Why would a black hole be a gateway to another universe?

[acesuv]

I'm reading Einstein's Cosmos by Michio Kaku, and he describes Kerr black holes; which are apparently rings of matter stabilized by centrifugal force. Anyway, Kaku throws out that if you go through the event horizon of a black hole, you will be transported to another universe; he says this as if its common sense and just continues on.

WHERE DOES HE GET THIS FROM? How the heck would he know that?

 

[mfb]

If you go through the event horizon, nothing special happens - you cannot go back, of course, but you are still in this universe.
There are some speculations that the interior of black holes (the "center") could be related to something special - not necessarily a "different universe", but at least something we don't know yet. But those are just speculations.

 

[Naty1]

Kaku is perhaps drawing on the idea of a white hole:

[of course no one knows if there are other universes]

A white hole, in general relativity, is a hypothetical region of spacetime which cannot be entered from the outside, but from which matter and light have the ability to escape. In this sense, it is the reverse of a black hole, which can be entered from the outside, but from which nothing, including light, has the ability to escape. White holes appear in the theory of eternal black holes. In addition to a black hole region in the future, such a solution of the Einstein field equations has a white hole region in its past.[1] However, this region does not exist for black holes that have formed through gravitational collapse, nor are there any known physical processes through which a white hole could be formed.

http://en.wikipedia.org/wiki/White_hole

 

[acesuv]

Kaku is perhaps drawing on the idea of a white hole:

[of course no one knows if there are other universes]




http://en.wikipedia.org/wiki/White_hole

If you go through the event horizon, nothing special happens - you cannot go back, of course, but you are still in this universe.
There are some speculations that the interior of black holes (the "center") could be related to something special - not necessarily a "different universe", but at least something we don't know yet. But those are just speculations.

He sure didn't make it seem like a speculation... Thanks

 

[PeterDonis]

He sure didn't make it seem like a speculation

That's Kaku for you; he's going for entertainment value, not scientific accuracy. Brian Greene's books and TV specials are similar.

 

[phinds]

He sure didn't make it seem like a speculation... Thanks

Kaku used to be a physicist. He is now a gadfly-popularizer who mostly just says dumb crap on television. Do NOT take him seriously.

 

[dkotschessaa]

I think the somewhat questionable line of reasoning goes something like this

black hole --> "laws of physics break down" --> this can't happen in our universe ---> therefore it's not our universe --> therefore it must be some other universe.

Kaku's style is interesting. He uses phrases like "it could be.." and "it might be..." a lot, but he spends so much time in Couldbeland and MightbeLand that he starts to make it seem like something other than speculation.

 

[WannabeNewton]

What Kaku is saying is perfectly valid theoretically. The extended charged Kerr space-time is not like the extended Schwarzschild space-time. In the Kerr case one can pass through the inner horizon and pass through the ring singularity so as to enter the white hole region and end up in a new asymptotically flat region. Let's not berate scientists prematurely.

 

[PeterDonis]

In the Kerr case one can pass through the inner horizon and pass through the ring singularity so as to enter the white hole region and end up in a new asymptotically flat region. Let's not berate scientists prematurely.

I don't think such an observer would have to pass through the ring singularity; see the Penrose diagram at the bottom of this page:

http://jila.colorado.edu/~ajsh/insidebh/penrose.html

See the blue line on the diagram.

Also, the fact that all this is mathematically possible is a long way from saying it's physically possible. AFAIK any small perturbations to the Kerr geometry will destroy the inner horizon and what's behind it, and any real black hole will have small perturbations. The fact that Kaku never mentions any of these caveats is one reason why I say he's going for entertainment value, not scientific accuracy. It's like all the talk about warp drives without ever mentioning that they need exotic matter that violates energy conditions.

 

[WannabeNewton]

I should have said that the infalling observer can either pass through the ring singularity so as to enter a new asymptotically flat region or directly enter the white hole region and enter a new asymptotically flat region; apologies on my part for phrasing that incorrectly. Regardless, what he is saying is not technically incorrect so to insult him and claim that he is saying "dumb crap" is quite absurd. If that's true then Hawking & Ellis and Wald etc. are all saying "dumb crap" for mentioning these theoretical possibilities.

 

[PeterDonis]

what he is saying is not technically incorrect so to insult him and claim that he is saying "dumb crap" is quite absurd. If that's true then Hawking & Ellis and Wald etc. are all saying "dumb crap" for mentioning these theoretical possibilities.

I didn't use the phrase "dumb crap", but I do think Kaku is doing science a disservice.

Hawking & Ellis, and Wald, are written for scientists who are supposed to be able to understand the difference between what is theoretically, mathematically possible and what is physically possible, physically reasonable, etc.

Kaku's audience is lay people who do not have that background, and so the effect of what he says is to make people think that things which are mathematically possible but not at all physically reasonable, are actually physically reasonable. That misrepresents the science, which IMO is never a good idea, no matter how many books it sells or how many TV viewers it attracts.

 

[Nugatory]

I should have said that the infalling observer can either pass through the ring singularity so as to enter a new asymptotically flat region or directly enter the white hole region and enter a new asymptotically flat region; apologies on my part for phrasing that incorrectly. Regardless, what he is saying is not technically incorrect so to insult him and claim that he is saying "dumb crap" is quite absurd. If that's true then Hawking & Ellis and Wald etc. are all saying "dumb crap" for mentioning these theoretical possibilities.

For me, the question isn't whether it's "not technically incorrect" (and phrasing it that way is not exactly a ringing endorsement ) but rather whether it's presented in a way that advances the understanding of the intended audience. From that point of view, Hawking is not beyond reproach, but Kaku and Greene are irredeemably bad.

 

[acesuv]

I don't think such an observer would have to pass through the ring singularity; see the Penrose diagram at the bottom of this page:

http://jila.colorado.edu/~ajsh/insidebh/penrose.html

See the blue line on the diagram.

Also, the fact that all this is mathematically possible is a long way from saying it's physically possible. AFAIK any small perturbations to the Kerr geometry will destroy the inner horizon and what's behind it, and any real black hole will have small perturbations. The fact that Kaku never mentions any of these caveats is one reason why I say he's going for entertainment value, not scientific accuracy. It's like all the talk about warp drives without ever mentioning that they need exotic matter that violates energy conditions.

Actually, he did mention that it might not be physically possible.

 

[WannabeNewton]

I didn't use the phrase "dumb crap", but I do think Kaku is doing science a disservice.

Oh I wasn't talking about your comment. Another poster used that phrase.

 

[Naty1]

acesuv: If you want to read more about 'time travel'...gateways...Check Wikipedia under WORMHOLE...it should describe why it is not deemed physically realistic.

There is also nice illustration. And its good to recall Einstein did not believe black holes were 'realistic' either..."just math"...

 

[webboffin]

If a black hole was not in this universe then why would it have mass in this one?

 

[Naty1]

If a black hole was not in this universe then why would it have mass in this one?

Nobody said that here...so far, there is no evidence of anything 'outside' this universe because the universe is defined as 'everything'.

Multiverses, parallel universes, bubble universes, parallel worlds,many worlds, etc have been hypothesized, but so far the Lambda CDM cosmological model for one universe seems the best bet.

 

[Naty1]

acesuv:
FYI...I have several of Kaku's books and enjoyed the easy introductory style. As already posted, he can possibly lead you astray; on the positive, side, he does discuss some interesting possibilities I know I might not have considered. So by all means finish your book!

Two more technically accurate books than Kaku's I read, without math, which would be good next steps for reading, would be Leonard Susskind's THE BLACK HOLE WAR [his decades long arguments with Stephen Hawking] valuable for his unique perspectives, and Kip Thorne's BLACK HOLES AND TIME WARPS for a more detailed discussion/interpretation of where the mathematics leads.

 

[webboffin]

Nobody said that here...so far, there is no evidence of anything 'outside' this universe because the universe is defined as 'everything'.

Multiverses, parallel universes, bubble universes, parallel worlds,many worlds, etc have been hypothesized, but so far the Lambda CDM cosmological model for one universe seems the best bet.

I can accept that.