Questions tagged [universe]

Questions regarding all of time and space and its contents.

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277 views

Are there ways to estimate size of the “whole universe”?

Words escape me, but by "whole universe" (I think) I mean everything that's spatially connected to the observable universe in a conventional sense. If there is a better term for it, please let me know!...
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267 views

Is our Universe a hologram? [closed]

I watched a documentary where I heard some very strange theories that are difficult for me to comprehend. It is even difficult for me to explain what I heard. "Objects that fall into a black hole ...
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196 views

Contradict the expansion of the universe?

Lets say that we observe in a distant galaxy cluster, which in all the galaxies move far away from us. and here we see in the same cluster a galaxy that move away from us in a much lower velocity ...
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93 views

How do astrophysicists handle the topic 'boundaries'?

The naive perception, at least mine, is that in astrophysics the objects of investigation evolve in an infinitely large environment. Since the scenery is so much larger than the events unfolding in it,...
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136 views

If objects don't move when the universe expands, how can the expansion result in redshift?

I am approaching this topic from a layman's perspective and view this as a logic puzzle, but when someone tries to get me to accept the logic, I'm never convinced by their arguments. According to ...
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158 views

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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420 views

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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390 views

If the universe keeps expanding, can we travel to the edge of the universe? [duplicate]

If the universe keeps expanding, is it possible to travel to the edge of the universe?
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3k views

Does every object in the Universe have gravity? Space has no gravity, why?

My science teacher told me that every object in Universe has gravity but space is a part of Universe too, so, why does the space have no gravity?
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481 views

Calculating the age of the universe

Is the calculated age of the universe that of the visible universe or the entire universe? I dont know how the age is calculated but if it is believed that all we see visibly IS the entire universe ...
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435 views

The reason behind Big Bang

It always amuse us to research about things around us and we always start our research with a question that - what must be the reason for happening of that phenomenon? As we know that the formation ...
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37 views

Does the critical density of the Universe also include Dark Energy?

It is often said that it seems that the Universe is quite close to critical density (for example https://astronomy.swin.edu.au/cosmos/C/Critical+Density). Does this include Dark Energy as well (apart ...
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839 views

Are objects in the universe moving away from each other at the same acceleration?

This is a follow up question to Does the universe expand at the same rate everywhere in the universe?. If the universe is expanding, then it would seem necessary for each object (ie galaxy) to be ...
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Is the Oort Cloud actually opaque, or is the “cloud” used euphemistically because minor planets inside of it are too dim to be seen?

I did read several of the Oort Cloud questions/answers which I found very helpful and instructive, but this question still persists for me: Is the Oort Cloud actually opaque, or is the "cloud" used ...
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132 views

How was an infrared picture of the entire universe taken?

(click to enlarge) How was this picture of the supposed entire universe taken in infrared? Also, why does it seem as though almost all of the matter is in a line formation over the center? It makes ...
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1answer
826 views

If we lived in a multiverse, what would our universe most likely then be named? [closed]

For instance, we live in the Milky Way Galaxy. We don't just call it "The Galaxy", because we know there are multiple different galaxies. So if we lived in a multiverse, it wouldn't make much sense to ...
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88 views

What is the composition of the Universe in terms of Types Of Stars?

There are Main Sequence Stars Red Giants White Dwarfs Red Dwarfs Neutron Stars and other types of Stars. How many % of stars are Main Sequence? How many are Red Giants? and so on. I searched ...
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107 views

Did universe have finite hydrogen

According to this video stars at end of time and many others on fate of universe they all agree on one thing that stars will eventually convert all the hydrogen into heavier elements and eventually ...
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1answer
88 views

Looking at the Expanding Universe through the lens of relativity [closed]

The basis and most observable metric for how the universe is understood to be expanding at an accelerating rate is the red shift in observable light. I am assuming it has been thought about or maybe ...
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104 views

What was the process of calculating how much darkmatter/matter/dark energy the observable universe consists of and how did it come at this conclusion

In 2015 the Planck satellite consortium released an analysis of data collected by the Planck satellite that showed this percentage break down of the universe’s mass/energy. Ordinary matter: 4.9% ...
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147 views

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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127 views

Why aren't other kinds of energies considered in the mass-energy of the universe?

Mass-Energy of the Universe: 5% ordinary matter, 27% dark matter, 68% dark energy What about other energies such as thermal energy, potential energy, kinetic energy, chemical energy, and radiant ...
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605 views

Finding equation for energy density of matter

I'm trying to get an equation for the energy density of matter of the universe $\rho(t)$, assuming the number of particles is conserved and rest mass energy is much greater than kinetic energy. $\rho(...
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1answer
111 views

How can space expand in accelerating speed when dark energy is constant?

I came to know that dark energy is constant.As mentioned in the Friedmann equations How can a constant energy cause an ...
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2answers
312 views

How is a Galaxy formed?

How is a galaxy formed? I know that the center of our galaxy is considered to be Sagittarius A* and it's surrounded by a lot of stars (also a lot of neutron stars). But what makes this happen? I mean,...
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133 views

Why can't different regions of the universe be the same as they have the same origin?

The horizon problem states that because of the speed of information can't be faster than light and the distances between far regions are too big there is a problem because they look quite the same. ...
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1answer
81 views

Sources of astronomy-related dataset?

I'm doing a project for a statistics class, and I thought it may be interesting work with a dataset associated with astronomy. I know absolutely nothing about astronomy, unfortunately, and I wouldn't ...
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1answer
137 views

Are we moving away or towards each other?

There are numerous theories about the shape of the Universe. I've read somewhere most probably in 'A Brief History of Time' that there is a possibility that the Universe is spherical. So is it ...
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471 views

Can we know whether any distant galaxy is moving away in same direction or in opposite direction w.r.t. our galaxy?

The Hubble law states that the recessional velocity of a galaxy is proportional to its distance from us. It takes redshift and angular sizes (for distance) of the galaxy to determine velocity, and ...
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1answer
47 views

Picking two random points in space and drawing a line between them, what is the chance the line intersects anything?

I thought of this question after pondering how most of the observable universe is observable. If we can observe it, then the space between us and that object must have been unoccupied to allow the ...
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1answer
78 views

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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1answer
154 views

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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1answer
513 views

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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1answer
157 views

Centerless expansion or a matter of perspective [duplicate]

I get this question a lot: Where is the center of the Universe? I see this question on the internet all of the time: Where is the center of the Universe? Now I have a question regarding all ...
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358 views

Is the universe moving through infinite space time as it expands?

What I mean by this, is imagine a person blowing up a balloon. As the balloon expands, the person blowing it up is also walking. At a much grander scale, apply this concept to the universe. As the ...
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294 views

How do we know that the Universe is still expanding now?

Yes, I know that most galaxies have a red shift and that means they are moving away from us. The problem is that the farthest galaxies are 13.8 billion light years away. That means that the info is ...
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284 views

Infinite universe? How? [duplicate]

So it seems the overall thought is that the universe is infinite. I don't get how. Most depictions I read mention something to the effect of "at 1^-20 seconds the universe was the size of _". (...
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60 views

Why is rotational motion absolute, is the universe spinning? [duplicate]

When considering any object, one can say its translational movement is relative, depending on the point of view or reference frame adopted. If it moves at 1/4c relative to some observer, one might say ...
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What book(s) should I read to get started learning about astronomy? [duplicate]

I'm an undergrad software engineer but I also love physics and math. I'm starting to get going in AI/Machine Learning techniques and I'm going to use NASA data-sets to conduct analysis. However, I am ...
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54 views

24th Nov 2019.0515 hrs.GMT +1.saw a line of stars moving in a staright line.straight.what could it be? [duplicate]

While doing our morning navigation watch.. we saw stars moving in line.. it continued for atleast 10 mins.. not a airplane or shooting stars.. Can it be satellites orbiting??
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49 views

What is the largest cluster of merging galaxies?

Reading about the Andromeda–Milky Way collision, a galactic collision predicted to occur in about 4.5 billion years between the two galaxies, I went to the galaxy merger page and Wikipedia states that ...
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44 views

Probability of collision of another bubble universe with our universe

This is rephrased from a previous question and expanding on it. Considering the model of an "inflating" universe which extends infinitely in past (and possibly future) time, constantly creating new ...
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66 views

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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102 views

Which physical quantity is the real/definitive tracer of galaxy evolution? [closed]

Which physical quantity is the real / definitive tracer of galaxy evolution? Let me explain better: if you aimed at understanding as much as possible about the evolution of galaxies and you had to ...
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1answer
234 views

Second Big Bang [duplicate]

Just say you are immortal and will live forever. Since the universe is claimed to be unstable, what would happen after it ends? Would all of the universe's mass just fly back into another compressed ...
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1answer
81 views

Invisible Mass Affecting the Expansion of the Universe

Are there enough neutrinos & other invisible particles in a cubic light year of space to significantly affect the expansion of the universe,& at a very rough estimate without taking into ...
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100 views

Energy to expand

I do have a small question, which may seem a bit stupid but we are all here to learn. Anyways my question is: Is the universe expanding using the energy it had from the Big Bang? if so what would ...
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141 views

Regarding the age / size of the Universe [duplicate]

I believe the current estimated age of the Universe is around 14 billion years. I just read in another post on here that the diameter of the Universe is around 90 billion light years. This doesn't ...
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3answers
2k views

How to leave the Universe

If the Universe is flat and expanding at the speed of light, that must mean that we could never leave it, because one would have to travel faster than the speed of light which is not possible. However,...
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139 views

What is the shape of Universe?

What we can assume by the shape of universe. As I know when we talk about universe we talk about multi dimension structure but that structure should have some shape. I wonder that if we look the ...