Markus Hanke

Standard quantum physics explains entanglement very well, without the need for hypothetical constructs such as superluminality. Also, as you know, correlation does not imply causation.

These aren’t basic principles of science, they are basic attributes of classicality only. There is no good reason to believe they are scale-independent.

My assumption is only that interactions between particles are adequately described by the framework of QFT. This trivially preserves causality, but not necessarily locality and/or realism. It is the current scientific consensus. You can choose to not follow that consensus of course (as you seem to be doing here), but that doesn’t automatically make it “wrong”. You are merely putting forward a different hypothesis. In what sense then are they preferred? What mathematical definition of “preferred” are you using? Can you formalise this for us? I’ll be blunt with you - your very rejection of what you consider “dogma” appears to have become dogma itself for you. The paragraph I quoted the above from really lets that shine through very strongly. At least that’s the vibe I’m picking up. Physics should not become a partisan issue - it is not about metaphysical notions of “right” or “wrong”, but about what model works best in describing aspects of the universe as we see them. Sometimes models are “right” in some circumstances, but “wrong” in others. It’s an epistemological endeavour, not an ontological one. The map isn’t the territory, but it does need to accurately represent the relevant aspects of the terrain, on the relevant scales. Quantum theory / QFT actually does this rather well. As for the specific example of entanglement, since no exchange of information is necessary at the time of measurement, causality never even comes into it at all. By letting go of either realism or locality (or both), we eliminate the very need to exchange information, and hence no artificial notions of superluminality, preferred frames etc are necessary in the first place. Causality is trivially preserved, since the measurement always happens after entanglement has been created, and the outcome of measurements is compared following the usual rules of SR, which again trivially preserve causality. There really is no problem here that needs to be “solved” somehow. The problems only emerge if one demands that notions which appear fundamental in the classical domain (such as locality and realism) must be scale-independent, i.e. necessarily apply on all scales. Why should that be necessarily true? Again, it isn’t about what is right or what is wrong, but about what model best fits the universe we observe. To that end, there is no problem whatsoever in setting aside notions of realism and locality, of absolute time and space, if the resulting model is in good agreement with available data. Realism and locality are not sacrosanct notions somehow built into the foundations of the universe on small scales, rather, they originate in what us humans think the universe should be like; they are a reflection of our own experience, which is, after all, rooted in classicality and the low-energy regime. The unscientific act would be to unquestioningly assume that such notions apply across all scales. There is no apparent reason why they must, but plenty of reason to believe that they don’t. I think even the notion of causality itself may not necessarily be scale-independent. This remains to be seen. To make a long story short - not only is it no problem for me personally to set aside locality and/or realism, but I think it is a perfectly reasonable thing to do, if the resulting model describes very well what it is supposed to describe, while at the same time respecting other principles of physics, such as diffeomorphism invariance. To me, introducing preferred frames and space-like world lines creates many more problems than it solves. Don’t get me wrong here - investigating the implications of such things as preferred frames and space-like separations is quite a valid endeavour, but it doesn’t seem to add any value to physics as it stands. It just creates unnecessary problems and complications. Now, if you could put forward a model that preserves locality and realism without the need to add superluminality and preferred frames...that would indeed be something!

The causal influence happens at the time when the entanglement is first created, which involves an interaction between the particles. This interaction follows the standard rules of QFT. After that has taken place, the system of two particles is described by just one wave function, irrespective of their spatial separation, so that no decomposition of said function into separate, independent parts is possible. This fully accounts for the statistical correlation, no causative exchange of information takes place at the time of measurement. For general curvilinear coordinates, this should actually be \[ \square X^{\lambda } =\frac{1}{\sqrt{-g}} \partial _{\nu }\left[\sqrt{-g} g^{\mu \nu } \partial _{\mu } X^{\lambda }\right]\] I don’t quite understand how the above is even related to the discussion of quantum entanglement?

Apologies if it came across wrongly, the intention was not to make you aware of anything “wrong” you might have said. It wasn’t even directed at you as such, it was more of a general comment. My intent was simply to point out that looking at the situation in terms of geometry of world lines is the easiest and most straightforward way to do it, since that geometry is a quantity that all observers agree on. This is as opposed to reference frames, observers, clocks etc, which makes the situation unnecessarily confusing. But maybe that is just me

This is it, plain and simple. If you have two events in spacetime (start and finish), with initial conditions being equal, there is precisely one unique inertial world line connecting these events. This is geometrically the longest possible world line, i.e. the one that accumulates the most proper time. Formally, this world line is a geodesic of the spacetime, meaning you have \(a^{\mu}=0\) everywhere along it. The only way to obtain a different world line connecting these same events, with all other things remaining equal, is to violate the above condition - i.e. introduce proper acceleration at some point, which leads to a world line that is shorter than the inertial one. Of course you can decide to vary initial conditions as well between observers, in which case they will trace out different inertial world lines between the same events - but then you are no longer comparing like for like.

Or you can simply compare the geometric length of their world lines (given shared events to begin and end at), and be done with it

I think it should also be noted that the notion of “gravitational potential” as we are used to it from Newtonian mechanics can only be meaningfully defined for specific types of spacetimes - at the very least they need to be stationary, spherically symmetric, and asymptotically flat. It is not a universally valid concept in GR.

Time dilation is a fundamental feature of the world, it applies to all clocks irrespective of their internal make-up - be they mechanical, electromagnetic, atomic, light, or whatever else. It also applies to statistical processes such as the decay of elementary particles, which have no internal structure or mechanisms at all. Crucially, all other things being equal, the amount of time dilation is the same in all cases, regardless of what type of clock you use. This alone already shows that it is not an artefact of the clock mechanism. Atomic clocks are not light clocks. A pendulum clock is subject to time dilation, but it is also subject to external forces, so it is an unnecessarily complicated measuring device for this purpose. However, you can use the pendulum clock, if you know how to interpret the observed effects correctly. Locally in a small enough area, tidal effects can be neglected, and what we observe as “gravity” is entirely down to time dilation. So, it’s not that gravity causes time dilation, but gravity is time dilation - it’s curvature in the time direction. Newtonian tabletop mechanics aside, the theory of relativity is the most well-tested model in all of physics, and in perfect agreement to all experimental data within its domain of applicability. Length contraction can be directly observed in a number of different contexts, not just MM. Most notable here would be pretty much any particle accelerator experiment, atmospheric muons, the entire model of electrodynamics, undulator radiation, and so on. Note that kinematic time dilation and length contraction are just two aspects of the same phenomenon.

Not even to mention that you’d be standing at an angle to the surface of a disk-shaped Earth, unless you are right at its center! I’d be a funny world.

The source of gravity is any form of energy-momentum, not just mass. Also, because gravity is non-linear, in some sense it also forms its own source - so “gravity gravitates”. I don’t know what you mean this, as spacetime is not a medium. Gravitational waves are periodic changes in the curvature of spacetime, and their source is a quadrupole or higher multipole moment (unlike EM radiation, which is dipole in nature).

There is no discussion about this in the scientific world; we know what the shape of this planet is, because we have to take it into account in countless everyday and not-so-everyday applications. There is only FE adherents talking at (not with) everyone else - they like to cultivate an air of there being some kind of serious debate about this, as if Flat Earth was a viable concept that needs to be confirmed / ruled out. But of course it isn’t, and it doesn’t; this debate was settled centuries ago. FE is not a concept that can work, unless of course you reject pretty much all of known physics; of course there will always be people who are prepared to do just that. I wonder what will happen once private commercial space travel becomes a thing, and anyone with the necessary cash will be able to travel into orbit purely for touristic purposes, and see for themselves? What spin will the FE community put on this, I wonder? It sounds like sci-fi right now, but I think we are only a few decades away from the beginnings of that.

The interaction of gravitational waves with background curvature due to gravitational sources, as well as with other gravitational waves, exhibits nonlinear dynamics. This becomes more pronounced in the strong field regime, und you will get effects such as backscatter, frequency shifts, tails etc that don’t exist for EM radiation (which is governed by linear dynamics). It would be very difficult to draw conclusions as to propagation speeds from gravitational lensing alone. A better way to test the propagation speed is to have not one, but several gravitational wave detectors, preferrably in orbit. You can then just look at the delay between detectors picking up the signal, which immediately tells you the propagation velocity. Unfortunately at this point in time we have only a very small data set involving only two earth-bound detectors, so the error margin is too big for this to be very meaningful; nonetheless, every additional detection event will statistically improve the bounds, so it is just a matter of time really. Here is the current data: https://arxiv.org/abs/1707.06101

Water is much more dense than air, so it generates much greater resistance owing to the need of the falling/sinking object to displace it. Gravity is (for all intents and purposes) the same, but there is a counterforce from having to displace the water as the spear sinks, making it appear “lighter” and move slower. I say “for all intents and purposes”, because the value g=9.81m/s^2 is specific to the Earth’s surface - if you were to go high up (or tunnel deep down), this numerical value will change accordingly. Even on the surface, this value can vary ever so slightly between different locations, depending on how dense the Earth’s crust and mantle are at that place. Also, the Earth isn’t a perfect sphere either. But for most everyday applications, 9.81m/s^2 is a sufficiently good approximation.

Static gravity does not propagate, so no gravitons need to escape an event horizon. Gravitons would need to be massless spin-2 bosons, and as such move at exactly the speed of light, just like photons and gluons. As a side note - whether superluminal motion would guarantee the ability to escape an event horizon is a question (albeit a purely academic one) that isn’t straightforward to answer.

In the same way as a surveyor gets the territory to fit his map.

To see whether gravity is a force, simply attach an accelerometer to a freely falling test particle. You will find that the instrument reads exactly zero at all times, even though the trajectory of the test particle makes it obvious that it is affected by gravity. And then of course you have other effects, such as gravitational time dilation, that can’t be explained by forces at all. Thus, gravity isn’t adequately described as a mechanical force. It completes the “zoo” of those particles which the Standard Model predicts within the energy ranges that we can probe with current technology. The hypothetical graviton interacts so weakly that it would be extremely difficult to detect it directly. The entire idea of a “graviton” is based on the notion that gravity can be quantised using the usual framework of quantum field theory. It is in fact easy to write down a QFT for gravity - but the problem is that such a QFT is not renormalisable, and exhibits infinities that cannot be removed via any known method. Essentially, the resulting QFT is useless, in that one cannot extract many meaningful physical predictions from it. So evidently, QFT is not the right method to quantise gravity. Based on current knowledge, it would seem that gravity is conceptually different from the other fundamental interactions, and is hence not amenable to the usual quantisation schemes. This puts a huge question mark behind the notion of a “graviton” - treating gravity as the interchange of vector bosons may not be a meaningful concept. But if it is, then it would not be difficult to incorporate it into the Standard Model (you’d just add an appropriate term to the Lagrangian). This is an area of ongoing research.

I should point out to you that you don’t seem to be following the scientific method, which is a big red flag. You appear to have arrived at a conclusion (electron is composed of photons), and now you are working at making everything fit that conclusion. That is not how science is done. In the scientific method, you start with the data - in this case the known dynamics and properties of electrons -, develop a model to describe that data, and then test that model. If the model does not work, you either amend or abandon it. Crucially, any new model must fit in with all the rest of what we know about physics. If you come up with an idea, and then find yourself unable to abandon that idea even in the face of overwhelming evidence that it doesn’t work and cannot work, then you have a problem. I think you should stop wasting your time with this, and reinvest your resources into learning what we already know about the physics of particles. Only when you are familiar with what we already know, can you make meaningful inroads into what we don’t know yet. Just some friendly advice.

Well pointed out. It bears mentioning though that in standard GR the Levi-Civita connection is used, which is torsion free.

GR does not make reference to any concept of mass within the gravitational field equations, it references only \(T^{00}\), which is energy density, as well as \(T^{\alpha 0}\) and \(T^{0 \beta}\), which is momentum density. Note that these are densities. Gravitational self-influences do not explicitly appear in the field equations (they can’t, because the associated quantities are not covariant), but are encoded in the non-linear structure of the equations themselves. In GR, the source of gravity is neither invariant mass, nor relativistic mass, but the stress-energy-momentum tensor. This is a generally covariant object, so when you go into a different frame of reference, the components of the tensor may change, but they will change in such a way that the relationships between these components - and thus the overall tensor - remain the same. So, having relative motion may change how different observers measure individual quantities such as densities, momenta, stresses etc, but it will not change the source term in the gravitational field equations. This is also relevant in vacuum, because distant sources determine vacuum solutions in the form of boundary conditions. So essentially what I am saying is that relative motion between test particle and source has no bearing on the geometry of spacetime due to that source, it only changes how the observer labels events in that same spacetime. This is of course provided that the test particle’s own gravitational influence is negligible (otherwise we have a GR 2-body problem, which is much more complex). Because in the energy-momentum tensor, a change in one component also implies potential changes in all other components. In this example, if momentum density becomes non-zero, then energy density and all other relevant components will also change in such a way as to “compensate” (so to speak) for that change. You are basically just shifting around things within the tensor, without changing the tensor itself. This is wrong, SR says no such thing. In fact, SR is a model of flat Minkowski spacetime, it has nothing to say at all about the gravitational influence of anything.

The equivalence principle states that uniform acceleration is equivalent to the presence of a uniform gravitational field within the rocket. Any region of spacetime with uniform gravity is in fact flat, it has no curvature. This is why you can derive what happens in this rocket from SR, which is a model of flat Minkowski spacetime. The same is not true for the surface of the Earth - the gravitational field of any central mass is not uniform, but tidal. If you had sensitive enough instruments, you could detect geodesic deviation within the rocket (though the effects would be small, so the field within such a small region is very nearly uniform). So these two scenarios are physically distinguishable, at least in principle, given sensitive enough instruments.

Gravity is not an observer-dependent phenomenon; if you have some \(R^{\mu}{_{\nu \alpha \delta}} \neq 0 \) in one frame, then you will find the same in all other frames as well. When an observer and a gravitational source are in relative motion, what changes is only the form of the metric - however, the metric in the rest frame of the gravitational source and the metric in the rest frame of the observer will be related via a simple coordinate transformation, so we are actually dealing with the exact same spacetime. So very simply put, if a gravitational source is in relative motion, the metric might look “distorted” in some way to an observer, but it will produce the exact same physics. Essentially, relative motion just means we are using different coordinates to describe the same spacetime. The relevant solution to the field equations for this scenario is called the Aichelburg-Sexl ultraboost.

Yes, that is indeed true.

There are no calculations in that document that concern photon orbits in curved spacetimes.

We can measure plenty of things that have nothing to do with mass, length or time. This is the “Theoretical Physics” section of a science forum; the above is thus completely off-topic.