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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How much larger will the "observable by us" universe be when JWST becomes operational?

Right now, using all our various current means of observing, we can "see" a sphere of X diameter around us. Webb will increase that to Y diameter. So our observable volume will increase by ...
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Is the solar system the only survivor of cosmic evolution? [closed]

A question has entered my mind, we know that all the phenomena in the universe are several thousand light years away from us, so the light we see from them is related to the past few years, now my ...
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7 votes
1 answer
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How is observable matter distributed in the universe?

The observable matter in the universe is distributed and arranged into various structures, including black holes, stars, nebulae, and the much more diffuse regions of the inter-stellar and inter-...
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Can we consider the Universe to be some kind of 3-sphere?

This is probably a naive question. I'm learning a bit of cosmology and I've recently covered the so called angular size-redshift relation, which states that in an expanding Universe the angular size ...
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How can the JWST telescope detect matter “shortly” after the big bang?

Since space is expanding, and accelerating, with distant locations accelerating at such a high rate that they are receding at greater than the speed of light, how can the Webb detect these distant ...
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Is the number of galaxies in the observable universe increasing? [duplicate]

Is the number of galaxies in the observable universe increasing? Are more and more galaxies coming into view? Or is the number decreasing? If it's increasing then when will it reach a maximum? If it's ...
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0 votes
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If the ratio of actual total mass to critical mass (Ω) in the universe is only about 0.3, why do cosmologists believe it is flat, as far as we see?

What about astronomical observations makes scientists believe our universe is flat, at least as far as they can tell? Despite the critical Friedmann density being less than one, plus the existence of ...
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If we could fly off edge of observable universe what would happen? [closed]

If we could be at the edge of expanding universe in a fast space ship such that we could go beyond the edge, what does the science think we might experience? Would we still be floating in space? Would ...
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Can we observe galaxies after their recession velocity exceeds the speed of light? [duplicate]

It doesn't make sense to me that light could ever reach us from a galaxy moving away from us faster than the speed of light. But this video says that it can happen. Is this true? Could someone ...
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4 votes
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Logically, how can the universe be infinite in size?

Many people have told me that the “universe doesn’t care what you think” in my regards to it being infinite in size, and I know something that seems logical doesn’t mean anything when measured by ...
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4 votes
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Can we estimate the number of stars which have died in the observable universe?

We know there are currently between 10^22 and 10^24 stars in the observable universe, but can we make an estimate of how many stars have died so far? Or, in other words, how many supernovæ have taken ...
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Why would a quantity like the 'Hubble contrast' be squared, then have its square root taken?

From Sabine Hossenfelder's recent video, New Evidence AGAINST Standard Cosmology: And her source.... Figure 2. The variation with increasing void radius of the variance of the Hubble parameter, the ...
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What defines Universe's Boundary? [duplicate]

We consider Heliopause as our solar system's boundary, Galaxy has its own boundary, certain theories says that there can be lots of universes, only when we define a boundary we can distinguish a ...
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Universe is a cluster of orbiting Galaxies?

Like planets orbiting stars, solar systems and other celestial objects orbiting a blackhole in the center of a galaxy, are the Galaxies and Galaxy clusters orbiting the centre of a universe (for ...
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4 votes
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Is quasar 2M1310-1714 outside the observable universe?

This Einstein ring Image credit: NASA / ESA / Hubble / T. Treu / Judy Schmidt shows multiple images of the quasar 2M1310-1714. Its distance is quoted at 17 billion light years and although the age ...
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8 votes
1 answer
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How distant were the furthest currently-observable cosmic events when their currently-observed radiation was emitted?

(Edited for clarity. Thanks to James K and Connor Garcia.) This question about the most distant, observable cosmic objects made me wonder if we know the distance that was between us and them at the ...
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5 votes
2 answers
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How does the hypothesis of the "inconstant Hubble constant" solve the current crisis in cosmology?

It was published in a paper more or less like two months ago. I'd like to know also if more accurate measurements are necessary to close the gap between the model of the universe and the data reported....
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Volume of the observable universe [duplicate]

What about the volume of the observable universe? Can we find it? And what is the result in cubic light years?
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1 vote
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Is it "nonsense to even talk about" objects outside the observable universe not having gravitational influence on us? (finite speed of gravity)

In this supplemental answer to Is the zero gravity experienced in ISS the “artificial” kind? in Space Exploration SE I said: Gravity moves at the speed of light so nothing outside out observable ...
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What are the one-dimensional observables that can reveal the matter clustering properties of the Universe?

As we all know, the distribution of galaxies, which depend on the spatial coordinates, can help us understand the large-scale structure of the Universe. We can measure the distribution of galaxies ...
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If we watched extremely red-shifted galaxies near the edge of the observable universe for a very long time, how would they change? Would more appear?

I have understanding sphere eversion as #1 on my bucket list (if I ever get a round tuit) but understanding metric expansion seems to be a rapidly receding possibility :-) Question: Suppose it takes ...
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Can the other side of the observable universe be seen as a black hole?

When looking at the objects near the horizon of the observable universe, the objects seem to emit radiation that is red-shifted. Time seems to advance at a slower rate than our own and at the horizon ...
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Is the dark matter just regular matter out of the observable universe?

Could it be that darkmatter is actually the gravitational influence of regular matter that is situated out of the observable universe?
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How many galaxies are predicted in the observable universe? Does it contain dwarfs? Is there any size-ratio diagram?

According to quite recent research the observable universe contains about 2 trillion galaxies ($2 \cdot 10^{12}$). But what is counted there? Does this number also contain dwarf galaxies? According to ...
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7 votes
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Rotation of far away and near by galaxies

Do the far galaxies rotate the same as does the milky way and the near by galaxies?
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Eccentricity of Exoplanets

The field of astrobiology specifically discovering other planets that revolve around the sun-like star (also known as Exoplanets) has risen since 1990, but certain orbits of exoplanets are observed to ...
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How long does it take for a galaxy (or other object) to disappear behind the cosmic sight horizon?

After looking at this question, I am wondering, how long does it take for a galaxy or other space object, to disappear from our view from the Milky Way due to the expansion of the universe? Assume GN-...
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4 votes
2 answers
399 views

Is the age of the Universe really 13.8 billion years?

Ok, I know this has been asked by a lot of people, but my reason for asking this question is a bit different. Please read further. I was watching a video by Fermilab (Start at 6:30, at 8:30 he ...
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Computing the over-density of Lyman-alpha emitters

Let's assume that I have observations of $N$ galaxies in a projected area $A$, within a redshift range $\Delta z = z_{max} - z_{min}$. What is the correct way of computing their number volume density? ...
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How far away are objects whose light will never reach us, because of the expansion of the universe?

I thought I had read this question on Stack Exchange before, but now I cannot find it... In fact, I thought I had posted this question before, somewhere, on Stack Exchange... I believe the answer ...
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Why can't we point the centre of the universe from inflation graph we see?

This question is not about whether it makes sense to have a centre of the universe or not instead, it's about the inflation graph we used to see while describing the Big Bang. From the inflation graph ...
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1 answer
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Are the most distant known objects in the universe more than 14 billion light years away? [duplicate]

When I hear about the most distant objects in the universe, such as the recently discovered galaxy GN-z11, their distances are usually stated to be a little under 14 billion light years away.... But, ...
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40 votes
3 answers
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How do scientists know that the distant parts of the universe obey the physical laws exactly as we observe around us?

How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us? The question might look a bit odd but I am really stuck on my head. We know, ...
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1 vote
2 answers
133 views

How are younger objects outside our observable universe when the older CMB is an observer's temporal "edge"?

We know the observable universe is limited to objects whose light has had time to reach us and that an observer very far away will see a slightly different (assuming cosmological principle) observable ...
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1 vote
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Why is the Cosmic Microwave Background at the same distance no matter the direction we look?

I've read from different sources that: The CMB is visible at a distance of 13.8 billion light years in all directions from Earth, leading scientists to determine that this is the true age of the ...
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How did we measure the mass of the universe?

In an wiki article, observable universe, it was mentioned that, Mass (ordinary matter) 1.5×10^53 kg I wonder how did we measure the mass of our observable universe?
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1 vote
1 answer
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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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1 vote
1 answer
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Kardashev scale [closed]

Why is becoming a type 3 from a type 2 civilization the hardest? I have watched many videos on the topic and still can't figure out why? Also is there a difference in technology between a type 4 and a ...
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2 votes
0 answers
31 views

Demonstration of scales for the two components (transverse and perpendicular) of Baryonic Acoustic Oscillations (BAO)

I transfer here a post that has not had any answer pn physics exchange, so I am going to delete this latter. Maybe I will have more luckiness here. In an astrophysics context about BAO (Baryonic ...
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1 vote
1 answer
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Intuitive explanation for why the Doppler effect (and red-shift) happens?

I was looking for an intuitive explanation as to why the Doppler effect happens. I haven't found any, but this is what I thought: -Waves emitted travel at a constant speed -The source emits a wave -If ...
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can we calculate the velocity of galaxies at the edge of the observable universe?

I read this post Does the edge of the Universe travel faster than the speed of light? but there was no calculation, so I tried it thusly: The observable universe is 28.5 Gpc (gigaparsecs) = 28500 ...
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1 vote
1 answer
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How frequently do Jupiter & Regulus have triple conjunctions?

I am wanting to know if the triple conjunction of Jupiter with Regulus in: Sep 10, 3 BC Feb 7, 3 BC & May 8, 2 BC with Jupiter later having a conjunction with Venus in Jun 17, 2 BC has happened ...
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5 votes
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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 ...
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With the expansion of the universe is time also increasing?

With more space being created would there be more time in that new region formed? Is the over all universe increasing in time? This is my first question so go easy on me. PS. Would that also mean that ...
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1 vote
0 answers
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Various stars moving in a line [duplicate]

I from India saw various stars moving in a line from North-West direction to the South-East direction at 5:27 AM on date 13 february 2020... They all are moving rapidly and can be easily seen from the ...
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Earth as a grain of sand

If Earth was a grain of sand in Buenos Aires in what point in this observable universe map would be LA be?
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1 answer
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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, ...
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5 votes
1 answer
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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 ...
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2 votes
2 answers
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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 ...
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3 votes
3 answers
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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 ...
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