| Subject: How to uniquely identify the existence of general
relativistic black holes?
Date: Wed, 03 Sep 2003 15:30:20 +0300 From: Dimi Chakalov <dchakalov@surfeu.at> To: Lee Samuel Finn <lsfinn@psu.edu>, odreyer@perimeterinstitute.ca, kelly@gravity.psu.edu, badkri@aei.mpg.de, garrison@cl.uh.edu, rlopez@uprrp.edu CC: Floyd.W.Stecker@nasa.gov, sorkin@physics.syr.edu, kip@tapir.caltech.edu, saul@astro.cornell.edu, israel@uvphys.phys.uvic.ca, shapiro@astro.physics.uiuc.edu, Charles.Bennett@gsfc.nasa.gov, Gary.Hinshaw@gsfc.nasa.gov, halpern@physics.ubc.ca, office-hannover@aei.mpg.de Dear Colleagues, In your "Black Hole Spectroscopy", gr-qc/030900, you wrote (p. 15): "We have shown that, given at least two QNM signals, from the same source and with sufficiently large signal-to-noise, we can cleanly distinguish black holes from other astrophysical sources." I'm wondering, can you formulate the conditions under which GR waves can not be observed *in principle*? Please see http://members.aon.at/chakalov/faq.html#QM http://members.aon.at/chakalov/Nature.html#note http://members.aon.at/chakalov/Requardt.html It seems to me that, in order to address properly the question in the subject line, we need quantum gravity, http://members.aon.at/chakalov/Pestov.html#note If so, what are the "observables" of quantum gravity? Please see Rafael Sorkin's "Causal Sets: Discrete Gravity", gr-qc/0309009, p. 15: "In the context of canonical quantum gravity, this issue is called "the problem of time". There, covariance means commuting with the constraints, and the problem is how to interpret quantities which do so in any recognizable spacetime language." Regards, Dimiter G. Chakalov
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Subject: How to uniquely identify the existence of general relativistic black
holes? ====== Is the solution to the problem of time and the "observables" of quantum gravity (cf. Rafael Sorkin above) relevant to the task of detecting the putative gravitational waves? Not only relevant but conditio sine qua non for understanding those "ripples" of spacetime metric that we call 'gravitational waves' and the medium in which they "propagate", the putative global mode of spacetime. Recall that we never actually measure the gravitational field itself but "the changes of motion of matter that we interpret as being due to an underlying gravitational field" (J. Halliwell, quant-ph/9902008). The confinement of the gravitational field is due to the basic idea in GR that "the gravitational field is nothing more nor less than a change of the space-time metric" (Landau L.D. and Lifshits E.M., The Classical Theory of Field, Pergamon Press, Oxford, 1985, p. 313), and hence the detection of the change of the metric would inevitably require a new reference frame with respect to which we can identify such changes -- more than one, as in the example with Leonardo da Vinci’s Vitruvian man, courtesy from Barry Barish. Trouble is, there is no place to go. In GR we are confined inside spacetime, and, to detect any change of spacetime itself, we would have to move "outside" spacetime, in some truly empty space. But "there is no such thing as an empty space, i.e., a space without field. Space-time does not claim existence on its own, but only as a structural quality of the field", says John Stachel, referring to the local mode of spacetime. The bi-directional "talk" of matter and gravity, as explained eloquently by John Wheeler, makes the spacetime not only a dynamical quantity but removes all traces from some background or 'back bone'. There is nothing in GR that you could try to 'hold onto', and hence "time" should not exist at all, ever. If you trust GR and claim that some clock does indeed read some "time", then you must define such "time" relationally -- that's the magic word! -- but then you encounter the paradox of Baron von Münchausen: everything is interdependent and you have to 'act on yourself' in order to move, hence register a change in "time". The only chance you might have to recover "time" is to try 'the only truly isolated system', the whole universe, but you again hit the problem of time: it is frozen, with respect to any local inertial frame 'inside-the-universe'. But you don't give up, you desperately need this "time", since standard QM requires a background causal structure, otherwise it does not make sense at all. So, how can you recover this mysterious "time"? Solve the problem of time in canonical quantum gravity (A. Peres, gr-qc/9704061), find the "observables" of quantum gravity (empty waves), then solve the Macro-Objectification Problem, expel the 'observer' from QM (Popper K.R., Quantum mechanics without ‘the observer’, in Quantum Theory and Reality, ed. by M. Bunge, Springer, New York, 1967, pp. 7-44), and finally recover the notion of time that could make sense in QM. Then go back to GR and find the notion of time that makes sense. It shouldn't be too difficult, since your brain reads that same time that makes sense. I would be deeply surprised if any of the physicists working with GR and QM decides to reply. I'm doing this mainly for Albert Einstein and for the readers of my CD ROM. It will be available well before 2007. The fun part may be just around the corner!
September 3, 2003
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