Markus Hanke

We cannot dispense legal or career advice here, just to be clear on that. I did spend some time working in HR in the past, though, so here are my two cents, which is to be taken as personal opinion only. In principle it would not be legal to discriminate against job applicants on the basis of past criminal convictions (in fact, in most cases it isn’t even legal for employers to ask about this), unless the conviction is directly relevant to the nature of the proposed employment. So for example, if you were to apply for something that is solely based in a lab, or at a computer terminal etc, then it is unlikely to become an issue. However, there are some jobs that legally require an employer to perform police vetting on you prior to making a job offer - most teaching jobs are like that, and definitely anything that involves contact with vulnerable or underage people, among some other scenarios. I would also imagine that direct contact with medical patients in healthcare facilities etc will fall under this, as those are included in the definition of ‘vulnerable’. It goes without saying that such avenues of employment are no longer open to you, and you may even be legally required to disclose your RSO status in certain circumstances, even if no vetting is done on you (it’s your responsibility to check with local authorities on this one). So yes, you can still make a living in science - but there are certain careers that won’t be accessible to you.

As I said earlier, I am not an expert in the discipline of philosophy, and I haven’t read Kant yet - however, I do speak fluent German, so what this term (which translates roughly as ‘thing-in-itself’) refers to would be external reality before it undergoes processing by the sensory apparatus and the mind. So it is meant to be that which exists independently of any perceptual process, the true essence of reality, unsullied by mental constructs, so to speak. The trouble is that we have no way of accessing that external reality, except through sensory and perceptual processes. Anything you are aware and conscious of is a construct of your own mind - it is at best some representation of the ‘ding-an-sich’, but a representation that will be more or less incomplete and distorted in ways that are not necessarily readily apparent. So it may very well be that there is an underlying external reality of some kind (though I would think one could make a valid case questioning this), but we will never be able to access it directly, all we can ever know is our mind’s representation of that reality. It’s much like being stuck having to look at a map, without ever being able to go to the actual territory. In what sense would a single elementary particle be a ‘chair’? How many particles does it take before the ensemble acquires ‘chair-ness’? No, QM does not allow us to conclude that there are no elementary particles (or quantum fields, whichever way you wish to look at it). It does, however, make it clear that the dynamics of those constituents cannot be classical, due to the existence of observables that don’t commute, and due to statistical correlations between measurement outcomes that are stronger than classically allowed (entanglement). I’m not sure what you mean by this.

Under the FLRW model, when we say that the universe is ‘flat’ (one of three possibilities, depending on the choice of the k parameter), then what is meant is the Gaussian curvature. But this is only one isolated aspect of the geometry of the manifold (roughly equivalent to the average spatial curvature) - the complete description of the geometry is given by the Riemann curvature, which is never zero in the FLRW model. How could it be? It is an interior solution to the field equations after all. So essentially, for FLRW cosmology, the Riemann tensor doesn’t vanish: \[R{^{\mu}}{_{\nu \lambda \delta}} \neq 0\] But in order for a region of spacetime to fall under the dynamics described by SR, it has to be Riemann-flat: \[R{^{\mu}}{_{\nu \lambda \delta}}=0 \] This means you can’t use SR to describe the universe at large. The FLRW spacetime can be spatially flat in a Gaussian sense, but its geometry is never Minkowskian, as is required for SR to apply.

I am not sure I fully understand my own thoughts on this Also, my own thoughts are really only half-formed, and in a constant state of flux. I don’t have any coherent idea or model, I am just trying to reconcile my understanding of physics with the phenomenology of my own direct experience. But I think you captured the essential idea. Basically I am questioning whether, if one really wants to understand the universe, it is wise to disregard the subjective observer, because maybe - just maybe - the two aren’t as separate as we think they are. Physics attempts to arrive at a completely objective description of the world based on a perfect subject-object duality, and - while this has lead to some very useful results and applications - I am wondering whether that duality has any ontological status, and whether any description of the ‘world’ can and should ever be objective. Or perhaps put it this way - if you had some other sentient species with a completely different sensory apparatus, and a mind/consciousness that is structured sufficiently differently from our own (e.g. their thought processes could be non-linear or even chaotic, their memory space multi-dimensional, their perception processes non-dual etc etc), would they arrive at a model of the ‘world’ that is compatible with our physics? Would we as humans even recognise it as a model of the world? If not, then what does that say about the concept of ‘objective reality’? Interesting, and somewhat like I was pondering. But I would go a step further and ask whether space and time are not themselves ‘categories’ (just like causality), rather than a background stage for the ‘ding-an-sich’ to exist on. Of course science makes models - its relationship to what it describes is the same as that of a map to the territory which it maps out. Science isn’t an explanation for reality, it’s a description of it. But the point is that the mapping isn’t arbitrary, because even though it is not identical to the ‘territory’, it has to capture the relevant structure of it - like the contours on a topographic map that capture the elevation profile, for example. And it is that structure that makes it useful. I have Kant’s text on my eReader, but haven’t gotten around to actually reading it yet. I shall be looking forward to it I think relativity isn’t too difficult to incorporate into that, but the implications of QM on the ontological status of ‘reality’ are indeed profound. In light of the - by now well established - violations of Bell’s inequalities, we can’t even take global Einstein locality for granted any longer. What scientific progress over the centuries is showing us is that we cannot and should not trust our intuitions on what is irrefutably true about reality. Perhaps at the very core that is what I have been trying to say here.

Well, even if space and time were organisational principles by the mind, that wouldn’t imply that those principles need to be Euclidean. What we already know about physics would of course remain valid, it’s just that they are no longer merely statements about an external world. In essence, it would mean that our physics are what they are not because of some deep physical reason, but because they reflect the structure of the observer’s mind, being a construct of and by it. The mind itself would be a constraint on what worlds are possible, and on how these options can differ. Don’t get me wrong, I am not making any claims nor do I wish to introduce any alternative models. The comment was merely meant as something that is perhaps worth pondering. I am just not sure that the “me-world” duality really is as clear cut as might appear. What the details of this would - or could - look like, I don’t really know. Actually, I haven’t I don’t know much about what philosophy as a discipline has to say on those things, though I do intend to rectify that in the near future. For the moment, I am just in the habit of pondering such questions myself, based on my own physics knowledge and the phenomenology of my own mind, which I am also in the habit of observing very carefully. So these are my own thoughts; if I am taking on a particular philosophical stance, be it Kantian or someone else’s, then that is not by design, but rather by accident. Yes, that’s the question, isn’t it? But I think specifically with time, it can be taken quite far. We initially started off with Newtonian time, which is an absolute background to everything that happens. People once thought this notion to be so fundamental that it requires no further consideration. Later the paradigm shift to relativistic physics happened, and suddenly time became purely local, and thus relative, albeit still an essential ingredient. Then quantum mechanics came along, and time lost its central status; it also turned out that on those scales physics are no longer fully local in the classical Einsteinian sense. This can be somewhat alleviated by combining the two latter models into quantum field theory, but of course the property of entanglement remains, not just between states (which are relative), but more importantly with the algebras of observables. Lastly then, going one step further into hypothetical models of quantum gravity, there are examples of models where both space and time completely loose their ontological status as fundamental entities. For example, in Loop Quantum Gravity, spacetime is not a fundamental entity, it emerges only on larger scales from the dynamics of the model (though it is yet to be shown that it reproduces the correct semi classical limit). So we have arrived at a situation where we describe the world without making any reference to space nor time, which are taken to be emergent quantities on larger scales only; the fundamental entities of the model are not themselves of a spatiotemporal nature, nor do they require - or indeed even permit - any a priori spacetime background. I am just bringing up LQG as an example here, I am not saying it is a correct or physically useful model of quantum gravity. But it does demonstrate that it is possible in principle at least to write down a coherent description of the world without explicit reference to space and time as fundamental entities. A manifold does not necessarily need to be endowed with a metric. It is indeed possible to meaningfully work with non-metric manifolds, which is what the discipline of differential topology does. Most relevant tensorial quantities and operations can be defined without any reference to a metric, all you need is a connection. It is in fact surprising just how much one can actually do without the presence of a metric! However, it is of course not possible to introduce any notion of measurement on such manifolds, as you rightly point out.

These are questions that have kept Western philosophy busy for the past few millennia, and there are as many opinions on it as there are philosophers. My own thoughts on this are (currently) that all we can observe are objects of consciousness - we do not have observational access to anything else. The thing with this is that all objects of consciousness are mental constructs - hence everything we can observe has been pre-processed by the mind in some way. Assuming that there is such a thing as an external reality on which what the mind presents us with is based (I am making no claims whether or not there is), then the big question becomes how the mental model we observe maps to external reality. How accurately does it reflect external reality, and which parts of the model have ontological status, and which parts are ‘merely’ phenomenological? At the very least the model will be extensively filtered and incomplete, since it can only be based on our own limited sensory apparatus (meaning some other sentient being with different sensory apparatus will construct a model of the world that may be fundamentally different from our own). It will also be subject to all manner of distortions and biases, since the way the mind interprets sense data is necessarily based on memory and prior experience; we never get “just reality”, but only some reflection of it plus the mind’s own running commentary, so to speak. The most crucial question, so far as it connects to the discipline of physics, is what kind of ontological status - if any at all - the various fundamental categories have which the mind uses to structure this model. By this I mean things like spatial and temporal relationships, object-subject dualities, etc etc. For example, are space and time really attributes of external reality, or they just categories the mind uses to construct a suitable model of the world? What about the fact the very ideas of ‘observer’, ‘observed’, ‘reality’, ‘mind’,...are all themselves mental constructs? These are tough questions, but I think it is important to ask them, because it may turn out that things really aren’t the way they initially appear to be. Our scientific models may say just as much about the structure of our minds as they do about the ‘external’ world. And then of course there is the question of whether such a thing as an ‘external world’ actually exists, in what sense it can or cannot exist, and if/how we could find out. I have personally started out on my own journey as a staunch ‘scientific realist’, but I am finding myself growing increasingly doubtful of this. I think it may be a mistake to try to eliminate all reference to our experience of the world, because such a thing as ‘objective reality’ and its description may ultimately be a meaningless concept. This doesn’t mean that science is on the wrong track, but its domain of applicability may be limited in ways that we are failing to account for as of yet.

How about if space and time are simply methods of the mind to structure information? Essentially, the mind takes certain raw data and uses this to continuously construct a model of reality, which we then become aware of as an object of consciousness. It is difficult to imagine what such a mental model could look like without some method to introduce spatial relationships and causal structure between its constituent parts. In that view, spacetime is quite real, just not necessarily as an attribute of the ‘world an sich’ (to paraphrase Kant, not that I necessarily agree with all his ideas), but rather as a function of the mind - which, interestingly, is itself part of the created model.

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.

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.

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.

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?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Well, I am not an expert in philosophy, so I can’t really comment on that. So far as GR is concerned, depending on what kind of spacetime you are dealing with, it is often possible to foliate the entirety of the manifold. However, there will always be infinitely many possible foliation schemes, so there is never any preferred notion of time. This is in keeping with the principle of relativity, of course. The relationship between these clocks is simply the coordinate transformation that relates the metrics. For example, the stationary far-away observer can use the Schwarzschild metric, whereas the observer in free fall uses the Gullstrand-Painleve metric. These are simply related by a coordinate transformation, since both frames are of course in the same physical spacetime. But they use different notions of what ‘time’ means, so defining a notion of simultaneity is not in general possible if the observers are separated in time and/or space, unless there are certain very specific symmetries present. At best, it might be possible to foliate spacetime in a manner that both observers can agree upon, using a suitable coordinate system and foliation parameter; but this works only in certain highly symmetric cases, and the foliation parameter is not something that any physical clock would actually show in either of the two frames, so I don’t see how it is helpful here. You may be able to do this in certain special cases that are highly symmetric, which is why I put the qualifier “in general” as part of my original comment. Flat Minkowski spacetime is a trivial example. I don’t think it is possible in Vaidya spacetime though, which is what we would be talking about when it comes to evaporating black holes. Crucially, I don’t think it is helpful to even consider the concept of simultaneity in curved spacetimes, since it is not a generally applicable concept - in my experience, it is bound to lead to more confusion than clarity. I agree, it has little to do with topic of the thread, so I’m not sure why it was brought up at all.

Yes it will be. If you look at the above equation, if c is variable, the covariant derivative will contain extra terms including derivatives of c. These terms don’t cancel out, so there is no way to not violate the relation.

No, we have to take this locally. It’s Schwarzschild coordinate time, so this is what a far-away stationary clock measures locally in its own frame of reference. It is not what physically happens anywhere else. In GR, time is always a purely local concept. Again, this is not possible. Time is a purely local concept in GR; there is, in general, no notion of simultaneity across extended regions of curved spacetime, and you can’t map notions of space and time local to some far-away observer into anything that happens anywhere else. In particular not to test particles in free fall, which aren’t stationary. You can define static hypersurfaces of simultaneity based on the coordinate system you have chosen (in Schwarzschild, these will be nested spheres), but that is not the same thing. It talks about the conventional model for this - that means you use Schwarzschild spacetime, allow the mass terms to vary, and see what happens. This is meant as an approximation and a teaching tool, because the maths are easy to do on paper, unlike is the case for a full description. But as I have attempted to point out several times now, in actual fact any kind of black hole that isn’t stationary can’t physically be Schwarzschild, so it is little surprise that the conventional model does not actually work too well. That was kind of the point of Hawking’s original paper (I recommend you read it) - he started with a conventional Schwarzschild black hole, and examined if and how it is compatible with quantum field theory; and unsurprisingly he found that it isn’t, so Schwarzschild black holes cannot actually occur in nature. At the very least, they have to be generalised to their radiating counterparts, the aforementioned Vaidya black holes. Yes we do. We can use quantum field theory in conjunction with the Vaidya solution to model Hawking radiation in a non-stationary spacetime. This has been done by several authors, e.g. here. However, the result of this is a geometry that is vastly more complex than Schwarzschild, and contains several different types of surfaces - event horizons, apparent horizons, Killing horizons, and trapped surfaces. In particular, in can be explicitly shown that a far-away observer will receive information about the black hole’s state in finite coordinate time, unlike would be the case in Schwarzschild.