Comments on: Fractal Black Holes on Strings

By: Lila Sovietskaya

Lila Sovietskaya — Wed, 30 Mar 2011 22:31:02 +0000

Great math, but does it reflect reality. Could a really well skilled physicist explain this to an illiterate Bedouin? or to a high school dropout? or to somebody who has a BS or to liberal Arts PHD? Trying to write for the average tax payer to convince that research in this issue is worth the money is as challenging as to proof that this cylindrical black hole can or cannot extend into a sixth spatial dimension or beyond

By: Sean

Sean — Wed, 09 Mar 2011 20:25:34 +0000

The thing about conjectures is, they are attempts to capture something true without necessarily being able to state that true thing precisely. Cosmic censorship is roughly “there are no naked singularities.” But it’s easy to get naked singularities, so you have to say something like “unless they are there to begin, or if you allow exotic forms of energy.” Then Choptuik and collaborators proved that you could have exquisitely finely-tuned initial conditions that gave rise to naked singularities; so the caveat “arising from generic initial conditions” was added. Now it looks like naked singularities arise from generic initial conditions in five dimensions, so “in four dimensions” needs to be added. There’s still not a proof that even that is true.

By: beginner

beginner — Wed, 09 Mar 2011 19:44:34 +0000

Sean, when you say that cosmic censorship is a conjecture, what do you mean exactly? The Wikipedia page says there are spacetimes for which it is known to be true and others for which it is known to be violated; is there some succinct way of characterizing the class of spacetimes for which it is unknown? Is there a specific unknown case that is particularly important?

By: TimG

TimG — Tue, 08 Mar 2011 04:31:05 +0000

Sean, I found your first comment helpful in clarifying things. If I might suggest an illustration: Taking your first picture (where the large dimensions are represented as a single dimension), you could make a round dot on the surface of the cylinder (to represent the black hole which is smaller than the extra dimension). Then reproduce the picture again with the size of the dot increased so that it becomes a band which wraps all the way around the cylinder (representing the black hole which is larger than the extra dimension).

By: Lievo

Lievo — Sun, 06 Mar 2011 15:27:18 +0000

@Mitchell 23: I screwed my question: I should have say that the compactified dimension should be expected to be at least as large, not smaller, than the tiniests BHs. So it’s an evidence against the space-time being continuous up to any desired precision. As you said this is to be expected anyway. Thx for your insight.

By: 5 March 2011 am « blueollie

5 March 2011 am « blueollie — Sat, 05 Mar 2011 23:12:47 +0000

[...] Black holes: do at least some come from black strings which collapse and bead them off? [...]

By: Mitchell Porter

Mitchell Porter — Sat, 05 Mar 2011 22:42:39 +0000

Lievo @8, these are all purely classical (non-quantum) calculations. A quantum theory of gravity should explain what happens where they break down.

By: Anders Tell

Anders Tell — Sat, 05 Mar 2011 19:42:03 +0000

Can someone help me out and explain how to understand 5 dimensions “exactly”
I can see that a two dimensional plane is as a surface without extension in the direction of the third, -and all other dimensions above the plane must be felt as time if “something” -say a “being” restricted into perceiving only that plane. “Our” third direction don’t “exist” in the two of the plane. Third dimension repeated infinitely in the direction that is not in two, makes a form in same way as the first.. a line repeated infinitely makes two dimensions.
Likewise – fourth dimensions is for us the “direction” of time, -together with the dimensions existing above felt as same for us, in “three”. Yes? And same with sixth, five repeated infinitely?
In same way as three dimensions behave on a smaller or bigger scale then our size. As electrons is smaller then 0 in our scale and dimensions – but with theirs extension in repeating infinitely, their fifth and sixth dimensions -make traces in “our” and form for us the mirage of three.
Or ..-do you mean something else with “dimensions”?

By: Lab Lemming

Lab Lemming — Sat, 05 Mar 2011 18:06:45 +0000

So do the little ones get pinched off into black holes small enough to evaporate?

By: Low Math, Meekly Interacting

Low Math, Meekly Interacting — Sat, 05 Mar 2011 15:18:57 +0000

Hm. OK, thanks, Sean. Seems like you’re saying the cylindrical horizon is a necessary component, and the overall phenomenon isn’t so easily generalized.

I guess it still is interesting (for me, anyway) to wonder if the instability of the Kerr singularity has a thermodynamic origin, or, at least, can be thought of as an inevitability due to the 2nd Law.

By: Evan Keane

Evan Keane — Sat, 05 Mar 2011 14:32:32 +0000

I’m with Sean Matthews (comment 3) on this. This is, although cool, just a calculation done for a model which has no known connection with reality. It may represent something real but it seems to be more Maths than Physics.

Ok, now to continue the quest for a pulsar – black hole binary, wherein the Cosmic Sensorship Conjecture could actually be tested …

By: GregH

GregH — Sat, 05 Mar 2011 07:55:17 +0000

Thanks Sean Carroll for tweeting this article and excellent blog. The graphic looks spookily like saliva stretched between two fingers with the little blobs that form from surface tension.

By: Nex

Nex — Sat, 05 Mar 2011 01:50:42 +0000

Haha, I’ve read the “of course” part as a funny joke, though maybe it was meant to be serious…

By: Sean

Sean — Sat, 05 Mar 2011 00:50:31 +0000

LMMI– in the Kerr solution, the singularity is a ring, but the event horizon is still a sphere. Here we’re really talking about a cylindrical black hole.

The Kerr singularity is a funny thing — there are some lurking instabilities, but I don’t think anyone thinks it will break off into pieces. The phenomenon is known as “mass inflation”:

http://online.itp.ucsb.edu/online/colloq/hamilton1/oh/inflation.html

By: Low Math, Meekly Interacting

Low Math, Meekly Interacting — Fri, 04 Mar 2011 23:58:42 +0000

Doesn’t the Kerr solution give one a “black string” of sorts in 4 dimensions? I imagine that could wiggle around, too. Would entropy be maximized if a Kerr ring started pinching off segments? If so, could this be a general phenomenon of extended black holes, regardless if spatial dimension, i.e. would this ever happen in a universe we can describe empirically, vs. a toy universe? I’ve read in a couple places that the spin of a one or more stellar black holes has been measured to be very close to the the maximum velocity allowed to preserve cosmic censorship. Maybe we might see one that exceeds that speed limit. Maybe something like this might allow it? Seems possible to at least measure rotations of real black holes to see if any naked singularities might exist. Maybe something like this is an observable phenomenon.

Just speculating wildly.

By: ossicle

ossicle — Fri, 04 Mar 2011 23:13:17 +0000

Stephen @6, you misread that part of Sean’s post. His “(Of course.)” was a totally hilarious acknowledgment of how non-self-evident this stuff is.

By: SleazyCarl

SleazyCarl — Fri, 04 Mar 2011 23:02:22 +0000

Is it me or does all this talk of naked singularities, black G(ravity)-strings and what look like adult beads kind of kinky?

Wishful thinking? Mmmmaybe. But not on my part.

By: ossicle

ossicle — Fri, 04 Mar 2011 22:30:25 +0000

Thanks, Sean@2 and James @7! Sean: (1) just to super-duper-clarify, I wasn’t even remotely complaining. I never want to be the guy who whines about the flavor of free ice cream people are giving him. And (2), I finally bought your book last weekend, look forward to starting it tonight or tomorrow!

By: Sean

Sean — Fri, 04 Mar 2011 22:13:52 +0000

Not every post can be a gem of explanatory transparency. Sometimes we must content ourselves with the dazzle.

By: Jordan

Jordan — Fri, 04 Mar 2011 21:37:24 +0000

I have no idea what you just said, but that is the coolest headline I’ve ever seen.