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Questions tagged [observable-universe]

Questions regarding the region of space containing all the objects that we can detect using any method of observation.

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Can Einstein-Rosen bridges - if they exist - link two points of which one lies outside of the observable universe of the other?

So there's stuff very far away that is, due to expansion, accelerating away faster than the speed of light, so fast that its light will never reach us even with infinite time - and we can't reach that ...
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2answers
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how do we know the universe is STILL expanding?

According to Hubble more distant galaxies are moving away faster but since the light took billions of years to reach us we should say they WERE moving away faster billions of years ago. How do we know ...
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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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4answers
141 views

Why there are less massive stars than low mass stars?

What factor determines the selection of star mass? And how we know that the number of massive stars is less than the number of low mass stars?
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1answer
65 views

How thick is the cosmic microwave background, including the part we cannot see within the observable universe?

What I want to know is how thick the observable universe is from the point of the cosmic microwave background and beyond. It appears the thickness of the cosmic microwave background itself (the part ...
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2answers
67 views

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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1answer
98 views

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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1answer
121 views

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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1answer
91 views

What is the present day radius of the observable universe?

The radius of the observable universe is generally taken to be ~45 billion light years. However, we see distant galaxies as they were many millions of years in the past, so there are two ways I can ...
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3answers
154 views

Is the shape of observable universe and shape of space same?

I have read that Euclidean space is considered as flat space and Minkowski space is flat space-time. So when we say our observable universe is flat are we saying that the space is flat or space-time ...
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Bousso bound within particle horizon, discrete Q.field theory

I have 2 questions: Could you please give me arxiv numbers of papers dealing with the Bousso bound for the particle horizon (known Universe), from masters level upwards, with also some papers a bit ...
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1answer
91 views

Is there a physical limit to how far we can go?

Is there a physical limit to how far we can go? I am thinking there could be based on the following: 1: There are parts of the universe expanding faster than the speed of light that we will never be ...
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1answer
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If I look beyond (about same region, higher redshift) a galaxy, will I see its progenitors?

Is there a range of redhsift dz, such that if I look at z+dz from a massive object at redshift z, I will see its progenitors? (in a LCDM scenario of halo assembling, with smaller halos evolving ...
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1answer
55 views

false to stable vacuum transition [closed]

if the universe transitioned from a meta-stable vacuum to a stable vacuum we assume a universal death scenario. However since it cannot propagate faster than the speed of light, from any particular ...
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1answer
149 views

Can an infinite universe explain the Fermi Paradox?

Explanation of potential problem: We're not completely sure exactly how unlikely an event Abiogenesis was, given both the extreme unlikelihood of nucleotides randomly assembling into anything making ...
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1answer
331 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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3answers
385 views

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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3answers
356 views

Maximum distance light can travel? [duplicate]

If we assume that there is nothing except the sun in the universe then how far the light can travel ??
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1answer
74 views

Find a planet with incomplete information of a star chart [closed]

I am wondering why it was so hard to locate Luke in Star Was Episode 7, if you already have the small part of the map. Suppose we have a sector of our galaxy that roughly equals the one missing in ...
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3answers
311 views

Is our universe flat?

I heard our universe is flat. Then one question is puzzling in my mind. If our universe is really flat, why we measure distance from any point across in a spherical way. In other words, why we say, ...
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2answers
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The # of Estimated Galaxies increased 10 fold. Where does that leave our # of stars estimate?

I have found oddly different answers through my multiple google searches. I found one article that mentioned this did not alter the estimated number of stars in the universe. Link: http://www....
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2answers
155 views

Are any galaxies partially in the observable universe?

Are there any galaxies that are partially with the visible universe? It seems unlikely as most of the universe is empty space however our circumference makes it seem likely as well. It would be a ...
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1answer
343 views

How can the observable universe shrink in a Big Rip?

As far as I know, the Big Rip occurs when the scale factor reaches infinity in a finite time. This will only happen in a universe dominated by phantom energy (i.e. a universe with an equation of state ...
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2answers
342 views

What fraction of galaxies in the observable universe have we actually observed?

There are a finite number of currently observable galaxies due to the finite age of the universe and the speed of light. What fraction of these galaxies have we actually observed (by eye, telescope, ...
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Are they talking about the observable universe or the unobservable universe? [closed]

When people say that 95% of the universe is dark matter and dark energy, are they talking about it being in the observable universe or the unobservable universe? Because surely all matter in the ...
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2answers
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How do you measure something that has already left the observable universe?

They say that the observable universe is only 5% of the entire equation. The rest of it consists of dark matter and energy. I believe that they are trying to find a way to see something that cannot be ...
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1answer
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Does the recent news of “ten times more galaxies” imply that there is correspondingly less dark matter?

Nature: Universe has ten times more galaxies than researchers thought NASA feature: Hubble Reveals Observable Universe Contains 10 Times More Galaxies Than Previously Thought Headlines sometimes ...
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Does the age of the universe take into account General Relativity / Special Relativity?

It is generally accepted that the age of the universe is approximately 12-15 billion years old based on the speed of the expansion of the universe. Since everything is moving very fast away from us, ...
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1answer
386 views

Can information leave the observable universe?

From what I gather, the observable universe is expanding at the speed of light. In addition, information cannot travel faster than the speed of light. It seems as though these two facts would imply ...
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1answer
101 views

How fast would we have to go for the red(/blue)shifts of galaxies ahead of us to differ from those behind us with statistical significance?

Here, we are looking for a statistically significant difference between the mean redshifts of galaxies ahead and those behind, with reference to a prior-specified direction. For example, suppose that ...
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1answer
95 views

Can one calculate the size (i.e. the radius) of our universe? [closed]

If one can estimate the mass of our universe, might one also calculate its ultimate size, (after it fully expands), based on the Schwarzschild formula for the radius of a black hole? Please note that ...
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1answer
72 views

Intuitive explanation for why the universe is flat

I went through Prof. Hitoshi Murayama's online lecture where he describes why the universe is flat. One of the evidences for a flat universe is the evenness of CMB radiation on all directions. My ...
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2answers
3k views

How long would it take to reach the edge of the reachable universe?

How long would it take to reach the current edge of the reachable portion of the universe, with the following bounds in mind: We figure out a way build a space ship to provide a constant 1 G ...
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2answers
627 views

Are there any galaxies which fell out of sight horizon due to cosmic expansion?

If farthest galaxies run away from us with acceleration making them exceed speed of light, we should expect them to disappear from sky among time with increasing quantity. Did we observe this? Can we ...
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1answer
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Since the Universe is expanding, is it accurate to say that a galaxy is 5 billion light years away?

Isn't it better to say that the light from the galaxy took 5 billion light years to reach us and it is a very old picture of it? However, if light travelled back to the galaxy at the constant speed ...
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2answers
1k views

Why can we observe the Cosmic Microwave Background no matter the direction we look?

I often read that the CMB was released from everywhere in the Universe, in every direction. If that statement is true, can someone elaborate what "everywhere in the universe, in every direction" ...
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Star Formation in the future [duplicate]

From what I understand stars form in dense clouds of hydrogen and helium molecules. Only so much hydrogen and helium were "created" from the Big Bang or rather formed if you may. Is it conceivably ...
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1answer
200 views

Has the most luminous object in the universe been found?

It's hard to search through the entire (observable) universe, but the most luminous thing there is must on the other hand be easy to find. Can we now say that the most luminous quasar we know, is the (...
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1answer
160 views

How can the observable universe be so small if there are so many stars in it?

The observable universe has a radius of about 46.5 billion light years. That’s big but I just wonder how that can be big enough to fit in everything we know exists in the universe. There are hundreds ...
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1answer
160 views

A universal reference point [duplicate]

I would like to use a system of co-ordinates (x,y,z,t) based on a specific well known point. My original choice (the center of the universe in the big bang theory, Bigbang0), was wrong as the universe ...
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3answers
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Is it just the observable universe that is expanding?

Is it possible that it is just our observable part of the universe that is expanding, in the time that we exist, and other parts are both expanding and contracting at different rates and times? Would ...
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2answers
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Is the diameter of the observable universe a relative quantity?

The diameter of my observable universe is 90 billion ly measured in proper distance. But isn't lenght a relative quantity in the theory of Relativity? Could an observer moving at a different velocity ...
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8answers
10k views

Why can't we see distant galaxies with the naked eye?

If light keeps travelling in a straight line, why can't we see distant galaxies with the naked eye? Surely if you stared long enough, the light from them would eventually hit your eye? I apologize if ...
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2answers
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How can I see a nebula?

I've recently been seeing a bunch of pictures of nebulae and I'm just fascinated by their beauty and complexity. Is there any kind of telescope that would make it possible to view it from here on ...
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1answer
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Does CIBER Experiment from Caltech suggest that there can be lots of stars which are not in any galaxy?

My question is about the implications of the observations recently made by the Cosmic Infrared Background Experiment, or CIBER, from Caltech. I've read at Caltech web site: "The total light ...
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1answer
100 views

Red shifting galaxies

I am an amateur astronomer please correct if any of my understandings are wrong. We all know that from the Hubble's ultra deep field image the most distant galaxies which were created shortly after ...
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1answer
504 views

Objects entering or leaving the observable universe

Have there been any observations of objects entering or leaving the observable universe? When looking at the physical limit of observing something like this I will to assume that the "object" would ...
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1answer
325 views

What is the radius of observable universe- 46 billion LY or 200 yottameters?

I have found two answers for the radius of the observable universe. Wikipedia (and other places, including this site) say approximately 46 billion LY. I am researching this to study for the National ...
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2answers
133 views

Why aren't the farthest objects close to each other?

The last years we find some objects like this : MACS0647-JD which are more than 13 billion light-years away from us. This means that the picture we get was created only some million years after the ...
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1answer
648 views

Can we see the Big Bang happen if we look far enough?

The observable universe is constantly expanding as more light from the Big Bang reaches us. This light has been travelling for billions of years, so we are looking at the universe as it was a few ...