Markus Hanke

I define them as gravitational because they are direct consequences of the presence of gravitational sources. For example, a gyroscope not subject to any other interaction does not precess if there are no gravitational sources - planets etc - nearby. Some of these phenomena will happen regardless of which model for gravity you use, but only GR predicts them all with the correct magnitudes. For example, Newtonian gravity predicts neither frame dragging nor time dilation, and gets both light deflection and perihelion precession pretty badly wrong. Neither GR nor QM have anything to say about this proposition, because it makes no sense. I notice you didn’t answer my question, which I find to be important - what about massless test particles, ie photons? Is radiation subject to your proposed effect? If you base this on F=ma then the answer should be no.

I do not actually know precisely how one would go about doing this in a numerical algorithm. If I was to be tasked with figuring this out, my approach would be to use a linear approximation. I would linearise the field equations, and solve for each source in isolation initially taking into account only lower-order correction terms to keep things simple. Since this is now a linear model, you can simply add up the solutions. I would then redo this in iterations, taking into account more and more high-order correction terms with each iteration. With each step this will become increasingly more complicated - so I’d terminate once the calculation takes too long, or I reach the required accuracy. Another idea would be to “pixelate” my spacetime, ie do a lower-resolution approximation rather than use continuous functions. This is just brainstorming.

Velocity does not factor into the gravitational field equations, because it is irrelevant to the geometry of spacetime - or, to put it differently, relative motion is not a source of gravity. Where velocity does play a role is in determining which of the possible geodesics a test particle in free fall will follow. The geodesic equation is a system of partial differential equations - so, in order to find a particular solution, you need to supply boundary conditions. Initial velocity - as a vector - is usually one of these. It’s like selecting the correct geodesic out of all the possible ones. However, which ones are possible, and how exactly these look, is determined by the metric and the connection - ie the geometry of spacetime. And this has nothing to do with any velocities. Lack of education isn’t an obstacle, as it can be remedied easily - these days, you can learn any topic you like using freely available resources online. This is especially true for maths and physics. What is an obstacle is thinking you can simply dismiss a well-established model that you know little to nothing about, and replace it with an idea of your own based solely on it making sense to you. Surely you can see the problem yourself. You cannot visualise gravity in all its degrees of freedom - even I can’t do that, after spending many years on this. To this day I sometimes get surprised by totally unexpected and counterintuitive results, which one can only find using the maths. That’s how it is.

Do you mean I’m wrong about what GR says? Certainly not - what I told you is a basic fact about the model. I can show you the maths, if you like, or you can just take my word on it that I spent years studying it in detail, and kind of know what I’m talking about. It’s my area of expertise. Or do you mean GR is wrong about gravity being geodesic deviation? Well, you must realise that it is an exceptionally successful model, which has been extensively tested over the past century. It works far to well for its basics to be “wrong” in any meaningful sense. So it’s probably best if you don’t stick out your neck all too far...

You cannot add them. GR is a nonlinear model, which means that, in general, the sum of two valid solutions to the field equations isn’t itself a valid solution. What you’d have to do is solve the equations using a distribution of multiple sources as boundary condition. This is quite difficult, and can, in general, only be done numerically.

Locally, GR reduces to SR, so you are right. Nonetheless, all the specific phenomena I listed are gravitational ones. So that means only massive objects are affected by this, but not electromagnetic radiation?

Gravity in GR is geodesic deviation, meaning the failure of initially parallel geodesics to remain parallel due to the geometry of spacetime. This has nothing to do with velocities, and involves both time and space.

But you are the one who made that claim in the first place? If you can’t answer this, what do you base your claims on? No, the opposite is true - once you cross the event horizon, there are no longer any stationary frames. You can be at rest with respect to the BH by locating yourself along its axis of rotation, and firing your thrusters until you hover above the horizon. You’d be stationary there (no orbiting, no in-fall).

The amount of sunlight the Earth receives will vary if you vary the orbit, which would of course have an impact. Exactly what those impacts are in detail is a question better asked to someone dealing with the Earth sciences (not my area of expertise).

Of course not. But the phenomena I listed in my post are all gravitational phenomena.

So if I’m at rest with respect to that black hole, I won’t experience time (ie I will stop ageing)? Is that what you are saying?

It doesn’t. What happens is that the relationship in spacetime between clocks nearer to the black hole and reference clocks far away changes. Time dilation is a relationship between frames, not something that happens locally. They are the exact same as everywhere else in the universe, because nothing changes locally. This is why all classical laws of physics can be written in a form that remains the same irrespective of the geometry of the underlying spacetime.

I don’t know what you consider “something special”, but we observe quite a number of phenomena that have nothing to do with speed of gravity - such as gravitational time dilation, gravitational red shift, geodetic precession, Shapiro delay, Thirring-Lense precession, tidal stretching, and gravitational light deflection. That’s just the ones that immediately come to mind. All of these are correctly predicted by standard GR, and they’re either absent or wrong in Newtonian gravity.

Yes, this is what I meant.

Motion with respect to what? Motion is a relationship between frames, and not an inherent property. I’m at rest with respect to the floor I stand on, but I’m moving at nearly the speed of light with respect to the many billions of neutrinos that penetrate this body every second. Both of these are true simultaneously, so how do you define “my” time as motion through space in a consistent manner? What is your reference point? Are you advocating some kind of absolute frame? And if you do, then, if I’m at rest with respect to whatever frame you propose, will I stop experiencing time, ie will I stop ageing?

As I said, there is no proper acceleration for free fall motion, so no forces are acting on the test particle. There is only coordinate acceleration as calculated by any specific outside observer using his own set of coordinates, but this does not correspond to any physical force, since no accelerometer exists that reads this quantity. It’s merely a frame-dependent accounting device. Either way, if you wish to present and discuss your idea, it will be best to open your own thread in “Speculations”. This here is not the right place for it.

A test particle in free fall under the influence of gravity does not experience any forces - which is to say that an accelerometer comoving with such a test particle reads exactly zero at all times. This needs to be true in all potential models of gravity, since this is what we observe in the real world. If that weren’t so, the motion wouldn’t be inertial, and thus the test particle wouldn’t trace out a geodesic.

What do you mean by “essence of gravity”?

No. You’d have to account for quantum effects, since those can’t be ignored on scales of subatomic particles.

That’s right, but the SS isn’t a massive body - it’s a multi-body system. Thus, if you are somewhere close but outside the SS, there will be small variations as the various planets go about their orbits. However these would be tiny, since almost all of the total mass is in the sun. Once you go far enough away, the SS will behave like a single body, since these variations will be too small to be detectable by any reasonable means.

It doesn’t really matter much whether or not the frames are perfectly inertial - non-inertial frames experience time dilation, too. The difference is just that the relationship between such frames is more complicated than a simple Lorentz transformation, but Special Relativity handles that just fine. For practical applications - such as particle accelerators - the deviation from perfect inertiality is usually negligible. If you do want a perfectly inertial frame, you can use clocks in a satellite or on the ISS as your reference; they are in free fall and thus locally inertial.

Except that’s not what happens - in fact, the opposite is true. Kinematic time dilation in inertial frames is symmetric; ‘we’ see the receding clock slow down, yet from the frame of the clock it’s ‘us’ who’s seen to be time dilated. That’s because time dilation is a relationship between frames in spacetime; it is not a physical property of any one frame. And since that relationship is the same irrespective of which of the two inertial frames you are in, you see the same thing from either vantage point.

I also do not think that Dark Matter exists in the way it is generally conceived of, ie as a particulate substance made from hitherto undiscovered particles. However, neither do I believe that any of the currently existing alternatives provide a better solution than standard cosmology does. Furthermore, some of the assertions made in this article are concerning, eg the claim that (paraphrase) “all predictions made by MOND have been verified”. This is quite simply wrong (some of its predictions are in fact in direct contradiction to observation), and I am very surprised that a qualified astrophysicist would say something like this.

I will suggest one other axiom, then: 1) The opening post of this thread is meaningless word salad This being an axiom, no further proof or discussion will be necessary - its veracity is self-evident.

I have followed the debates about the nature of the ‘dark sector’ for many years now, and have looked at the mathematical formalisms of all the various candidate models and ideas, some of them in detail. So I’m drawing from a diverse range of sources, not just a single paper or author. If you look at the bigger picture, you’ll find that many of the alternative models may be better at explaining specific phenomena - but at the cost of failing miserably with other observational data. Furthermore, very many of these alternatives require extra fields or extra dimensions, or make ad-hoc assumptions that aren’t based on any known physics - so they try to explain one unknown by proposing other unknowns, which is kind of useless. For example, the paper you quote assumes the existence of sterile neutrinos below a certain critical mass limit in order to match observations. Other known problems with MOND are never addressed at all. On a meta level, taking into account all available observational data at this point in time, standard GR still provides the best fit. Im aware of the problems in standard cosmology of course, but I don’t think any of the currently existing alternatives provides a good enough solution. That includes MOND and its relativistic generalisations.