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Markus Hanke

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Markus Hanke last won the day on June 26

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  1. So far as I know (without having been successful in completing the calculation myself, due to the presence of off-diagonal terms) they do. It is in Schwarzschild spacetime that coordinate time to the horizon diverges, but not in Vaidya spacetime. In either case, your argument was based on Schwarzschild spacetime, not Vaidya, so this isn't relevant to what you said. I'll see if I can get these maths worked out sometime. More than one poster here has explained to you multiple times why it isn't. Actually, I haven't got too much of an issue with that bit (though it is problematic too). What bothers me is that in my opinion they are not using the correct energy-momentum tensor, so that would be my main point of criticism. Either way, there are certain differences between the KMY model and the traditional black hole which should be reflected in the gravitational wave signature of black hole mergers. At present we don't have enough data to support either one (afaik at least), but I am sure we will in the very near future. Let nature speak. Until then, there is little else to add to this thread. Personally I would be happy if it turns out that there are no horizons, because that places valuable constraints on possible models of quantum gravity (my main interest); but if that turns out to be so, then it won't be for the reasons you were trying to argue. And if they do exist, then that is fine with me too, as that in itself is also a valuable finding. As it stands though, the current consensus in the physics community is that horizons are part and parcel of black holes.
  2. Yes. I have been thinking about this some more, and there is something else that has been omitted - the fact that, if a horizon forms during the collapse process, it will initially do so in the interior of the collapsing mass. This divides the overall spacetime into three distinct regions: 1. The interior of the collapsing mass below the horizon - containing only mass-energy 2. The interior of the collapsing mass between horizon and surface of the mass - this contains both the mass distribution and Hawking radiation 3. The exterior spacetime - containing only Hawking radiation Each of these regions has a distinct energy-momentum tensor, and thus its own metric as a solution to the field equations in that region. The overall solution for the entire spacetime is a metric that is has to ensure that spacetime remains smooth and differentiable at the boundaries between these regions, which introduces additional constraints on the overall geometry. None of this has been accounted for by the aforementioned paper.
  3. The problem here is that those people do not respond to reason, so debating them is pointless. There is literally nothing you could say to them that would change their world view. As the old saying goes, you can't reason someone out of a position that hasn't been arrived at by reason in the first place.
  4. You don't need to reference any particular coordinate system for this, you just look at the curvature invariants of the Riemann tensor. They are all finite at the horizon, unlike is the case for the curvature singularity at r=0. You can also look directly at whether the region is geodesically complete or not, which, again, is independent of any particular coordinate choice. GR is purely classical, so it does not say anything different. I'm at a loss on a different point - the paper talks about a geometry that resembles a 'decaying white hole', but to my understanding there is no white hole counterpart in Vaidya spacetime, unlike in the Schwarzschild case. Or am I getting this wrong?
  5. Your initial claim in this thread was that evaporating black holes cannot exist (see very first sentence of OP). This paper does not support such a claim - in fact it is actually about the information loss paradox. Furthermore, it makes it explicitly clear that evaporating black holes are not Schwarzschild, which is what we have been attempting to explain all along; it does not attempt to dispute that they exist, as you seem to do.
  6. Well, I'll be damned. One wave of the hand, and 5+ billion of us, who just happened to be born into non-Christian cultures, sentenced to burn in hell for all eternity. Makes me wonder just which of those two guys to blame, really.
  7. And to add to this, after all my years on amateur science forums, there are two other crucial problems I see: 1. People often develop an intense focus on one particular or narrow point/source/information, and may even possess a good grasp on it; but then they fail to understand how it fits into a larger context. For example, I have met lots of people who have a good handle on Minkowski spacetime (SR), but then they naively try to add in gravity, and fail to understand why this does not work. Or people who become almost obsessed with one paper by one author, without grasping the context in which it was written, and thus draw the wrong conclusions from it. Nothing in the sciences stands in isolation, knowing and understanding the larger context is as important as any individual piece of knowledge. 2. Too many people seem to be entirely unable to distinguish valid sources of scientific information from pop-sci, personal opinions, or outright woo. Access to information is useless - even dangerous - if one is not equipped to judge the scientific value (or lack thereof!) of it.
  8. Interesting, thanks! I just wonder if there is a mathematic model that describes the evolution and dynamics of the system? Again, just as a matter of curiosity. Just as a quick note - my own personal sense of achievement comes from pursuits that have no monetary value, and my most valuable asset (basic necessities of survival aside for now) is free time that enables me to engage in those pursuits. It is a mistake to assume that a sense of achievement can only result from having paid work; many of the greatest achievements of humankind cannot be measured in monetary terms.
  9. I don’t know anything about global macroeconomics from an academic point of view, but this discussion got me wondering what the underlying symmetries of this closed system actually are, mathematically speaking. My immediate impulse here would be to describe the global flow of funds/money (not the same things, right?) similar to how we do fluid dynamics, using an appropriate differentiable manifold. Has anything like this ever been done? I’d be curious to see the resulting maths - what field equations govern the evolution of the system, what the local and global symmetries are, etc. I would also expect the dynamics of this system to be fully determinate, but having a rapidly increasing uncertainty factor when it comes to predictability, i.e. a chaotic system. Not trying to make any particular point at all here, this is just a matter of curiosity on my part.
  10. If you disregard fatalities due to direct acts of violence, some 1.2 million people died in the four years of the Khmer Rouge regime from hunger, disease, and other ‘natural’ causes linked to malnutrition and inadequate health care. Of course it is difficult to disentangle how much of this is a direct result of economic policies (or rather their absence), but you get the idea - it didn’t end well for the people of Cambodia. I think Google is your friend here, I am not in a position to do that kind of research for you. Keywords such as “communities without money” will get you a lot of search results, both for historical communities, and current ones. They definitely do exist, but once you read between the lines (remember that much of the material will be biased one way or the other), it becomes apparent quickly that the absence of money - just like an abundance of it - is not necessarily correlated to increased happiness. There are always trade-offs of one kind or another, usually related to personal freedom, or opportunities to pursue things other than basic survival. I actually personally know an individual who chooses to live without money for ideological reasons (he isn’t part of any community) - he makes it work for himself, but his days consist of hard toil from morning to late, just in order to secure his basic survival. I know that he has little to no time nor resources for any other type of pursuit. To be honest, that would not be my idea of a fulfilling life, but each to their own.
  11. So did the Khmer Rouge during their regime in 1970s Cambodia - they abolished all currency and pretty much any trace of a money-based economy, and reverted to bartering between communes instead. We all know how this turned out. In my humble and wholly unqualified opinion money is a dangerous thing if it is not seen for what it really is (a social convention), but I would be enough of a realist to recognise that currently there are few if any alternatives that would actually work in practice. Many attempts have been made throughout history to set up communities/societies that don’t use money, and to the best of my knowledge none of them have worked out in the end.
  12. Very well put +1 True, if you have large local variations in curvature (as would be the case in the actual universe), such a global foliation will not in general be possible.
  13. I did not make any reference to Newtonian gravity or any particular form of potential, I am only using the fact that the energy-momentum tensor has to be locally conserved. The relation I gave follows from Noether’s theorem, and not any particular theory of physics. The point was simply that, if you allow c to vary, this conservation law no longer holds, because the underlying symmetry that gives rise to the conserved quantity is no longer there. If c is not constant, energy-momentum cannot be conserved, irrespective of what else you attempt to change.
  14. Yes, well put. Ok, I see. In Vaidya spacetime this issue never arises, since (unlike with Schwarzschild) this coordinate time for a far-away observer remains finite. No, you are correct. What I meant is that it is sometimes possible to foliate all of spacetime given a particular coordinate choice, i.e. from the point of view of a particular observer. There are infinity many possible observers, and each one of them will use a different foliation scheme; hence the foliation is never objective and shared by everyone, it is always observer-dependent, even if it spans the entire spacetime. There is no such thing as universal time, of course. BTW, slicing up 4D spacetime into an ordered sequence of 3D hypersurfaces is called the ADM formalism of GR.
  15. Again, gravitational potential - if it can be meaningfully defined at all - is a gauge field with a gauge freedom to choose a zero point, whereas Planck’s constant obviously isn’t. It is not physically meaningful to relate the two in this manner.
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