Questions tagged [cosmological-horizon]

Questions about the size of the observable universe.

Filter by
Sorted by
Tagged with
1 vote
0 answers
28 views

Is it possible to infer information about the structure of the universe beyond the observable one?

Is it possible to infer information about the structure of the universe beyond the observable one, by observing its effects on the parts we can see? Can for example gravity from sources we cannot see ...
user avatar
  • 685
1 vote
0 answers
70 views

Objects beyond 13.3 billion light-years away are (apparently) moving away from us at faster-than-light speeds? [duplicate]

That is, if you use the cosmic distance ladder method, and a value of about 73.5 for the Hubble constant.... But, if you plug in the Planck CMB value of about 67.5, you get a distance of about 14.5 ...
user avatar
  • 3,333
0 votes
1 answer
244 views

How do you calculate comoving distance and light's travel distance? According to the formulae below?

According to Wikipedia, Distance measures (cosmology), Comoving distance: $${\displaystyle d_{C}(z)=d_{H}\int _{0}^{z}{\frac {dz'}{E(z')}}}$$ Light-travel distance: $${\displaystyle d_{T}(z)=d_{H}\int ...
user avatar
  • 3,333
1 vote
1 answer
252 views

Transverse Comoving distance

I don't understand the link between the comoving distance and transverse comoving distance : how can they be equal ? Here an example of definition that I have found : Angular Diameter Distance : The ...
user avatar
2 votes
1 answer
103 views

What's the furthest distance that something could travel and eventually come back to Earth?

Imagine u shoot a photon into the sky at a mirror far away in space, and you want the photon to bounce off the mirror and eventually come back to you. Considering the cosmological constant, what's the ...
user avatar
2 votes
0 answers
128 views

Clarifications about distances in cosmology

I would like to get clarifications about some usual notions of distances in cosmology. First, is the comoving distance the current distance of objects whose light has been reached by us now, i.e. ...
user avatar
2 votes
2 answers
98 views

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 ...
user avatar
  • 3,333
2 votes
1 answer
85 views

Must time pass more slowly, relative to our inertial reference frame, inside galaxies that are currently located at half way to the Hubble Horizon?

Trying to understand simultaneity of events and time-dilation on a Universe scale, I would like to know must time pass more slowly, right now, relative to our current inertial reference frame, inside ...
user avatar
3 votes
1 answer
108 views

Expresion of comoving distance

I have a simple question : How to prove the following relation : The comoving distance to an object at redshift $z$ can be computed as $$r(z)=\dfrac{c}{H_{0}} \int_{0}^{z} \dfrac{\mathrm{d} z}{E(z)}$...
user avatar
1 vote
0 answers
46 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 ...
user avatar
2 votes
1 answer
46 views

Can we observe changes in the CMB (surface of last scattering) over time? [duplicate]

It is hard to determine the age of the Sun, because it won't change much over 100 million years or so. But what about the cosmic microwave background radiation, that is being mapped with ever better ...
user avatar
  • 10.8k
2 votes
3 answers
286 views

Is the universe older than 13.7 Billion years?

I came to know that the cosmic horizon is the part of universe beyond which we cannot see. So if the light from 13.7 billion years ago is what we can observe, does that mean the universe is older than ...
user avatar
1 vote
1 answer
247 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 ...
user avatar
  • 31.5k
11 votes
2 answers
886 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!...
user avatar
  • 31.5k
0 votes
1 answer
97 views

How long would a photon take to reach us if it's emitted from a galaxy receeding at c?

A galaxy at the boundary of the Hubble sphere is receeding from us at the speed of light, right? If it emits a photon now, how long will it take to reach us?
user avatar
3 votes
1 answer
508 views

Why is cosmological event horizon closer to us than the particle horizon?

From what I learned, cosmological event horizon is the horizon that moves away from us at/more than the speed of light. And particle horizon is the horizon that particles inside the horizon can have a ...
user avatar
3 votes
3 answers
368 views

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?
user avatar
2 votes
1 answer
145 views

How strong is the gravity from half of the distant universe?

I would like to know, how strong would the gravity be from the distant universe if we were somehow able to remove half of it. For example, if everything behind us did not exist, how strongly would ...
user avatar
  • 3,919
0 votes
1 answer
284 views

How strong is the gravitational stretch we experience from the edge of the universe?

How much gravitational effect do we experience (e.g. maybe -.00001 G or smaller) from the edge of the visible universe? By edge of the visible universe, I am talking about the region of the cosmic ...
user avatar
  • 3,919
0 votes
1 answer
325 views

How can there be anything "beyond" the CMB?

Two things we take, for this purpose, to be axiomatic: The CMB is the oldest thing we can observe directly The cosmological red shift tells us how "old" something we are observing is Yet we also ...
user avatar
4 votes
1 answer
277 views

Can Hubble red shift be interpreted as time dilation?

Can we interpret the de Sitter universe as a spherical cosmic horizon null surface of finite radius, centered at Earth, and containing the Hubble volume of space where time is dilated and radial ...
user avatar
  • 1,199
1 vote
1 answer
109 views

Does cosmological horizon grow or decrease as it radiates?

Black holes decrease as they evaporate and their radius decreases as well. So what is with a cosmological horizon? If cosmological horizon is just a black hole centered at the opposite side of the ...
user avatar
  • 1,199
7 votes
2 answers
174 views

Does the radius of the Universe correspond to its total entropy?

I heard a claim that due to holographic principle, the surface area of the cosmic horizon corresponds to the universe's total entropy. As such the initial state had zero surface area and later ...
user avatar
  • 1,199
14 votes
1 answer
2k views

How many galaxies disappear beyond the Hubble Bubble horizon every year now? [duplicate]

The accelerating expansion of space means that the space between us and far away galaxies expands faster than light can travel through space. There is a horizon of possible observation beyond which ...
user avatar
  • 10.8k
3 votes
2 answers
232 views

A black "superhole" possibility?

When matter crosses the event horizon, it is easy to imagine that matter is torn apart into their individual components by tidal wave effects. Atoms would be ripped apart eventually. At one time, the ...
user avatar
  • 1,177
1 vote
1 answer
53 views

Do more objects appear on sky in time?

I would assume that, with light from more distant areas in space reaching the earth, we should be able to see more distant (and older) objects. However there's lot of weird stuff regarding the space ...
user avatar
5 votes
2 answers
294 views

What does black hole evaporation correspond to in the accelerating universe / black hole analogy?

In the same way, as a black hole emits Hawking radiation corresponding to its temperature $$ T = \frac{\hbar}{r_{BH}} $$ the accelerating universe can be described as all of the stuff falling ...
user avatar
  • 789
6 votes
4 answers
745 views

Can it be inferred that our cosmological horizon has increased over time?

If I am right, we can see only those stars that lie within our cosmological horizon, and there may or may not be any stars beyond that. Given last 150 years of using telescopes, and since then our ...
user avatar
  • 163