms of $a$ (the scale factor) and $t$ (time) and ...
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0answers
29 views

CMB radiation and holography

If in principle someone have the exact data of the CMB of our universe and unlimited computability power, to what extent it is possible to determine how the universe should look like? Does it fully ...
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0answers
118 views

Does space expand locally without restriction in freefall to central region of black hole?

It is often stated that a distant observer will observe a freefalling object as experiencing an infinite journey to the event horizon, but that a traveler in the local frame will experience a ...
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0answers
94 views

Can universe be a closed manifold?

I had a question at MSE which gave a rise to another question. Maxwell equations can be written in form $$d\star F = J$$ Then by Stokes theorem we have $$ \int_U J = \int_U d \star F = ...
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0answers
148 views

Total positive charge in the Universe

In their last homework, some of my students miscalculated a charge to be $10^{20}$ C over a squared meter and I was wondering if there was as much positive charges in the entire Universe. It would do ...
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0answers
54 views

What is the age of the Universe from the big-bang light perspective?

What is the age of the Universe from the big-bang light perspective? We all agree that the universe is around 14 billion years, from the perspective of a hypothetical observer moving in a galaxy, ...
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0answers
63 views

What is the future of our universe?

Is the universe heading towards a Big Freeze, a Big Rip, a Big Crunch or a Big Bounce? Or is it part of an infinitely recurring cyclic model?