Questions tagged [universe]
Questions regarding all of time and space and its contents.
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Is our universe stable or metastable?
I've been reading and thinking about this subject for some time, but I can't seem to find a clear answer.
After reading Q14:
Aspects of the Higgs boson suggest that our Universe is only
“...
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Is the universe always expanding
Currently we observe that the universe is expanding. And this expansion even goes faster and faster.
Why do we know (or presume) that this expansion started slowly at a singularity (i.e. big bang) ...
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What is the total number of stars in the universe? [duplicate]
I mean a total number of stars, not the only ones that we can see.
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How much of the Universe is subatomic? [closed]
How much does subatomic particles such as photons, tachyons, and electron being the biggest particles etc. occupy space? If put in a ball how big of a ball would that be?
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Why Is The Expansion of The Universe Allowed To Move Faster Than Light? [duplicate]
Why is the expansion of the universe allowed to faster than light if everything that moves within a vacuum can't reach the speed limit of light?
I've read that astronomers looked at the distance ...
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3-sphere universe [closed]
I have just read on this site that there is a Newtonian solution to Einstein's field equation but that it is spherically symmetrical and therefore not isotropic (having a centre for example) and so ...
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How can the universe be expanding? [duplicate]
I assume expansion implies an increase in the volume of the universe. But if the volume of the universe is increasing, does that not imply the area it is expanding into's volume is being reduced?
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What happens for a "closed" universe without any content?
Let an universe with no content and positive curvature.
Friedmann-Lemaître equation
$$H^2=\frac{8\pi G}{3}\left(\rho_m+\rho_r+\rho_{\Lambda}\right)-\frac{k\, c^2}{a^2},$$
where $a$ corresponds to the ...
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Is the acceleration of the expansion of the universe a direct observation or an interpretation?
Is the acceleration of expansion we observe with supernovae direct or is this an interpretation according $\Lambda$CDM model ?
I mean what we observe is luminosity distance versus redshift, so to see ...
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Is it possible that the Universe is expanding due to additional Big Bang events?
Is it theoretically possible that the Universe is expanding due to additional Big Bang events that have occurred at the same location that the original Big Bang occurred at?
Perhaps there has been an ...
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Light beam (1 photon) in the limited universe?
If our universe is not infinite, what happens with the light beam (or photon) when it will travel through the whole universe?
For example, observable universe according to wikipedia has diameter 93 ...
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Why do we presume that the universe has always expanded?
When I read about the universe having always expanded from a 'singularity', I can't help but wonder if that is perhaps not the case. If a singularity is a point at which everything is infinite and is, ...
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Does the edge of the Universe travel faster than the speed of light?
The Universe is expanding faster than the speed of light then does that mean matter at the edge of the universe is also traveling at the speed of light or are ether opposite sides of the universe are ...
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Yet another Question about the expansion of universe
A galaxy 13 billion light-years distant is 94% of the way to the big bang. The universe was 800 million years old when the light was emitted. That galaxy today is traveling away from us at 94% of the ...
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Methodology for size of Universe
I understand that the Universe could be either finite or infinite and that it is, at the least, "very large". :)
My question is, why doesn't the math involved in making the CMB and other predictions, ...
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What explains the existence of energy/matter if it cannot be created or destroyed?
If the energy/matter that was contained in the singularity before the Big Bang had always existed, and if it’s true that energy/matter cannot be created or destroyed, then what explains its existence?
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Influences from outside the observable universe explaining dark energy and expansion?
Could some influence from outside the observable universe be causing the expansion?
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How can heavy elements exist when the universe is young compared to the lifetime of a star? [duplicate]
Our sun is said to be incapable of producing heavier elements, and these are thought to originate from older stars dying and going supernova. If our sun is 4-5 billion years old, and has a lifetime of ...
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Will a black hole swallow the universe?
If black holes swallow stuff, will a big black hole eventually swallow the universe? The universe will eventually go dark, because there will not be enough matter to make stars, and all that will be ...
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How to derive the equation for the age of a flat universe with a positive cosmological term?
Can anyone show the steps involved in deriving this equation from the friedmann equation with the cosmological constant involved
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Does the CMB pattern evolve in a human lifetime?
I was thinking, as CMB is a snapshot of a slice of the Universe during recombination, how much the cmb is changing with time ?
I mean as we progress in time we look a CMB a bit more faraway each time, ...
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Question on Friedman equation involving cosmological constant
This is the question:
By considering both the Friedmann and acceleration equations, and assuming a pressureless
Universe, demonstrate that in order to have a static Universe we must have
a closed ...
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Where can I find source data for the graph of metric expansion over time, as shown in this ESA web page?
This web page from ESA/Hubble, shows the size of the universe over time. (I know that "size of the universe" is a gross simplification and open to multiple definitions and ambiguity, but this kind of ...
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Account for radiation energy in the statement "total energy of universe is zero"
I've read in Hawking's book The Theory of Everything that total energy of the Universe is zero. He explained this by saying that if there are two bodies separated by a distance and having some mass, ...
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Why black holes are extremely cold?
"The most massive black holes in the Universe, the supermassive black
holes with millions of times the math [sic] of the Sun will have a
temperature of 1.4 x $10^{-14}$ Kelvin. That's low. Almost ...
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SETI search for extraterrestrial life [closed]
In all these years of listening, why hasn't SETI detected anything ? Is there no intelligent life out there or is it too far away to detect ?
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Is the Cosmos a super set of the Universe and any hypothetical multiverse(s)? [closed]
I'm quite lost on the definitions of words like omniverse, megaverse, multiverse, meta-universe, universe, and cosmos. I used to think the Universe and the Cosmos were essentially the same things, but ...
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What would happen to a polished marble statue left in space for a million years?
Consider it doesn't collide with any other objects. Would it be preserved perfectly in the vacuum or would its surface be damaged by anything like UV rays, radiation, gas, space dust, etc?
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what happens when we keep going radially away from earth?
Is the generally accepted belief in the science community, that if one sits in a spaceship and move away from Earth where r (distance between earth and my ship) is continuously increasing, can one ...
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Use of type-I a supernovae as standard candle
Why only type -Ia supernovae are used as standard candle to calculate age of universe and why not type II, type Ib, type 1c ?
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What happens if one day aliens want to talk to us. How can we talk to them? [closed]
Always I wonder about that if some day alien wants to talk to us, then how can we talk to them? They didn't know any of the language on the Earth.
What will be the basic building blocks for it?
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If the Universe is Flat, why does it look 3D from our View?
So I know that the universe is flat in a 4D point of view, but what about a 3D point of view? The universe does not SEEM flat from our view, so how can it really be so? Please answer more simple, im ...
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Is there any way to tell which way is the next universe? [closed]
Is there a observable void outside our universe that can give a clue on how far the next on is? How many universes can surround ours? What does a universes gravity well look like?
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How to fix a Direction in the context of universe? [duplicate]
My question is regarding the direction/orientation of earth. Is it a constant with reference to universal parameters?
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Can the shedding of radiation of stars contribute to the red-shift of the universe?
The sun is losing mass(1.5cm per year) by emitting radiation and the orbits of the planets are widening because of the weakening gravity of the sun.
Are most of the stars shedding mass via ...
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Universe becoming finite
If sometime in the distant future, the Universe stopped expanding, would this mean that the Universe was no longer infinite?
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Would a future hole in the Cosmic Microwave Background show us the edge of the universe?
If my understanding is correct, the Cosmic Microwave Background always come from our event horizon. By event horizon I mean the edge of the observable universe.
If the universe is finite does it mean ...
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How can we ge to the exoplanet Proxima b? [closed]
I would like to know please how can we get to the exoplanet Proxima b. I heard it is the potentially habitable exoplanet closet to Earth at only 4.2 light years away. So exciting!
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Are there more stars in the universe than grains of sand in the Earth?
My ten year old daughter asked me this question at breakfast and I initially said yes, but on second thought I was also puzzled.
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What is a probability of a particle launched from earth hitting any object in the universe?
Imagine I pointed a laser into the night sky. How likely is it that a particular photon will ever hit anything?
This question bothered me for a while. I know very little about astronomy. When I asked ...
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What will the universe be like in a googolplex years time?
It will be cold and dark in 10^(10^100) years.
What else can be said of the state of things in the far distant future? Will everything have fallen into supermassive black holes and then radiated ...
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What is beyond the observable universe? [closed]
What is beyond the edge of the observable universe? Scientists say that the Big Bang is the cause of all creation in the known universe, but it would seem the bang must have happened in the center of ...
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How can the universe be expanding faster than speed of light? [duplicate]
So the story goes like this:
A long time ago, 13.799±0.021 billion years to be exact, something happened. It was a big bang, loud explosion and universe came to existence. It grew and grew, and now ...
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Is an expanding universe equivalent to a universe in which everything is shrinking?
Why do we always think of the universe as expanding?
Surely, from our perspective an expanding universe would look exactly the same as a universe in which everything is shrinking away from ...
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Will universe's lakes get boiled by the CMBR?
From what I can understand, Cosmic Microwave Background Radiation (CMBR) is microwave now, but was initially visible light emitted long time ago.
The microwave is producing a wave that’s about 12 ...
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Is the age of the universe relative to an observer's location in that universe?
According to Wiki the age of the universe is 13 billion years old, and I was taught that background radiation made the universe uniform in all directions.
Doesn't this define a sphere of space in the ...
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Does the Milky Way move through space?
Does our galaxy moves through space? Or does it stay in a single location? If it does move, what causes it to move?
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What's the name of outside the cosmic horizon?
The word we use to refer to what's inside the cosmic horizon is the 'universe', so what would you call the empty space outside of the horizon?
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Why do we we even exist? [closed]
It came to my mind one day that why does this universe even exist and why do we even exist and like we are enclosed in the so called atmosphere and a floating rock in space called the Earth, so is ...
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Based on the smallest number of photons that can deliver information about a star, what is the largest size of the universe?
I was watching a summary video about the Banach-Tarski paradox and it led me to a question.
If I (a) assume the universe is infinite and (b) assume it is possible to receive a single photon of light ...
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