Markus Hanke

Of course. The problem here though is that a duality is not a contradiction. You are making a category mistake. For example, consider the below picture, which is a rectangle-circle duality; there’s no contradiction, because the object in question is neither a rectangle nor a circle, yet contains aspects of both. Likewise with wave-particle duality - quantum objects (any type, not just electrons) sometimes exhibit particle-like behaviour, and sometimes wave-like behaviour, depending on how you look at them - while at the same time ‘being’ neither of those things. They are a separate ontological category to classical waves and particles. Which information is accessible depends on the observer.

This is not directly related to relativity of simultaneity, since in the twin experiment, the reason for differential ageing is that part of the travelling twin’s journey isn’t inertial, so the symmetry between frames breaks down. That’s a different mechanism. You can see differential ageing in particle accelerators when using ion beams - fast beams spread slower (Coulomb forces) than slow beams, in the lab frame. A second ago on the distant observer’s clock; at t=0 at the place of the event; maybe a year in the future for yet another observer. That’s precisely the point - there is no universal time frame. It depends on the observer, and their relationships. Remember this is about simultaneity. And this is all correctly accounted for in the math, as pointed out.

May I just throw in here that religion does not necessarily equal theism. Not everyone who identifies with a religion believes in a creator deity.

An ‘observer’ in quantum physics is any means by which some of the available information may be accessed. In this case, it is simply a screen at a certain location. The point is, an ‘observer’ does not need to be sentient or conscious. However, different types of observers may provide access to different information, so they do have a role to play in that sense. This isn’t a causal relationship though.

No it doesn’t, because the geometric length of a world line in spacetime is not identical to an observer’s measurement of spatial length - as I have pointed out in my post. You are correct of course, my use of terminology was sloppy. Thanks for pointing it out! Length contraction - like time dilation - has real-world physical consequences that are directly detectable, so the very notion of it being illusory isn’t tenable. - The classic example being of course atmospheric muons - Another classic example is the change in interaction cross section of relativistically colliding gold ions at the RHIC - Magnetic forces on test particles passing currents at relativistic speeds (Purcell, Electricity and Magnetism) - Free electron lasers - Flux quanta in Josephson Tunnel Junctions - Changes in ionisation energy levels for relativistically moving particles Among many others. None of these things are ‘illusions’, these are very real, directly detectable phenomena that are direct consequences of relativistic physics; some of these are relevant to engineering applications.

In SR, when a frame is said to be ‘in motion’ with respect to another frame, that means it is rotated about a hyperbolic angle in Minkowski spacetime, again with respect to the coordinate system of the reference frame. This is why speed can be expressed as an angle, called rapidity. This is just what Lorentz transformations do - they deliver a rotation, plus a boost (which is irrelevant here). Measurements of length are the projection of the world line onto the spatial axis of the associated coordinate system; measurements of duration are projections onto the time axis. Now, if you rotate the coordinate system about some angle (=relative motion!), then this will quite naturally alter the magnitude of these projections. This is why we see kinematic time dilation and length contraction. Note that the geometric length of the world line itself does not change - all observers agree on it. They are just looking at the same thing from a different angle in spacetime - quite literally so. Note also that the rotation is a hyperbolic one in Minkowski spacetime, which is not quite the same as a Cartesian rotation in Euclidean space. None of this is in any way in conflict with the ‘block universe’ picture, nor are there any contradictions anywhere. It’s just elementary hyperbolic geometry.

That’s not quite right - it’s about the availability of which-way information, not its being known. If such information is accessible, even just in principle, then no interference is seen. This is irrespective of whether or not there is a conscious observer who actually knows the information, so the observer does not alter the outcome of the experiment in a causal-mechanical sense. Ultimately the issue is information-theoretic - some degrees of freedom of the entire (!) spacetime region representing the experimental setup become entangled with some degrees of freedom of the observer, wherein ‘observer’ just means any part of the environment external to the double slit (no sentience, sapience, or intentionality is necessary - just a screen is enough). It is precisely that - which degrees of freedom become entangled - that determine what ‘mix’ of particle and wave aspects of the quantum system becomes apparent to the observer. If you put your observer (=detector) directly into a slit, you end up with a different set of degrees of freedom as opposed to when the screen is far away, so it is not surprising that the pattern on the screen is not the same. You’re simply dealing with different information.

That’s not true - relativity of simultaneity is explicitly about distant simultaneity, ie events and observers at different spatial coordinates. Within the mathematical treatment, this spatial separation as well as the finite propagation speed of light are explicitly accounted for within the necessary Lorentz transformation.

Mass is what usually comes to mind first - but it’s important to realise that other forms of energy also have gravitational effects. Examples are pressure, stresses and strains within materials; electromagnetic fields; and even the gravitational field itself acts (at least in some sense) as its own source. Hence, gravity is a lot richer and more complicated than the simplified picture most of us are taught in school.

You are still missing the crucial point: there is nothing to be decided. Quantum objects sometimes exhibit particle-like behaviour, and sometimes wave-like behaviour, while not “being” either of those things. It’s not an “A or B” kind of situation, but a duality.

I think you are missing the point entirely throughout this discussion - quantum object “are” neither waves nor particles, nor are they both or neither. You are attempting to shoehorn something that isn’t classical into a classical category. The point is that quantum objects sometimes exhibit particle-like behaviour, and sometimes wave-like behaviour, depending on the relationship between the object and the observer; this is called contextuality. It is meaningless to say that a quantum object “is” something or “has” certain properties, unless within the context of interaction with another system. These aspects are relational in nature, not ontic. A limited analogy (!) in the classical world would be electromagnetic fields - sometimes you see magnetic fields, sometimes electrical ones, and sometimes a mix - depending on the relationship between observer and source. But the underlying entity is the electromagnetic field, which “is” neither of these. Wave-particle duality is similar, except that now you are in the quantum world, so you have to also consider counterfactual definiteness.

Apologies if that was how it came across, that wasn’t the intention. Of course there are other aspects - besides non-commutative observables there is superposition of states, and the violation of Bell’s theorem which implies there are correlations which are stronger than classically allowed. I don’t think these things are wholly independent though. Of course. But we are talking about observables of the theory, which these are not.

No sentience is required either. An observer in the QM sense is simply an external physical system interacting with the setup.

So long as the relationship between emitter and observer remains the same, the particles are subject to the same probability distribution. You don’t need human involvement. You can just set this up and let it run without a human observer being present; the result is the same.

That’s right...nonetheless there is a clear conceptual cut at the end of the inflationary epoch. Inflation itself is a bit speculative; we don’t have a GUT, just a bunch of candidate models; and we don’t have a model of quantum gravity that would describe physics at the Planck epoch either (again just some candidate models). So everything prior to the electroweak epoch is either speculative, or unknown.

Actually, it’s domain only starts at 10^(-32)s, which is the end of the inflationary epoch. What happened before is speculative at best, and, once you get to the Planck epoch, simply unknown.

I think clarification is in order. Firstly, I was the one who posted this, not iNow. Secondly, I said only that ‘the world is essentially quantum’ - a statement I do stand by. What I meant by this, in the context of the discussion, is that there is no ontological difference between the macroscopic and the microscopic world; what is different is only the degree by which these domains are subject to decoherence; the larger the system, the more quickly it will generally decohere. This is why you don’t normally observe interference effects in the macro world. Classical mechanics is thus an effective description in the macro domain. But do remember that there is no law forbidding such effects - if you can find a way to delay decoherence for long enough, even macro objects would in principle exhibit such behaviour, at least for a short time. This is an engineering problem, not one of fundamental physics. I don’t believe that this is really in contention. None of this implies that ‘everything is quantised’, which clearly it is not. Even in standard QM the spectrum of hermitian operators is continuous until you impose boundary conditions on your evolution equation - it’s only this that yields discreteness of observables. Quantum-ness does not necessarily equal discreteness; it means primarily that there are pairs of observables that do not commute. And yes, I fully agree that quantisation of spacetime is very much under debate. I did not mean to imply otherwise.

It should also be mentioned that the spacetime interval of Special Relativity is a crucial building block of quantum field theory. You couldn’t have the Standard Model without SR.

Fair point, I shouldn’t have said “only” reason. Is it? How would one resolve the classical<>quantum transition other than via decoherence?

That is why I mentioned ‘using appropriate components’ in my post. Anyway, what the experiment establishes is a general property of quantum systems, and nothing inherently to do with photons.

But this has nothing to do with optics - you can send any kind of quantum object through the apparatus (with the appropriate components), and get the same behaviour. The outcome isn’t specific to photons/light - the outcome is in fact totally independent of the type of quantum object used.

Fundamentally, the world is quantum, irrespective of the size of the system you are looking at. The problem is just that superposition of states can persist only as long as no observation takes place, which means as long as the system does not interact with its environment (‘decoherence’). And the larger the size of a system, the harder it is to keep it isolated, and thus the more rapidly it decoheres. That’s the only reason why you never see quantum effects in the macroscopic world. There is no sharp ontological boundary between quantum and classical - the distinction is a relational one.

Seems to me that this is a bit off topic for this thread...? Anyway, I don’t think anyone doubts the existence of NDEs, they are a well documented phenomenon. The question is why you feel the need to give them a supernatural interpretation? It seems clear that such experiences would feel very powerful, and I’m sure they have a deep impact on the experiencer - but that doesn’t mean they are of supernatural origin.

You don’t need to use light, you can use any type of quantum object (electrons, protons,...), or even something as large as a C-60 molecule. The result is always the same - you get individual local hits on the screen (particle), and many such dots will over time produce an interference pattern. This is true also if the emitter only produces one such object at a time.

For the purpose of attempting reduction. I may not have formulated this very clearly, I just meant that knowledge of the parts here does not equal knowledge of the whole system; there’s extra information there. Measurement of any part of the system breaks entanglement. Yes, it’s what I meant.