Is the Big Bang Actually a White Hole?

[rootone]

TL;DR

big bang white hole

We know that black holes exist in the universe, but white holes don't, as far as we know,
Although white holes are not an impossibility in GR.
Is it reasonable to ask if the big bang singularity is in fact a white hole, and is the only white hole in the Universe?
Is the place where everything inside every black hole re-emerges as fundamental particles.
I'm sure somebody else must have considered that and according to some or another theory, it's not a very good idea
Or is it?

 

[PeterDonis]

Is it reasonable to ask if the big bang singularity is in fact a white hole, and is the only white hole in the Universe?

It's reasonable to ask, and the answer is no, it's not.

Is the place where everything inside every black hole re-emerges as fundamental particles.

This is not what a white hole is.

I'm sure somebody else must have considered that

Yes, and using the PF search feature to search for "big bang white hole" will turn up plenty of previous threads.

 

[Orodruin]

Summary: big bang white hole

Is it reasonable to ask if the big bang singularity is in fact a white hole, and is the only white hole in the Universe?

No. It is a very different geometry than the early Universe.

 

[rootone]

OK, thanks both.
I know we are advised to not speculate here, so into the bin goes that idea.
I was never great at geometry anyway, 2D computer games always made more sense to me than 3D ones,
Black holes singularity and the big bang just seemed to me to be an unexplained coincidence,

 

[timmdeeg]

Black holes singularity and the big bang just seemed to me to be an unexplained coincidence,

But black holes apply to Schwarzschild geometry and the big bang applies to FRW geometry. And as to the apparent coincidence we don’t know the physical state in either case.

 

[PAllen]

White hole geometry has distinguished directions (tangential, versus radial; thus not isotropic). It also distinguishes position (a translation generally produces a change in locally measurable tidal gravity). Thus it is also not homogeneous.

In contrast, the big bang geometry is homogeneous and isotropic everywhere. No positions or directions are distinguished.

A big distinction, don't you think?

 

[PeterDonis]

Black holes singularity and the big bang just seemed to me to be an unexplained coincidence,

Not all singularities are the same. A black hole singularity has tidal gravity--more precisely, Weyl curvature--increasing without bound as the singularity is approached. The big bang singularity has zero Weyl curvature. As has already been noted, they are very different geometries. The only thing they have in common is geodesic incompleteness, which is the definition of "singularity".

 

[rootone]

OK. thanks for helping.
So some coincidences are just that; coincidences.

 

[PAllen]

White hole geometry has distinguished directions (tangential, versus radial; thus not isotropic). It also distinguishes position (a translation generally produces a change in locally measurable tidal gravity). Thus it is also not homogeneous.

In contrast, the big bang geometry is homogeneous and isotropic everywhere. No positions or directions are distinguished.

A big distinction, don't you think?

I want to add that the above is true outside the horizon of a white hole.

Inside, you have an additional spacelike killing vector field, in addition to those defining spherical symmetry. As a result, spatial slices based on the KVFs provide homogeneity - translation anywhere on such hypercylinder simultaneity slice (of S2XR topology) leaves the metric unchanged.

However, then nowhere do you have isotropy. The tidal gravity at each point produces compression in the axial direction (of the additional killing vector field), and tension in the two orthogonal directions. [Note, this tension/compression is the opposite of the black hole interior, where the axial direction has tension].

This is a good example of how homogeneity does not imply isotropy.

 

[rootone]

Thanks.
It still seems to me too be a bit too much of a coincidence,
but then why is Pi what it is, and not some other number?

 

[Orodruin]

It still seems to me too be a bit too much of a coincidence,

What is a coincidence? That the two geometries are fundamentally different and have very little to do with each other?

 

[jbriggs444]

why is Pi what it is, and not some other number?

Are you operating on the assumption that $\pi$ is defined in terms of the ratio of the measured circumference of a circle divided by its measured diameter and that it is, thus, a property of the space that one inhabits?

The problem with such a definition is that in some (most?) spaces, it leaves $\pi$ undefined since there is no single ratio that holds for all circles. The ratio can depend on the size of the circle.

I believe that if you take the limit as the size of the circle decreases toward zero, you will get the mathematical constant $\pi$ in almost all cases.

 

[Orodruin]

The ratio can depend on the size of the circle.

... and the position of the circle.

 

[PAllen]

Are you operating on the assumption that $\pi$ is defined in terms of the ratio of the measured circumference of a circle divided by its measured diameter and that it is, thus, a property of the space that one inhabits?

The problem with such a definition is that in some (most?) spaces, it leaves $\pi$ undefined since there is no single ratio that holds for all circles. The ratio can depend on the size of the circle.

I believe that if you take the limit as the size of the circle decreases toward zero, you will get the mathematical constant $\pi$ in almost all cases.

On the last point, in all cases for smooth Riemannian manifolds. However, if you take the limit divided r³, so the units are inverse area, it converges to a constant related to Gaussian curvature.

 

[rootone]

What is a coincidence?

It seemed to me to be a bit of a coincidance that geometrically we can describe space so that it is possible for things to just disappear and no longer be in the Universe as far as any observer is concerned, then at the same time, the Universe can start to exist, when any observer didn't see that before,

 

[PAllen]

It seemed to me to be a bit of a coincidance that geometrically we can describe space so that it is possible for things to just disappear and no longer be in the Universe as far as any observer is concerned, then at the same time, the Universe can start to exist, when any observer didn't see that before,

umm ... there were no observers before. This is again, a fundamental asymmetry. A BH horizon is never in the causal past, A WH horizon is never in the causal future. This latter means there cannot be an observer who "didn't see the WH, then later did".

 

[PeterDonis]

A WH horizon is never in the causal future. This latter means there cannot be an observer who "didn't see the WH, then later did".

The same is true of the initial singularity in FRW spacetime, which I think is what @rootone was referring to with "the Universe can start to exist".

 

[rootone]

Ok, thanks for your comments.
What I meant is that the Universe came into existence at some point, otherwise it would not be there.
I did not mean to imply that some "thing" enabled it to be so.

 

[PeterDonis]

the Universe came into existence at some point, otherwise it would not be there

Not necessarily. It might have always existed--more precisely, it might have existed indefinitely into the past, with no beginning. We don't know for sure at this point.

 

[rootone]

So why is the Universe given an age, of about 14bn or so years?
This is not so certain?

 

[PeterDonis]

So why is the Universe given an age, of about 14bn or so years?

That is the time since the Big Bang, which is the hot, dense, rapidly expanding state that is the earliest state of the universe of which we have good evidence. In inflationary cosmologies, it is the state at the end of inflation. It is not the "initial singularity", although many pop science treatments talk as if it is.

 

[Orodruin]

Let me point out that "singularities" in theories typically are not seen as physical but rather as regions where a more general theory is required, a sign that something is amiss in our description of Nature.

 

[rootone]

Let me point out that "singularities" in theories typically are not seen as physical but rather as regions where a more general theory is required, a sign that something is amiss in our description of Nature.

Well yes, I absolutely accept that.
In both cases there is a sign that something is amiss in our understanding,
and my question is in effect, can that misunderstanding be the same thing?