Questions tagged [observable-universe]

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

Filter by
Sorted by
Tagged with
55
votes
3answers
14k views

What is the hottest thing in the universe?

Straight from my 7 year old to you, exactly what it says on the cover: What is the hottest thing in the universe? To make it Stack Exchange-friendly, I'll add the following caveats: it should be ...
24
votes
8answers
12k 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 ...
21
votes
1answer
3k views

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 ...
16
votes
2answers
1k 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 ...
16
votes
1answer
1k 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 ...
11
votes
1answer
213 views

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 ...
8
votes
1answer
176 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, ...
8
votes
2answers
369 views

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 ...
7
votes
3answers
2k 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" ...
7
votes
1answer
114 views

Anecdote of an astronomer looking for correlations in antipodal pairings of stars; what am I remembering?

The question Are the stars distributed in uniform distribution, on the celestial dome, with respect to brightness? brings to mind a different study that I vaguely remember hearing about a while ago, ...
6
votes
1answer
657 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 ...
5
votes
2answers
104 views

How is the gravitational effect of galaxies outside of the visible universe on galaxies within the visible universe currently modeled?

Given currently accepted models of the universe, How much mass is outside of the visible universe? What is the gravitational effect of that mass on the visible universe? The question How strong is ...
5
votes
2answers
425 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, ...
5
votes
3answers
450 views

Can two planets in an empty universe meet/be pulled together?

For this question assume that the entire universe is completely empty. The universe is not expanding or contracting, it is completely motionless since time immemorial and has never moved before. Only ...
5
votes
1answer
137 views

At what rate is the observable universe expanding?

The observable universe is $4.4 \times 10^{26} m $ in every direction. I told this to my daughter and then added, "And guess what? It's a little bigger today than it was yesterday." "Wow!" But by ...
5
votes
1answer
684 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 ...
5
votes
1answer
711 views

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 “...
4
votes
4answers
531 views

Photon Paradox?

Imagine a photon reaching the Hubble Space Telescope today had originally been emitted from a star in the early universe 13 billion years ago. Einstein’s Special Relativity tells us, traveling at the ...
4
votes
2answers
433 views

Where is the North of the Universe

Does it exist North of the Universe? (Which is probably used for determining coordinates of far galaxies.) If so, then where it is? On what is it aligned? (Is it orientated on Earth, Sun, Milky Way, ...
4
votes
1answer
477 views

How many new galaxies enter the observable universe each day/year/decade?

Each day light has more time to reach our eyes from distant galaxies. In one day, light travels 2.59×10^10 km. So our observable universe (assuming my simple math skills apply here and there isn't ...
4
votes
1answer
146 views

Necessary steps to calculate photon's path by using null geodesic equation

Can anyone please give me an explanation on how to calculate photon's path by using the null geodesic equation? N.B. I know all of the non-zero values of Christoffel symbols.
4
votes
1answer
525 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 ...
4
votes
1answer
117 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 ...
4
votes
0answers
70 views

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 ...
3
votes
2answers
2k views

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, ...
3
votes
3answers
214 views

Does the universe curve in on itself?

I've read a little bit about the universe, but its not clear to me if there is a place in the universe beyond which there are no stars. For example, is there anywhere in the universe that one could ...
3
votes
3answers
702 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 ...
3
votes
2answers
4k 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 ...
3
votes
4answers
526 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?
3
votes
2answers
123 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 ...
3
votes
2answers
98 views

Can the range of the observable universe be extended through an intermediary?

I understand that the so called observable universe has a limit we cannot see through. My question is whether we might get information through an intermediate hypothetical actor located halfway to ...
3
votes
2answers
142 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 ...
3
votes
1answer
92 views

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 ...
3
votes
0answers
103 views

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 ...
3
votes
0answers
28 views

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 ...
2
votes
3answers
431 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, ...
2
votes
2answers
6k views

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 ...
2
votes
1answer
212 views

What exactly is wrong with this plaque in Neil deGrasse Tyson's “back yard”? Has it been fixed?

The Wikipedia subsection Observable Universe; Misconceptions on its size shows this image of a plaque, with the caption: An example of the misconception that the radius of the observable universe ...
2
votes
3answers
243 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 ...
2
votes
1answer
129 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 ...
2
votes
1answer
109 views

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 ...
2
votes
2answers
88 views

Could different views of the universe simply be different points in time?

I'm not sure if this is the correct stackexchange site for this question. I've been reading this article on Vice Motherboard There’s Growing Evidence That the Universe Is Connected by Giant ...
2
votes
2answers
159 views

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 ...
2
votes
1answer
275 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 (...
2
votes
1answer
279 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 ...
2
votes
1answer
566 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 ...
2
votes
1answer
211 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 ...
2
votes
3answers
170 views

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 ...
2
votes
3answers
897 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 ??
1
vote
1answer
185 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 ...