Sfdwhf

How old can references or sources in a thesis be?

What is the command to reset a PC without deleting any files

How do I create uniquely male characters?

Example of a relative pronoun

Is there really no realistic way for a skeleton monster to move around without magic?

How to type dʒ symbol (IPA) on Mac?

declaring a variable twice in IIFE

A newer friend of my brother's gave him a load of baseball cards that are supposedly extremely valuable. Is this a scam?

How is the claim "I am in New York only if I am in America" the same as "If I am in New York, then I am in America?

How is this relation reflexive?

What Brexit solution does the DUP want?

How can I fix this gap between bookcases I made?

How to add power-LED to my small amplifier?

Is there a familial term for apples and pears?

Pronouncing Dictionary.com's W.O.D "vade mecum" in English

Why don't electron-positron collisions release infinite energy?

How to report a triplet of septets in NMR tabulation?

Can a German sentence have two subjects?

I probably found a bug with the sudo apt install function

How do we improve the relationship with a client software team that performs poorly and is becoming less collaborative?

Why Is Death Allowed In the Matrix?

How is it possible to have an ability score that is less than 3?

Is it possible to do 50 km distance without any previous training?

Schwarzchild Radius of the Universe

Schwarzchild Radius of the Universe

Is the “far” universe expanding more quickly?Does the math work out for there being enough time for the formation of the heavier elements and their distribution as seen in today's universe?How is the universe expanding?What would happen in the final days of the universe?How much of the universe is observable at visible wavelengths?What's the point of looking at distances beyond $13,7$ billion light years?How long was the universe radiation dominated?physical meaning of dark matter virial radiusWhat happens in the event that the cooling radius is shorter than the virial radius of a Cold Dark Matter Halo?The Cosmic Microwave Background Paradox

1

$begingroup$

According to the Wiki on the Rs, the Rs of the observable universe is 13.7BLY.
https://en.wikipedia.org/wiki/Schwarzschild_radius
(The observable universe's mass has a Schwarzschild radius of approximately 13.7 billion light-years.[7][8])

The reference for this statement is:

https://arxiv.org/abs/1008.0933 and the Encyclopedia of Distances

Can someone please explain this to me... Is this simply because to get into the non-observable portion of the universe, you have to go faster than the speed of light?

astronomy

share|cite|improve this question

edited 16 mins ago

Rick

asked 5 hours ago

RickRick

620315

$endgroup$

add a comment | 

1

$begingroup$

According to the Wiki on the Rs, the Rs of the observable universe is 13.7BLY.
https://en.wikipedia.org/wiki/Schwarzschild_radius
(The observable universe's mass has a Schwarzschild radius of approximately 13.7 billion light-years.[7][8])

The reference for this statement is:

https://arxiv.org/abs/1008.0933 and the Encyclopedia of Distances

Can someone please explain this to me... Is this simply because to get into the non-observable portion of the universe, you have to go faster than the speed of light?

astronomy

share|cite|improve this question

edited 16 mins ago

Rick

asked 5 hours ago

RickRick

620315

$endgroup$

add a comment | 

$begingroup$

According to the Wiki on the Rs, the Rs of the observable universe is 13.7BLY.
https://en.wikipedia.org/wiki/Schwarzschild_radius
(The observable universe's mass has a Schwarzschild radius of approximately 13.7 billion light-years.[7][8])

The reference for this statement is:

https://arxiv.org/abs/1008.0933 and the Encyclopedia of Distances

Can someone please explain this to me... Is this simply because to get into the non-observable portion of the universe, you have to go faster than the speed of light?

astronomy

share|cite|improve this question

edited 16 mins ago

Rick

asked 5 hours ago

RickRick

620315

$endgroup$

share|cite|improve this question

edited 16 mins ago

Rick

asked 5 hours ago

RickRick

620315

share|cite|improve this question

edited 16 mins ago

Rick

asked 5 hours ago

RickRick

620315

asked 5 hours ago

RickRick

620315

asked 5 hours ago

RickRick

620315

1 Answer
1

active

oldest

votes

3

$begingroup$

In this paper, the author begins by defining the radius of the observable universe as the radius of the Hubble sphere $r_{HS}=frac{c}{H_0}$, where $H_0$ is the Hubble constant. He then assumes that the universe is a homogeneous and isotropic collection of matter with density $rhoapprox rho_c$, where $rho_c=frac{3H^2}{8pi G}$ is the critical density of the universe at which the curvature of space is zero.

Since he assumed that the universe is homogeneous and isotropic, the author uses the classical definition of density $rho=frac{3M}{4pi r_{HS}^3}$, where $M$ is the total mass of the observable universe, and with a bit of algebraic manipulation comes up with $r_{HS}=frac{2GM}{c^2}$. The author then asserts that $r_{HS}$ is the Schwarzschild radius of the universe, because what he came up with looks like the formula for a Schwarzschild radius.

This is where the big problem is: the conditions that the author assumed in the beginning are not compatible with the conditions that admit the definition of a Schwarzschild radius. The Schwarzschild solution of the Einstein field equations requires that all of the mass of the universe is concentrated in a physical singularity at $r=0$, and the rest is vacuum. The author assumes essentially the exact opposite: that the mass of the universe is as spread out as possible, so that none of it is concentrated anywhere, there is no vacuum, and the universe has uniform density. As such, calling this a Schwarzschild radius doesn't really make sense, as it has nothing to do with the Schwarzschild solution besides sharing a superficial similarity in how we express their definitions. Just because he calls it a Schwarzschild radius doesn't mean that it is one.

The moral of the story: though finding similar expressions in different contexts can often be a useful tool to guide intuition, it doesn't actually prove any connection, and isn't a substitute for an actual proof.

share|cite|improve this answer

answered 4 hours ago

probably_someoneprobably_someone

18.8k12960

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  probably_someone is still being kind ... the paper's author does not seem to understand even the basics of Einstein's formulation of general relativity ... the OP should just ignore this paper
  $endgroup$
  – Paul Young
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  It did not make any sense to me either which is why I posted the question. Thanks for the confirmation...
  $endgroup$
  – Rick
  18 mins ago
  

  
  
  
  

add a comment | 

Your Answer

StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "151"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fphysics.stackexchange.com%2fquestions%2f471160%2fschwarzchild-radius-of-the-universe%23new-answer', 'question_page');
}
);

Post as a guest

Name

Email

Required, but never shown

3

$begingroup$

In this paper, the author begins by defining the radius of the observable universe as the radius of the Hubble sphere $r_{HS}=frac{c}{H_0}$, where $H_0$ is the Hubble constant. He then assumes that the universe is a homogeneous and isotropic collection of matter with density $rhoapprox rho_c$, where $rho_c=frac{3H^2}{8pi G}$ is the critical density of the universe at which the curvature of space is zero.

Since he assumed that the universe is homogeneous and isotropic, the author uses the classical definition of density $rho=frac{3M}{4pi r_{HS}^3}$, where $M$ is the total mass of the observable universe, and with a bit of algebraic manipulation comes up with $r_{HS}=frac{2GM}{c^2}$. The author then asserts that $r_{HS}$ is the Schwarzschild radius of the universe, because what he came up with looks like the formula for a Schwarzschild radius.

This is where the big problem is: the conditions that the author assumed in the beginning are not compatible with the conditions that admit the definition of a Schwarzschild radius. The Schwarzschild solution of the Einstein field equations requires that all of the mass of the universe is concentrated in a physical singularity at $r=0$, and the rest is vacuum. The author assumes essentially the exact opposite: that the mass of the universe is as spread out as possible, so that none of it is concentrated anywhere, there is no vacuum, and the universe has uniform density. As such, calling this a Schwarzschild radius doesn't really make sense, as it has nothing to do with the Schwarzschild solution besides sharing a superficial similarity in how we express their definitions. Just because he calls it a Schwarzschild radius doesn't mean that it is one.

The moral of the story: though finding similar expressions in different contexts can often be a useful tool to guide intuition, it doesn't actually prove any connection, and isn't a substitute for an actual proof.

share|cite|improve this answer

answered 4 hours ago

probably_someoneprobably_someone

18.8k12960

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  probably_someone is still being kind ... the paper's author does not seem to understand even the basics of Einstein's formulation of general relativity ... the OP should just ignore this paper
  $endgroup$
  – Paul Young
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  It did not make any sense to me either which is why I posted the question. Thanks for the confirmation...
  $endgroup$
  – Rick
  18 mins ago
  

  
  
  
  

add a comment | 

3

$begingroup$

In this paper, the author begins by defining the radius of the observable universe as the radius of the Hubble sphere $r_{HS}=frac{c}{H_0}$, where $H_0$ is the Hubble constant. He then assumes that the universe is a homogeneous and isotropic collection of matter with density $rhoapprox rho_c$, where $rho_c=frac{3H^2}{8pi G}$ is the critical density of the universe at which the curvature of space is zero.

Since he assumed that the universe is homogeneous and isotropic, the author uses the classical definition of density $rho=frac{3M}{4pi r_{HS}^3}$, where $M$ is the total mass of the observable universe, and with a bit of algebraic manipulation comes up with $r_{HS}=frac{2GM}{c^2}$. The author then asserts that $r_{HS}$ is the Schwarzschild radius of the universe, because what he came up with looks like the formula for a Schwarzschild radius.

This is where the big problem is: the conditions that the author assumed in the beginning are not compatible with the conditions that admit the definition of a Schwarzschild radius. The Schwarzschild solution of the Einstein field equations requires that all of the mass of the universe is concentrated in a physical singularity at $r=0$, and the rest is vacuum. The author assumes essentially the exact opposite: that the mass of the universe is as spread out as possible, so that none of it is concentrated anywhere, there is no vacuum, and the universe has uniform density. As such, calling this a Schwarzschild radius doesn't really make sense, as it has nothing to do with the Schwarzschild solution besides sharing a superficial similarity in how we express their definitions. Just because he calls it a Schwarzschild radius doesn't mean that it is one.

The moral of the story: though finding similar expressions in different contexts can often be a useful tool to guide intuition, it doesn't actually prove any connection, and isn't a substitute for an actual proof.

share|cite|improve this answer

answered 4 hours ago

probably_someoneprobably_someone

18.8k12960

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  probably_someone is still being kind ... the paper's author does not seem to understand even the basics of Einstein's formulation of general relativity ... the OP should just ignore this paper
  $endgroup$
  – Paul Young
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  It did not make any sense to me either which is why I posted the question. Thanks for the confirmation...
  $endgroup$
  – Rick
  18 mins ago
  

  
  
  
  

add a comment | 

$begingroup$

In this paper, the author begins by defining the radius of the observable universe as the radius of the Hubble sphere $r_{HS}=frac{c}{H_0}$, where $H_0$ is the Hubble constant. He then assumes that the universe is a homogeneous and isotropic collection of matter with density $rhoapprox rho_c$, where $rho_c=frac{3H^2}{8pi G}$ is the critical density of the universe at which the curvature of space is zero.

Since he assumed that the universe is homogeneous and isotropic, the author uses the classical definition of density $rho=frac{3M}{4pi r_{HS}^3}$, where $M$ is the total mass of the observable universe, and with a bit of algebraic manipulation comes up with $r_{HS}=frac{2GM}{c^2}$. The author then asserts that $r_{HS}$ is the Schwarzschild radius of the universe, because what he came up with looks like the formula for a Schwarzschild radius.

This is where the big problem is: the conditions that the author assumed in the beginning are not compatible with the conditions that admit the definition of a Schwarzschild radius. The Schwarzschild solution of the Einstein field equations requires that all of the mass of the universe is concentrated in a physical singularity at $r=0$, and the rest is vacuum. The author assumes essentially the exact opposite: that the mass of the universe is as spread out as possible, so that none of it is concentrated anywhere, there is no vacuum, and the universe has uniform density. As such, calling this a Schwarzschild radius doesn't really make sense, as it has nothing to do with the Schwarzschild solution besides sharing a superficial similarity in how we express their definitions. Just because he calls it a Schwarzschild radius doesn't mean that it is one.

The moral of the story: though finding similar expressions in different contexts can often be a useful tool to guide intuition, it doesn't actually prove any connection, and isn't a substitute for an actual proof.

share|cite|improve this answer

answered 4 hours ago

probably_someoneprobably_someone

18.8k12960

$endgroup$

share|cite|improve this answer

answered 4 hours ago

probably_someoneprobably_someone

18.8k12960

answered 4 hours ago

probably_someoneprobably_someone

18.8k12960

answered 4 hours ago

probably_someoneprobably_someone

18.8k12960