Markus Hanke

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.

What force would counteract gravity in this case, in order to keep the object stable and stop it from collapsing?

The trouble is that MOND is a non-relativistic theory, so comparing it to standard cosmology is kind of useless. At a minimum you’d have to use one of its relativistic generalisations - TeVeS being the most common and popular. And here’s where the issues start, because TeVeS has some serious problems, both so far as observational data is concerned, and in terms of mathematical consistency. And even if you could get it to work properly, you end up with various extra vector and scalar fields that are needed in the model - for which of course there’s no experimental evidence whatsoever. So in the end you just replace Dark Matter and Dark Energy with a bunch of extra unknown fields. It really doesn’t solve anything, on a conceptual level.

Yes, light from outside would be able to reach you, but your visual field would be heavily distorted. No. The global geometry of spacetime used to model the Big Bang is very different from that of a black hole.

The event horizon surface area is a function of mass, charge, and angular momentum. The 3-volume enclosed by this surface depends on the observer, so that can’t be answered in general (the actual calculation itself would also be quite cumbersome). Bear in mind also that the EH is now no longer a sphere, so talking about “radius” will depend on the latitude.

Yes, sure. Local physics in the interior follow the same laws as anywhere else (singularity aside). Not sure what you mean by this... The mass is encoded in the sense that the surface area of the EH is a function of said mass. But it doesn’t mean that the mass is concentrated into a shell of some kind. The EH is a region of empty and regular spacetime, so you can fall through it. Schwarzschild black holes. The same principles hold for all the Kerr-Schild metrics (which are electro-vacuum solutions), in that all parameters in the metric are global properties of the entire spacetime, and not localisable. This is thus true also for charge and angular momentum.