Big Bang singularity vs Black hole singularity

Click For Summary

Discussion Overview

The discussion centers on the comparison between the singularities associated with the Big Bang and black holes, exploring their properties, geometrical differences, and implications for entropy. Participants examine theoretical aspects, including entropy states, curvature, and the nature of singularities in cosmology and general relativity.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the Big Bang singularity has extremely low entropy, while black hole singularities are associated with high entropy, raising questions about their fundamental differences.
  • Others argue that geometrically, the singularities are distinct, with black hole singularities being confined to future light cones and Big Bang singularities to past light cones.
  • A participant notes that a black hole singularity is collapsed mass-energy, whereas the Big Bang singularity involves the collapse of everything, including space-time.
  • Some contributions reference the Weyl curvature, suggesting that the Big Bang had a small or vanishing Weyl curvature compared to diverging Weyl curvature at black hole singularities.
  • There is a discussion about the necessity of repulsive forces in the context of the Big Bang, with some asserting that a Big Bang cosmology does not require such forces, while others suggest it may relate to quantum cosmology.
  • One participant mentions the different symmetries of the two types of singularities, noting that near a black hole singularity, spacetime exhibits cylindrical symmetry.
  • Some participants express uncertainty about the distinctions being made, with one questioning whether the differences are merely terminological.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the distinctions between the Big Bang and black hole singularities, with multiple competing views remaining on their properties, implications, and the role of entropy.

Contextual Notes

Discussions include references to specific theoretical frameworks and concepts, such as Weyl curvature and light cones, which may depend on particular definitions and assumptions not universally accepted among participants.

quantafyre
Messages
4
Reaction score
0
One speaks of the Big Bang initial condition as a singularity possessing an extremely low entropy (to explain the growth of entropy throughout time to our present stage of the universe). If that singularity truly possesses infinite density, that would make perfect sense, since what would become sub-atomic particles later can have no meaningful individuality within the BB singularity when the density state is infinite. To my way of thinking the infinite density would demand some kind of amorphous 'blob' of matter/energy in a continuous rather than discrete form. To speak of micro states in this condition would have no meaning, since the blob can only exist in one micro/macro state. So far, so good (for me).

Assuming black holes also exist as a singularity at its 'heart,' the same condition found in the BB singularity, namely infinite density, would also require the same kind of 'one micro/macro state for the black hole's singularity. I say this not knowing if the BB singularity is identical to the black hole's singularity. If 'you've seen one singularity, you've seen 'em all' is true, why then do we believe that the entropy is in its highest form for the black hole, just the opposite of the BB's singularity? Since I do not know for sure if a singularity has true infinite density I may be wrong in that assumption.
 
Last edited by a moderator:
Physics news on Phys.org
Geometrically these singularities are different.
 
Last edited by a moderator:
tom.stoer said:
Geometrically these singularities are different.

To amplify on this a little, you can classify singularities according to whether they can exist in the past and/or future light cones of an observer. A black hole singularity can only be in an observer's future light cone. The big bang singularity can only in in someone's past light cone. A naked singularity can be in both.

[EDIT] In addition, a black hole singularity has an event horizon, and the way an event horizon is normally defined doesn't really make sense if you try to apply it to a cosmological spacetime.

The following FAQ is relevant: https://www.physicsforums.com/showthread.php?t=506992
 
Last edited by a moderator:
quant posts:
I say this not knowing if the BB singularity is identical to the black hole's singularity.

they are NOT the same as already posted...

One big difference is that a BH singularity is collapsed mass-energy while the BB singularity is collapsed everything, even space-time. The BB never became a black hole due to gravitational attraction; apparently it did the opposite due to some repulsive phenomenon.

Here are some descriptions I have saved trying to understand different viewpoints:


From THE NATURE OF SPACE AND TIME, Hawking,Penrose:

Penrose observes that (in my possibly inaccurate paraphrase):

(1) The Big Bang was not a generic state. A generic Big Bang state would have had a large Weyl curvature, but the universe we see looks nothing like the one that would have resulted from such an initial state. Our Big Bang appears to have had a small or even vanishing Weyl curvature.

(2) The evolution of our universe has led to a state with nonvanishing Weyl curvature. (At black hole singularities, we even have diverging Weyl curvature.)



from Roger Penrose THE ROAD TO REALITY...PG 766:

Let us now think of a universe evolving so that an initially uniform distribution of material [with some density fluctuations] gradually clumps gravitionally, so that eventually parts of it collapse into black holes. The initial uniformity corresponds to a mainly Ricci-curvature [matter] distribution, but as more and more material collects gravitationally, we get increasing amounts of Weyl curvature...The Weyl curvature finally diverges to infinity as the black-hole singularities are reached. If we think of the material as having been originally spewed out from the Big Bang in an almost completely uniform way, then we start with a Weyl curvature that is...[essentially] zero. Indeed, a feature of the FLRW models is that the Weyl curvature vanishes completely. ...For a universe to start out closely FLRW we expect the Weyl curvature to be extremely small, as compared with the Ricci curvature, the latter actually diverging at the Big Bang. This picture strongly suggests what the geometrical difference is between the initial Big Bang singularity- of exceedingly low entropy- and the generic black hole singularities, of very high entropy.




A Quantum Gravity Extension of the Inflationary Scenario
Ivan Agullo, Abhay Ashtekar, William Nelson
(Submitted on 7 Sep 2012)
http://arxiv.org/abs/1209.1609

This strong repulsive gravitational force due to quantum geometry is a pre inflationary dynamic applicable from a Planck scale big bounce to the onset of slow roll inflation.

anda from a related paper by the same authors:

This paper …. provides a detailed extension of the cosmological perturbation theory to the Planck regime. ..., the FLRW space-times of interest are invariably incomplete in the past due to the big bang singularity where matter fields and space-time curvature diverge.
 
Last edited by a moderator:
Naty1 said:
One big difference is that a BH singularity is collapsed mass-energy while the BB singularity is collapsed everything, even space-time.

I don't think this is really a correct distinction. Both are collapsed everything.

Naty1 said:
The BB never became a black hole due to gravitational attraction; apparently it did the opposite due to some repulsive phenomenon.

You do not need repulsion (e.g., a cosmological constant or violation of an energy condition) to get a big bang cosmology. The first BB cosmologies were developed with \Lambda=0 and normal forms of matter.

(1) The Big Bang was not a generic state. A generic Big Bang state would have had a large Weyl curvature, but the universe we see looks nothing like the one that would have resulted from such an initial state. Our Big Bang appears to have had a small or even vanishing Weyl curvature.
This has more to do with distinguishing our BB from hypothetical high-entropy big bangs. It's not that closely related to distinguishing a big bang from a black hole (although I suppose it's true that no-hair theorems apply to black holes but not to big bangs).
 
Last edited by a moderator:
Isn't this related to Glenn Miller compactification :-)
 
Last edited by a moderator:
Thank you all who replied to my initial post. Your observations, comments and citings were as fascinating and insightful as one would expect from such talented minds!
 
Quote by Naty1
One big difference is that a BH singularity is collapsed mass-energy while the BB singularity is collapsed everything, even space-time.

bcrowell: I don't think this is really a correct distinction. Both are collapsed everything.
[well, you LOOK 'uncollapsed!] [LOL]Note to Marcus: Look what YOU did...got me in trouble with crowell! [LOL]
The BB never became a black hole due to gravitational attraction; apparently it did the opposite due to some repulsive phenomenon.

bcrowell: You do not need repulsion (e.g., a cosmological constant or violation of an energy condition) to get a big bang cosmology. The first BB cosmologies were developed with Λ=0 and normal forms of matter.

I was referring only to the initial bang...not the subsequent inflation...such an initial repulsive force seems an aspect of quantum cosmology...maybe even keeps collapse finite...
 
In addition to which, a black hole singularity and the big bang singularity have different symmetries. Near a black hole singularity, spacetime is cylindrically symmetric, collapsing in the radial directions and expanding along the axis.
 
  • #10
Quote by Naty1

One big difference is that a BH singularity is collapsed mass-energy while the BB singularity is collapsed everything, even space-time.

bcrowell:
I don't think this is really a correct distinction. Both are collapsed everything.

I had the misfortune of thinking about this after I signed off and would like to explore
this issue a bit more. Of course maybe it's just terminology.

Marcus actually made such a post [I saved it] and I liked it because it matched my understanding that when an inertial observer free falls towards a black hole, time and space are normal as the observer passes the Schwarzschild radius, r= 2M...the event horizon...so it seems space and time exist inside the horizon and only as the observer reaches near the singularity do space and time and everything else appear to be squished into a 'quantum foam'...an apparent 'singularity' if you wish.

So where am I going wrong here?? Is there a more refined description?
 

Similar threads

Undergrad Does Kerr's argument against singularities apply to all black holes?
  • · Replies 12 ·
Replies
12
Views
3K
Undergrad What is the Connection Between Black Holes and the Big Bang?
  • · Replies 2 ·
Replies
2
Views
3K
Undergrad Kerr disputes singularities in Kerr Black Holes
  • · Replies 7 ·
Replies
7
Views
4K
Graduate Does the New Paper on Singularities Offer Proof of Their Existence?
  • · Replies 6 ·
Replies
6
Views
1K
Graduate Do Black Holes have Singularities?
  • · Replies 20 ·
Replies
20
Views
3K
High School Question about the Entropy of a Black Hole Singularity
  • · Replies 17 ·
Replies
17
Views
4K
High School Can we see 2 black holes orbiting each other?
  • · Replies 57 ·
2
Replies
57
Views
4K
Undergrad Do any real macroscopic black holes have a singularity?
  • · Replies 11 ·
Replies
11
Views
2K
High School Why Don't We Live Inside a Black Hole?
  • · Replies 3 ·
Replies
3
Views
2K
Graduate Assumptions of Hawking-Penrose 1970 Singularity Theorem
  • · Replies 35 ·
2
Replies
35
Views
4K