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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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The pure energy released from antimatter annihilation can reveal the mysteries of universe [on hold]

The pure energy released from antimatter annihilation can there be any use of this clean energy for research purposes like the use of light in LIGWO for gravitational waves study can we use it ...
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2answers
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Speed of at expansion at the start of the big bang [duplicate]

If I understand the basics of the big bang correctly it starts with a very small dense point. At the moment of the big bang, less then microseconds after, the universe is already the size of our solar ...
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2answers
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In what planetary system can we have arbitrarily long winters?

Unlike on Earth where the length of seasons are almost of the same duration each time, the hypothetical planet on which Game of Thrones took place has seasons of arbitrary length i.e. some winters ...
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Is the location of everything relative? [duplicate]

I have heard that everything in our physical reality is relative. But I wonder: Does the universe have an edge? In an expanding sphere, there would be an edge is it like that? If the above is true ...
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2answers
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How bright was the universe after Big Bang during photon epoch?

After 10 seconds of Big Bang, most of the leptons and antileptons annihilate each other leading to an outburst of photons. The universe was said to be dominated by photons resembling a glowing fog. ...
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What is the shape of the universe? [duplicate]

If it's flat then how a volume can be flat? And I've read that it's actually not flat .....it's a "Poincaré dodecahedral space". Any suggestions for books posts or articles are highly appreciated.
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Can the shape of our Universe be a Mobius strip? [duplicate]

The Friedmann Equations describe three possibilities for the shape of our using General Relativity, I read in a book that the shape of our Universe is a 3-sphere such that in any direction if you ...
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56 views

Where‘s the coordinate origin of the universe? [duplicate]

Given all mass originated from 0/0/0, what point do we have approximately? In km
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1answer
43 views

How do they know the numbers of the energy pie chart of the universe?

They say that the total energy of the universe consists of 4.9\% ordinary matter, 26.8\% dark matter and 68.3\% dark energy. I hear this pie part in virtually every lecture in cosmology. How do we ...
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Is physics as we know it possible in a hyperbolic space? [closed]

I understand that the overall curvature of the universe can take many different values, and as far as we know the actual total curvature for our universe is near 0. I understand it is possible ...
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1answer
61 views

Is Hubble's Law Only Valid Nearby?

I am looking this paper by LIGO, and it claims at the very beginning, At nearby distances $(d \lesssim 50 \text{ Mpc})$ [the Hubble constant] is well approximated by the expression $$v_H = H_0d, \...
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2answers
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Existence of things outside the observable universe

I've read multiple physicists talk about stuff (e.g. galaxies, black holes, etc.) "existing" outside the observable universe, but it's unclear to me in what sense these things "exist". By definition ...
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1answer
120 views

Is universe symmetric about a point?

We have a good amount of discussion and theories on the formation of universe. I want to ask is universe symmetric about a point? I think that the answer should depend upon the uniformity of ...
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2answers
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When did the radiation domination end and matter domination start?

After the inflationary era the Universe became radiation dominated. The era of radiation domination is defined as the phase during which the temperature of the Universe was so high that the kinetic ...
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2answers
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What would happen to our universe if an object of infinite mass suddenly appeared? [closed]

The scenario is this: randomly, an object of infinite mass but of a limited size appears in our universe. What would happen to the rest of the universe? My intuition is that everything else in the ...
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0answers
58 views

There is what is faster than the light [duplicate]

I have read a paragraph in "Extra Dimensions in Space and Time" book https://books.google.com.au/books?id=fFSMatekilIC&pg=PA27&redir_esc=y#v=onepage&q&f=false it says that universe ...
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Is the universe a closed system?

Most places say it is. But according to the multiverse hypothesis, gravitons and other quantum particles could travel from one universe to another. Wouldn't matter-energy then be transferred and thus ...
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3answers
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Which place in the universe that does not have force at all

Does a place without force exsist, if it so where or how could it be. I mean if we include Gravity and friction as our force in universe.
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4answers
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Does the universe have a fixed centre of mass?

Does the universe have a fixed centre of mass? If it does, doesn't it necessarily mean that every action of ours has to be balanced by a counteraction somewhere in the universe so as to neutralize the ...
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1answer
53 views

Olber's paradox with Rational Numbers [closed]

Does Olber's paradox claim that in an infinite universe (both in space and in time) light should be able to reach you from any direction? Consider the thought experiment of placing an infinite number ...
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1answer
56 views

Black holes as universal “anchors”? [closed]

I'm not a Physicist, but was watching a program about black holes. As I understand it time and space "stop" at the singularity of a black hole, which made me think of a black hole as some kind of "...
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1answer
59 views

Schwarzschild Radius of the Universe Part 2 [duplicate]

There seems to be some confusion as to what I am asking, so I am editing this for clarity. I know the universe is not a black hole. But if I could take all of the matter, (seen and unseen including ...
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0answers
35 views

Does the entire Universe prevent transforming the observable Universe into a black hole?

Consider the for us observable Universe (the entire Universe is many orders larger). It is (I think) common knowledge that the Schwarzschild Radius (SR) exceeds the radius of our observable Universe (...
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Is the Universe inside the event horizon of a white hole or a black hole or none? [duplicate]

I have read this question: Is the observable universe analogous to a white hole? But it does not have a satisfying answer. And this one: Is the observable region of the universe within the event ...
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1answer
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The largest black hole [duplicate]

The Schwarzschild radius involves an expression in terms of Newton's constant $G$, the mass $M$ inside a radius $r$, and the speed of light squared $c^2$. Current estimates of the universe's matter ...
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1answer
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The possibility of non-carbon-based lifeforms [closed]

Given what we know now. My understanding is that all life requires the combustion of oxygen and expelling carbon dioxide. Could it be possible in any form then that anything exists that is not carbon-...
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1answer
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Dark matter should be nonrelativistic at $1$ KeV or earlier. Why?

If the dark matter (DM) is non-relativistic at freeze-out and if the kinetic decoupling occurs much later than freeze-out, it is called cold dark matter. More precisely, it is stated that if the DM ...
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1answer
29 views

How does cosmological principle imply an expanding space?

My understanding of cosmological principle is this: Space looks same in all directions and is homogeneous. But this principle was under heading of Observational Evidence for expansion of space in this ...
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1answer
84 views

Evidence for zero curvature of universe (besides CMB)

There is a beautiful argument, based on the spherical harmonics of the cosmic microwave background, which calculates the curvature of the universe. Are there any other methods of computing the ...
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0answers
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Is there a “smallest unit of time”? [duplicate]

I am aware of the planck-length, being the smallest unit of space. I was wondering if there was such a thing as the smallest, undividable unit of time, something like 1 x 10 to the power of -35 ...
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0answers
56 views

What is the co-moving distance to a point, at which the late-time acceleration of the universe began?

First of all sorry for my English - it is not my native language. According to the following wonderful diagram made by Pulsar, the late-time acceleration of the universe began at $t_{acc}=$ 7.7 ...
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1answer
74 views

Is space expanding?

Is the observed stretching of the SNIa lightcurves, ie the delaying of the emitted photons at reception, evidence that space is expanding or should this be explained otherwise and how?
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3answers
352 views

Does the expansion of the universe explain why the universe doesn't collapse?

Notes: 1. I'm in 8th grade so i don't have in-depth schooling on this. Lengthier explanations with more extra information that would improve understanding would be much appreciated. 2. I asked a ...
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1answer
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As space expands does the density of matter remain same or increase? [duplicate]

I learned that space is always expanding. Even between sun and earth, it's just gravity is stronger. Imagine space as graph paper and there is a square object that fills it. Space expands, 1x1 cell ...
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Is there a cosmological model where the observable universe is bidirectionally infinite and yet finitely bi-limited?

Is there a cosmological model where the observable universe continues to shrink as we go back in time, and continues to expand as we go forwards in time, and such that at both directions it never ...
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2answers
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What happens when the wavelength of light becomes as large as the observable universe? [closed]

Say the wavelength of a photon became so large that it approached the size of the observational universe. Does something unexpected happen?
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1answer
122 views

Solution of Friedmann equation in terms of conformal time

We know that for the flat geometry of lamda CDM model, the solution for Friedmann equation is $$ a(t) = \left\{ \frac{Ω_{m,0}}{Ω_{Λ,0}} \sinh^2 \left[\frac{3}{2} \sqrt{Ω_{Λ,0}} H_0(t - t_0)\right] \...
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1answer
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Did the observable universe come from nothing?

Does the big bang theory hold that there is a possibility that the whole of the observable universe came out from NOTHING? I mean if all of this universe was occupying an extremely small size of a ...
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Total mass-energy of a system in GR [duplicate]

the Gravitation book confirm that "for closed universe the total mass-energy and angular momentum is undefined and undefinable" why many cosmologists claim that the total energy of a closed universe ...
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2answers
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If the universe is random, why does it contain structure? [closed]

Ive read that the scientific community agrees on that the universe works in a non deterministic way. However, because we have some kind of structure in the universe I assume (from a super novice ...
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1answer
75 views

Experimental status of the Big Bang theory

Take the most successful version of the Big Bang theory I'm aware that the Big Bang theory have unanswered questions related to the very first moments of the Big Bang. I also know that for our ...
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1answer
92 views

Can our universe be a true vacuum bubble?

The paper "Spontaneous creation of the universe from nothing" by Dongshan He, Dongfeng Gao and Qing-yu Cai claims that our universe was created by the quantum fluctuations in the metastable false ...
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1answer
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Pridictions and Observational evidences of No Boundary Condition of S.Hawking

Reference: http://www.hawking.org.uk/the-beginning-of-time.html Predictions of No Boundary Condition proposal: 1) Irregularities in the current universe same as the Big Bang theory predicts and it ...
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Energy quantization in macroscopic world [duplicate]

Is energy quantized in macroscopic world according to principle of correspondence ? Can an object have quantized kinetic or potential energy ?
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0answers
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Is the Universe an isolated system? [duplicate]

I am not a physicist but this question has bugged me for a while now. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. However, if the ...
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0answers
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Was the filament structure of the universe due to the same process as in the continuity equation?

In this long Twitter thread, Dr Phil Metzger suggests that the large-scale filament structure of the universe is due to the same process that determines the continuity equation. The entire tweet ...
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0answers
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Photon will deform through time? [duplicate]

Is it possible that photon will deform through time? so after millions of years a single photon will get redshifted? Can we test this possibility by current technology? If this is true, what ...
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1answer
65 views

Gravitation inside spherical hole in universe

I was doing a little thought experiment and ran into a paradox. How to compute the gravitational field inside a spherical hole in a universe that is otherwise filled with uniformly distributed mass? ...
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Why the large-scale structure is hierarchical? [closed]

Reading a lot after asking my question, I understood that it is too broad. So, I asked only the second part of my question.
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5answers
88 views

Does the Universe itself move to any direction on top of expansion?

So the universe expands right, but does this expansion move to any direction in hyperspace as an expanding cluster of matter somewhere? It's like if you would explode a bucket of paint under the. ...