Questions tagged [universe]
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 the universe
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Noether's Theorem in relativistic cosmologies [duplicate]
Is Noether's Theorem valid within the context of relativistic cosmology? If not, does this mean that the universe does not conserve energy on cosmological time and distance scales?
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What would an inter-universal medium be like?
I don't really believe in the Multiverse Theory, but hypothetically, if universes were like soap bubbles in a foam, what might that foam be like? I know this seems like an opinion-based question but ...
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Horizon problem, what if our observable universe is roughly equal to the whole universe, especially in early times?
How do we know that at a time of 380.000 years, when CMB got free, the observable universe was not equal to the actual universe? Maybe they were roughly the same and couldn't that explain the horizon ...
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How does one draw the Penrose diagram for an FLRW universe with three different epochs?
Let's model the universe with the FLRW metric
$$ ds^2 =-dt^2 +a(t)^2\big(d\chi +R_k(\chi)^2 d\Omega^2\big)$$
where $a(t)$ is the scale factor and $R_k(\chi)$ is $\chi$ for a spatially flat ($k=0$) ...
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Does vacuum decay create/destroy energy?
From what I understand, vacuum decay involves the release of potential energy, but where does this energy come from? Is it created in the moment and how does it affect the energy already present in ...
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Can the universe be unpredictable but still have only one possible history? [closed]
This question will involve concepts in quantum mechanics.
So unless you believe in many worlds theory, certain outcomes out of a series of outcomes occur. But there seems to be an assumption that one ...
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Another universe due to a rogue wave fluctuation
Let us consider our Universe at its heat death state, and the rogue wave phenomenon that is due to improbable superposition of small waves. Is it possible that a rogue wave-like quantum fluctuation ...
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Could the universe have a form of a $T^3$-torus?
Cosmological measurements suggest that we live in a flat universe. However, what might be less clear is its topology. So could the flat universe have the form of a $T^3$-torus, i.e. the torus whose ...
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Was "flow of time" equally fast during the life of universe? Is Doppler Effect the only interpretation of "shift to red"? [duplicate]
I'm an IT developer and recently I created a project where I tried to send signals between two threads in a slowing down environment. I simulated two points with their own clocks and tried to send a ...
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Cosmic web shape
Does anybody know why the cosmic web is shaped like a web? I feel like it would be more likely that it is more like a galaxy with a supermassive black hole in the center, if that were true, what would ...
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Why does the total gravitational potential in the universe exactly equal the total mass energy RIGHT NOW? [duplicate]
In the zero energy universe model, the gravitational field has negative energy, and this negative gravitational energy of all the distant mass exactly balances and cancels the positive mass-energy in ...
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Does going to the other side of Milky Way galaxy mean seeing different observable universe?
What if there was a robot that got sent to the other side of the Milky Way by just traveling with a fusion engine and started orbiting a planet that has around Earth's gravity in order to avoid any ...
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Solve Friedmann equation for non-zero curvature and non-zero cosmological constant
I tried to find an elegant way to solve (without approximating for low densities)
$$\dot{R}^2=\frac{8 \pi G}{3 c^2} \rho R^2-k c^2+\frac{c^2 \Lambda}{3} R^2$$
for $k=\pm 1$ and $\Lambda \neq 0$ (one ...
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Can we measure temperature in an isothermal Universe?
It is envisaged that ,in the future ,Universe can end in a big freeze, where there will be no energy gradient. It is also theorised that Universe was isothermal(with some irregularities I guess) in ...
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Are there any ways to conceptualize the relationship between gravity and space-time other than curvatures?
This might sound like a random question, but it came to me while I was trying to conceptualize the size of the universe and started thinking of entire galaxies resembling grands of sand floating ...