Giorgos G

For a somewhat crude but perhaps more straightforward example, you wouldn't generally say that Newtonian Gravity doesn't exist, because Relativistic Gravity was established. Rather you'd describe one as the refinement of the other. Once you establish Relativistic Gravity, it's also important to show how Newtonian Gravity is derived from it at the Newtonian limit.

Similarly, if a field theory can explain everything that particles can't in terms of fields, that's great. But if that's the case, I might expect an answer of this sort "This is the quantum-field-based description of the phenomenon that virtual particles attempt to explain, if inadequately". Rather than say that virtual particles don't exist, describe the more fundamental field-based explanation.

At that point, yes you can discard the particle concept with respect to self-contained analysis of the theory, but the connection to former concepts in former theories is still important for the purposes of communication and establishing that we are still talking about the same universe.

@PeterKravchuk That is understandable, but a field theory that attempts to explain classically (i.e. anything prior to QFT) particle-like phenomena must be able to recover such particle-like description at the appropriate limit. In that sense, whatever more fundamental description QFT provides that doesn't necessarily behave like a particle (virtual or not) in general, but does in those conditions could be said by extension to be the same concept in this new QFT context, but better explained.

Besides, it's not like you can't define these questions in more concrete ground: If "Do virtual particles exist?" is too vague, you can ask "Do non-particle effects occur on the quantum field level?" (a more rigorous description of what non-particle and quantum field evel mean might be needed, but this is a comment). While the effect itself may not be observable its effects on particles might be. Isn't that the idea behind the Casimir effect after all?

There is a level of this topic that is philosophical/semantic. Whether or not you count anything that occurs on the quantum field level as existing or if you only consider observables to exist is a choice you can make. Even though I personally think there's a more reasonable choice to make here, not everyone will agree. That being said, there's definitely a level where answers can get misinformative despite the subjectivity by answering in much too absolute and objective terms without defining the context within which that answer applies.

@PeterKravchuk That's to be expected. What I meant to convey by bringing that up is that general concensus (whether mistaken or not) isn't even the same every time the same question is asked.

@Idran I'm no expert, but I think GR doesn't assume a discrete form of matter. The Quantum description of matter is not included in the theory and a smoothly continuously distributed mass is probably a good enough approximation for macroscopic object. It makes sense to want to apply GR on actual particle matter, of course, rather than hypothetical smooth matter, but it sounds like it wouldn't be immediately obvious how a particle obeying QFT would interact with an event horizon. You probably need QG for a real answer.

@SolomonSlow My point in regards to that was that the SR as calculated for a BH + an object A inside the EH, for a BH + A just outside and for a BH + A very far away is always the same (assuming no interference from other objects B getting closer to the black hole than the object we're speaking of). Thus, the event horizon approached by A does not grow smoothly or discontinuously, it's always been that size. I guess, though, in the case where B comes closer to the BH than A, then the EH would gradually grow, as its volume would gradually pass A, which might be the point you were making.

@SolomonSlow Oh I get that, but the discussion here is exclusively about what an outsider observer sees, not about the perspective of the infalling object. Of course in that perspective, the horizon is crossed.

Does that mean that the collapsing star also never actually reaches the event horizon either? It's just that by the time we discover these black holes, the light from the star has been so red-shifted we can't detect it any more? Or is there a mechanism that allows the collapsing star to collect in the region that the black hole will occupy, because time dilation is not extreme yet?

I think I see. The problem with my thinking is probably that in the first place the second object would have to be inside the new SR it created, for it to become an event horizon. This is never the case, so it wouldn't affect the first object either. I'm not sure I get how an event horizon could grow smoothly honestly (though it doesn't necessarily matter). The way I see it, it's just that each object approaches a different event horizon, but that event horizon has always been there (more or less), since the total SR calculated for the combined mass does not require the object to be close.

@John Rennie I get the argument that an object can never reach an event horizon (when viewed from outside), however what happens if an object reaches a radius where there is no event horizon at the time but where one will form in the future due to the influence of other objects? The object does not then need to approach the event horizon, because it has already passed it at the time of its formation (I imagine that this is more or less how black holes would form in the first place, because otherwise a collapsing star would never reach the growing event horizon either).

What about if we then consider the second version of my syllogism, wherein for instance one object starts falling into a black hole and after a long time gets very close to the horizon and then another object starts also falling into the black hole? In that case the total radius would increase again and it wouldn't envelop the second object, but is it possible that it could increase enough to envelop the first?

So, if I understand this correctly, essentially you're saying that any event horizon (no matter when it was created or its exact size) experiences infinite time dilation and as a result the object will end up asymptotically approaching the new horizon instead (or whichever horizon is most readily accessible in a general case) rather than the old one. It's sort of like the new horizon hides the old one, so that the object can no longer try to approach the one that's behind the barrier of the new horizon.