Markus Hanke

No, I am referring to all the many different types of tests that have been performed to test for Lorentz invariance (not just MM type setups), and which are listed in the link I gave you. By your comment I deduce that you haven’t bothered even looking at the link. Very disappointing, but not very surprising. There are no (repeatable, peer-reviewed) instances where violations of Lorentz invariance have ever been observed. The problem has been identified a century ago, namely that non-relativistic physics fail to accurately describe the world around us. The solution is relativistic spacetime. It has already been pointed out multiple times that this is an example of data misinterpretation. The so-called ‘Twin Paradox’ is neither an inconsistency, nor is it a logical paradox; it is an expected and experimentally verified consequence of relativistic physics. Not at all, because all other types of experiments also gave null results. Even without Einstein and his theory of relativity, the idea of an aether would have been completely untenable, and physicists already knew this. I think you really need to start actually reading the links you are being given. Just saying. Of course we can, so long as they all give the same results and agree with observational data. A model in physics is no different than a map drawn of a piece of terrain - there are many different ways to map out the same terrain, and all these maps can be equally correct. There are in fact numerous concrete examples, such as: you can write the gravitational dynamics of anti-deSitter space in terms of a gravitational theory of its bulk, but you can also write it in terms of a conformal field theory on its boundary. These are completely different models, but they describe the same physics. Numerous other such dualities are known to exist.

Well, what you have defined here is an interval between two points on a differentiable manifold. Of course you can interpret this quantity as ‘time’ in some sense (ref the usual maths of GR), but I don’t think that is a necessary, sufficient, or even obvious conclusion. In the physics sense, time is what clocks measure, and unfortunately in a 3D universe no physical clock can ever measure \(ds^2 \), because all physical clocks are stationary and extended objects, just like the tea cup; ie. their world lines are equal to their spatial embedding. This quantity is thus simply a spatial distance in 3D. Also, in our own normal universe (but not in 3D of course), you have physically realisable world lines for which \(ds^2=0 \); does this imply that no time exists? Obviously not - a photon still propagates at a well defined speed and momentum - so there is a notion of change - even though no proper time elapses for it. So I wouldn’t equate this quantity with time in a general sense (even though it can sometimes be useful to do so), and definitely wouldn’t draw conclusions from it as to the existence of time. Indeed - for precisely the reasons pointed out You mean there is a sequence of operations in doing maths? That is of course true, but that sequence isn’t inherent in the structure of maths, at least not in my opinion. Consider for example the two statements \[ y(x)’=y(x) \] and \[y(x)=ae^x +C\] Of course one can - and frequently will - construct a sequence of statements in between these, i.e. solve the equation analytically. However, in structural terms, these two statements about y(x) are exactly equivalent. It’s simply two formally different ways to make the same statement about y(x). So there is no notion of ‘sequence’ or ‘time’ inherent in the maths themselves - only in the process of formally showing the equivalence with pen and paper, which is a different thing altogether. Both of the above statements are true simultaneously, and are simultaneously equivalent.

Local Lorentz invariance (the symmetry that underlies SR and QFT) has been extensively tested by a very large number of experiments, both historical ones and modern high-precision ones. No instances of genuine Lorentz violations have ever been observed by anyone thus far. The Silverstone experiment is a well known instance of the misinterpretation of data. https://en.wikipedia.org/wiki/Modern_searches_for_Lorentz_violation

Hmm, I think I may be misunderstanding what the term ‘qualia’ is conventionally taken to mean. For me, I am aware of pain, and I am also aware of the unpleasantness of it; these two aren’t the same things at all. Pain is simply a sensation, and that is all it is; the unpleasantness of it is how the mind reacts to that sensation, and it is that which I am referring to when I say ‘qualia’. It is quite real to me. Remember the old Buddhist adage : ‘Pain is inevitable, suffering is optional’. That is precisely how I understand qualia, but perhaps that is not how the term is used in the philosophy of mind...? Well, I am also a practicing Buddhist (albeit in a different tradition) and intellectually inclined, but Dennett’s views - to the extent that I am aware of them and understand them - do not seem to resonate with me. But like I said, I am really not qualified to address them formally from within a philosophical tradition. As mentioned above, in my own meditation practice it appears intuitively obvious to me that an object of experience (e.g. pain) is quite separate from what it is like to have that experience (unpleasant). If I was able to intuitively and immediately experience objects just for what they are (e.g. pain as being just a sensation like any other sensation, and just that, and nothing else), then there wouldn’t be an issue - the process of ‘selfing’ (as I call it myself) couldn’t happen, and thus no suffering could arise. Likewise, if the ‘unpleasantness’ was inherent in pain, rather than separate, we’d be trapped - there would be no way out of suffering. But luckily for us this is not so. On the other hand, in some sense Dennett does have a point though, because the way the mind reacts to objects of experience is ultimately conditioned by ignorance, i.e. by wrong view, by not seeing things clearly. So in that sense the ‘unpleasantness’ of pain is illusory, because pain is just pain, it’s by nature neither pleasant, nor unpleasant - the untrained mind doesn’t see it like that simply because it doesn’t know any better, until insight into the issue eventually arises. So qualia are at the same time quite real, but also inherently empty. I guess in Buddhist philosophy the term ‘qualia’ would encompass sañña (labelling) and sankhārā (conditional formations) within the ‘Five Aggregates’ template; we suffer because we identify with these, and fail to see that they are transient, unsatisfactory, and not-self.

‘Satisfactoriness’ is not a property of scientific models; internal self-consistency, empirical testability (in the sense of making testable predictions), and falsifiability are. And QM does rather well in those regards, all of the debates around different interpretations of the formalism notwithstanding. The standard way of modelling ‘delayed choice’ type experiments may appear unsatisfactory to you only because you tacitly (and perhaps unconsciously) think of the world as classical, which is what we as human experience. More precisely, you tacitly assume locality. But embedding a quantum system such as a delayed-choice eraser setup into spacetime is non-trivial, and in particular not possible so long as one demands Einstein locality to hold. However, we know now for pretty much certain (ref Alain Aspect et al) that Bell’s inequalities are violated in quantum systems, so Einstein locality must be violated; when one takes this into account, a self-consistent and testable model of this experimental setup is easy enough to write down. However, such an explanation will always seem non-intuitive and ‘unsatisfactory’ to us, because it has no analogue in the classical domain.

To be honest, I do not really understand Dennet’s argument, it doesn’t make any sense to me. I can see why he would want to argue against the existence of qualia, given his overall views on the science and philosophy of mind and consciousness, but I really don’t follow his claims. It is obvious that those attributes - an apple’s redness, a pain’s unpleasantness etc - do not exist separate from the mind; in a physical sense, an apple simply reflects light of certain wavelengths, and neurons simply transmit electrochemical signals. Redness and unpleasantness aren’t properties of the ‘ding-an-sich’, in Kantian terms, and believing otherwise is of course a mistake. However, I don’t experience wavelengths of a certain kind, nor do I experience electrochemical signals - I directly experience redness, and the unpleasantness of pain. That’s the whole point. It is in fact precisely the other way around - it is the very concepts of ‘wavelengths’ and ‘electrochemical signals’ that are in some sense at least the illusory fiction here, because these are abstract ideas created by the mind, and at the same time they do not correspond to direct experience (yet they are also real as mind-objects in themselves). Even a newborn infant knows what it is like to see red, or to feel the unpleasantness of pain, though they know nothing as per yet of colours or sensations (as concepts). They experience redness, but do not know that it is ‘red’; they hurt, but do not know that it is ‘pain’. Even my cat manifestly knows what it is like to be a cat, though she does not know that she is a ‘cat’. Any parent who has ever had to console a colicky infant knows that the unpleasantness of their pain is quite real to them, and they are not shy and very vocal in letting you know! Explaining to someone suffering in a dentist’s chair that it is ‘just electrochemical signals’ isn’t likely to alleviate their suffering in any way. Even ethically, such a viewpoint as Dennet’s is very highly problematic. That qualia are subjective (i.e. mind-generated) and possibly lack a physical correlate is obvious, but that does not make them any less real. For any observer, at any given instant, real is what they experience in that precise moment of consciousness; whether the objects of consciousness have a physical correlate or not is really quite irrelevant to that. Even if one hallucinates, and knows that is a hallucination, then both the experience of the hallucination itself and of their beliefs about it are both real. Reality is inherently subjective and observer-dependent; if it weren’t, in what sense could it be ‘reality’? Unfortunately I do not have the philosophical background knowledge nor vocabulary to formally refute Dennet’s claims, but they don’t ring true to me at all, and they most certainly do not correspond to my own phenomenology of experience. In fact, they sound like a cop-out - it seems he is quite desperately attempting to explain away something the existence of which poses a fundamental problem to the rest of his world view.

You got it That being said, our hypothetical tea cup system here is a stationary system, since nothing else is possible in a 3D universe. Meaning, if the cup is empty, it cannot ever be filled, since that would necessarily require a change with respect to some coordinate other than a spatial one. This would be a pretty boring universe

This is not really correct, because gravity has the right degrees of freedom so that it can propagate in the form of gravitational radiation - and such radiation fields never propagate at more than the speed of light. This is a non-sequitur, because there are fundamental interactions other than gravity happening in the universe.

In Newtonian physics, gravity is a linear interaction - meaning the field does not self-interact, so it is not possible to attribute mass to it. One could thus have guessed at the end result without needing to solve this (really awkward) equation. For a model of gravity that is non-linear, i.e. where the field self-interacts, have a look at General Relativity as well as it numerous off-shoots and alternatives.

Sure why not? Mathematically, instead of having quantities that change with respect to some time coordinate, you can always have quantities that change with respect to one another, without reference to any notion of time. ‘Change’ doesn’t imply time, and time doesn’t imply change. Derivatives (in the calculus sense) with respect to some quantity other than time are well defined and commonly used. For example, imagine you have a purely 3D universe, without time, that contains a tea cup. The handle of the cup has a certain curvature; the interior surface of the cup also has curvature, which is probably numerically different. So the surface curvature changes with respect to spatial coordinates, rather than time. So you have a universe that encompasses changes, but no time. This is perfectly consistent and valid, at least in my mind

Perhaps though there is a third option, which is somewhere in between these - mathematics could be a human invention/convention (a type of language), however, the structures underlying that language correspond in some sense to structures in the real world. Much like the elevation profile on a topographical map in some sense maps into terrain altitudes, or elements of natural languages map to elements of human experience. No, it’s not too far out there. I have at times speculated myself about a possible link between consciousness and entanglement, in an information-theoretic sense; the idea was that you have two complex systems, the brain and the external world (not necessarily entirely independent). If these systems were entangled somehow, then the composite system ‘world+brain’ would have to be described by a state that is non-separable, meaning you need information not just about each of the subsystems, but also about how they are related. Perhaps consciousness is somehow linked to precisely that ‘extra’ information, which would need to have a very complex structure. Of course I am referring to information-theoretic generalised entanglement here, not necessarily the narrower concept of quantum entanglement. Again, this was just some Sunday afternoon type speculation. Ok, I may have been going a bit too far off the rails. Out of interest though, in philosophical terms, where is the difference between causation and correlation? Correlations come in degrees of strength, so at what point does a correlation become a causation? Very interesting notion. I will need to think about this some more. Phenomenological qualia? For every conscious observer who can perceive colours, it is always like something to see ‘blue’. The subjective content of those qualia is likely slightly different for every observer, but their ontological status (i.e. the fact that qualia accompany experience) is a real regularity - that cannot be described mathematically. Or am I seeing this wrong? You are probably right, mine was a very far-fetched speculation. Note however that such structures are possible in principle, i.e. they are compatible with the laws of physics even as we know them. Take for example the concept of gravitation geon - these are topological structures that are held together solely by their own gravitational self-interactions. So basically you’d have a completely empty vacuum region of spacetime, which nonetheless has a non-trivial geometry and topology associated with it. Something similar can be done if you combine gravity and electromagnetic field. In principle at least such structures could be arbitrarily complex; but of course I couldn’t think of any natural process that would give rise to them, so in that sense it is indeed very far-fetched. Well, in Buddhist philosophy (and in other Eastern thought systems as well) the subject-object duality that we take as being so fundamental to experience isn’t fundamental at all. Given enough practice with the right techniques, one can eventually realise the illusory nature of that duality, giving rise to the state of ‘atammayatā’, which is a state of non-dual awareness where there is no longer ‘this mind’ going out to ‘that object’. By ‘illusory’ here I don’t mean that the duality doesn’t exist, but rather that it is based on a wrong view, and is thus void of any substance, once seen through. Most notably, this world view is very empirical, in that it isn’t taught as a mere abstract fact to be believed, but as part of a practical path to be practiced. In other words, given enough practice and perseverance, one can go and find out for oneself what ‘atammayatā’ is like. In the East, philosophy is often based upon direct personal experience, rather than metaphysical speculation.

I think Newtonian mechanics is actually highly problematic when it comes to causation. If you really think about it, the notion of “force” which Newton suggested boils down to instantaneous action across arbitrarily large distances (most clearly seen with gravity), in the complete absence of any plausible causative mechanism. So I think a strong case can be made for it actually being a non-local theory based on correlations, not causation. In that sense David Hume may have made a pretty valid point - though of course that doesn’t explain why the model works so well. This immediately leads to the much more general issue of why any mathematical structure should correspond to processes in the real world. They are observable by us in our daily lives - Newtonian mechanics is fundamentally about human experience, because it describes precisely that domain of the universe that is directly accessible to human perception. This is, the low energy, low velocity, classical domain, as modelled in the human mind. If the starting point was some other sentience that “lives” in a different domain - for example a hypothetical being made only of light, or gravity - would their intuition of the world be based on Newtonian mechanics? Probably not. What would it be like to exist while eternally propagating at the speed of light, without having a rest frame of any kind? I think the description of the world such a being comes up with would seem exceedingly strange to us, and may not contain any references to space and time as we know them.

I think this very much depends on how you define “time”. In the context of physics it is what clocks measure, and it is also a geometric property of the macroscopic universe. Mathematically speaking it is no problem to have empty vacuum spacetimes (they are valid solutions to the gravitational field equations), so you can have time without any process of change happening.

Indeed - which is trivially true for all spacetimes, only the magnitude of the ‘range’ changes

Thanks, I will need some time to read this paper, before I can formulate a meaningful reply. But I don’t really understand where the argument is going, because the thought experiment implies the notion of time without change (which seems trivially true to me), and at the same time it is clear that you can have change without any notion of time. So the relationship between time and change is at best described as a correlation, but it is not causative nor an identity in the ontological sense.

Yes, that seems trivial to me. Something being a chair - or anything else - is of course not inherent in the object, the recognition and labelling is something that happens during the process of perception. I have the English version on my eReader, but could of course also read it in German if there is any advantage to it. I am not sure if I would actually agree with Kant on this. I certainly do agree that some form of structure must be imposed on a data set, before it can become ‘knowledge’ in the epistemological sense; but I don’t think that structure necessarily has to be spatiotemporal. If I once again may bring up Loop Quantum Gravity as an example - none of the fundamental dynamical quantities in the model are spatiotemporal, but everything still remains well defined, and one can extract observables from it - this is, knowledge. Space and time are emergent properties in this model. Likewise, I am sure that some basic requirements need to be met in order for knowledge to be possible, but I don’t think that necessarily must include space and time. Or maybe it is necessary for the human mind, but that does not allow us to make the claim that space and time are thus independent principles. The problem I have with that is two-fold: 1. Empirically there certainly is a correlation between thought patterns and brain states; but this does not automatically imply a causative relationship. Also, if you get a group of people together and perform this experiment, no two brain states will be exactly the same, even if you get them to think about the same thing / the same thought. So you get a large number of empirically different brain states mapping into the same moment of experience - that’s problematic, to say the least. 2. Even if the relationship is causative, there is still a subjective layer to it that cannot be explained by those patterns - there is the thought process itself, and then there is the subjective experience of having it; it is like something to have that thought. I would answer this using the anthropological principle - the direct experience of what it is like to be a conscious, fully functioning Homo Sapiens is possible only if the representational model of reality that our minds construct are structured using (3+1) spatiotemporal (macro-)dimensions. That was my original pondering - if you get some other sentient being with a mind that is structured completely differently, would they be presented with a similar model by their minds? Perhaps there isn’t just one notion of ‘this universe’, perhaps there are many different ones depending on the observer, and they are all right, even if they disagree on some aspects. Not unlike reference frames in relativity - they can disagree on space, time, simultaneity etc, but they nevertheless have correct models of the world in their own local frames. So essentially what I am pondering is a principle of ontological relativity, if you so will. Well, in quantum mechanics you can separate the grin from the Cheshire Cat, and the grin may also not be strictly localisable to the cat’s face. That’s weirder than any novel

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.