Universe began at a singualrity at the big bang

photon
Theoretically, the Universe began at a singualrity at the big bang. Inside of a black hole, there is a singularity. And a black hole eventually evaporates leaving the singularity in an unobservable region of space-time.
Couldn't this very well be how our Universe began, and therefore mean that black hole=singularity=newuniverse?
What would cause this singularity to expand?

[oo]

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FZ+
Inside of a black hole, there is a singularity.

Well... maybe. New theory is out that BH contain not a singularity, but a shell. But that's fuzzy at the moment.

And a black hole eventually evaporates leaving the singularity in an unobservable region of space-time.

Now this is doubtful. Many disagree that such a "naked" singularity can exist independently of the gravity etc that caused it's existence.

Couldn't this very well be how our Universe began, and therefore mean that black hole=singularity=newuniverse?
I don't think so. The initial singularity of the universe is considered as not just an entity in spacetime, but spacetime itself. The comparison IMHO is inadequate.

What would cause this singularity to expand?
Quantum fluctuations is what most people think.

The need for a singularity

A singularity, a point at which mass becomes infinite, can only be possible if you assume that space/time can be warped or curved to an infinite degree by an infinite mass.

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Originally posted by SamBuckler
A singularity, a point at which mass becomes infinite, can only be possible if you assume that space/time can be warped or curved to an infinite degree by an infinite mass.

welcome SamBuckler, there is a point of view that says that
a "singularity" is a place (it doesn't have to be a point, it can be an extended region of some kind)
where a specific theory breaks down
so that you can't calculate further with that particular theory

General relativity--theory of gravity based on shape of space---happens to break down at a point inside black holes

but another theory might conceivably NOT break down and therefore there would be no singularity at the center of a black hole (for that theory) although there would still be a singularity for GR.

the beginning of the expansion of space is also a boundary beyond which GR cannot be pushed (ie. a "singularity" for General Relativity, where the model no longer works to calculate with) but that boundary might not be there for another theory.

So, according to that view, a "singularity" is something in a theory and not something in nature.

It is not a thing like an apple or an atom.

For example in (loop) quantum general relativity it was recently calculated that the curvature does not blow up at cosmological time zero---the beginning of expansion. The quantized GR continues to be able to calculate and therefore has no singularity
at time zero.

This is a new result (2001) and the results are still preliminary, but
it does suggest that whenever a quantum theory of the shape of space does get established and successfully tested, the theory may very possibly not have a singularity at time zero.

(this part is durable or "robust" in the sense that in all the different loop quantum cosmology models tried so far the singularity goes away in all of them, regardless of different assumptions)

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photon
articles

Send them in marcus.

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Originally posted by photon
Send them in marcus.

this one is kind of a mishmash of technical and non-technical style---so some parts might be intuitive and readily understood and other parts not

"Quantum Geometry in Action: Big Bang and Black Holes"
by A. Ashtekar
http://arxiv.org/math-ph/0202008 [Broken]

that gets you a short summary and then underneath the summary there is a format menu with "PDF" to click on

I have some more, and this one has some references too,
Look at the discussion of Big Bang on page 2, and the
longer discussion of BB on pages 7-10

the whole article is only 18 pages so it is quick to download and print off----tho only page 2 and pages 7-10 are relevant to BB.

Sample quote: "It is widely believed that the prediction of a singularity, such as the big-bang of classical general relativity,
is primarily a signal that the physical theory has been pushed
beyond the domain of its validity. A key question to any quantum
gravity theory, then, is: what replaces the big-bang?..."

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Marcus, I've just started to read up on canonical quantum gravity, how do singularites behave in the LQG?

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Originally posted by jcsd
Marcus, I've just started to read up on canonical quantum gravity, how do singularites behave in the LQG?

JCSD, the big-bang singularity goes away in LQG. Or so it would seem--this has been the finding in a number of papers by various people. It is recent work and you have to judge for yourself.

the first paper was by Martin Bojowald (2001)
http:arxiv.org/gr-qc/0102069
"Absence of Singularity in Loop Quantum Cosmology"

Bojowald is not as senior or well-known as major LQG figures like Astekar and Lewandowski. However they weighed in later and
confirmed the main findings
"Mathematical Structure of Loop Quantum Cosmology"
by Ashtekar, Bojowald, Lewandowski (2003)
http:arxiv.org/gr-qc/0304074

there have been a bunch of papers in 2002-2003 by various combinations of people: Bojowald, Morales-Tecotl, Hinterleitner, Vandersloot, Ashtekar

The most readable is by Ashtekar (2002)
"Quantum Geometry in Action: Big Bang and Black Holes"
http:arxiv.org/math-ph/0202008

What the researchers have been doing is trying various assumptions that one makes in cosmology---isotropic, homogeneous, isotropic and homogenous---and doing the
LQG analysis of the universe around time zero in various ways
and each time they do not get a singularity.

So the absence of the singularity is "robust" as Ashtekar says, in the sense that it seems not to depend on how you do the analysis or on some particular set of assumptions.

BTW people call LQG various things including "Quantum General Relativity" and "Canonical Quantum Gravity". The latter is the favorite of Thomas Thiemann. (I find Thiemann's style hard to read
compared with some others, Rovelli say). You say you are reading up on LQG. What author(s)? I hope you've found some writers to your liking

Strings or Loops

I've been trying to get a handle on string theory, easier said than done admittedly. And I've come across references to loop theory and the animosity between researchers from either camp but I haven't looked further yet. One migrane being ample for the moment. But is there a two minute version of the difference between strings and loops. Loop Theory for Dummies ;-)

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Originally posted by SamBuckler
I've been trying to get a handle on string theory, easier said than done admittedly. And I've come across references to loop theory and the animosity between researchers from either camp but I haven't looked further yet. One migrane being ample for the moment. But is there a two minute version of the difference between strings and loops. Loop Theory for Dummies ;-)

Quantum loop gravity is a developmewnt in canonical quantum gravity, string theory and QLG are two very distinct theories.

Marcus is very much in the loop theory camp, so he should be able to provide a short non-techincal summary, I've only just started reading up on it myself.

Marcus- Yes, I have heard that the BB singularity disappears in QLG, I meant BH singularties, I've heard that they derived (i.e. they arrived at the same result)the Bekenstein-Hawking entropy of a black hole by taking a QLG approach.

Originally posted by marcus
there is a point of view that says that
a "singularity" is a place (it doesn't have to be a point, it can be an extended region of some kind)
where a specific theory breaks down
so that you can't calculate further with that particular theory

I had hoped we wouldn't start using that definition here. A "singularity" means, or used to mean, a point of infinite density (not infinite mass, BTW), where mass and volume are so compressed that they occupy a single point in space, with measurements of zero in all directions, and time is infinitely dilated, occupying only a single moment in time. Hence the name. If we're talking about something that isn't a single point in both space and time, we shouldn't call it a "singularity", IMHO.

As to what would cause a singularity to exand, it is possible that once a black hole has evaporated below 3 SM, and is no longer massive enough to be a black hole, it may expand (rather violently, I should think) sponateously.