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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Conformal boundary of universe with matter, radiation and cosmological constant

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 ($k=0$) ...
P. C. Spaniel's user avatar
1 vote
1 answer
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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 ...
KleinMoretti's user avatar
-1 votes
0 answers
53 views

A proof that the total mass of the universe is zero using Newtonian mechanics?

The principle of relativity posits that the fundamental laws governing physical phenomena remain invariant across all inertial frames of reference. However, a pertinent quandary arises: it requires ...
kiwiPhysics's user avatar
3 votes
4 answers
2k views

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 ...
user avatar
5 votes
1 answer
594 views

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 ...
Hulkster's user avatar
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2 votes
1 answer
113 views

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 ...
Frederic Thomas's user avatar
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0 answers
49 views

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 ...
aerion's user avatar
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1 answer
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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 ...
Kellan Heerdegen's user avatar
0 votes
1 answer
63 views

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 ...
L Turner's user avatar
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2 answers
56 views

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 ...
MiltonTheMeme's user avatar
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1 answer
59 views

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 ...
Vincent ISOZ's user avatar
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2 answers
37 views

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 ...
SacrificialEquation's user avatar
0 votes
0 answers
71 views

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 ...
cosmic_ocean's user avatar
1 vote
1 answer
32 views

Question about light and distance

If we see into the past with light and distance travelling so we can’t see things how they are currently, only how they were in the past; and James Webb took a photo from the beginning of the universe ...
Mary Cox's user avatar
2 votes
0 answers
74 views

An unusual calculation of our universe's age? [closed]

Does the following make sense? And has anyone else come across this odd ~’cosmological coincidence’ before?… …If we posit that our total universe mass is: (1) $$M_{U}=\frac{{M_{pl}}^4}{{M_{p}}^...
user86742's user avatar
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How big was the universe after inflation? [duplicate]

If we assume the universe is a closed 3-sphere, how big was the universe after inflation, compared to nowadays? Was, relatively, most space already there? If we envision the universe as a 2-sphere, a ...
Il Guercio's user avatar
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96 views

Movement of galaxies vs expansion of space

I can readily accept the theory that the universe is expanding as a mathematical model to explain the fact that all galaxies are moving away from each other, but I have difficulty understanding ...
Ruye's user avatar
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2 votes
5 answers
470 views

What is the branch of physics that asks the question 'what was before the Big Bang'?

What is the branch of physics that asks the question 'what was before the Big Bang', assuming the Big Bang is truly what happened at the beginning of the universe? If there could be a better model ...
Bruce M's user avatar
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0 answers
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Planck time - what would I see? [duplicate]

Impossibly hypothetical, but to communicate the question: when the universe "ticks" a plank second, what does a particle do? I'd imagine the natural conception that it moves from position a ...
Rabbi Kaii's user avatar
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0 answers
28 views

Complete Old Figure of Friedmann Universe Models

I have found this quite old figure (R. D'Inverno, Introducing Einstein's Relativity. Clarendon Press, 1992) that I want to modernize for a course using TikZ/LaTeX. My questions are: Do you know if ...
Vincent ISOZ's user avatar
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0 answers
76 views

Numerical solution for the Mukhanov-Sasaki equation with Bunch-Davies vacuum state

I have the Mukhanov-Sasaki equation in terms of $u_k$ \begin{align*} u''_k(\tau)+\left(k^2-\frac{a''(\tau)}{a(\tau)}+f(\tau)\right)u_k(\tau)=0 \end{align*} and also the initial condition from Bunch-...
Julian Yussef's user avatar
10 votes
6 answers
4k views

Why do we say that temperature of Universe is around 2.7 K?

I am little confused, so please correct me if I am wrong. Temperature of Universe is calculated using cosmic microwave background and it is around 2.7 K. The cosmic microwave background is the relic ...
SacrificialEquation's user avatar
0 votes
0 answers
46 views

Big Bang as stretching space time?

I am still new to researching the big bang so please be patient. I am having trouble envisioning the expansion. As I understand under current theory it is not to be thought of as a singularity ...
Stargazer's user avatar
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Asymptotic development of the black-hole metric

In the Kruskal-Szekeres extension of the Schwarzschild metric parallel universes appear. In a couple of questions on this site, for instance: Where does the parallel universe in the Penrose diagram ...
Frederic Thomas's user avatar
-3 votes
3 answers
183 views

David Deutsch says "number of atoms in universe is finite", but then says "number of programs of all finite lengths is infinite". Contradiction? [closed]

From book "Fabric of reality" by David Deutsch (page 127 chapter 6 "universality and limits of computation"). We know from quantum theory that all such variables are quantized, ...
srghma's user avatar
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2 votes
2 answers
433 views

Why can't we see past the observable universe?

Why can't we see light from beyond the observable universe? I've done a lot of research on this and all I've found is unsatisfactory answers and straight up nonsense. Some claim that the universe &...
Krokodil's user avatar
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1 vote
0 answers
60 views

Is the universe closed or flat?

Apparently there is a tension in the measuring of the curvature of the universe (https://arxiv.org/abs/2307.07475) as apparently in 2018 the Planck collaboration got a series of results consistent ...
vengaq's user avatar
  • 2,224
-2 votes
2 answers
94 views

Since the instant of the big bang, has the progression of the universe been entirely determined?

[Note I am asking up to, but not including, consciousness as this bleeds into philosophy and is a much messier question] Assuming that the laws of physics have remained constant across space & ...
Runeaway3's user avatar
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8 votes
2 answers
415 views

Are the mass, diameter and age of the Universe frame dependent?

Mass of the observable Universe is known to be $1.50×10^{53}$ kg. Age is approximately known to be 13.7 billion years.The observable Universe is a sphere with diameter of roughly $8.8\times10^{26}$ m. ...
SacrificialEquation's user avatar
0 votes
3 answers
107 views

Is Dark Energy Taking Over?

First question, trying to keep it simple 😃 Because it's constant it grows in magnitude as the universe expands, whereas normal matter does not? Is this accurate as far as we know?
Wileyo's user avatar
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0 answers
23 views

Is the size/age of the universe dependent on your velocity? [duplicate]

As Photons do not experience time or space, then according to my thought experiment, all photons must occupy some kind of singularity as well as what WE observe from earth. I was also thinking that ...
Martin Clem's user avatar
0 votes
2 answers
90 views

Is the time evolution of the universe cyclic? [closed]

If we can assume that quantum mechanics does not have a bound on its applicability, i.e. there are no inherently classical properties of the universe, we can represent the physical state of the entire ...
Joel Järnefelt's user avatar
3 votes
4 answers
2k views

Is the universe really a closed physical system? [closed]

It is assumed in most physics discussions that the universe is a closed physical system. But is it really? I am defining the universe as the entirety of everything physical, not merely the observable ...
user107952's user avatar
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3 votes
2 answers
131 views

Planck Units of the Universe

Is it a coincidence, or is it chosen this way, that the size of the width of the universe is approximately 10^61 planck lengths, the mass is 10^61 planck mass, and the age is 10^61 planck time?
Test's user avatar
  • 133
-4 votes
1 answer
77 views

The background of the universe [closed]

Mass(-energy-momentum) curves space(-time). However - what is space-time? Is it (the background) necessarily flat(without something in it) ? If there were an empty universe - is there still spacetime ...
MartyMcFly's user avatar
0 votes
1 answer
57 views

Radius of a ball to exceed the Schwarzschild Radius of the enclosed mass for a given density, for example universe's average density

Given a mass (energy) density of $\rho$, a ball of radius $R$ has a mass of $M(R)=4\pi/3\cdot R^3\cdot\rho$. The Schwarzschild Radius of this mass in dependence of $R$ is $$ r_s(R) = \frac{2GM(R)}{c^2}...
Harald's user avatar
  • 739
2 votes
5 answers
1k views

Why is it that the further a galaxy is, the greater is its recessional velocity?

The exam question is: Explain how red-shift provides evidence for the Big Bang theory. One of the points in the answer is: the further away the galaxy is, the greater is their recessional speed ...
Radhi's user avatar
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1 vote
0 answers
30 views

Infinite energy from net charge of a closed, finite universe

I have read that a net charge in a closed, finite universe would result in the electric field from the charge "winding" forever which would lead to infinite energy. However, wouldn't the ...
user1070280's user avatar
1 vote
1 answer
48 views

What is the rough distribution for number of galaxies with a given mass in the observable universe?

Is there a rough formula for the fraction of galaxies in the observable universe with masses between M and M + dM? Or perhaps a graph that displays the same information? I've looked online but can't ...
Thanos's user avatar
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6 votes
4 answers
2k views

What does it mean for the laws of physics to "break down" at a singularity? [duplicate]

When the statement says: As you get to the center of a singularity the laws of physics "break down". What exactly does that mean?
Perleedee's user avatar
0 votes
1 answer
46 views

Is it true to say that there is a single electric field and it is inhabited by and affected by all charges in the universe? [closed]

I don't see why or how this could be argued against or if it really matters, but that's why I ask the forum. I am just trying to understand the nature of the fields in the universe. Am I correct in ...
SubparBeginner1's user avatar
2 votes
0 answers
58 views

Space expansion or generation [duplicate]

When physicists assert that space is expanding, does this imply the creation of new space? If so, why do they use the term "expansion" instead of "generation"?
omid's user avatar
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0 votes
0 answers
90 views

All possible models to explain the hierarchy problem?

There is an interesting paper by Arkani-Hamed and collaborators (https://arxiv.org/abs/1607.06821) to address the hierarchy problem. There, they consider many possible models of fundamental particle ...
vengaq's user avatar
  • 2,224
-1 votes
1 answer
110 views

Is it possible that if the universe collapses, it reaches the same state as in its beginning? [closed]

Suppose the universe were to eventually collapse in a Big Crunch. How closely could the universe's final moments resemble those at the beginning of the universe? Could the universe return to its ...
vengaq's user avatar
  • 2,224
1 vote
0 answers
31 views

In Cyclical Cosmology (Big Bounce) is it possible the new universe will be different or the same? [closed]

Could it be a universe with similar laws to ours but a different configuration of matter, so there may be another earth like planet in this new universe?
Adam Shakeel's user avatar
-1 votes
1 answer
128 views

Is there an upper limit to temperature in the universe?

The Sun's core temperature has been modelled to be $\approx 1.57 \times 10^7$ K In supernovae: "In lower mass cores the collapse is stopped and the newly formed neutron core has an initial ...
Brendan Darrer's user avatar
1 vote
1 answer
117 views

Why easiest path from Big Bang to Heat Death is not followed by nature? [closed]

Why after Big Bang it is not going to Heat Death in the easiest path, actually the energy can get distributed uniformly to all directions. Instead we see the energy in Big Bang is being converted to ...
Shafeek's user avatar
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1 vote
1 answer
85 views

Is matter in space, or independent from it, but interracts?

Considering the "hierarchy" of the Universe, or the world in a broad sense, as I understand it consists of matter, matter consists of "substance" (fermions), and fields and so on. ...
Stdugnd4ikbd's user avatar
2 votes
1 answer
72 views

Are we surrounded by Big Bang? [duplicate]

Maybe the questions is too stupid to be asked or I do not know the technical words, but I could not find any answer to this question. Here is how I started to think the title: First I thought of if we ...
Veysel's user avatar
  • 23
0 votes
1 answer
160 views

Are black holes the edge of our universe?

Are black holes the actual edge of the universe? Because spacetime is another dimension, I would assume the universe doesn’t have perceived corners or edges. At least humans cannot perceive it. The ...
Mekkel's user avatar
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