leaving black holes
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From: eric gisse on 5 Oct 2009 04:44 YKhan wrote: > On Oct 3, 6:08 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> We don't live in a black hole. Do catch up. > > And how can you prove that? > > Yousuf Khan Read what I said. Its' relevant.
From: eric gisse on 5 Oct 2009 04:46 YKhan wrote: > On Oct 3, 5:10 pm, eric gisse <jowr.pi.nos...(a)gmail.com> wrote: >> Yousuf Khan wrote: >> > eric gisse wrote: >> >> bz wrote: >> >>> If I remember correctly, "someone" has calculated that the amount of >> >>> matter is "close" to the amount that would be needed for a black hole >> >>> the size of the known universe. >> >> >>> Perhaps we live inside a black hole. >> >> >> Which direction is the singularity? >> >> > Towards the past. :) >> >> An unexpectedly correct answer. >> >> Now which direction is the singularity in a black hole? >> >> The future. > > A black hole inside another black hole reverses its direction of time. It doesn't work that way. > > Yousuf Khan
From: Tom Roberts on 5 Oct 2009 11:28 eric gisse wrote: > A black hole has the unique feature of swapping the role of time and space > inside the event horizon. This is not true. Indeed, there is no way to "swap" such incommensurate things. Say, rather, that for the usual Schwarzschild coordinates on Schwarzschild spacetime, the coordinates labeled by the symbols "r" and "t" interchange roles in the two DISJOINT regions r<2M and r>2M (note no "=" there -- NEITHER coordinate chart is valid at the horizon). Note this is a peculiarity of these specific coordinates, and is not a property of the underlying manifold (as your words seem to imply). In particular, an astronaut falling through the horizon of a super-massive black hole would observe no unusual behavior inside his spaceship as the horizon is crossed. "swapping the role of time and space" would certainly be unusual :-). If he is looking outside watching distant stars, the behavior of their images would permit him to locate the horizon. But no local experiment can detect the location of the horizon. > A freely moving observer marches - unstoppably - > towards the singularity, just as a freely moving observer marches towards > the future in Minkowski spacetime. Yes, inside the horizon. You cannot evade tomorrow. > The observable universe is not like this. We are not in a black hole. Yes. Moreover, in the context of GR, there is a singularity in our past (as shown by the singularity theorems; see for example, Hawking and Ellis). The FRW manifolds have the right geometrical structure to be models of cosmology, while none of the black hole manifolds do. But recent observations are undermining the validity of the FRW manifolds.... Tom Roberts
From: "Juan R." González-Álvarez on 5 Oct 2009 17:41 Tom Roberts wrote on Sat, 03 Oct 2009 09:44:39 -0500: > Juan R. González-Álvarez wrote: >> Tom Roberts wrote on Fri, 02 Oct 2009 09:34:18 -0500: >>> Using different >>> coordinates does NOT "move" the horizon, or make it be at a "different >>> place", it makes the (fixed) locus of the horizon be at a DIFFERENT >>> VALUE OF THE COORDINATE YOU HAPPEN TO LABEL WITH THE SAME SYMBOL, "r". >> >> Unfortunately you get totally confused again by your superfitial >> knowledge of those topics Tom. > > It is not my "superficial knowledge" here, it is YOURS, and/or your > failure to keep your theoretical context straight. > > >> In my original message I refered *explicitely* to renormalized >> coordinates, which do NOT describe "the same manifold". > > Look to the earlier posts in this thread. The context is the > Schwarzschild solution of GENERAL RELATIVITY, not some other theory you > might wish to discuss. In GR, a change of coordinates has NO EFFECT > WHATSOEVER on the manifold, and a different set of coordinates always > describes THE SAME manifold. > > This is just VERY basic geometry, applied to GR. > > Indeed, it is difficult indeed to have some other theory in which a > change of coordinates changes the manifold, as you seem to be claiming. > That would violate cherished beliefs that go far deeper than GR: that > the world we inhabit does not depend on humans or their descriptions of > it. Indeed, without this being valid it is not clear how there could be > any physics at all. > > While YOU might mean something rather special by "renormalized > coordinates", to the rest of us that phrase suggests a re-scaling of the > coordinates, which clearly does nothing special IN THE CONTEXT OF GR. > > >> In fact for r<<2M there is a large difference between both coordinates >> (in the renormalized spacetime there is NOT central singularity for >> instance). > > Again, in GENERAL RELATIVITY this is nonsense. A mere change of > coordinates cannot possibly affect the singularities of Schwarzschild > spacetime. And how did you switch from "renormalized coordinates" to > "renormalized spacetime" -- those phrases appear incommensurate. In the > context of GR, there is a single manifold (a single spacetime), but an > arbitrary number of coordinate systems that map regions of the (one) > manifold onto regions of R^4 in different ways. > > > I repeat: you have a lot of misinformation about GR in your head. You > need to STUDY the actual theory. And if you are trying to discuss some > other theory, you must EXPLICITLY state so. > > > Tom Roberts What bunch of nonsense! Did you even know the stuff which you are supposedly replying? I do not wait you to reply some medium advance question but could you write down the renormalized coordinates which I refered in my previous messages? -- http://www.canonicalscience.org/ BLOG: http://www.canonicalscience.org/en/publicationzone/canonicalsciencetoday/canonicalsciencetoday.html
From: eric gisse on 5 Oct 2009 19:23
Tom Roberts wrote: > eric gisse wrote: >> A black hole has the unique feature of swapping the role of time and >> space inside the event horizon. > > This is not true. Indeed, there is no way to "swap" such incommensurate > things. > Close enough. I'm not saying something stupid like 'your clock starts ticking backwards' but the ability to move through time and space is inverted from that of Minkowski space. [...] |